Mollusks (phylum Mollusca)

Phylum Mollusca

-110,000 species-2nd to Arthropods. (poor fossilization of 70,000 ancestor, soft parts, so difficult to understand) -Clam-snail-octopi-oyster-mussel-squid -No "typical" mollusk generalization -size range from 1-2mm to 12m

osphradium

-A chemoreceptor/ tactile receptor (osphra= G: a smell) -Generally located next to ctenidium. -Mollusca chemo/touch reception

General Characteristics

-mantle -Radula (not present in bivalves) -locomotory or clinging foot

Ctenidia means

Greek- comb

Shells of mollusk

Most molluscs have shells consisting primarily of calcium carbonate, CaCO3 (set in a protein matrix)

Molluscum Means

Soft.

Pelecypoda

class of mollusks that includes clams, mussels, and oysters

Radula

(in a mollusk) a rasplike structure of tiny teeth used for scraping food particles off a surface which is located in the esophagus and drawing them into the mouth. (circular band of teeth-not present in bivalves)

odontophore

(tooth bearing) is a supportive cartilage-like structures underlines the radula. -odontophore-radular assembly + musculature = buccal mass (Bucca- L: Cheek)

Taxonomic summary Phylum Mollusca

-Class Polyplacophora (chitons) -Class Aplacophore -Class Monoplacophora -Class Gastropoda (snail and slugs) -Class Bivalvia (clam, mussels, oysters, shipworms) -Class Scaphopoda (tooth shells, tusk shells) -Class Cephalopoda (squid, octopus, cuttlefish, chambered nautilus)

Shells Characteristics

-Periostracum layer -prismatic layer Both organic and inorganic compartments of shell are secreted by specialized tissue known as the mantle

buccal mass

-odontophore-radular assembly + musculature = buccal mass (Bucca- L: Cheek)

Molluscan coelom

-very small -Restricted to the area surrounding the heart and gonads -no locomotory role

mollusc gills

-work on principle of countercurrent exchange -Exceptions: squid and other cephalopods -increases efficiency of gas exchange between blood flowing within ctenidial filaments and water flowing over them -blood and water flow in opposite direction

prismatic layer

A thick calcareous middle layer of the mollusks shell

Muscles extent...

7 classes. (one class Aplacophora has no fossil record) Evolutionary relationships are still under debate.

pearls formation

A grain of sand, parasite, or other foreign particle that is trapped between mantle and shell's inner surface of the oyster then crystalline material coats over it (same as in shell) Natural forming-rare. (1/1000)

Mantle

A sheath of tissue that encloses the vital organs of a mollusk, the dorsal epithelium forms the mollusk's shell by secreting calcareous spicules

pearls (man made)

Cultivating pearls -surgically implanting piece of shell or plastic spheres -keep oyster alive 5-7 years -harvest

Sessile

Describes an organism that remains attached to a surface for its entire life and does not move

Radula structure

Feeding structure -firm, ribbon, composed of chitin and protein -numerous rows of sharp, chitinous teeth -ribbon produced from radular sac -underlined by supportive cartilage-like structures called odontophore. -old teeth wear down, new teeth are continually made-added to ribbon's posterior end in radular sac

Oysters

Pelecypoda ex. ___, clams, mussels. Sessile mollusks Member of the class Bivalvia Mollusk that is famous for pearls

Bivalvia

The class of the phylum Mollusca that have two valves joined together; filter feeder; lack radula; clams, oysters, mussels

Ctenidia

The ctenidia in mollusks are a comb-like molluscan gills; pairs of grooved flap like structures that are between the mantle and the viscera- mantle cavity. They absorb oxygen from the water or can aid in feeding

Periostracum

The shell of mollusks thin, outer organic layer

locomotory or clinging foot

a ventral body wall muscle structure of the mollusk which was developed for movement

Molluscan blood sinuses

are comprising a hemocoel ("blood cavity") are well developed -serves as a hydrostatic skeleton in locomotion of some molluscs

calcareous spicules

mollusks secrete this from the dorsal epithelium which forms the mantle

ctenidium

singl. for ctenidia -has a respiratory function or may also function in collection and sorting of food particles (within the exit site for excretory, digestive, and reproductive systems)