2000 Coddington&Colwell Arachnids(1)

8/11/2019 2000 Coddington&Colwell Arachnids(1)

1/20

A R A C H N I D S

Jonathan

A .

Coddington*

and

Rober t

K .

Colwe ir

Smithsoniannst i tut ion;'Univers i tyof

Connecticut

I.

verv i ewof

A r a ch n i da

II .r a n e a e

III.c o rp i onc s

IV .pi l iones

V .

maller

Arachnid

O r de r s

V I.car i

GLOSSARY

b o o k l u n g s

n e

to

four

pairs

of

a b d o m i n a l

re spi ra to ry

o r g a n s

c o ns i s t i ng

of

at h i n ,

mult i fo ldedm e m b r a n e

( the

book' spages )ov er

whic h

b l o o dc i rcula t es

a n d

t h a t

s

pe n

o

n

i r-l led

avi ty

on

h e

u t s i d e ,

i tse lf

ope n

to

th eex t er ior

via

aspiracle .

G a s e s

pas-

s ive lyiffuseack

n d

or th

c ro s s

h ee m -

b r a n e .

ch e l i c e r ae

chelate)

h eirstpair

of

pr e o r a lap p end -

a g e s .They a re

a tmost

t h r e e

s e g m e n t e d ,

usual ly

t w o ,

an d

usua l ly th e

d i s ta l

s e g m e n t ac t saga i n s t

th e

penul -

t imateto

grab

o r

ho l d

preyo r

objec t s .fth e

b a sa l

s e g m e n t

a s i n g e r - s hap ed

u t g r o w t h

ga ins t

wh ich

th e

d i s ta l

s e g m e n t

op era t e s ,

th e

che l i c erae

ar e

che la t e

a s

in

s cor p i on s

o r

harv e s t men ) .

f

n o t ,

th e

che l i c erae

a resu bch e l a t e ,

asn

sp iders

a n d

ai l less

w h i ps cor p i on s .

In

parasi t icmi t e sth eche l i c eraear e

mod i f i edi n topierc ing

s tylets .

m o n o p h y l y r u e ,

i s torical ,

v o l u t i ona ry

i n eage

c o ns i s t i ngof

a n

anc e s t o ra n d

a ll

ofit s

d e s c end an t s ;

d e f i n ed

b y

sh a r e d ,

der ived

character s .

o vo v iv ipa ro us

o u n gar ebom l ive,

u t

h e

m o t h e r

s imply

re ta in s

e g g s

wi th in

h er

b o d y

u n t i l

t h ey ha t c h .

paraphy ly

g r o u p

coiisisting

of

a nanc e s t o r

a n d

o n l y

s o m eof

it s

d e s c end an t s .Def ined

b y

primit ivech a r -

acter s .

pedipalpsh e

s e c o n d

pair

ofpreora lap p end age s .

T h e y

a remu l t i s e g me n t e d n dprimit ivelyeg-l ike.

T h e y

m a y

b e

raptor ia l

o r

s e n sor y

(likea n t e n n a e )o ru s e d

a s

walk in g

l egs .

phoresy m e t h o dof

l ong - range

i spersa l

nwhic h

th edisper s inga n i m a la t t a c he si tse lfto a n o t h e r

an i -

m a l

(e .g . ,

be e t l e ,

w as p ,

o rb i r d )t ha t

carr i e s

th edis -

perser

l on g

with

t

nt i lh e i spers er rop s

off

o r

d i s embarks .

polyphyly

g r o u p

in

wh ich

th e

m o s t

r e c e n t

c o m m o n

anc e s t o r

of

th e

n c lu de d

taxa

is

e xc lu de dfromth e

group .Def i n ed

b y

con ve r g e n t ,nonhomologous

ch a r -

acter s .

s p e r m a t o p h o r e

ch i t i n ou s

con t a i n e r pr odu ce d

b y

th e

male

to

ho l d

spe r m .

t

m a y

b e

at tached

to

th e

s ub -

s t ra t e

fo r

th e

f emaleto

f ind

o r

passedtoth ef emale

fromth e

maled u r i n gm a t i n g .

spinneretssual ly

t h r e e ,

rar e ly

four

pairs

ofmod i f i e d

t e rmina l

b d o m i n a lp p end age sn

sp iders

ea r i ng

o n e

to

h u n d r e d s

of

h o l l ow

sp i g o t s

from

wh ich

silk

is

d r a w n .

t r a c hea e

sys t em

of

h o l l o w ,b ranc hedoru n b r a n c h e d

a i r - con du c t i n gu b e s

us ed

o resp i ra t i on ,

p e n i n g

vi a a b d o m i n a l

spiracles .

Theym ay or

m a y

n o te x t e n d

i n toth ec p ha l o t ho rax

o rl egs .

t r i ch obo ih r i ao n g ,

del i ca t e , sl ende r

s e tae

s e t

in

b r o a d ,

sh a l l ownnerv a t ed

ocke t s

n

h e

ut ic l e .

Tr i c ho -

b o th r i a

reens i t iveo i b ra t i on r

ear-f ie ld

ir

m o v e m e n t

a n d

ar eamajors e n s eo r g a n

of

a r a ch n i d s .

Encydoptiaoj

BiodivaiUy.Vo lumf

J

Copyr igh i

2001 y

Academic

Press .Al l

r igh t s

o f

reproduc t ion in an y

i o tm

re s erved .

19 9


2/20

M ARArHvin

T A B L E

La t in

n a m e

C o m m o n

n a m e

No .ofFamil ies

No .

of

G e n e r a

No .

of

Descr i bedspec i e s

Arachn i da

Arachn i ds

648

9241

92,680

Araneae

Spidere

10 8

3200

37,000

Palpigiadl

Micro -whip

sco rp ions

2

6(5)

80

Uropy g i

W h i ps corpion s

1

16

10 1

A mbly py g i

Whip

sp id e r s ,

ta i l l e ss

whip

sco rp ions

3

20

12 6

Sch i zomi da

Sch izomid s

2

31

19 5

Soli fugae

Wi nd

sp id e r s 12

15 3

1,065

P s e u d o s c o q j i o n e s

P s e u d o s c o r p i o n s

24

430

3,100

Ric inu l e i

Ric inu l e id s 1

3

53

Opi l i one s

Harves tman

44

1554

4.300

Scorp ione s

Scorp ions 18

15 6

1 260

Acari

Mites ,icks

431

3672

45,200

Modi f i ed

from

Adi s

a n dHarv ey

(2000),

wi th

data

fo r

th e

Acari

f rom

Walt er

a n dProctor

1999).

ArachnidaisaclassofthehugephylumArthropoda.

Familiararachnids

are

spiders,

scorpions,

ticks,

mites,

and

harvestmen,butarachnids

nclude

manyesser-

knownterrestrialarthropodgroups

as

well.

I .

OVE RVI E WOF

ARACHNIDA

Theknown

diversity

of

arachnidsisapproximately

640

famihes,

9000genera,

and

93,000

species(Table

1),

but

there

are

many

thousands

of

new

mite

andspider

spe-

cies

still

undescribed

and

hundreds

o

housands

of

undescribed

species

intheremaining

orders.

Together

withthemarinehorseshoecrabs(Xiphosura)andse a

spiders(Pycnogonida),arachnidscomprisethe

arthro-

pod

subphylum

Chelicerata,

named

fo r

thecharacteris-

ticfirst

pair

of

preoral

appendages,

thechelate,

or

pinch-

ing,

outhparts.n

ome

rachnidroupshe

chelicerae

are

further

modified

into

venomousfangsor

piercing

styletstosuck

bodyor

plant

fluids.Arachnids

aretheonlyterrestrialchelicerates.Alongwith

the

in -

sects,

arachnids

arebyfa r

the

most

species-rich,

abun-

dant,

ndidely

istributederrestrialrthropods.

Acarologists

(scientists

who

study

mites

and

ticks)

esti-

matethat

there

m aybeasmanymitespeciesasbeetles,

implying

that

total

extant

arachniddiversitymay

exceed

1

million

species.

Arachnids

are

animportantcompo-

nent

ofeveryterrestrialecosystem,

but,

apart

from

sev-

eral

specialized

mite

lineages,

none

areaquatic

or

ma-

rine.

Althoughmostarachnidsshare

manyancestral

similarities

in

bodyplanand

lifestyle,

manyextremely

speciahzedgroupsexist,

especiallyamonghe

mites

(Acari ) .

Although

rachnidsre

ommonly

istaken

or

some

sort

ofpeculiarinsect,

thegroupsarequite

distinct

and

onlydistandy

elated.

Arachnids

have

our

pairs

of

walking

eg s

ather

han

hree

except

he

young

stages

of

mites

and

the

related

Ricinulei),only

tw o(not

three)majorbodyparts,andsimplerchelatemouth-

parts

rather

than

the

more

complexfeedingapparatus

of

nsects.

heanteriorbodypart

s

specializedor

locomotion

and

the

posterior

fo r

digestion

and

repro-

duction.Arachnidslackthewings,

antennae,

and

com-

poundeyesusual

in

insects.nmanygroupshefirst

pair

fwalkingeg se.g.,mblypygids,ropygids,

schizomids,

solifuges,

palpigrades,

and

many

mites)

are

elongate

and

functioninmuch

the

same

w ay

as

insect

antennae.

igure

epicts

consensus

viewof

he

positionofarachnidsin

thearthropodevolutionarytree.

Arachnids

andhexapods

whichinsects

dominate)

differinfundamental

ways,

possibly

because

their

m a-

rine

ancestors

were

already

distinct

lineages

inthe

Silu-

r

Hexapoda

Progoneata

rust ce

Arachnida

Xiphosura

Pycnogonida

FIGURE

Phy logene t i c

posi t ion

of

Arachn i da

a m o n g

a r t h r o p o d s .

r

helicer t


3/20

A R A C H N I D S

2 0 1

rian

nd

oth

olonized

and

ndependently.hey

thereforesolvedthefundamentalchallengesofterres-

trialexistence

support,

breathing,

waterbalance,re-

production

in

dryenvironments,andnitrogenous

waste

management)indifferentways.The

arachnid

skeleton

is

hydrauhc;

arachnids,

except

scorpions

and

pseudo-

scorpions,lackextensormusclesat

ke yjoints.Instead,

the

animalpumps

blood

intothe

limb

toextend

it .

The

basic

arachnid

uses

wo

orfour)

pairs

of

book

lungs

(gas-permeable,

gill-likemembranes

with

bloodon

one

side

and

open

o

heairon

he

other)

o

exchange

carbondioxideforoxygen

rather

thantracheae.Many

arachnids

possess

udimentary

rachal

ystemshat

supplementor

eplacebook

ungs,

but

ventilation

s

passive,ot

ctive.

nlike

nsect

racheae,

arachnid

tracheaegenerally

do

notramifythroughouttheentire

bodyor

penetrate

insidebodycells.For

all

hese

rea-

sons,

nsect

racheae

more

efficiendy

deliver

oxygen

directly

to

tissue,andinsects

ingeneral

can

lead

more

energy-intensive

ifestyles

hanarachnids.

rachnids

havesignificantlylowermetabolicratesthanotherter-

restrial

arthropods,

speciallynsects.Whereasmale

insects

transfer

spermdirectly

tohe

female

using

an

intromittent organ,in

mostarachnids

males

eitherejac-

ulateontoaspecialstructureand carrythespermmass

witha

specializedappendage

until

the

femaleisencoun-

tered

or

hey

deposit

he

sperm

mass

n

pecially

built

receptacle(spermatophore)

fixed

to

the

substrate,

whichthe

emale

picks

up.Majorexceptionsinclude

theharvestmen,stigmaticites,ndpidermites,

which

ransfer

sperm

o

he

emale

by

means

of

an

intromittentorgan,and

he

watermites

Prostigmata.

Hydracarina),whichtransfersperm

directly

by

oppos-

ing

the

male

gonoporetothe

female

gonopore.

Arachnids

are

pecuhar

among

animals

in

using

gua-

nine(three

nitrogen

atoms

per molecule)

as

well

as

the

much morecommonuricacid

(two

nitrogenatomsper

molecule)

to

eliminate

nitrogenous

wastes.Insects

have

compound

eyes,whichproviderelativelyexcellentvi-

sion.

Arachnidslostcompound

eyesearlyin

theirevolu-

tionary

history

but

retain

usually

one

to

five(commonly

four)pairs

of

simple

eyes,

muchinferior

n

acuity

o

compound

eyes.

Schizomids,

palpigrades,

icinuleids,

mites,

andother

mainlyhtter-dwellingarachnid

groups

arenearlyalwaysblind.Visionis

much

less

important

to

arachnids

than vibration.

Many

structures

(slit

sense

organs,

trichobothria,

and

lyriformorgans)

are

special-

ized

to

detectminutevibrationsand

slight

aircurrents.

Arachnidsarealsopeculiar

in

that

speciesofmost

arachnid

groups

digest

oo d

externally.They

have

strongpumpingstomachthatrhythmically

vomits

and

sucks

digestive

juicehrough

preoralcavity

ormed

by

hebasal

articles

ofhepedipalpsbackandorth

overheirprey.Theprocesscontinuesuntilonlythe

hard,

indigestible

parts

ofthepreyremain.Only

liquids

or

very

small

particles

are

actually

ingested.

S omemajor

groups

of

arachnids

have

internal

digestion,

however.

Opilionidsandseveralgroups

of

mites

are

particulate

feeders,

and

parasitism

of

plants,

vertebrates,

and

inver-

tebrates

has

arisen

epeatedly

n

he

mites.

xternal

digestion

s

a

major

obstacleoife

nfresh

wateror

thesea.Arachnidsare

also

notable

or

their

ability

to

withsund

starvation.

Fastsofweeksorevenmonths

are

outine

orargerarachnids.Somescorpionsand

mygalomorph

spiders

live

fo rmore

than

1year

without

food,and

adult

softticks

Argasidae)

cansurvive

fo r

years

without

feeding.

A.

Reproduction

and

Growth

Like

ll

arthropods,arachnidsgrow

by

molting

heir

exoskeletons

and

expanding

he

arger

skin

beneath

with

blood

pressurebeforethardensntoheusual

tough

covering.Thenumber

of

molts

to

maturityvaries

widelybetween3

and

10-12;fiveisperhapsthemost

common.Lifespansalsovarygreatly.Themajorityof

mites

and

spiders

live

lessthan

year,

but

several

years

is

common

amongthelarger

forms,

andmygalomorph

spiderscan

live

20-30

years

incaptivity.

S ome

arach-

nids

cease

moltingatadulthood

but

others

continue

to

moltperiodicallyuntil

death.

Theancestral

reproductive

pattern

of

sperm

transfer

is

vi a

spermatophore,

modifiedinspiders,harvestmen,

mites,

and

ricinuleids.

Exceptamongpermanently

so -

cialspeciesand

many

mites,the

se x

ratioisequal,and

parthenogenesisis

rare.

In

the

vast

majority

ofspecies,

males

and

females

meetonly

to

mate;

cohabitation

and

parental

care

are

uncommon.

Nevertheless,

various

spi-

ders,corpions,chizomids,ropygids,ndmbly-

pygidsm ay

carry

and

ee d

heir

young,and

n

some

harvestmen

he

male

cares

fo r

he

eggsn specially

built

nest.

Pseudoscorpion

emales

nourish

eggs

with

secretionsi-omheirbodies,andscorpionsbearonly

live

young.Femalescommonlyguardtheireggsuntil

theyhatch,

but

theyoung

are

usually

abandoned

soon

thereafter.

Mites

are

more

diverse

in

reproductive

strat-

egiesthannonacarinearachnids.

B .

Ecology

DespitehugenumbersofspeciesTable) ,arachnid

biologyis

coherent

in

manyways(eventhoughexcep-

tions

tonearlyeverygenerahzationexist).Mostarach-

nid

ordersconsist

of

fluid-feeding predators,

and

prda-

tion

till

ominatesheseroups

oday.

owever,

opilionidsandw oofhehreeordersof

mites

are


4/20

.ARACHNIDS.

particulate-feedersondetritus,

fungi,

andsmall

inverte-

brates.Additionally,parasitismof

vertebrates,

inverte-

brates,andplants

has

arisennumerous

imes

within

the

Acari

and

radiations

withintheselineages

account

fo r

mostofthe45,000described

species

of

mites.

Non-acarine

arachnids

tend

to

be

at

the

op

of

the

terrestrial

invertebratefood

chain

wherevertheyoccur.

A t

one

site

inIsrael,

mites

comprised3 5%of

thetotal

soil

arthropod

population;

in

the

Amazon

ranges

from

3 5

o

55 %havebeeneported.

S ome

harvestmen

eat

deadordecayinganimalor

plant

material.Arachnids

aregenerally

nocturnal,

despite

numbers

of

diurnal

har-

vestmen,spiders,and

mites.

Nocturnal

orms

hidein

darkcrevicesand

burrows

duringthe

day;

severalor-

dersare

morphologically

specialized

o

nhabit

small

spaces.

Withtheexceptionof

thewindspiders(Solifu-

gae),arachnidstend

to

betorpidandsedentarynone

fly,

fo r

example,

nor

do

anymove

constantly

like

ants

orother

active

insects.

The

basic

arachnid

forages

with

a si tand

wait,

solitarystrategy.They

move

rarely

and

waitorpreyo

encounter

hem.

Preys

hen

seized

witha

quick

strikeandimmobihzed.

Highlyorganized

social

systems

re

known

only

n

ew

spiders,but

looseaggregations

spiders,

harvestmen,andpseudo-

scorpions)arenotuncommon,usuallyinresponse

o

highpreydensityorimitedefugia.

Most

arachnids

arewelldaptedo

ast

or

ong

periods

weeks

or

months)ithout

ood;

nhe

aboratory

some

av e

survived

ormore

han year.Onlyjumpingspiders

amongarachnidshavenotablygoodvision;otherwise,

they

orient

primarilyviavibrationsand

touch.

Arachnids

occupy

ll

errestrial

habitatsdeserts,

forests,

undra,grasslands,mountaintops,soils,litter,

caves,tc.ydrachtiniditesapproximately000

species)are

important

components

of

most

freshwater

ecosystems;

other

mitesareparasitesofmarine

organ-

isms,

whereas

others

inhabit

marinesediments,includ-

ing

thedeepest

oceanic

trenches.Otherwise,arachnids

are

exclusively

terrestrial.

A

few groups,suchas

scorpi-

ons

andwind

spiders,

conserve

body

wateraswellas

any

arthropod

and

thus

tend

to

dominatein

deserts.

The

majority

needs

moist

conditions

to

survive.

Schizomids,

palpigrades,

and

ricinuleids

are

apparently

restricted

to

the

nterstices

ofmoistropical

andsubtropicalea f

litter

orequally

constant

and

moisthabitats.

C .Phylogenyand

Taxonomy

The

most

commonly

encountered

arachnidsarespiders,

scorpions,

harvestmen,and

mites,butthe

class

contains

seven

smaller

groups

of

terrestrial

arthropodsless

famil-

iartothegeneralpublic(Fig.

).

Thelargestandheavi-

es t

arachnid

is

the

African

scorpion

Pandinus

imperator.

whichmayreachalengthof

18-20

cm .

Thesmallest

are

perhapsth e

gall

mites

a t

80

ptm.

No

group

of

arach-

nids

is

well-known

by

vertebrate,butterfly,

or

vascular

plantstandards.Popularmanuals

are

available

fo r

only

asmatteringofthemostcommonspeciesof

spidersin

Europe,

North

America,

and

Japan;

ll

others

require

technical

hterature

and

specialist

knowledge

toidentify.

Myriad

species

re

undescribed

and

undiscovered;at

best,the

approximately93,000known

arachnidspecies

arebut

one-third

oftheprobable

otal,

andprobably

much

less.

Most

undescribed

arachnid

species

are

mites.

The

study

of

arachnidss

called

arachnology.

The

principal

international

scientificsociety

fo rnonacarines

has

approximately

60 0

membersbut

many

more

belong

onlytoregionalsocieties.

The

taxonomyof

arachnids

is

till monumentalask

and

an

obstacle

o

better

ecologicalandbiotechnologicalunderstandingofarach-

nids,butthe

number

of

arachnid

taxonomistsissmall

and

decreasing,

and

new

students

are

notbeing

trained.

There

arenocomprehensive

arachnology

texts

appro-

priate

oruniversityeaching

three

exist

orAcari) ,

althoughmodem

biologies

are

available

orspiders,

scorpions,

solifuges,

pseudoscorpions,andvariousas-

pects

ofmitebiology.

D .

Paleontology

Arachnidawereamongtheearhestterrestrialanimals.

The

marked

similarity

betweenfossilandrecentforms

inverallody

lan

nd

orphologysuggestsew

changes

over

hundreds

of

millions

of

years.

The

earliest

sitesforterrestrialarachnidsareEarlyDevonian(400

M a)andLate

Silurian

414

Ma );

the

extinct

arachnid

order

Trigonotarbida

igures

prominently,

butmites

are

ls o

present.

The

ossil

recordof

al l

arachnids

s

comparatively

poorlyknown.The1 3

living

and

extinct

ordersare

till

known

romless

han

50

majorim e

horizons

since

the

Silurian;

gaps

remain

more

common

than

ossils.

Arachnids

seem

to

have

invadedandin

theSilurianandreachedapinnacleofordinal

diversity

bytheCarboniferous.

The

latestdatesforheextinct

ordersTrigonotarbidaand

Phalangiotarbi

are

Permian

and

arboniferous,

espectively.

o

rder

eems

o

have

succumbed

to

the

endCretaceous

event

that

ehmi-

natedhedinosaurs.Theearliest

arachnid

ossilsare

aquatic

scorpionsfrom

the

Late

Silurian.

Spiders,

pseu-

doscorpions,

terrestrial

scorpions,and

mites

are

known

from

heevonian.hecorpion-hkeurypterida,

whicharesister

to

trueArachnida,alsomayhavebe -

comextinctthe

ermo-Triassic

oundary;

he

youngestfossils

are

also

Carboniferous.

Thephylogeny

in

Fig.

2impliesthatmanyarachnidclades

must

predate

all

scorpionfossils;analternateopinion,basedonless


5/20

.ARACHNIDS

2 3

m

Palpigradi

raneae

Amblypygi

Uropygi

Schizomida

Ricinulei

Acari

Opiliones

Scorpiones

Pseudoscorpiones

Solifugae

FIGURE2 P h y l o g e n y

of

arachn i d

o r d e r s .

evidence,

is

that

scorpionsinsteadar e

sister

to

eurypter-

ids,and

hathe

phylogeny

ofFig.will

be

shown

to

bencorrect.

mall

izemay

explainhearity

of

schizomid

and

palpigrade

fossils,

but

mites

inthe

Dev-

onian

showthatsmall

arachnid

fossils canpersist.Given

the

sparse

record,

it

ma y

well

be

that

a ll

arachnid

orders

were

distinct

and

essentially

modem

in

appearance

by

end

Silurian-Early

Devonian

times.

The

most

detailed

arachnid

ossils

re

inclusions

namber,hichs

fossilized

umrreeap.

he

rganismsecame

caughtin

the

wetsapandwere

ossilized

alongwith

the

sap.Cenozoicamber

arachnid

fossils40-80

million

years

ol d

canmostly

beplaced

n

modern

genera;

n

some

ases,

heossils

re

difficult

or

mpossible

o

distinguish

ro m

modemspecies.

Ecological

relations

arealsopreserved:Parasiticmites

occur

ontheirinsect

hosts,

fo rexample,

thus

documenting

the

antiquityand

diversityof

mite

parasitism.

II .

ARANEAE

Araneaeisthesecond

largest

arachnidorderwith 08

families,3200

genera,and

approximately37,000

spe-

ciesdescribedsecond

o

ites).

piders

re

distin-

guishedrom

other

arachnidsbyheirsilk-producing

spinnerets

attheendof

theabdomen

andthe

prosomal

poison

glands

exitingthrough

theirchelicerae

modified

as

fangs(Fig.3 ) .Spiders

are

among

the

very

fewanimals

FIGURE

3

SpiderAranea e :

C t e n i d a e ,

Cupienn ius

sp. )

pho tograph

b y J o n a t h a n

A.

C o d d i n g t o n ) .

that

us e

ilk

hroughout

heir

entire

ives.

A

narrow

stalkjoinstheabdomen

to

theprosoma,

allowing

great

flexibilityandprecise

orientation

of theabdominalspin-

nerets.

Pedipalps

areleg-likeandshort.Colors

arepre-

dominantly

dulltans,browns,

and

blacks,

but

spiders

ar e

occasionallyvery

colorful,

even

iridescent.

Th e

ab -

domenfmostspidersshowsoraceofancestral

segmentation,unlike

that

of

other

arachnids.TheNeo-

tropicaltarantulaTheraphosa

leblondi

(Theraphosidae)

is

the

largest

spiderat

about1 0

cm

in

body

length.

The

smallestspidersarethetinyorb-weavingSymphytog-

nathidae;adultsarelessthan m mlong.

A.Eco logy

Spiders

are

veryabundant.

One

calculation

estimated

5millionanimalsperhectarenanEnglishmeadow.

Another

ound

29,0(X)per

cubic

meter

in

an

English

sewage

treatment

plant.These

are

extreme

values,but

average nondeserthabitatprobablysupportsat

least

1andasmanyas800spiderspersquaremeter.

Ma n y

spiderspeciesdispersebyballooning.Ballooningspi-

ders

spin

a

silk

line

until

it

is

caughtbythe

wind

and

lifted

aloftpotentially

fo r

hundredsorthousandsof

kilometers.

One

study

estimated

hat

216,000

spiders

per

hectare

m ayballoon

nto

illed

ields

during

he

growingseason.

Point

diversities

per

hectare

may

vary

from

00

species

inmoderatetemperatezones

to

60 0

ormoreinthe

wet

tropics.

Borealdiversities

are

ess,

perhaps

20-50speciesperhectare.

Spiders

are

the

only

animals

to

use

silk

throughout

their

Hves.Silk

s

one

of

he

strongest

and

oughest

naturalfibers

known

andcompares

favorably

withthe

bestman-made

filaments.Eight

different

kinds

of spider

silk

havebeen

discovered,

but

the

maximum

made

by


6/20

2 4

- A R A C H N I D S

any

singlespecies

is seven.

Orb

webspinners,

fo r

exam-

ple,

make

w o

varieties

of

stiff,

oughsilk

fo r

weight-

bearingstructuralfibersandsafety

lines,

cement

to

fix

silk

toitself

and

substrate,

sticky

silkorglue

to

capture

prey,ubberysilko

carrythe

stickysilk

in

he

web,

specialized

silk

fo r

eggsacs,

and

hin,

weak

silk

spun

as

multiple

ibers

o

wrap

prey,

cradle

eggs,

and

or

othergeneralpurposes.A llspiders

ar e

capableofspin-

ning

silk

assoonas

they

leavetheeggsac,and

allmake

at

east

afetyinesdragUnes )

ndhecemento

attachthem

to

substrate.Approximatelyhalf

of

spider

speciesspinwebs

o

captureprey.Webarchitectures

are

taxonomically

specificandprovidemanycluesfor

reconstructing

spider

evolution.

The

remaining

spiders

areambush

predators

suchas

the

crab

spiders,which

lurk

inside

flowers

to

attackpollinators,tubeorretreat

dwellersthat

forage

inthe

very

limitedareaatthebur-

row

outh,

r

agabond

redators

uch

s

olf,

ground,

or

jumpingspiders.

B .ReproductionandGrowth

Reproductioninspidersrequiresthe

male

to

ejaculate

sperm

onto

a

specially

constructed

spermweb.H ethen

sucksup

the

sperm

into

specialized

sperm

transfer

or-

gans

at

the

pedipalpal

tips.Only

adult

males

have

such

structures;

heir

form

isusuallyspecies-specific.

With

his

palpsilled,heal ehen

searches

or

errules.

Femalesareusuallymoresedentarythan

males.

Lifeis

short

or

adult

males,

both

because

of

prdation

and

becausethey

ea t

little

as

adults.The

duration

of

court-

shipand

copulationvaries

rom

seconds

o

days,but

itendswithhensertionofhe

male

pedipalpand

transfer

ofspermnto

he

emalegonopore.

Females

store

the

sperm

and

sometimelaterconstruct

a

silken

eggsacntowhich

1-2500

eggs

are

placed.

gg s

are

fertilized

only

astheyexitthe

female's

body.

Parental

caresareandhighlyvariable,anging

ro m

simple

guardingofeggsactoactively

feeding

thebabies.Inat

least

onecrabspider

he

emale

dies

as

he

juveniles

emerge

from

the

eggsac,

which

theneattheir

mother's

body.

About

20

species

of

spiders

are

extremely

social.

Males

arerare(1:40-100),generations

overlap,foodis

shared,

andpreycapture

and

brood

careare

coopera-

tive.Colony

sizes

range

from

a

dozen

to

several

thou-

sandindividuals.

C.

Phylogeny

and

Taxonomy

Spidersare

the

seventh

largest

zoological

order

on

Earth

(after

Coleptera,Hymenoptera,Lepidoptera,

Diptera,

Hemiptera,andAcari),andofthesetheyaretheonly

one

for

which

all

taxonomic

literatureis

fully

cataloged.

Catalogs

greatly

facihtate

all

kinds

of

researchbecause

scientists

ca n

easilydetermine

hecurrent

axonomic

statusandhistoryof

any

describedspeciesandhus

decide

whether

a

given

specimen

belongs

to

a

described

species

or

not.

A t

higher

axonomic

evels

approxi-

mately,amily)

basic,

irst-draft

phylogenyisnearly

complete.

A t

thespecieslevel

theeasiestspecies-specific

charactersarefoundin

he

male

and

femalegenitalia.

Species

boundaries

nspidersaregenerallyclear-cut.

However,

the

speciestaxonomy

ofspiders

is

basedover-

whelminglyonmorphology.If morecostly

and sophis-

ticated

molecularmethodswereroutinelyappHed,the

number

fdistinguishable

pider

taxa oulder-

tainlyincrease.

Thefundamentalphylogenetic

division

in

spidersis

betweentheprimitive

mesotheles

(spinneretstowards

themiddleof

the

abdomen)

and

the

opisthotheles

(spin-

nerets

terminal).

Within

opisthotheles

here

are

again

tw o

basic

groups,hemygalomorphstarantulas

and

their

llies)ndaraneomorphsso-called

true spi-

ders)

Mesothelesandmygalomorphsarenotparticu-

larly

diverse

t

he

species

evel;

araneomorphs

cur-

rently include

9 4%

ofall

known

spider

species

and

this

disparity

will

certainlyincrease.Within

araneomorphs

the

basal

taxaare

a

fewrelictually

distributed

famiUes

in

northand

southemperate

egions.

Araneomorph

haplogynes

are

diverse,but

gaincomprise

relatively

few

species.

Thearaneomorph

Entelegynae

includesthe

bulk

of

modern

spiders.

Seven

spider

families

currently

contain

more

than 00 0speciesallareentelegyne.

During

a

ecent39-year

period,

an

verageof314

new

species

were

describedper

year

(12,200total),but

anannual

average

of1 04

old

names

were

synonymized,

fo r

net

gainofapproximately

200speciesperyear

(8800

otal).

Estimatesof

total

spider

diversity

range

from

76

to170,000.

Lower

estimates

mostly

extrapolate

from

heproportionsofnew

versus

knownspeciesin

taxonomicpublicationsor

re

basedoncomparisons

towell-known

groups.

Thehigherestimatestakeinto

account

hat

many

egions,

particularlyhose

ichest

in

spider

species,

are

disproportionately

undercoUected.

Inanycase,hereal

diversity

ofspiderswillneverbe

known

because

a

potentially

great

fraction

wdll

certainly

go

extinctbeforebeingdiscovered,

much

less described.

1 .Major

Lineages

a.

Mesothelae

Liphistiidae

is

the

onlyextantfamilyandislimited

to

areasofSoutheastAsiaandJapan.Onlyaewdozen


7/20

ARACHNIDS

.205

speciesare

known,

butsomearecommonwherethey

occur.Liphistiids

retain

many

primitivemorphological

features,

such

as

eight

ratherthan

six

or

fewer)

eg -

mented

spinnerets

hat

nsertnteriorly

atherhan

terminally

on

the

semi-segmented

abdomen.Their

biol-

og y

may

likewise

represent

the

ecological

ground

plan

for

spiders.Liphistiids

live

insilk-linedtubesequipped

with

udimentary

rap

doorsn

banksand

av e

n-

trances.

Sometimes,

silk

trip

lines lead

a wa y

from

the

burrowentrance

o

extendhesensoryadiusofhe

animal.

They re

nocturnal,

ambushpredators.

They

live

fo r

5-8

years,

are

remarkably

sedentary,

and

con-

sumeacatholic

diet

ofmainlywalkingprey.

b.Mygalomorphae

Mygalomorphs

includethetarantulas

or

baboonspiders

(Theraphosidae),

rap-door

spiders

Ctenizidae,

Acti-

nopodidae,

Migidae,

etc.),

purse

w eb

spiders

Atypi-

dae),unnel

w eb

spiders

Hexathelidae),

and

several

other

families

with

no

common

name.

Mygalomorphs

number 5

amilies

andapproximately

2200species,

butseveralofthefamiliesarepara-orpolyphyletic.A

more

realistic

estimate

is20-30family-level

groups.

Like

mesotheles,mygalomorphs

tend

to

live inburrows

and

forage

atthe

burrow

entranceorforaverylimited

distancearoundit.Some

theraphosids

are

arboreal

and

spinelaboratesilkenretreats.Dipluridsmakeextensive

webs

but

revirtually

unique

among

mygalomorphs.

Thevenomous

Australian

funnelwebspiders

{Atrax

an d

Hadronyche:

Hexathelidae)

were

responsible

or

many

deathsuntilanantivenin

w as

developed

in

the 980s.

Thelargetheraphosidbaboonspidersare

not

seriously

venomous

o

humans,

espite

heir

popular

eputa-

tion.

c.Araneomorphae

Araneomorphsncludeapproximately

9 4%

ofknown

spider

species.

Eventhemostprimitivearaneomorphs

are

very

different

frommygalomorphsandmesotheles.

Basa l araneomorphs

tend

to

be

much

smaller,

and

most

are

obligate

w eb

spinners

with

elaborate

spinneretsca -

pable

of

making

adhesive

cribellate ilk.

ribellate

silkisadhesive

due

to

theextremely

fine

threadsdrawn

from

the

cribellum,

the

verymodifiedand

fused

anterior

pair

of

spinnerets.

Adhesive

silkmakes

feasible

a

greater

variety

of

w ebarchitectures,andhesebasal

araneo-

morphs

spin

elaboratecatching

webs.

Thesistergroup

ofa ll

remaining

araneomorphs

is

the

family

Hypochili-

dae;

its

dozen

or

so

species

are

hmited

tothe

Appala-

chianountains,

ew

laces

n

estern

orth

America,andequallyrestrictedsitesinChina.

i aplogynae

aplogynae

comprises7amilies

of

spiders

of diverse

habitsand

worldwide

distribution.

Filistatidae

re

cribellate

web-spinningspiders.Their

webarchitectureisnot

much

different

from

thatofthe

mygalomorph

dipluridsasheet

that

narrows

to

a

silk-

lined

retreat

n

a

ube

or

crevice.

Diguetids

make

dry

silk

webs.

he

majority

of

haplogynes

re

eaf-litter

speciahstsand

re

vagabond,weblesspredators.The

venomousbrown

recluse

spiders(Loxoscelesspp.)are

haplogyne

icariids.

Thesister

groupofLoxosceles

n

southern

Africa

(Sicarius)has

also

beenimplicatedin

medicallyserious

bites.

ii.

ntelegynae

heemaining

70

families

of

spi-

ders

are

the

Entelegynae.

Entelegynes

share

many

evo-

lutionary

novelties.

Females

have

a

convolutedabdomi-

nallaterotectingheir

onopore,

hich

ale

genitalia

must

navigatesuccessfully

to

achieve

insemi-

nation.

Sperm

re

stored

n

unique

flow-through

system

o

hat

heemale

eproductiveract

has

wo

apertures

to

theoutside.Femaleentelegynesalsomake

special

silk

used

exclusivelyn

eggsacs,although

ts

exact

role

isunknown.

The

lateral

eyespossessa

canoe-

shapedtapetum

that

in

some

spiders

enables

orientation

via

polarized

light.

Althoughthehigherphylogeny

has

been

workedoutor

many

entelegyneineages,some

very

large

ones

remain

unstudied,

andtherelationships

between

entelegynelineagesare

also

controversial.

Lycosoidea

ncludes

1

amilies

ofmainly

hunting

spiders,somewithcommonnames:lynx,wolf,fishing,

ortropicalwolfspiders.

Lycosidae

wolfspiders)

and

Pisauridae(fishingspiders)ar ecommon,

cosmopolitan

lycosoid

spiders.

Lycosoids

occur

in

all

terrestrialhabi-

tats,

and

someare

semiaquatic

in

heir

abilityo

un

acrosshesurfaceofhewaterordivebeneathhe

surface.Web

spinning

isareamonglycosoids;some

mayhave

regained

it

after

evolutionary

loss.

Most

spe-

cies

re

agabondredatorsr,

ccasionally,

ube

dwellers.Active

at

night,

theymove

sporadically

or

wait

untilpreyapproachesand

henattackwithpowerful

frontlegsandchelicerae.

They

are

built

stronglyand

run

andjump

with

agility.

TheSouth

American

ctenid

Phoneuta

is

venomous

to

humans.

Dionychancludes

7

families

ofspiderswithw o

tarsal lawsand uftof

hair

ather

han

hemore

commonthree

clawsand

noclaw

tufts.

The

monophyly

of

Dionycha

is

by

nomeans

certain.

Dionycha

are

also

huntingspiders

andavehabits

similarohoseof

lycosoids.

rabspiders

Thomisidae)

wait

or

nsect

prey

in

flowers. Jumping

spiders

(Salticidae),

the

largest

spideramily,canbe

very

brightlycoloredandoften

prefer

to jump

rather

than

walk.Theirvisionis

superior


8/20

6

.ARACHNIDS

toanyother

arachnid;

sahicids

arehe

only

izable

spiderlineagethatis

strictly

diurnal.

Orbiculariae

includes 4famihesofspidersand

ap-

proximately

2,000pecies.

Mostorbicularians

spin

prey-catchingwebs,butafewgroupshavesecondarily

lost

the

web-spinning

habit.

The

primitive

w eb

architec-

ture

seems

o

be

he

or the

classic

spiderweb

of

radially

symmetric,

stiff,

dry

spokes

supporting

a

spiral

ofsticky

silkbutmoreorbicularianspecieshavelost

or

modified

theorb

architecture

than

retained

it .

Web

spidersrelyexclusivelyon

webs

fo r

preycapture.

Arane-

idae

(common

orb

weavers),Linyphiidae

(sheet

weav-

ers),andTheridiidae

(cobweb

weavers)

are

the

largest

families.

he

venomouswidow

spidersLatrodectus)

areheridiidsandare

distributed

worldwide;everal

speciesrepread

by

humans

andare

now

cosmo-

politan.

IllSCORPIONES

About

256

species

of

scorpions

are

currentlyknown

in

56

generaand 8amiliesFig.4) .

Scorpions

are

one

ofthebetter

collected

arachnid

groups

so

that

huge

FIGURE

4

Scorpi on

(Scorpi ones ;

Vaejov i dae ,

Uroctonus

sp.)

(pho to -

graph

b y

J a m e s

C.Cokendo lphe r ) .Se ealso

co l o r

inse r t ,th i s

v o lume .

increasesndiversity

are

not

asikely s

nmites

or

spiders.Estimatesof totaldiversity

run

as

high

as

7000

species.

ll

scorpionsave

arge,

bvious

pedipalps

modified

s

incers,bothodyegionsrebroadly

joined,

hedistalabdomenisnarrowed

into

alexible

tail

bearing

a

venomous

stinger

at

he

end,

and

ven-

trally.

The

abdomenbearsapairofcomb-likesensory

appendagesknown

aspectines.Colorsvaryfromtrans-

lucent

o

brownorblack.

uriously,

hey

luoresce

under

ultraviolet

light,

a

discovery

that

hasgalvanized

recent

field

esearchon

hese

animals.

The

ongest

is

Hadogenestroglodytesat21cm ,butPandinusImperator

isnearlyaslong

and

much

heavier.Theexternalmor-

phology

of

recentscorpions

is

impressively

similarto

Silurianfossils.Formerly

scorpions

were

thought

to

be

thesistergroupof

all

otherarachnidsbecausehey

closely

esembleheextinct

marine

eurypterids

hat

are

the

sister

group

of

a ll

arachnids.Better

analysis

of

morphological

data

Fig.

) ,

weakly

corroborated

by

molecularevidence,suggestshatscorpionsaremore

deeplyimbeddedinthearachnidcladeandmerelyre-

tain

many

primitivefeatures.Th e

issue

is

controversial.

Scorpionsare

theonlyarachnids

witha

narrow

post-

abdomen

( tail )

terminating

in

a

venomous

sting.

The

sting

ismost

oftenused

fo r

defense,althoughscorpions

will

sting

largeor

strong

prey.

The

sting

of

most

scorpi-

ons

s

painfullikewasp

or

hornet

stingsbut

not

dangerous.

haracteristically,

scorpions

with

slender

pedipalpsar emorepronetostingtheir

prey,

whereas

those

withobustpedipalpsend

o

crushprey.The

CentralAmericangenusCentruroides,

B razilian

Tityus,

and

Old

WorldAndroctonus^Leiurus,

Mesobuthus,and

Parcd}uthus

arevery

venomous

andmedically

important.

InMexico,entruroidespp .ting300,000andkill

10 0 0

peopleannually;Androctonus,

Leiurus,

andMcso-

buthus il lhousandsannuallyinEgyptandPakistan

alone.

Excepting

icks

hat

spread

disease,

scorpions

arebyar

he

most

dangerous

arachnids

ohumans.

Scorpions

arecorrespondinglyprominent

in

mythology

andfolklore(e.g.,thezodiacalconstellation

Scorpio ).

Scorpion

venoms

typically

contain

multiple

low-molec-

ular-weight

proteinaceousneurotoxins.

Scorpion

blood

inactivates

scorpion

venom,

but

if

the

venom

is

injected

directly

in

anerve,the

animal

rapidlydies.Parabuthus

transvaalicusand

P.

villosus

squirtvenom

o

damage

corneas,like

spitting

cobras.

A.

Eco logy

Scorpions

are

most

diverse

ndeserts

or

similar

dry

areas,

although

they

are

reliably

presentinmoist

ecosys-

temsif thetemperature

isnot

too

cold.They

nowoccur


9/20

.ARACHNIDS,

2 7

on

llmajor

andmassesxceptAntarctica.avored

habitats reburrows,under

bark,stones,or

ogs,or

inside

small

crevices.

Burrowsmay

be

as

deepas40-80

cm ,

serving

o

escape

he

hot

daytimeemperatures

indeserts.B eca useheyhkehardsubstratesanddry

conditions,

scorpions

adapt

well

to

human

structures.

Most

scorpions

are

ground

dwelling,

but

manyspecies

are

arboreal,

especiallyn

he

neotropics.

n

canopy

fogging

atfour

AmazoniansitesinPeru,allofapproxi-

mately

00

specimenswereButhidae

J.

Ochoa,

per-

sonalcommunication).

Aewareimitedoightless

caves.

Scorpions

arealmostinvariably

nocturnal,

although

theAfricanP.

villosusspredominantlydiurnal.

The

eyesseemto

detect

luminosity

at

best.

Prey

movements

are

detected

by

tarsal

senseorgans

tdistances

upto

15cm ,and

prey

re

attackedn

single

motion.

A t

distances

up

to

3 0

cm

prey

are

located

through

orienta-

tion

responses.

The

large,pincher-like

pedipalpsimmo-

bilizeprey;

thereafter,

piecesare

torn

offby

the

chelic-

erae

and

digestednhe

pre-oral

cavity

beforebeing

suckedintothegut.

Scorpions

canbeimportant

con-

sumers

in

somecommunities.InIsrael,

Scorpio

maurus

annuallya te

an

averageof

1 1 %ofthe

isopod

population,

which

w as

not

theonly

item

in

their

diet.

A t

moderate

densities

of

1 .5kg/ha,

Urodacus

yaschenkoi

ate

an

an-

nual

verage

of

7.9

kg/ha

of

prey.annibahsmand

prdation

byotherscorpionspeciesar ethoughttobe

the

most

important

sourcesof

mortality,

but

other

top

invertebrate

predators

(e.g.,

spiders)

and

vertebrates

ar e

alsoimportant

scorpionpredators.Generally,mortality

ishighestimmediatelyafterbirth,lowerforintermedi-

ate-agedanimals,andhighfo radults(e.g.,65 ,3 0,and

60%,respectively,

per yearfo r

the

Australian

Urodacus

manicatus).

corpion

ortality

s

articularlyigh

amongmalesbecauseoftheirhighactivitylevelsand

mobihtyduringthebreedingseason.

Cannibalismby

females

is

a

significant

cause

ofmale

death.Biased

adult

se x

ratios

of1.2-1.4:1

are

typical.Communal

behavior,

however,doesoccur.

For

example,

amily

groups

up

to

5individualsoftheB razil ianOpisthacanthus

caya-

porumcooperateoconstructandoccupycommunal

chambers

in

the

center

of

termite

mounds.

The

African

Heterometrusspp.also

construct

and

share

a

communal

burrow,

inhabitedby

individuals

of

various

ages.

Piles

of

0-30

ndividualsfentruroidesxilicaudare

found

in

he

winter

months.Groupsof5ndividuals

ofMesobuthusmartensi,a llof

the

same

ag eand

all

with

their

heads

orientedtoward

centralspot,

have

been

foundunderwet

rocks

intheintertidalzone.

The

vastmajority

ofscorpion

species

are

subtropical

or

tropical.Pointdiversity(thenumber

of species

sym-

patric

at

on e

site)

peaksn

subtropical

desertsand

is

particularlyhigh

6

or7,with maximumof 2)

n

BajaCalifornia.Tw o

o

hreespecies

per

sitesmore

usual.Vaejovis

littoralisreachesunusuallyhighdensi-

ties

(8-12/m^)in

the

driftUne

along

theGulf

ofCahfor-

nia.

The

North

American

FaruTOCtonus

oreus

occurs

as

fa rnorthas

B ri tish

Columbiaand

Alberta,

andthe

EuropeanEuscorpiusermanus

eaches

he

outhern

Alps.

ven

ropical

scorpions

sometimes

nhabit

ex -

treme

conditions;

Orobothriurus

rassimanus

w as

col-

lected

at5560minthePeruvian

Andes.

B .Reproduction

Reproduction

n

corpionssia

permatophore

attachedtothesubstrate.Themalecompletes

produc-

tion

of

the

spermatophoreinsidehis

body,deposits

the

sperm

nside,

and

attaches

he

spermatophore

o

he

substrate,

all

thewhileholdingon

to

thefemaleduring

preliminarycourtship.Thespermatophoresspring-

loaded and

catapults

the

sperm

mass

into

heemale

gonopore

when

a

lever

is

touched.

Scorpions

are

exclu-

sively

ovoviviparous

or

viviparous.

The1-105young

arebomliveandchngtohe

mother

fo rtheirstfew

molts.

Afew species

areparthenogenetic.Scorpions

live

4or5

years

(rarely

8);

heydo

not

moltas

adults.

C .

Phylogeny

and

Taxonomy

Thehigher

classification

ofscorpions

has

changed

dra-

matically

as

classical

data

have

been

reinterpreted phy-

logenetically.The

old

system

proposed

ew ,huge,

polyphyleticfamilies

aboutwhichnothingmuch

in

gen-

eral

couldbesaid;

now

1 6

or

1 8

famihes

wdthincreas-

ingly

coherent

biologies

are

recognized.

Species

limits

inscorpionsar eoften

difficultbecause

scorpion

genita-

lia

areusually

not

species-specific.

B yradition,scor-

pion

taxonomistsuse

thesubspeciescategorymore

than

most

arachnologists.

About

50

subspecies

are

recog-

nizedin

addition

to

the

1 2 6 0

species,

but

becausethese

are

easily

distinguishedthey

are

probablydistinctspe-

cies.

A

classic

exampleisthe25non-overlapping,fully

distinct

subspecies

of

Scorpio

maurus.

Species-leveltax-

onomiccharactersncludehesurface

sculpturing

of

theexoskeleton,

morphometric

data,

henumber

and

positionof

pedipalpaltrichobothria,

and

th e

hemisper-

matophoresinternal

male

structures

that

producethe

spermatophore.

1

Major

Lineages

Thebasaldivision

n

Scorpionessbetweenhebu-

thoidsandremaining

scorpions.

New

and

Old

World


10/20

8

.ARACHNIDS.

buthids

are

also

distinct

lineages.

Scorpionoids

and

the

vaejovoid-chactoid

ineage

are

heemaining

major

scorpionneages.haerilidaendseudochactidae

{ChaenluSy 21species;

Pseudochactus

ovchinnihovi,

from

Kazakhstan) remonogeneric

andenigmatic;heyare

like

none

of

the

other

scorpion

families

and

their

rela-

tion

o

othermajor

lineages

is

obscure.

They

m ay

be

basalbulhoidgroups.

Buthidaeisthelargestandmostwidely

distributed

scorpion

family

withapproximately

74

generaand53 1

species.

Buthidae

is

most

diverse

in

the

African

tropics

andPalearcticegions.Buthidsendohaveslender,

elongatepincers,

obust

tail,

andusuallyaubercle

under

heting.A llscorpionsconsidereddangerous

to

humans

re

buthids.

Buthids

realsohemost

di-

verse

ecologically

and

occupyhumid,mesic,

and

dry

habitats.

The

small

familyMicrocharmidaeisan

Afro-

tropical

uthid

egregate

ith

wo

enera

nd

ix

species.

The

Scorpionoidea

(36generaand

3 55

species)is

a

large,

monophyleticlineagethatincludesBothriuridae,

Diplocentridae,

eteroscorpionidae,emiscorpiidae,

Ischnuridae,Scorpionidae,

and

Urodacidae.Scorpioni-

daelack

a

tubercle

under

thestingand

the

sidesof

the

sternum

are

parallel.heamilycontains

he

genus

Scorpio

from

heMediterranean

andNear

East ,

much

mentionedinclassicalGreek,

Egyptian,andChristian

myths,andPandinus,thegiant

African

blackscorpion.

Theongest

andheaviest

scorpions

are

scorpionids,

which

ar eexclusively

Old

World.

Therelationshipsandmonophylyof

thevaejovoid-

chactoidlineages(43generaand495species:Chacti-

dae,

Euscorpiidae,

luridae,

Scorpiopidae,Superstitioni-

dae,

roglotayoscidae,and

Vaejovidae)rehe

most

problematicreas

f

scorpion

higher

axonomy

and

phylogeny.

The

arge

amilies

uridae

andChactidae,

in

particular,aredoubtfullymonophyletic,lthough

each

includes

many

clearly

validgroups.Together,

the

vaejovoid-chactoid

lineages

comprise

about

one-fourth

ofknown

scorpion

species,

including

the

mostcommon

species

inNorth

America.

IV .

OPILIONES

The

describedworld

fauna

ofOpiliones(harvestmen

or

daddy

longlegs)

comprisesapproximately

44

families,

1554

enera,

ndbout00 0

pecies

Fig.

) .

he

largestharvestmanisTrogulustorosusat2 .2cmlong.

Theanterior

and

posterior

bodyegions

rebroadly

joined andthe

abdomen

is

rather

short, givingthe

body

a

wider

and

ounderappearance

han

hoseofother

FIGURE Harves tman

Opil iones:

Pha lang i i dae ,

adrobunus

sp.)

(pho tograph

b y

J o n a t h a n

A.

C o d d i n g t o n ) .

arachnids.

The

second

pair

of

walking

legs

is

usually

the

longest.Opilionshavejusttw oeyes

(cave

orlitter

groups

are

sometimesblind).

A llharvestmenhaveapair

ofglandsthatopenvialarge

pores

ontheanterolateral

margins

of

thebody;

the

functionof

their

secretionsis

apparently

diverse.

Harvestmen

are

theonly

arachnids

inwhichales

have penis.

emales

have

ong,

flexible,andextensibleovipositor

(a s

domanymites).

The

mostcommongroup

in

north

temperate

regions,

the

Phalangioidea

(daddylong

legs),

have

soft

and

flex-

ible

bodies,

weakmouthparts,

and

extremelylong

legs

(commonly13timesthe

body

length),

butjustas

many

harvestmenare

fantasticallyarmoredwithbizarre,

huge

chelicerae,

raptorialpedipalps,

andshort,stiff legs.

Oth-

ers

are

mite-hke,

and

still

thers

are

dorsoventrally

flattened.

Colors

are

usuallysubtlepatterns

of

brown,

gray,orblack,butropicalormscanivalanything

seeninspidersormites.Inhelong-leggedforms,the

distaleg

tip

is

divided

intonumerousalse

segments

that

form

prehensile

ip .

tcanbe

wrapped

around

objects

to

achievea

very

firm

andadaptablegrip.The

long

secondlegsmaydoubleasfeelers.

Therespiratorysystemisexclusively

tracheate.

The

very

long-legged

Phalangioidea

have

accessory

spiracles

ondistallegarticles.Touchandvibrationperception,

as

in

most

other

arachnids,

seems

to

be

the

dominant

sense.

The

eyes

at

bestdistinguishlight

and

darkand

direction

of

light.

Opilions

consume

a

broaderdietthan

any

other

arachnids

other

thanmiles.The

basic

pattern

is

prdation,

butsome,

fo r

example,

specialize

onsnails,

which

are

otherwise

arely

consumedby

nonacarine

arachnids.

Opilions

also

are

known

to

eatdead

insects,

fruit,ndecayingegetableatter.nlikether

arachnids,arvestmenanngestolidarticles,s

shownbysclerotizedbits

in

theirexcrement.


11/20

.ARACHNIDS,

.209

Ma n y

harvesttnendefend

themselves

againstattack

by

shedding

legs.

Onestudyoftw o

species

in

Louisiana

foundthatabouthalf

the

animals

hadlostoneleg,but

lesshan

0%lackedhree.Seven-leggedharvestmen

seemtosurviveandfunctionaswellas

intact

animals.

A

shed

eg

continues

o

jerk

and

witch

attractively

fo rminutes,permitting

heharvestman

o

escape.

A ll

harvestmenhavepairedrepugnatorial glandsonthe

front

margin

ofhe

body.

When

eg s re

pinched

droplet

of

fluid

appears

at

he

orificewhichmay

be

dabbed

on

an

attacker

with

aleg

or

allowedto evaporate.

The

secretionscan

also

help

aggregatingspecies

to

find

each

other,

and

some

showbroadantibioticandanti-

fungal

ctivity,resumablyusefuloitterandoil-

dwellingforms.Quionesarea

major

ingredient.

Soil-

dwelling

harvestmen

and

he

short-legged

Laniatores

areslowcompared

to

long-leggedharvestmen.

A.

Eco logy

In

general,

arvestmen

prefer

moist,

or

t

east

not

xeric,environments.Themite-likeCyphophthalmi

live

indarkleaflitter,

caves,

orunderstones.Thelargely

tropicalndsuallyhort-leggedaniatoresov e

slowlyover

vegetation

or

the

forestfloor.

The

usually

long-legged

Eupnoi

canbeanywhere,butheir

very

longlegswithprehensiletips

are

specialized

fo r

cross-

in gthelargegaps

between

heleavesoftrees,

shrubs,

andherbs.

The

northern

European

opilionid

fauna

com-

prises

pproximately

4

pecies

nd

hatf

North

America

approximately

23 5

pecies.

n

emperatere-

gions,diversitiesof morethana

dozenspeciesperhect-

areare

uncommon.

B .

Reproduct ion

Uniquely

among

non-acarinearachnids,

sperm

transfer

occursvi athemale

penis.

Matingoccursquicklyand

seemingly

writhout

courtship.

Themale

faces

the

female

and

pushesthe

penis

underneathherbody

or

between

her

chelicerae

andintothegonopore.

After

insemina-

tion,thesexes

separate

and

continue

theirsolitarywan-

derings.Femalesusetheir

long,

flexibleovipositorsto

depositeggs

in

suitably

protected

areas.Trogulidsde -

posit

heir

eggsonly

in

empty

snailshells,

andother

groups

oviposit

beneathstones,deep

into

soil,under-

neath

bark,r

nbore

holesn

plant

stems

eftby

insects,

usually

abandoning

the

eggs

once

laid.Newly

hatched

animals

re

ctive

and

esemble

adults.

Five

to

eightmolts

o

maturityarecommon.

A n

unusual

reversalof

sexroleoccursinthePanamanianharvest-

manZygopachylusalbomarginis.Malesfighttooccupy

existingmudnestsorconstructheirown.emales

wanderbetweennests,

courting

the

males,

mating,and

ovipositing

in

a

series

ofnests.

They

have

nothing

more

to

o

ithhe

offspring.

ales

accumulate

gg sof

different

ge s

and

rom

different

emales

anddefend

the

eggs

against

conspecifics

and

ants.

C .Phylogenya ndTa xo no m y

Thephylogenyof

Opilioneshasrecendy

beenclarified

a t

hesuperfamily

level,

but

many

additional

changes

are

expectedn

amilial

arrangements.

S ome

amilies

seem

to

bebasedonlyonprimitivefeatures(e.g.,Tra-

vuniidae,

Phalangodidae,

andTriaenonychidae).Eup-

noiand

Dyspnoiclassicallyformedthe

suborder

Palpa-

tores,

butincreasing

evidence

indicates

that

this

taxon

isparaphyletic.Thenumberof

recognized

families

has

approximately

doubled

n

he

past

0

years.

t

he

specieslevelthemorphologyofmalegeniuliaisespe-

cially

diagnostic.

1 .

MajorLineages

a.Cyphophthalmi

This

subordercontainsfive(or

six)

famiUes

and

about

1 00

species.tissister

to

al lremainingOpiliones(the

Phalangida ).Cyphophthalmiareeyeless,liveindeep

moist

leaf

litterorcaves,

and

range

in

sizefrom

1

o

7

mm .Theanimalshavea

hardened

plate

covering

the

entiredorsal

surface,

andtheyresemblemites.Sirois

North

American

and

European,

but

the

familyalso

oc -

curs

n

Southeast

sia,

Turkey,Japan,

exico,and

South

Africa.

Lifespans

of

up

to

7

years

have

been

re-

ported.

b.

Eupnoi

Thisgroupcontains

w o

superfamihes,

ncludinghe

classic

daddyong

eg sPhalangioidea:Phalangiidae,

Sclerosomatidae,Megalopsalididae,

and

Neopilionidae)

ofsoft-bodied,

ong-legged

arvestmen.

halangium

opilios

ommon

round

buildings

ndntroduced

throughout

he

world.

The

sclerosomatid

Leiobunwn

spp.

re

common

n

North

American

and

European

forests,

n

which

hey

move

easily

cross

heupper

vegetation.he y

arepredators

andcavengers.ad -

doidea

includes

onlyone

or

tw o

familiesofharvestmen

with

enlarged

eyes

and

short

legs,

sometimes

common

on

tree

trunks.

c.Dyspnoi

This

group

ls o

ncludes

wo

superfamilies,

but

has

manyewer

species

han

Eupnoi.schyropsalidoidea


12/20

210.

.ARACHNIDS

containsthreefamiliesand

just

sevengenera.

Ischyrop-

salisis

European

and

feedson

snails.

Troguloidea

con-

tains

fourfamilies,

tw o

monogeneric

and

several

genera

in

he

emainingamilies.

Nemostoma

s

commonn

caves.

Trogulidae

are

f>eculiarharvestmenthatlook

like

giant,

lattened

mites.

Legs

re

very

short.

Trogulids

live

under

stonesandin

leaf

litter;

snailsare

an

impor-

tant

part

of

their

diet.

d.Laniatores

Thisgroupsmorphologicallymorediversehanhe

previousgroupsandendso

be

morediversenhe

tropics,includingmanycolorfulspecies.Threesuper-

families

are

recognized:

Traviunoidea

(4

families),On-

copodoidea

(1family),andGonyleptoidea

(18-20

fami-

lies).olloquially,aniatoridsre

nown

sshort-

legged harvestmen

becausethe

mostcommonlaniator-

id sdohave

short

legs,

but

some

agoristenids,

cosmetids,

gonyleptids,

caelopygines,

progonyleptoidellines,

and

mitobatineshave

legs

comparable

in

length

to

those

of

Palpatores.

TheGonyleptoidea

contains18-20families

with

raptorial

pedipalps

for

prey

capture

and

enlarged

fourthcoxaewithspreadingappendagesperhaps

defense

against

being

swallowedwhole

by

predators

or

dragged

downtheburrow ofa

parasitoid.Gonyleptidae

areypicalheavilyarmored

and

spiny,

often

colorful,

and

usually

arger

han

4mm.

hey

are

exclusively

Neotropicaland,

withmorethan

00

genera, reone

ofthelargestfamilies.ThecloselyrelatedCosmetidae

superficially

esemble

gonyleptidslarge,

heavily

r-

mored,

often

colorful,

nd

slow-moving

N ew

World

harvestmen.Phalangodidae

isa

large

cosmopolitan

fam-

ily

ofmorehan

50

generadefinedainlybyhe

features

hey

ack.

For

years

t

hasbeenusedoile

taxawith

no

obviousrelatives,

and

therefore

its

biology

makes

littlesense.Althoughmost

diverse

inthenorth-

erneotropics,heiristribution

ncludesouthern

North

merica.

heir

edipalpsre

lattened

ith

spinymargins.

V .SMALLERA RA C HN I D

O R D E R S

Amblypygiwhipspidersoraillesswhipscorpions),

Uropygiwhipscorpionsorvinegaroons),Schizomida

(nocommonname),and

Palpigradi

(micro-whip

scor-

pions)are

ll

mall,

unfamiliararachnidgroupshat

are

closely

elatedo

each

other

and

ospiders

Fig.

2).

Like

primitivespiders,

all have

two

pairs

ofabdomi-

nalbooklungs,althoughthesecondpairismissing

in

thetiny

Schizomida

andpalpigrades

lackboth.The

first

pairofwalkingeg s

s

elongate

andeeler-like,with

falsearticulations

n

heerminalarticlestopromote

flexibility.

Pseudoscorpionespseudoscorpions),Soli-

fugae

(windspiders),

and

Ricinulei

(no

commonname)

are

a

miscellanyof

remaining

arachnid

ordersrelated

to

variousorders

already

discussed,

s

llustratedn

Fig.

2.

A.

Amblypygi

Approximately

1 25

species

ofamblypygids

in

2 0genera

and5

families

are

known

(Fig.

6).

The

American

Acon-

thophrynus

coronatusisthe

biggest,

atabout4. 5cm

in

bodyength.

Theusualadultbodysizes

about

4-6

cm .

Theirstwalking

eg s

of

amblypygids re

enor-

mously

ong,and

ullystretched

arge

animal

can

span

50

cm .

Whipspidershaveno

tail,

andtheirpedi-

palps remodifiedintoierce-looking,spinyraptorial

appendages.Amblypygids

are

easily

recognizedby

their

extremely

long

front

legsand

raptorial

pedipalps.

Col-

ors

aredull

brown

or

black.

Thebody

is

la t

and

leg

insertion

wisted

sothat

limbs

fold

in

he

same

plane

asthe

body(like

a

crab),

permitting

the

animals

to

edge

through

thin

openingssuchascracksin

hollow

trees.

They

movesideways

more

easily

than

forward

or

back.

Amblypygids

hunt

by

drifting

their

longfront

legs

gen-

tly

overhe

surface

aroundhem

o

ocate

preyand

usingtheir

raptorial

pedipalpsto

pounce.

Like

spiders,

allhe

abdominalgangliahavemigratedinto

the

pro-

soma

in

which,

fused,

theyforma

brain.Reproduction

isvia spermatophore.ikeuropygids,mblypygid

females

carry

their

eg g

clutches

inside

a

membrane

of

drieducus

lued

oheii

entral

bdomens.

he

15-50

young

hatch

and

remaininside

this

membrane

until

heyhaveundergone

their

first

molt.

Theyoung

chngtothemother

fo r

ashorttime.

F1GURE6

hipspider

o r

ta i l l e ss

w h i p

sco rp ion

(Amblypygi :Phryn i -

d a e ,Phrynus

$p.)

pho tographb y J o n a t h a n

A.

C o d d i n g t o n ) .Se e

also

co l o r

i n s er t ,

h is

v o l u m e .


13/20

-ARACHNIDS.

.211

Whipspiders

live

in

subtropical

andtropical

areas,

in

forestsandoftenin

caves.

Theyareexclusively

noc-

turnal

andfairly

common.Duringthedaytheyhide

in

hollow

trees

orlogs,underloosebark,orunderlarge

logs.

Onlyone

species

ivesn

eafitter

and

snot

known

to

burrow.

Their

diet

seems

to

be

a

broad

range

ofsmallerarthropodsintheirenvironment.

B .Uropygi

About

1 00

speciesofwhip

scorpions

ar e

known

in

6

generaandonefamily,Thelyphonidae(Fig.7).

A t

7. 5

cm ,heargestsastigoproctus

iganteusof

North

America,

but

3-5cm

is

usual.

Whip

scorpions

areeasy

toecognize

by

he

ong

posterior

whip

or

lagellum

(highly

modified

terminal

abdominal

segments).

Colors

arebrown

o

lack.

ropygids

av e

efensive

nal

glandshataccuratelysprayan

acid-smelling

luid

t

attackers.

The

smell

explains

the

common

name

vine-

garoon.

The

luid

of

M.giganteus

is

85 %

acetic

acid

but

t

also

containssubstances

o

educehe

surface

tensionofheepicutideohatheaceticacidcan

spreadwidelyandpenetrate.Vinegaroonsaresuppos-

edly notsensitive

to

their

own

spray.Reproductive

hab-

its

are

knownonly

for

a

ew

species,

but

presumably

spermtransferoccursviaaspermatophoreglued

to

the

substraten ll

pecies.

S omespecieshave engthy

courtship10hr

to

severaldays.Femaleskeepheir

12-40

eggsattached

to

their

ventral

abdomen.

Female

Thelyphonus

build

adeep

burrow

and

do

not

feed

while

guarding

the

eggs

fo r

4

or

5

weeks.

Uropygids

m ay

live

6-8

yearsorevenlonger.

Uropygidsar e

tropical

tosubtropicalanimals.

They

hideinleaf

litter,

burrows,underlogs

and

rocks,

and

insidedark

crevices

or

holes

duringtheday,emerging

^:>W

FIGURE

7

h ip

sco rp ion

(Uropygi :The ly phon ida e ,

Mast igoproctus

sp. )

pho tograph

b y

J o n a t h a nA.

C o d d i n g t o n ) .Se e

alsocolor

i n s er t ,

th i s

v o l u m e .

FIGURE

8

Sch izomidSch i zomi da:H u b b a r d i i d a e )pho tograph

b y

J e r e m y

A.

Miller) .

atnight

to

hunt.Notmuchisknownabout

their

prey,

but

presumably

it

consists

ofother

small

ground-dwell-

ingnsects,rachnids,

nd

rustaceans,

hich

hey

crush

between

heir

pedipalpal

segments

prior

on-

gestion.

C.Schkomida

About

200speciesin3 0

genera

andtw ofamilies(Pro-

toschizomidae

and

Hubbardiidae)

are

known(Fig.8).

Schizomids

(thereis

no

common

name)aremostlike

tiny

uropygids,

but

he

abdominal

lagellum

s

short

(three

segmentsbut

rarely

five).Colors

are

usuallylight

yellowoan

o

dull

green.

ssiduous

searching

n

moist

tropicallitterusuallyturns

up

aschizomid.The

largestschizomid

known

isAgastoschizomusucifer

at

about

2.7

mong,ut msypical.

ost

schizomids

lack

eyes

entirelyand

live

inmoist

tropical

or

subtropicaleaf

litter,

understones,

n

logs,

moist

crevices,

caves,

and

so

on .Reproductionis via

asperma-

tophoreattachedtothesubstrate,afterwhichfemales

la y

6-30

eggs

that

are

glued

to

the

ventral

female

abdo-

men

ntilhe

oung

emerge.

t

w omazonites

schizomidabundancesanged

from

5

o

1 0animals

persquaremeterpermonth.

Liketheuropygids

they

havebeenreportedtopro-

duce

a

defensivechemicalsmell.They

can

move

back-

wards

rapidly

andhaveenlarged

femora

apparentlyused

tohopbackwards.

D.Palpigradi

There

is

onlyone

family

(Eukoeneniidae)withfiveor

sixgeneraandabout80pecies.Palpigradesmicro-


14/20

2 1 2

ARACHNIDS

whip

scorpions)

are

tiny,lightyellow

to

white,

delicate

soil

and

leaf

litter

specialists

with

acosmopolitan

distri-

bution.

The

largest

is

Eukoenenia

draco

at

2 .8

mm

long,

but or2mmistypical.Theyresembletheyoungof

Uropygi.

Likewhipscorpions,

they

haveawidepreab-

domen

and

a

multi-segmented

whip-like

postabdomen.

Like

many

soil

organisms,palpigradeslackmost

of

the

organ

systems

equired

by

argeanimalshat

iv e

n

drierandless

constant

environments.Theylackeyes,

respiratory

organs,

and

a

circulatory

system

buthave

innervatedsetae

that

detect

vibrations.

Mostspeciesare

known

from

the

tropics;

several

palpigradesapparently

live

in

intertidal

or

shallow

marine

habitats.

Eukoenenia

janetschekiw astheonlyspeciesfoundattw oAmazon

sites,

buttw asairly

abundant

30-120

animals

per

square

meter

per

month).

E.

Ricinulei

One

family

(Ricinoididae),three

genera,

and

53

2000 Coddington&Colwell Arachnids(1)

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Transcript of 2000 Coddington&Colwell Arachnids(1)