Question

Difference between nautilus and gastropods

Answer 1

The Molluscs
Gastropods and Cephalopods

The Molluscs
• All Molluscs possess some or all of the following characteristics:
• A muscular foot
• a visceral mass 
• a mantle
• a radula
• a special respiratory gill 
• a shell 

Gastropods
• General - snails, limpits, nudibranchs, slugs
• The largest class of mollusc - over 40 thousand living species
• “stomach foot”
• Creep on their foot - most have a head with eyes and tentacles, and mantle usually secretes shell
• 3 subclasses
– Prosobranchs (forward gills) - most marine snails
– Opisthobranchs (backward gills) - sea slugs, hares, and nudibranchs
– Pulmanates (lung bearing) - land snails and slugs

Gastropods
• Ecology
• Marine, FW, and terrestrial 
• Algal grazers, detritus feeders, scavengers, predators
• Adapted to a wide variety of niches
• Variations in the radula

Gastropods
• Torsion
• Embryonic gastropods (veligers)- begin life with gills and anus in back
• During ontogeny entire visceral mass is forced to do a U-bend
• Gills reversed and in mantle cavity over head
• Anus discharges over head
• Why torsion? 

Gastropods
• Morphology
• Trochospiral shell - dextral coiling
• Whorls and sutures
• Aperture, operculum, siphonal canal
• collumellaCephalopods
• General - squids and octopus
• The most active and intelligent molluscs
• Foot = modified into a ring of tentacle around the mouth
• Large eyes, parrot-like beak, and relatively large brain
• Mantle cavity modified for backward jet propulsion
• Most shelled species = extinct

Cephalopods
• Almost all biological and ecological studies of fossil cephalopods - based on Nautilus
• Planispirally coiled shell
• Chambered - septa
• Protoconch - phragmocone
• Siphuncle - controls gas pressure through osmosis
• Negative buoyancy

Cephalopods
• Fossil forms occur in a variety of shapes - cones to coiled
• Three major groups
– Nautiloids - straight sutures
– Ammonoids - complex sutures (depth adaptation)
– Coleoids - shell internal or absent

Cephalopods
• Ecology 
• Active necktic predators to planktic
• Good eats