Gastropods Flashcards
8 mollusc clades
- Caudofoveata\ Aplacophora
- Solenogastres
- Monoplacophora
- Scaphopoda: tusk shells
- Polyplacophora: chitons
- Gastropoda: snails, limpets, slugs etc.
- Bivalvia: clams, mussels, etc
- Cephlapoda: octopi, squid
Characteristics of the Phylum Mollusca
One of the largest phyla - ~93,000 species (35,000 fossils)
Microscopic to ~18m (454kg)
Marine, fresh water and terrestrial
Grazers, carnivores, filter feeders
Most Gonochoristic, some hermaphrodites
All soft bodied (no skeleton), most secrete a hard shell
Coelomates
Three main parts
Muscular foot: involved in movement, contains sensory organs
Visceral mass: digestive, circulatory, respiratory, reproductive and sensory organs
Mantle: fold of tissue draped over visceral mass. Excretes the shell (where present)
Development
Most marine & aquatic molluscs have planktonic trochophore and veliger larval stages
Snails, slugs, limpets, whelks, conch, sea hares, periwinkles, sea slugs, sea butterflies
75% all mollusc species
Only molluscs to have invaded land
Univalve coiled shell typical
Variously coiled
Functional beauty of shells
The outer layer consists of conchiolin (tough protein)
The inner layers consist of calcium carbonate
The colours result from pigment in the calcareous layers
Circulationin of snails, slugs, limpets etc
Heat delivers blood (haemolymph) to head/foot and viscera in mantle cavity
Open circulation
Blood also has role in hydrostatic skeleton
Excretion (snails, slugs, limpets etc)
Only one nephridium (kidney) retained in gastropods
Waste from heart ultra-filtered into pericardial cavity
Drains into nephridium/kidney
Feeding (Snails, slugs, limpets etc)
Highly varied
Most herbivorous (grazers/browsers)
Ciliary feeders (slipper limpets)
Scavengers
Predators (Mollusca, invertebrates & vertebrates)
Mostly use radula which may be extremely modified
E.g. venomous Conus spp.
Gastropoda divided into 3 informal subclasses
Prosobranchia, Opisthobranchia, Pulmonata
Prosobranchia
Periwinkles, limpets, whelk, conch, abalone, slipper shells, oyster borers, rock shells, cowries
Opisthobranchia
Sea hares (vestigal shell), sea slugs, nudibranchs (cerata), canoe shells
Pulmonata
Land and freshwater snails and slugs, lack gills, mantle cavity acts as lung.
Nudibranchs
Nudibranchs have lost shells and brightly coloued
Dorid nudibranchs – make or accumulate toxins from food (sponges) secrete in mucus
Aeolid nudibranchs – graze on Cnidaria- have chitin coated gut & accumulate nematocysts in tips of protusions
APOSEMATISM- warning colouration
Pulmonata Reproduction
Penises are everted
Sperm exchange is external
1. The shelled Helicidea the vagina contains an oval dart sac
2. The sac secretes a calcareous spicule- the ‘love dart’
3. Dart secretes hormones that increase sperm survival & paternity
4. Copulating limacid slugs hang from a cord of mucus attached to a tree
5. The penes are 10 – 25cm long