ARTHROPODA

PHYLUM ARTHROPODAGr. Arthron, joint, + pous, podos, footMost numerous animals on earth (900,000 species)Spiders, scorpions, ticks, mites, crustaceans, millipedes, centipedes,

insects and some smaller groups.

STRUCTURE AND ORGANIZATION

Segmented body, metameric bodySegments are specialized for a variety of purposes, forming functional

groups (Tagmata) Head and thorax are two tagmata Head, thorax and abdomen Cephalothorax and abdomenTriploblastic coelomates with well developed organ systems

No backboneCuticular exoskeleton (chitin and tanned protein) ecdysis (or molting)

Skeletal support

• each somite bears a single pair of jointed appendages

-sensory activities, food gathering and feeding, reproduction and walking or swimming

Locomotion

with complete digestive systemMouthparts are modified from appendages and adapted for different

methods of feedingexhibit all modes of feeding: carnivorous, herbivorous, scavengers, filter-

feeding

Nutrition

Reproduction• are dioecious and undergo internal fertilization• may be oviparous or ovoviviparous• life cycle involves metamorphosis which include

molting process or ecdysis (shedding of exoskeleton)• Few species exhibit parthenogenesis

Respiration by body surface, gills, tracheae or book lungsOpen circulatory systemPoikilothermic

Respiration and Circulation

• excretory organs– malpighian tubules– excretory glands such as antennal, coxal, and

maxillary glands

Excretion

Nervous System• similar to annelid plan• Dorsal ganglia connected to double ventral chain of ganglia

I. SUBPHYLUM TRILOBITOMORPHA (LATIN: THREE-LOBED FORM)

extinct trilobitesconsist of three tagmata:

head, thorax, and pygidium

each somite (except for the last) has two lobes or biramous type of appendages

inner lobe/endopod: walking

outer lobe/exopod: burrowing, swimming, filter-feeding, respiration

II. SUBPHYLUM CHELICERATA (GREEK: CLAW)

body with two tagmata: cephalothorax (prosoma) and Abdomen (opisthosoma)with six pairs of appendages all

attached to prosoma first pair: chelicerae which are feeding organs,

second pair: pedipalps which could be feeding or sensory structures

last four pairs as walking legsmembers do not have antennaeincludes spiders, ticks,

scorpions, sea spiders, mites, harvestmen (daddy longlegs) and horseshoe crabs

II. SUBPHYLUM CHELICERATAClass Merostomata

Prosoma and opisthosomaAppendages on the

opisthosoma are flattened and modified for gas exchange as ‘book gills’

Elongated terminal portion called telson

Includes horseshoe crabs (Limulus polyphemus) and extinct giant water scorpions

II. SUBPHYLUM CHELICERATA

Class Arachnida

(Gr. arachne, spider)Segmented or

unsegmented abdomen (opisthosoma) with or without appendages and generally distinct from cephalothorax

Chiefly oviparousNo true metamorphosisIncludes scorpions,

spiders, ticks, and mites Dust

mites

Black widow spider

tarantulaTick (engorged)

Class Arachnidaa. Scorpionb. Pseudoscorpionc. Red spider mited. Black-legged ticke. Tickf. Solpugidg. Jumping spiderh. Common spideri. Opilionid (harvestmen

or daddy long-legs)

Pechenik, 2005

II. SUBPHYLUM CHELICERATA

Class Pycnogonida(Greek: thick knee)

Body not divided into tagmata

Unique proboscis at anterior end, with an opening at its tip to suck fluid from cnidarians

Variable number of walking legs among species

Includes sea spiders

III. SUBPHYLUM CRUSTACEA (LATIN: A CRUST)

mostly marine and few are terrestrial and freshwaterwith carapace as their exoskeleton which is composed of

chitin and calcium carbonatebody is divided into cephalothorax and abdomen Head bears 5 pairs of appendages

2 pairs of antennae 1 pair of mandibles 2 pairs of maxillae

Thorax 3 pairs of maxillipeds 5 pairs of pereopods (walking legs)

Abdomen 5 pairs of pleopods (swimming legs)

appendages are biramous (two-lobed)use gills for respirationIncludes brachiopods, ostracods, isopods, amphipods,

copepods, barnacles, shrimps, hermit crabs, crabs, lobsters

a. General anatomyb. Biramous appendages

Pechenik, 2005

III. SUBPHYLUM CRUSTACEA

Class Malacostraca - isopods (pill bugs, sow bugs, woodlice), amphipods (sand fleas), decapods (crabs, lobsters, shrimps, hermit crabs), krills

Class Branchiopoda- brine (fairy) shrimp, clam shrimp, water fleas

Class Ostracoda – the ostracodsClass Copepoda – the copepodsClass Cirripedia – the barnacles

III. SUBPHYLUM CRUSTACEA Class Malacostraca isopods (pill bugs

or sow bugs, woodlice),

amphipods (sand fleas),

krillsdecapods (crabs,

lobsters, shrimps, hermit crabs),

woodlicepill bug

sand fleas

krills

III. SUBPHYLUM CRUSTACEA

Class Branchiopoda

brine (fairy) shrimp,

clam shrimp, water fleas

brine (fairy) shrimp

clam shrimpwater fleas

III. SUBPHYLUM CRUSTACEA Class Ostracoda – the ostracodsClass Copepoda – the copepodsClass Cirripedia – the barnacles

ostracod

copepod

barnacles

IV. SUBPHYLUM UNIRAMIA (LATIN: A BRANCH)all are terrestrialincludes millipedes,

centipedes and insectsbody is divided into three

tagmata (body segments): head, thorax and abdomen

their exoskeleton contains tanned protein

head with only one pair of antennae

appendages are uniramous and are present on head and thorax but may be reduced or absent in the abdomen

use tracheae for respirationpossess malpighian tubules for

excretion of body wastes

IV. Subphylum Uniramia

Class Chilopoda‘100 legs’live in moist places and are carnivorouswith flattened bodies with each segment bearing a

pair of jointed walking legsthe appendages of first somite form poison clawspossess a pair of antennae, a pair of mandibles

and one to two pairs of maxillaeoviparousCentipedes

Class Diplopoda‘1000 legs’body consists of 25 to 100 segments, each bearing

two pairs of legshead with a pair of antennae and two pairs of

mouthpartsare herbivorous and live in a leaf moldoviparousMillipedes

Class Insectainsects

IV. Subphylum UniramiaClass Insectainsects are the most diverse

species of arthropodsmostly found in the tropicsconsist of three tagmata: head,

thorax and abdomen Head: six fused somites thorax: 3 somites Abdomen: variable number of

somites, usually 11 somitesthe head bears a pair of

compound eyes, with a pair of antennae and three ocelli

Mouthparts modified for different food habits

Thorax with 2 pairs of wings (sometimes 1 pair or none) and 3 pairs of jointed legs

Usually oviparousGradual or abrupt metamorphosis

MOUTHPARTS MODIFIED FOR DIFFERENT FOOD HABITS

Honeybee Housefly

Wallace and Taylor, 1997

Mosquito

Butterfly

MOUTHPARTS MODIFIED FOR DIFFERENT FOOD HABITS

Wallace and Taylor, 1997

Mouthparts modified for different food habits

IV. Subphylum Uniramia

Class InsectaSubclass Apterygota – wingless; silverfishes and springtailsSubclass Pterygota – ‘true’ or winged insects

Order Odonata - dragonflies and damselfliesOrder Orthoptera - grasshoppers, crickets, locustsOrder Isoptera - termites Order Lepidoptera- butterflies and moths Order Diptera - true flies such as mosquitoes Order Coleoptera - beetles Order Anoplura - sucking lice Order Hymenoptera - ants, bees, wasps Order Siphonaptera - fleas Order Hemiptera - true bugs like water striders, aphids, cicadas Order Blattaria – cockroachesOrder Mantodea – preying mantids

 

FIGURE 30.12

TAXONOMIC SUMMARYPhylum Arthropoda

Subphylum TrilobitomorphaClass Trilobita -trilobites

Subphylum ChelicerataClass Merostomata - horseshoe crabsClass Arachnida - scorpions, spiders, ticks, and mitesClass Pycnogonida - sea spiders

Subphylum CrustaceaClass Branchiopoda - brine (fairy) shrimp, clam shrimp, water fleasClass Ostracoda - ostracodsClass Copepoda - copepodsClass Cirripedia - barnaclesClass Malacostraca -isopods (pill bugs, sow bugs, wood lice), amphipods (sand

fleas), decapods (crabs, hermits crabs, lobsters, shrimps), krillsSubphylum Urinamia

Class Chilopoda -centipedes Class Diplopoda - millipedesClass Insecta

Subclass Apterygota (wingless insects)Subclass Pterygota (winged insects)

Orders (see previous page)