MOLLUSCS
This presentation is the property of its rightful owner.
Sponsored Links
1 / 16

MOLLUSCS PowerPoint PPT Presentation


  • 88 Views
  • Uploaded on
  • Presentation posted in: General

MOLLUSCS. Phylum Mollusca Subphylum Amphineura Class Polyplacophora – chitins Subphylum Cyrtosoma Class Monoplacophora – almost extinct Class Gastropoda – snails Class Cephalopoda – squid, nautilus Subphylum Diasoma Class Rostroconchia – Camb-Perm

Download Presentation

MOLLUSCS

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Molluscs

MOLLUSCS


Molluscs

Phylum Mollusca

Subphylum Amphineura

Class Polyplacophora – chitins

Subphylum Cyrtosoma

Class Monoplacophora – almost extinct

Class Gastropoda – snails

Class Cephalopoda – squid, nautilus

Subphylum Diasoma

Class Rostroconchia – Camb-Perm

Class Bivalvia – clams, oysters

Class Scaphopods – tusk shells

All major groups (ex scaphopods) appear in Cambrian, became important part of Mesozoic/Cenozoic faunas


Molluscs

Common features

unsegmented body – bilaterally symmetrical

head (most) - contains sensory organs

radula - with primarily organic teeth

foot – crawling, burrowing, or grasping

mantle – fleshy covering which secretes shell

shell (when present) periostracum/calcareous prismatic layer/nacreous layer

gills – in chamber in mantle

Phylogeny poorly understood


Molluscs

H.A.M.

Hypothetical

Ancestral

Mollusc


Molluscs

Diasoma “through body”

Cyrtosoma “curved body”

rostroconchs


Molluscs

Polyplacophora

body covered by 8 overlapping plates – poor fossil record

on eyes or tentacles, marine

Monoplacophora

faintly segmentedbody covered by cap-shaped shell

Cambrian-Devonian, Recent (1952)


Molluscs

Veliger larva

Trochophore larva

Gastropods

prosobranchs – (“forward gills”) marine

opisthobranchs – (“rear gills”) reduced shells

pulmonates – (“lungs”) air breathers

Habitats/niches

scape algae with radula

scavengers/ detritus feeders

predators (drills/harpoons)

suspension feeders


Molluscs

  • Torsion

  • Nerve cord in fig-8

  • Left/right gills reversed in cavity over head

  • Anus above head –fouling problems


Molluscs

Water circulation


Molluscs

  • Reasons for torsion

  • Larval retraction: larvae could retract head into mantle – no real advantage.

  • Larval settling: aids larva to balance shell over head – evidence contradicts

  • Veliger swimming: balance body mass for swimming - ?

  • Adapted adult: good for adult to have everything up front – primitive ones don’t

  • Adult retraction: allowed retraction into mantle cavity, closed by operculum – doesn’t work for primitive

  • Helicospiral coiling: better balance asymmetrical shell – doesn’t explain limpets


Molluscs

GASTROPODS

Hyperstrophic dextral – right-handed, whorls to left, carried diagonal, spire to front

Orthostrophic dextral – whorls to right, carried diagonal, spire to back


Molluscs

PROSOBRANCHS

Archaeogastropods - Primitive forms in which there are two auricles, two kidneys and two gills present.  Nerve system is never concentrated.  Shell is either coiled or secondarily symmetrical as in the limpets.  Largely marine but there are a few that inhabit brackish water, freshwater or even terrestrial habitats.


Molluscs

Mesogastropods possess one gill, one auricle and one kidney. An operculum may be present. Mostly marine but a few do inhabit freshwater. This is the largest order of gastropods and contains many common species. Appeared in Late Paleozoic – unipectinate gills, sometimes small siphonal notch (burrowing)


Molluscs

Neogastropods possess a concentrated nervous system and usually a shell with a siphonal canal. They are a carnivorous species having a radula containing two or three large teeth in each row.  Some possess a poison gland. Nearly all have an operculum. All are marine inhabitants. Appeared in Jurassic and became dominant group. Possess long siphon


Molluscs

Fossil record of Opisthobranchs and Pulmonates not as good.

Opisthobranchs appear in Mississippian

Pulmonates known from Pennsylvanian fresh water


  • Login