BIOL2712 Study Guide - Final Guide: Symmetry In Biology, Internal Fertilization, Bivalvia

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Mollusca
Mollis = soft
Malacology = study of molluscs
Highly diverse and distinctive
Triploblastic, eucoelomates
oTriploblastic = derived from 3 embryonic cell layers
Bilaterally symmetrical (mostly)
Definite head
Indirectly evolved from flatworm-like ancestors similar to annelid line
Trochophora larva, similar to annelids
oLarva is bearing a wheel-shaped band of cilia
Show some metamerism, but unsegmented
oMetamerism = having a linear series of body segments
90,000 living species
oestimated up to 200,000
o2nd largest phylum
o70,000 fossil species
ooriginated in Cambrian  500 mya
o12,000 species in Australia
Marine, freshwater terrestrial (esp. snails)
Tropics to polar seas
Benthis, pelagic
Predators, herbivore, deposit-feeders, filter feeders
Crawling, burrowing, boring
Size from um  18m
Body Plan
HAM
oHypothetical ancestral mollusk
Visceral mass
oDigestive, circulatory, respiratory and reproductive organs
Mantle
oTwo folds of skin
oProtective
oSecretes shell
Head-foot
oLarge, muscular
oOriginally for locomotion and support
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oAlso containing feeding and cephalic sensory organs
Head
oMouth
oSensory organs (eyes, tentacles)
oRadula (feeding)
oTeeth made from chitin, point backwards
Sit on cartilages (odontophore)  cartilaginous projection in mouth in
which radula is supported
Complex muscles
Foot
oVentral
oLocomotion
Crawling
Gliding (mucus, cilia)
oAttachment (disc)
oForms siphon jet in squid
Visceral Mass
oMantle & mantle cavity:
Gas exchange
House gill or lung
Removal of body waste and reproductive products
Secretes shell (when present)
oInternal structures
Open circulatory system, pumping heart, blood vessels and sinuses
Digestive tract
Specialized by feeding habits
Kidneys
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Metanephridia
Nervous system
Gonads
Shell
CaCO3 derived from food and the environment
Outer Middle Inner
Periostracum Prismatic layer Nacreous layer
Protein (conchiolin) CaCO3 in protein matrix CaCO3 over protein
Growth margin of shell Secreted by glandular
margin with growth
Secreted continuously by
mantle surface
Nervous System
Longitudinal ventral nerve cord
Variable cephalization from single ganglia to brain, cranium
Variable sensory systems from marginal tentacles to eyes, chromatophores
Most highly developed in cephalopods
Lenses analogous to human eyes
Respiration
Some aquatic species have no respiratory system
Most have gills called ctenidia
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Document Summary

Triploblastic, eucoelomates: triploblastic = derived from 3 embryonic cell layers. Indirectly evolved from flatworm-like ancestors similar to annelid line. Trochophora larva, similar to annelids: larva is bearing a wheel-shaped band of cilia. Show some metamerism, but unsegmented: metamerism = having a linear series of body segments. 90,000 living species: estimated up to 200,000, 2nd largest phylum, 70,000 fossil species, originated in cambrian 500 mya, 12,000 species in australia. Visceral mass: digestive, circulatory, respiratory and reproductive organs. Mantle: two folds of skin, protective, secretes shell. Head-foot: large, muscular, originally for locomotion and support, also containing feeding and cephalic sensory organs. Head: mouth, sensory organs (eyes, tentacles, radula (feeding, teeth made from chitin, point backwards. Sit on cartilages (odontophore) cartilaginous projection in mouth in which radula is supported. Gliding (mucus, cilia: attachment (disc, forms siphon jet in squid. Open circulatory system, pumping heart, blood vessels and sinuses. Variable cephalization from single ganglia to brain, cranium.

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