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)