Marine Invertebrates

Molluscs

Molluscs

• Snails, clams, octopuses, and other familiar forms are members of the phylum Mollusca

• There are more species of molluscs in the ocean than any other animal group

• 200,000 species, more than any other animal phylum with the exception of the arthropods

• Most molluscs have a soft body enclosed in a calcium carbonate shell

Molluscs

• Soft body• A shell may or may not be present• Body covered by a mantle, a thin layer of tissue that

secretes the shell• There is a ventral muscular foot• Most have a head that include eyes and sensory organs• A unique feature to molluscs is the radula– A ribbon of small teeth that is used to feed – usually

by rasping food from surfaces

Types of Molluscs

• Molluscs exhibit an immence diversity of structure and habit.

• Most molluscs belong to one of three groups– Gastropods (snails, limpits, abalones, and

nudibranchs)• Nudibranchs are gastropods that have lost their shells

– Colorfull branches of the gut or gills make them among the most beautiful of all marine animals

– Nematocysts from captured prey– toxins

• Bivalves (clams, mussels, oysters)– Body enclosed in two shells

• Cephalopods – head footed (octopus, squid, cuttlefish)– 650 species, all marine– Agile swimmers– Complex nervous system– Octopuses (octopus) – not octopi– Squid are better adapted for swimming than octopuses

Types of Molluscs

Humbolt Squid

• http://video.nationalgeographic.com/video/player/animals/invertebrates-animals/octopus-and-squid/humbolt_squid.html

Giant Octopus

• http://video.nationalgeographic.com/video/player/animals/invertebrates-animals/octopus-and-squid/octopus_giant_kills_shark.html

Cuttlefish

• Resemble squids• Internal hard shell that aids in boyancy

(cuttlebone)Other molluscs include the chitons (eight

overlapping shellparts)

Cuttlebone

Feeding and digesting

• The molluscan gut has a separate mouth and anus.• Digestion involves salivary and digestive glands that

release digestive enzymes• Some retain the chloroplast of photosynthesizes

intanct!• Some like the cone snails are carnivores• Most have open circulatory systems (not

cephalopods)

Cone snails

• A live Textile cone, Conus textile, one of the three most dangerous cones to handle.

• The bright colors and patterns of cone snails are attractive to the eye, and therefore people sometimes pick up the live animals and hold them in their hand for a while. This is risky, because the snail often fires its harpoon in these situations. In the case of the larger species of cone snail, the harpoon is sometimes capable of penetrating the skin even through gloves or wetsuits.

Cone snails cont.

• The "sting" of many of the smallest cone species may be no worse than that of a bee or hornet sting, but in the case of a few of the larger tropical fish-eating species, especially Conus geographus, Conus tulipa and Conus striatus, handling the snail can sometimes have fatal consequences.

• One of the fish-eating species, the geography cone, Conus geographus, is also known colloquially as the "cigarette snail," a humorous exaggeration implying that, when stung by this creature, the victim will have only enough time to smoke a cigarette before dying.

Medical use of the venom

• The venom of some cone snails, such as the Magician cone, Conus magus, shows much promise for providing a non-addictive pain reliever 1000 times as powerful as, and possibly a replacement for, morphine.

• http://video.nationalgeographic.com/video/player/animals/invertebrates-animals/other-invertebrates/snail_cone.html

Reproduction

• Most molluscs have separate sexes• Some are hermaphrodite• Female octopuses usually die after

reproduction because she eats little or nothing while guarding the eggs

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