MolluscaSlides - Molluscs soft bodied animals Phylum...

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon
1 Phylum Mollusca “soft bodied” animals • second largest animal phylum •110,000 living and 40,000 fossil species -Marine, freshwater, terrestrial -Seven classes of living species (3 major, 4 minor) •range from 1 mm to 18 meters long - the largest invertebrate ANY GUESSES? Molluscs “soft bodied” animals Extant (still existing; not extinct) molluscan classes: Monoplacophora Scaphopoda (tusk, tooth shells) Cephalopoda (octopus, squid, cuttlefish, nautilus) Bivalvia (clams, mussels) Polyplacophora (chitons) Gastropoda (snails, slugs) Aplacophora ancestry uncertain
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2 Molluscan characteristics: • triploblastic • organ level of organization • bilateral symmetry • eucoelomate but coelom reduced to pericardium + gonadial cavity • protostomes • trochophore & veliger larvae; some with direct development • exhibit 4 distinct body plan characteristics: head, muscular foot (from ventral body wall), visceral mass, & mantle (from dorsal body wall) • head & foot: contain sensory organs and muscles • visceral mass: contains digestive, reproductive, circulatory organs • mantle: secretes the shell (if present); mantle cavity contains gills or lungs Molluscs shell foot visceral mass mantle mantle cavity “HAM” (H ypothetical A ncestral M ollusc) ( HAM = an “abstraction derived from comparative morphology & embryology) See Fig. 10.3 (5 th ed.), 10.2 (4 th ed.) Fig. 10.3 (5 th ed.), 10.2 (4 th ed.) HAM: a hypothetical ancestral mollusc * * * * * * * * * water in water out (reduced) * * Shell secretion by the mantle: prismatic layers nacreous layers An etched, stained x-section through the shell of a clam. (calcium carbonate) prismatic layer outer periostracum nacreous layer
Background image of page 2
3 PEARLS: mollusc deposits layers of nacre around an irritant that gets lodged between the mantle and shell Fig. 10.5 (5 th ed.), 10.4 (4 th ed.) Deriving the molluscan classes from “HAM”: “HAM” Cephalopoda: • lobed foot • highly developed head • shell reduced or lost Polyplacophora: • shell consists of 8 plates Gastropoda: • torsion of body • coiling of the shell Scaphopoda: • ventral shell fusion Bivalvia: • bivalved shell • dorsal hinge & adductor muscles chiton “diversity” ventral view: the chiton foot - 8 shell plates * * (snails, slugs, etc.) Gastropoda: torsion of body coiling of the shell Bivalvia Cephalopoda Scaphopoda Gastropoda “HAM”
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
4 “before” see a 180° rotation of the visceral mass during development: • 1 st 90° rotation usually occurs at the veliger (larval) stage • 2 nd 90° rotation usually takes longer and occurs later • brings mantle cavity from the rear anteriorly over the head “after” ***Gastropod TORSION *** Basic shell is straight or coiled , with new shell deposited by the mantle at the margin of the open end (“leading edge”) during growth. new growth limpets (straight shell) snails (coiled shell) SHELL TYPES shell shifts over body for better weight distribution apex (“tip”) of shell extends out making the shell more compact planospiral shell conispiral shell Shell COILING (vs. visceral TORSION) ancestral condition (new whorls added outside of old ones)
Background image of page 4
Image of page 5
This is the end of the preview. Sign up to access the rest of the document.

This document was uploaded on 11/03/2011 for the course BSC2011L BSC2011L at FSU.

Page1 / 16

MolluscaSlides - Molluscs soft bodied animals Phylum...

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online