Shelled Animals. from the bottom of the oceans to 7000M above sea level

Size: px

Start display at page:

Download "Shelled Animals. from the bottom of the oceans to 7000M above sea level"

Rosalyn Stephens
6 years ago
Views:

1 Shelled Animals some of the dominant organisms since the Cambrian explosion are those that secrete a protective shell these organisms generally have a good fossil record and some have changed little for millions of years range from fairly simple organisms to some of the most complex and specialized of invertebrates includes: snails, limpets, clams, mussels, chitons, squid, oysters, nautilus, tooth shells range from microscopic to 20 M (50-60 = giant squid) and up to 1 ton (900 kg ) eg. the giant squid is most massive invertebrate up to 60 long & weighs almost a ton eg. Tridacna 1.5 M and 250 kg (500 lbs) but most (80%) less than 10 cm (~4 ) often brightly colored some can rapidly change color for camoflage or mating displays mostly are aquatic in both fresh and salt waters and some are even common on land found from the tropics to the polar seas from the bottom of the oceans to 7000M above sea level usually sluggish and sedentary, some sessile, and attached to the substrate with protein strands a few, such as squid & cuttlefish, are quite active Body Plan most shelled animals share the following 3 characteristics: mantle - secretes shell or becomes outer body covering itself shell - (internal or external) Mantle foot - usually used for locomotion usually it is a sheath of skin just under the shell the mantle actually secretes the shell also, in some filter feeding animals, posterior portions of mantle come together to form 2 siphons to circulate water for food and oxygen in some bivalves the siphons can be quite long 1409 Animals: Shelled Animals; Ziser Lecture Notes, Animals: Shelled Animals; Ziser Lecture Notes, in some shelled animals such as squid and octopi where the shell is internal, the mantle serves as the outer protective skin of the animal the mantle often contains various sense organs for detecting light, touch and chemicals the mantle in squid and cuttlefish is covered with chromatophores chromatophores are pigment cells tiny muscles surround each one to expand or contract the pigment cell to rapidly change the animal s color under nervous and hormonal control can produce general darkening and lightening flashes of pink, yellow, lavender can form bars, stripes, spots and blotches used to indicate danger, protection, or during courtship many deep sea forms have pockets of symbiotic bacteria on their mantles that make them bioluminescent Shell most secrete a hard external shell for protection the shell is secreted throughout life and often shows growth lines which can be used to age the animal the shell is made up of 3 layers: periostracum outer organic layer prismatic layer crystals of calcium carbonate nacre layer glossy mother of pearl great variation in shell form and structure may be a single shell, double shell or consist of several separate plates single shells may be tentlike, coiled, tubular or even internal Nautilus has a spiral shell divided into chambers can adjust gas in chambers for buoyancy to ascend and descend in the water column in certain species of clams the mantle can produce pearls pearl production is a protective action toward some foreign body between shell and mantle eg. sand grain, parasite, etc 1409 Animals: Shelled Animals; Ziser Lecture Notes, Animals: Shelled Animals; Ziser Lecture Notes,

2 mantle secretes layers of nacre around object commercial pearls are produced by some oysters & some freshwater bivalves some have internal shell completely enclosed by mantle eg. cuttlefish, squid shell secreted by thin membranous tissue =mantle shell made of calcium layers: calcium extracted from water, soil or food a. outer organic layer especially in freshwater species especially thick in freshwater molluscs à protects from acidity common in fw in many marine forms this layer is thin or absent b. thick middle layer of calcium crystals dense prisms of calcium carbonate crystals in protein matrix c. inner glossy layer (mother of pearl) thin film of calcium sheets produces shiny irridescent mother of pearl in clams, with 2 shells, they are held together by hinge and two powerful adductor muscles hold the shells closed shell grows throughout life new layers are added to the edges à often show growth lines shell is mainly used for protection but does have some other uses in some species: 4. Foot eg. shipworms use shell to burrow into wood and then feed on wood particles eg. some clams are able to bore into rock and concrete with spiny valves eg. scallops use shell for propulsion by quickly closing them together to force out water à can swim in any direction thick and muscular variously modified for locomotion: 1409 Animals: Shelled Animals; Ziser Lecture Notes, Animals: Shelled Animals; Ziser Lecture Notes, creeping movements are produced by waves of muscular contractions that move through foot eg. squid à tentacles or by creating a slime trail from mucous glands eg. snails à gliding movement or digging into sediment being extended from body into sediment hydraulically by engorging with blood to anchor then draw rest of body into sediment eg. bivalves eg. scaphopoda or for attachment: may secrete mucus or strong fibers (byssal threads or sea silk) to adhere to solid substrate eg. limpets, chitons, mussels in squid & cuttlefish part of the foot takes the form of a funnel water is forcefully expelled from the mantle cavity creating jet propulsion funnel is very mobile lateral fins used by some for steering making them excellent swimmers 1409 Animals: Shelled Animals; Ziser Lecture Notes, also in squid and relatives, the head is indistinguishable from the foot 3. Head the head-foot is elongated into 8 or 10 tentacles (up to 90 in nautilus) and arms mouth at center of arms; contains chitinous beak or jaws most groups have a distinct head only clams (bivalves) lack a distinct head head bears mouth and various sense organs sense organs: eg. eyes eg. sometimes with tentacles eg. chemical receptors Feeding and Digestion shelled animals feed in a variety of ways: detritus feeders burrowers & borers grazers carnivores 1409 Animals: Shelled Animals; Ziser Lecture Notes,

3 filter feeders a. most species are filter feeders: some use sheet like gills to filter food out of water food is strained out as water passes over gills trapped in mucous and moved by cilia to mouth others filter the water with feathery tentacles (=lophophore) b. some are deposit feeders: use long proboscis like organ formed from modified foot to collect food in sand or mud c. most snails are herbivores use radula to scrap algae off of surfaces d. some use their shell to bore into solid objects to extract food: eg. shipworms termites of the sea have long, wormlike appearance; long siphons use small valves as rasping organs to drill through wood and eat wood particles excavated bacteria in gut digest the wood and fix nitrogen for host e. some shelled animals are predators: 1409 Animals: Shelled Animals; Ziser Lecture Notes, eg. razor clams thrust a long proboscis between shells of other bivalves to kill and eat them eg. moon snail (Polinices) & oyster borer (Urosalpinx) uses radula to help bore hole through bivalves also chemically digests shell once hole is complete, snail thrusts proboscis through it and spends hours or days feeding on prey eg. cone shells radula has highly toxic venom the stings of some species are lethal to humans extend wormlike proboscis to attract fish then attack, kill and eat them eg. all squid and cuttlefish are predators use tentacles and arms to capture and handle prey suction cups strong beaklike jaws enclose tongue-like radula cuttlefish have poison glands to help subdue prey f. some clams get most of their food from symbiotic algae (dinoflagellates) that live in mantle tissue eg. Tridachna shelled animals generally have a complete digestive tract with mouth and anus 1409 Animals: Shelled Animals; Ziser Lecture Notes, à one way flow of food modified along the way for different functions: grinding food digestion of food absorption etc. in mouth is tongue like rasping organ = radula has up to 250,000 teeth can be used to scrape, pierce, tear or cut complex muscles move the radula also acts like a conveyor belt to move food into the digestive tract as teeth wear away, new rows of teeth are secreted at posterior end Respiration most aquatic species use gills to get oxygen some can get oxygen through their skin many terresrial species have their mantle is modified into a saclike lung for breathing air Circulation open circulatory system in most simple heart with a few open vessels body cavity is filled with blood beating heart keeps blood in motion in body cavity Nervous System squid and its relatives as a group have the largest & most complex brain of any invertebrate several lobes with millions of nerve cells much of our current knowledge of nerve cell function is based on studies of the large nerve fibers of the squid they can think and plan learn and react to their environment level surpassed only by some vertebrates àthin feathery sheets of tissue covered with cilia 1409 Animals: Shelled Animals; Ziser Lecture Notes, Animals: Shelled Animals; Ziser Lecture Notes,

4 generally considered the cleverest of all invertebrates can easily learn behaviors by reward/punishment eg. if they see another rewarded for a particular choice they will do the same thing eg. one octopus would short circuit the light over her tank by squirting water at it if someone forgot to turn it off at night some can use rudimentary tools eg. first example of tool use by an invertebrate; in Australia an octopus has been observed carrying around coconut shells and using them for cover when threatened by a predator. sensory organs are also better developed in this group eyes: most have very well developed eyes with cornea, lens retina very similar to our own can form images statocysts: large and more complex than in other classes important in controlling eye position tentacles: use tentacles for tactile exploration Protection & Defenses the shells provide very good protection but many of these animals have additional means of protection as well àgenerally secretive habits àsome can produce toxic secretions àsome can deliver an active blow with sharp edge of shell to deter attack àsome can even redeploy stinging cells from coral prey squid and cuttlefish have an ink sac for protection à creates smoke screen to allow them to get away still many shelled animals are eaten by insects, fish, birds & mammals Reproduction & Development most species are dioecious; some are monoecious in most à fertilization is external gametes discharged into mantle cavity and out excurrent siphon eg. oyster: 50 Million eggs released per season some shelled animals have internal fertilization eg. in some clams the gills become brood chambers many snails with internal fertilization perform courtship ceremonies 1409 Animals: Shelled Animals; Ziser Lecture Notes, Animals: Shelled Animals; Ziser Lecture Notes, eg. many land snails eject a dart from dart sac into partners body to heighten excitement before copulation after copulation, each partner deposits its eggs in shallow burrows eg. before cuttlefish mate, males often make color displays to compete against rival males sperm encased in packets = spermatophores and stored in mantle cavity arm of male is used to transfer sperm to female plucks spermatophore from its own mantle cavity and inserts it into females mantle cavity a few shelled animals brood their eggs and bear live young = glochidium some moms can shoot larvae into water column others produce a structure that looks like a small fish to entice predatory fish when fish bites the bait it gets a mouthful of glochidia which then attach to the lungs it attaches to gills of host fish and feeds on blood they parasitize gills of fish for several weeksà dispersal then release and sink to bottom to become filter feeders in other members of the group there is no larval stage eg. some freshwater snails eg. some cuttlefish eg. fw clams brood their eggs in side their gills in some aquatic species eggs may be attached to substrate or float freely in plankton some marine forms enclose eggs in wide variety of tough capsules most aquatic species produce some kind of swimming larva some freshwater clams produce a parasitic larva 1409 Animals: Shelled Animals; Ziser Lecture Notes, Animals: Shelled Animals; Ziser Lecture Notes,

5 Ecology of Shelled Animals 1. important in food chains in aquatic ecosystems and even in terrestrial ecosystems eg. snails are major source of Calcium for birds 2. oysters are keystone species since they tend to form reefs nearshore. the cracks and crevices provide homes for a large variety of animals creating a complex community of interactions 3. freshwater bivalves are now the most threatened group of invertebrates in the US once >300 species in rivers, lakes, etc today: ~24 are extinct (6%) >60 endangered (15%) 100 are threatened (23%) especially due to: hunting and harvesting & poaching were actively harvested by native americans for food, tools, jewelry meat often sold as pet food; some human consumption damming rivers pollution, sedimentation due to mining, industry & agriculture bioinvasions asian clam eg. zebra mussel named for its distinctive striped shell arrived in US in 1986 from ballast water of European freighter into Lake Erie now found throughout the Great Lakes voracious eaters that disrupt food chains by competing for same food as native clams able to strongly attach to any hard surface by byssal threads; have foound attached to a single 4 clam able to completely block water inlet pipes of water treatment plants and power plants able to cling to boats and have been able to quickly spread first report in Texas in 2017 early settlers collected massive quantities for food and pearls even today 1000 s are collected for pearls, 1409 Animals: Shelled Animals; Ziser Lecture Notes, Animals: Shelled Animals; Ziser Lecture Notes, Human Impacts of Molluscs 1. currency: tusk shells used as money (=wampum) by native Americans 2. as food: oysters, scallops, mussels, octopus, squid eg. >2 Billion pounds of oysters are eaten each year oysters first cultivated for food for 2000 yrs oyster middens are found from ancient roman times and are common at coastal archaeological sites certain species consumed cooked or raw eg. octopus, squid & cuttlefish: 3 million tons/yr are consumed; an industry valued at >$6 Billion eg. (1990): each night 1000 SE Asian boats set out ~25,000 miles of nylon drift nets that extend about 30 ft down from the surface to catch red squid the bycatch from this nightly activity; ~2000 dolphins ~300,000 tons of pomfret (a kind of fish) à these are discarded 1000 s tons of tuna, swordfish, salmon à are kept and sold on the black market 3. precious stones shell nacre à buttons, cameos, etc some species of oysters and some fw clams produce pearls generally produced when a parasite gets between the shell and mantle of the animal natural pearls take many years to grow and are very expensive cultured pearls use blank of polished shell placed under mantle of oyster, then allows layers to deposit for 3-6 years 4. ink à sepia dye much quicker process, much cheaper, preferred today 5. cuttlebone from cuttle fish 6. Pharmaceuticals eg. medication derived from cone snail venom alleviates some kinds of chronic pain that even morphine can t control 7. Materials Science Research eg. mussels have an amazing ability to attach to rocks. their glue is made from protein strands that can attach strongly to even teflon applications to develop aquatic glues, antifouling paints, stronger sutures 8. shell collecting 9. pollution control oysters consume nitrates and ammonia helping to clean & purify eutrophic waters 1409 Animals: Shelled Animals; Ziser Lecture Notes, Animals: Shelled Animals; Ziser Lecture Notes,

6 a project in Chesapeake Bay is using oyster reefs to remove 19 million pounds (8.6 M kg) of nitrogen compounds/yr from the bay waters 10. destructive species snails and slugs à gardens boring snails destroy oyster beds shipworms à damage wooden ships and warves some are not deterred by creosote treatment some bivalves can even bore into concrete bioinvasions; eg zebra mussel intermediate hosts to parasitic helminths 1409 Animals: Shelled Animals; Ziser Lecture Notes,

Bivalved molluscs filter feeders

Bivalved molluscs filter feeders Class Bivalvia Bivalved molluscs have two shells (valves). Mussels, clams, oysters, scallops, shipworms. Mostly sessile filter feeders. No head or radula. Class Bivalvia Part of the mantle is modified