Chapter 10: Mollusks

Phylum Mollusca

Phylum Mollusca

- Triploblastic - Bilateral symmetry - Visceral mass - Most are marine - Radula (tongue with scrapping spikes) - Feeding varies from herbivores, carnivores, filter feeders, and parasites - Some are brackish (areas where fresh and salt water meet) - Some snails became terrestrial (need moisture from humidity and calcium rich soils)

Giant Squid

Architeuthis harveyi, can grow to be 18 meters long and even scrape at whales

Ocean Acidification

Affects corals and anything with a shells, the amount of CO2 put into the air gets absorbed with the water which forms carbonic acid, this acid releases hydrogen atoms that make the water more acidic, extra acids then steal the bicarbonate and thus can't bond with calcium for the animals to receive

Visceral Mass

division of the mollusk body that holds the organs

Mantle

division of the mollusk body that is responsible for secreting the shell

Radula

"tongue" of mollusks that contains scrapping spikes in order to feed off of rocks and hard surfaces by scraping for their food, defining characteristic of mollusks

Nacre

This is what makes up the inner shell in shell carrying mollusks and can cover sand or irritants which creates a pearl

Veliger stage

develops from the trochophore, has the beginning of a foot, mantle, and shell in gastropods

Class Monoplacophora

- Was believed to be extinct until 1952 - Have one shell (univalved) - Known for repeating features (gills, gonads, etc.) - Dioescious - marine

Class Polyplacophora (Chitons)

- Chitons * 8 overlapping dorsal plates (shells) - Similar body design to a snail except for gills * Gills wrap around the whole foot (lines the mantle opening) - Mostly Dioecious - Secrete sperm into water and eggs hang out of the mantle cavity - marine

Class Scaphopoda

- Tusk or tooth shells - All marine - Foot burrows into mud or sand

Class Gastropoda

Most diverse class - Stomach-foot animal (crawl on their stomach) * Both marine, freshwater, and terrestrial - Univalve shells for protection - Most have operculum that allows shell to close if frightened - Bilateral in larval stage but as they grow they have torsion - Many are herbivorous (rasping algae, grazing, or feeding on plankton) - Some are scavengers - Some are carnivores such as cone snails - Mostly Hermaphroditic except some are Dioecious like snails

Torsion

where position of body parts change during development, this is shown when the GI tract is moved so that the anus is above the head, process is called ontogenetic torsion

Cone Snails

they use proboscis to inject toxins into their prey, venom can be strong enough to kill humans

Pulmonate Snail

air breathing snails lack gills and use highly vascular area (blood vessels) in mantle as a "lung"

Class Bivalvia

- Two shells * This class has evolved into a simplified body * Have a incurrent and excurrent siphon that brings water in and out of mantle - Have a hinge ligament that is used for identification - Adductor muscles allow for the valves to open and close by relaxing and contracting - Have cilia on inside of mantle to move water * Three chambered heart (red blood and blue blood mix, one atrium and two ventricles) - Most are suspension feeders (filter feeders, whatever is floating in the water) - Can move a little bit but some have byssal threads that are used to hold to sediment - Mostly dioecious (few monoecious) - Reproduction can be parasitic to fish gills

Siphon

This a tube that is used to expel water, release sperm, and receive sperm in many mollusks

Byssal Threads

Strong thread that are secreted in by bivalves in order to latch onto surfaces

Glochidium

larval stages of bivalves that have hooks that can fasten onto passing fish

Zebra Mussels

Dreissena polymorpha, invasive species of mussels

Quagga Mussels

Dreissena bugensis, invasive species of mussels

Class Cephalopoda

- Head is located by the foot and body is behind the head * All marine predators - Have beaks - Did have shells earlier on but involved into species with either no shell or internal shells - Well developed nervous system * Largest brain to body ratio of any invertebrate * Eyes are very complex and similar to humans even though they evolved separately - Have skin cells that expand and contract that allow them to change colors and camouflage - Most have an ink sac that empties out of siphon - Dioecious

Chambered Nautilus

only cephalopoda that still has their shell, they have gas chambers in their shells that provide buoyancy when deep in water

Cuttlefish

ten-armed oval-bodied cephalopod with narrow fins as long as the body and a large calcareous internal shell, cuttle fish shells is enclosed in the mantle

Branchial Hearts

Two hearts found on the ends of gills that pump blood through the gills

Convergent Evolution

this is when a similar feature or characteristic is found in two animals that evolved separately from each other, can be seen in cephalopods eyes and humans eyes

Chromatophores

cells that contain melanin that are found on the outer "skin" of the cephalopods like Octopi that expand or contract that allow the cephalopod to change color and camouflage

Ink Sac

holds dark melanin pigment that is released through the siphon for defense against predators

Reproduction of Octopus

octopus inserts sperm sack into female mantle, the male dies instantly while the female finds a den to lay her eggs and cares for her eggs by spraying water through her siphon and sits their slowly dying

Umbo

oldest part of a bivalve shell, this is the outgrowth of the shell