Chapter 7- Part 2Chapter 7- Part 2

Marine BiologyMarine Biology

Phylum Mollusca

Mollusks

•Greatest # of species•Body covered by mantle made of calcium carbonate

•Bilateral symmetry•Foot used for locomotion•Radula used to feed

Gastropods: •Snails•Mostly eat algae from

rocks- ex. Periwinkles

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•Some snails such as mud snails are deposit feeders

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•Snails such as whelks can be carnivorous preying on clams, worms, or small fish

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•Sea slugs are snails without shells. Often have noxious chemicals or nematocysts for protection

Bivalves:

•Clams, mussels, oysters•Body enclosed in shell•Gills filter food and used for breathing

•Mantle lines the inside of shell

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•Clams use foot to burrow in sand- water enters and leaves shell through siphon

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•Mussels attach themselves by using byssal threads

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•Oysters cement their left shell to a hard surface- often other oysters

•Pearl oysters are the source of most valuable pearls.

How a pearl is made:

•Particles merge in between mantle cavity and shell

•Oyster secretes shiny layers of calcium carbonate to coat irritating particle

•Oysters can be forced to make pearls by inserting an irritant in shell (cultured pearl)

Cephalopods:

•Octopus, squid, cuttlefish•Good swimmer•Complex nervous system•No shell

•Arms with suckers to capture prey

•Eyes on side of head•Move by forcing water out of their siphon, or funnel

Octopus

•8 arms (2 in to 9 ft in size)• bottom dwellers•Efficient hunters- crabs, lobsters, and shrimp

•Radula scrapes away flesh

•Some are toxic and their bite can paralyze

•Live in crevices and even discarded bottles

•Distract predators by spraying ink

Squid

•Better adapted for swimming

•Ten arms•Two of the arms are longer

and wider for catching prey•Sizes range up to 66ft in the

giant squid

Cuttlefish

•Similar to squid except the body is flattened

Biology of Mollusks

Digestion:

• Separate mouth and anus

• Radula can be modified from scraping or drilling through flesh

• Amount and strength of digestive enzymes range depending on matter being digested

Circulatory system:

• Most mollusks have a open circulatory system- blood flows out of vessels into open space

• Cephalopods have a closed circulatory system-blood always remains in vessels

Nervous System:

• Most mollusks have a ganglia

• Cephalopods have a more advanced brain, similar to humans

• Intelligent and remarkable learners- some cuttlefish can even change colors

Reproduction:

• Usually separate sexes

• Some hermaphrodites

• In bivalves and some snails-external fertilization

• Cephalopods and most snails- internal fertilization

• Cephalopods do not have larvae- young born from and egg. Mother usually dies after egg hatches due to lack of food while guarding egg.

Phylum Arthropoda

Arthropods

• Barnacles, shrimp, lobster, crab, etc.

• Segmented

• Bilateral symmetry

• Jointed appendages

• Exoskeleton

•Molt to grow-old skeleton discarded, animal takes in water to expand itself, grows a new skeleton

Crustaceans:

• Called the insects of the sea

• Gills

• Appendages used to swim, crawl, feed, and mate

• Two pair of antennae (sensory organs)

Small Crustaceans

• Copepods- planktonic, some parasitic

• Barnacles-filter feeders; live attached to surfaces

• Beach hoppers (amphipods)-tail and head curve down, strong jumpers

• Isopods- marine version of a roly-poly

• Krill- shrimp-like, filter feeders, main food source for many whales, penguins, and fish

Large Crustaceans

• Decapods- shrimp, lobster, crab (10 legs)

• Commercial importance

• 5 pair of walking legs

• First pair larger for obtaining food and in defense

• Shrimps typically scavengers

• Lobsters tend to be nocturnal (hide during day)- scavenge and catch prey

• Crabs are scavengers as well

• Female crab-U shaped abdomen for carrying eggs

• Male- V shaped abdomen

Digestion:

• Small teeth or ridges are found in stomach for grinding

• Digestive glands help digest and absorb nutrients

Nervous System:

• Small brain

• Compound eyes- In decapods at the end of stalks

• Body posture used for communication: mating, disputes, hunting, etc.

Reproduction:

• Mostly separate sexes• Males directly penetrate females

to reproduce• Reproduction in decapods takes

place directly after molting• Can store sperm

Phylum Echinodermata:

Echinoderms

• Sea stars, sea urchins, sea cucumbers, etc.

• Larvae –bilateral symmetry

• Adults-radial symmetry

• Lack a head

• Oral surface/aboral surface

• Water vascular system

• Tube feet and ampullae’s are part of this system

• Madreporite connects internal to the external

*Sea Stars

• Tube feet (with suckers) found in ambulacral groove

• Pedicellariae help keep surface clean

• Eat bivalves, snails, barnacles, etc.

*Brittle Star

• Long arms

• Tube feet lack suckers-feeding

• Organic matter, small animals

*Sea Urchins

• Round, rigid, spines• 5 ambulacral grooves with spines• grazers• Flat version with short spines-

sand dollar

*Sea Cucumbers

• Worm-like• No spines• Oral/aboral surfaces at each end• Tube feet modified and resemble

tentacles- used to pick up food

• Interesting defense methods:

~ discharge sticky substance through anus

~eviscerate internal organs

*Crinoids

• Better known as feather stars or sea lilies

• Deep waters

• Attached to bottom

*Digestion:

• Most extend stomach through mouth-digest food- and then pull stomach back in

*Nervous System:

• No brain

• Complex behaviors for the absence of a brain- camouflage, reposition itself if moved

*Reproduction:

• Separates sexes

• Sperm/egg shed directly into water

• Spawn all at once to ensure fertilization

• Asexual reproduction- if central disks is separated it can form into two new organisms (regeneration)