LAB 6 Flashcards
(34 cards)
How many classes are there in phylum mollusca
8 classes
what are the classes in phylum mollusca
Aplacophora, polyplacophora, monoplacophora, gastropoda, bivalvia, scaphopoda, cephalopoda
what are molluscs
molluscs are hemocoelomate protostomes with complete guts
what are molluscs key characteristics
triploblastic, bilateral symmetry, unsegmented, cephalised, eucoelomates, protosomes, open circulation (except cephalopods)
what is the molluscan body plan
head, foot, viscera mass, mantle cavity, shell and radula
what does the head contain in the body plan
sensory structures and mouth
what does the foot contain in the body plan
muscular ventral structure used in locomotion
what does the viscera contain in the molluscan body plan
main body containing internal organs (gut, kidneys, heart, reproductive structures)
what is the mantle (pallium) cavity?
the mantle is an epidermal-cuticular sheet-like organ growing from the dorsal surface of the body wall. it contains muscle layers and haemocoel chambers.
how is the mantle cavity formed?
formed by the mantle skirt, a double fold of mantle which encloses a water space
what does the mantle contain?
contains gills, anus, osphradium, nephridiopores and gonopores
what does the mantle function as?
a respiratory chamber (in bivalves = part of feeding structure; in cephalopods = locomotory organ)
what does the epidermis of the mantle secrete
calcium carbonate and conchiolin
what is the shell secreted by?
shell glands located along the mantle margin
what do mollusc shells consist of
various layers including the organic periostracum (containing conchin) and an inorganic calcified layer (ostracum) that is typically two layers (an outer chalky prismatic layer and an inner pearly lamellar layer or nacreous layer)
what are the two biggest mollusc classes?
gastropoda and bivalvia
what are class Aplacophorans key characteristics
most primitive mollusc, shell-less, mainly deep sea, worm-like burrowers, predatory (on small invertebrates) or parasitic (on cnidarians)
Class Monoplacophora key characteristics
3-40mm, deep sea, horse-shoe shaped mantle with 6-8 gills, selective deposit feeder and have a radula
what are polyplacophorans
chitons
class polyplacopohora key characteristics
all marine, shell formed from a series of 7-8 valves, head not well defined, thick girdle, pallial grove with multiple paired gills and feed on encrusting organisms
how many subclasses does gastropoda have?
3 subclasses - prosobranchia, opisthobranchia and pulmonata
how do prosobranchia, opisthobranchia and pulmonata differ?
prosobranchs shell either cup-shaped or coiled; Opisthobranchiahas a reduced shell; pulmonata are non-aquatic with mantle modified to form a lung
what is torsion
the rotation of the visceral mass, mantle and shell 180 degrees with respect to the head and foot of the gastropod. this brings the mantle cavity and anus to an anterior position above the head.
what does torsion result in?
major changes to the molluscan body plan and affected the location of the gills, excretory and reproductive ducts, the shape of the gut and the layout of the nervous system
