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BIOL 2030 Lecture Notes - Bivalvia, Circulatory System, Cephalopod

Course Code
BIOL 2030
Scott Kelly

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Large and diverse phylum of soft-bodied, usually unsegmented, coelomate animals,
many of which live enclosed in a ahrd shell. They include the classes Gastropoda (e.g.
winkles, whelks, slugs, nails, se slugs), Bivalvia (e.g. clams, cockles), and other smaller
classes of shells, and the the Cephalopoda (nautilus, squids, and octopuses). The
coelom is small and the main body cavity is a blood-filled haemocoel. Molluscs have a
heart and blood system, and well-developed sense organs and nervous system, esp. in
the Cephalopoda
Fold of soft tissue underlying shell in molluscs, barnacles and brachiopods, and which
usually encloses a space, the matle cavity, between it and the body proper
Short, broad organ with rows of chitonous teeth in mouth of most gastropod molluscs
Visceral mass
A comblike structure, such as the respiratory apparatus of a mollusc
Pallial groove
Pallial = “having a mantle”
External opening of excretory organs (nephridia) in invertebrates
Of aquatic molluscs, funnel-shaped structure from mantle cavity to exterior, through
wich water is drawn in and out, and which in some molluscs can be used as a means
of jet propulsion
The tooth-bearing organ in molluscs
Species having sex chromosomally determined as either female or male
The reproductive organ of naturally hermaphrodite animals, which produces both
eggs and sperm
Free-swimming top-shaped pelagic larval stage of annelids, bryozoans, and some
molluscs, forming part of the zooplankton. It has a ring of cilia around the rim and a
terminal ring or tuft of cilia in front of the mouth
Feeding trochophores on plankton (catch small plankton in prototroch)
Non-feeding trochophores which use large yolk reserves, short planktonic lives
Veliger larva
Second larval stage in some molluscs, developing from the trochophore
Membrane or structure similar to a veil
Glochidium larva
The parasitic larva of freshwater mussels such as Unio and Anodon
Egg case or receptable
Preoral circlet of cilia of a trochosphere larva
Blood-filled cavity constiting of spaces between organs, which is the main body cavity
in molluscs
Mollusca - most aquatic, very diverse, coelomate (triploblastic) >93K spp
Characteristically diverse, 1mm 18m in size, various speed (mmt), herbivores/detrivores/filter-
feeders/predators; 7km above sea level to anywhere deep
Gastopoda[most], Bivalvia [21.5%], Cephalopoda [1], Polyplacophora [1], Scaphopoda [1],
Aplacophora [0.4], Monoplacophora [0.03]
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**Life Tree**
SQUID: on dorsal side, an
internalized shell which facilitates
open-water mmt; Octopus shell
completely lost (hence ‘reduced
on chart)
Mantle specialized tissue formed by dorsal epithelium; secretes shell (s)
Radula tongue-like organ with teeth used for feeding (not in bivalvia)
“Foot” ventral body wall muscles developed for locomotion/clinging [head-foot]
HAM Hypothetical Ancestral Mollusc
Typical mollusc
1. Foot/head-foot
2. Visceral Mass includes gonads, etc. (digestive/circulatory/excretory)
3. Shell
4. Mantle Overhangs “mantle cavity”
protective gills area
Ctenidia respiratory organ: ciliated molluscan gills housed in mantle cavity
Cilia provide continuous
water current into/out of cavity
o Respiration
o Sensory detection
o Prevent fouling
o Waste elimination
[wash out excrements]
o Gamete dispersal
Cilia modified for filter-feeding (in some) [gills used to capture food particles]
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