chapter 35: mollusks and annelids

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Mollusca

characteristics of mollusks

filter feeders or predators

coelom

three part body plan

radula

*clams, squids, and snails are mollusks*

three part body plan- visceral mass, mantle, foot

trochophore- free swimming ciliated larvae of some worms and many mollusks

cilia

mouth

anus

radula- tongue like organ that is covered with chitinous teeth

not in bivalves

types of mollusks

gastropods- snails

bivalves- clams

cephalopods- squids and octopus

characteristics of gastropods

one shell or no shell

tentacles on head with eyes

undergo torsion they can pull themselves into their shell

torsion- visceral mass twists 180 degrees from the head before adulthood

parts of a snail

stomache

intestine

anus

gill

mantle cavity

bivalves

closes shell using powerful muscles

no radula or head region

cephalopod

nervous system is most advanced

closed circulatory system

releases "ink" when threatened

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annelids

characteristics of annelids

bilaterally symmetrical

segmentation

divided coelom

duplication of some organ systems ensures the organism can keep living even after some injury

bristles called setae

setae- external bristles on an annelid

parapodia- fleshy protrusions

number of setae and parapodia helps divide annelids into 3 classes

class oligochaeta

-live in soil or fresh water

-name means "few bristles"

-earthworm

movement

- divided into 100+ segments that are identical

- uses its muscles to anchor the middle segments to move and increases the pressure of its coelomic fluids

digestion

- ingest soil as they burrow

- food is sucked through by pharynx, passes through esophaus, stored in the crop, moves to the gizzard where it grinds the soil to release organic matter

typhlosole- infolding of the intestinal wall increases surface area for absorption and digestion

- earthworms play important role in keeping the soil fertile, and their burrows allow air to penetrate into the soil, they also loosed soil to make it easier for roots to grow

circulation

- closed circulatory system

- blood travels to posterior and then anterior

- aortic arches- link dorsal and ventral blood vessels near anterior of the worm.

contractions of the aortic arches and the dorsal blood vessel force blood through the circulatory system

respiration and excretion

- O2 and Co2 diffuse directly through the skin

- nephridia- excretory tubules that eliminate cellular wastes and excess water

each segment except the first 3 and the last one have a pair of nephridia

neural control

- chain of ganglia connected by ventral nerve cord

- most body segments have a single ganglion

- nerves from ganglia carry impulses to muscles

- cerebral ganglia processes info from sensory structures that respond to light, touch, chemicals, moisture, temperature, and vibration

reproduction

- worms are hermaphrodites, but individual cant fertilize own eggs

- during mating worms are held together by mucus secreted from the clitellum

- each worm's sperm moves to the seminal receptacle of the other where it is stored

- after a few days the worm's clitellum secretes a tube of mucus and a tough carbohydrate called a chitin where it slides forward to pick up eggs with the stored sperm, where fertilization occurs

class polychaeta and hirudinea

- polychaeta means "many bristles"

- bristle worms

- have antennae and specialized mouth parts

- only annelids that have a trochophore stage

- live in marine habitat, some are free sqimming predators and others feed on sediment

hirudinea

- smallest class of annelids

-consist of leeches in fresh water or moist vegetation on land

- no setae or parapodia

-has a sucker to attach to surfaces to feed

- uses sucker to move

- carnivores

- parasitic leeches such their hosts blood without the host knowing