Phylum Molluscalibvolume8.xyz/zoology/semester2/lifeanddiversityofanimalsnonchor… · Class...

Phylum Mollusca

Title: May 312:42 PM (1 of 23)

often referred to as molluskssecond largest phylumhas 7 classes only looking at 4bilateral symmetry, true body cavitythree germ layers


Classes we will look at:

Chitons

Gastropoda stomach footed(snail)

Bivalviatwo shells(clam)

Cephalopoda head footed(octopus)


• similar embryonic development and formation of gastrula

• trochophore larva stage

• same as larval stage of earthworms believed to be related.

• soft body that house organs ("inside shell")

• foot, mantle, shell, and radula (only found in mollusks).


Foot large muscular organ that function in movement

mantle fold of skin that surrounds body organs and secretes shell of most

radula rasping tonguelike organ found in some mollusks.


as food

as money

to make dyes

to make tools

as buttons

to make/ use as weapons

high concentrations of them lead to the finding of oil

get rich quick schemes


chitonsmarinebottom surface covered by foot upper covered by 8 over lapping valves


Class Gastropoda

largestmost have single heavy coiled shell have head, mouth, tentacles and eyes head is connected to the foot shell on top simple lungs or gills usually travel at night

tentacle!


General Features: source of food for humans shell made up of two parts ("Valves") soft body is protected between shell valves ligament holds valves apart on one edge two strong adductor muscles pull valves together; when they relax, shell opens shell usually slightly open with tube hanging out each end (siphons) incurrent siphon carries water + food into mantle cavity water leaves through excurrent siphon smooth, shiny innermost layer of shell just outside mantle is "mother of pearl" in some (scallops, oysters), mantle produces "mother of pearl" to wall off irritants like sand particles if enough "mother of pearl" is produced around irritant, a pearl is formed

Class Bivalvia

Title: Jun 11:51 AM (9 of 23)

Movement: most are sedentary because of heavy shells use their foot to pull themselves into the sand extends foot out into sand and blood fills it anchoring the end in the sand muscles in foot contract causing it to pull the shell towards the anchored foot some move periodically by opening and closing shells (scallops)

Note: Links may not work for a couple of days! I have to upload the files!


http://www.racerocks.com/racerock/eco/taxalab/ensy02/vdejesus.htm

Food Getting:

"filter feeders" since they filter foodstuff from water that passes through them

gills are large and covered with cilia which beat, drawing water in siphon

food (algae, small animals, dead material) in water passes over gills

food becomes embedded in mucus on gills forming strings

mucus/food strings are moved toward mouth by cilia

digestion occurs in stomach

undigested wastes exit via anus (near excurrent siphon)


Circulatory System:

open circulatory system heart pumps blood to body tissues through vessels vessels open into body spaces called sinuses where it bathes body tissues other vessels pick up blood from sinuses and carry it to gills for gas exchange then blood is carried to heart where it is pumped to body again

Title: Jun 14:37 PM (13 of 23)

Respiratory System: blood carried by vessels to gills where CO2 is released and O2 is picked up from H20

Excretory System: wastes from digestive system exit through anus (pore near excurrent siphon) pair of kidneys remove liquid wastes from blood and empty them via excurrent siphon


Nervous System: 3 pairs of ganglia connected to foot and body organs by nerves (control movement) sensory cells enable it to respond to chemicals, touch, and light

Reproduction: sexes are separate sperm leave male through excurrent siphon enter female through incurrent siphon eggs are held by gills where they are fertilized, released through excurrent siphon young bivalves pass through one or more larval stages before becoming an adult


General Features:

most complex/advanced mollusks only the nautilus has complete external shell the nautilus has a cluster of many slender, suckerless tentacles octopus has 8 equal tentacles, all with suckers; shell is absent so body is flexible squid has 10 appendages, 2 of which are longer and have suckers (tentacles) squid has pen (internal remnant of shell that holds streamlined shape) giant squid is probably largest invertebrate in the world (up to 18m long, ~ 4000 Ib) in times of danger, some discharge an inky fluid like "smoke screen" (to escape)

Class Cephalopoda


Food Getting: marine predators capture motile prey use tentacles to trap and grasp prey and draw them into mouth (at base of tentacles) digestion occurs in muscular stomach and short intestine nutrients are absorbed from stomach and intestine undigested material is excreted into mantle cavity


Circulatory System: closed circulatory system (note: bivalves and some others have open system) capable of maintaining high flow rate and blood pressure "gill heart" pumps oxygenated blood back to "systemic heart" which pumps to body important to have well developed circulatory system since move fast to catch prey

Respiratory System: use gills for gas exchange


Nervous System: highly developed with large brain containing several ganglia octopus brain has 10 lobes; apt learner, solve simple problems, able to remember squid and octopus have image forming eyes similar to vertebrates (imp to find prey)


Reproduction: they have separate sexes fertilization is internal squid eggs are deposited in capsules and both parents die after mating octopus eggs are attached to roof of cave or in crevice and female guards them

Movement: streamlined bodies permit rapid movement in water swim by expelling, a jet of water from their mantle cavity


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Attachments

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