General Characteristics
Torsion
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Shell Coiling
- ancient shells were coiled in a single plane with new coils wrapping around old coils
- most are asymmetrically coiled into a more compact form, with successive coils or wholes slightly larger than, and ventral to, the preceding whorl
- leaves less room on one side of the visceral mass for certain organs
Locomotion
- flattened foot that is ciliated, covered with gland cells, and used to creep
- mucous trail
- small organisms have cilia to move
- large organisms use waves of muscular contractions to move
Feeding and Digestion
- most feed by scraping algae or other small, attached organisms from their substrates using their radula
- are herbivores that feed on larger plants, scavengers, parasites, and predators
- digestive tract is ciliated
- Protostyle: a mucoid mass where food is trapped in mucous strings an incorporated into the protostyle; extends to the stomach and is rotated by cilia
- wastes form fecal pellets in the intestine
- Nephridium: consist of a sac with highly folded walls and connects to the reduced coelom, the pericardial cavity; modifies waste by selectively reabsorbing certain ions and organic molecules
Other Maintenance Functions
- gas exchange always involve the mantle cavity
- modern gastropods have 1 gill
- Siphon: a rolled extension of the mantle and serves as an inhalant tube
- Open Circulatory System: blood bathes tissues in blood sinuses
- they have a heart
- Hydraulic Skeleton: consists of fluid (blood) under pressure that may be confined to tissue spaces to extend body structures and to support the body
Nervous System
- Primitive: 6 ganglia in the head-foot and visceral mass; torsion twists the nerves that link the ganglia
- Now: untwisting of nerves; concentration of nervous tissue into fewer, larger ganglia, especially in the head
- Eyes are at the end of the tentacles; pits of photoreceptor cells or consist of lens and cornea
- statocysts are formed in the foot
- Osphradia: chemoreceptors in the anterior wall of the mantle cavity that detect sediment and chemicals in inhalant water or air; helps detect prey
Reproduction and Development
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Gastropod Diversity
- largest group is Subclass Prosobranchia
- most marine, but some freshwater or terrestrial
- herbivores or deposit feeders, some are carnivores