Gymnosomata

gastropod order

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June 29, 2026

Quick Summary

The term "Gymnosomata" refers to a division within the Pteropoda, which are small marine gastropods. These creatures are characterized by a foot modified into wing-like flaps used for swimming, and they inhabit the sea surface. The Gymnosomata specifically are those pteropods that lack a shell and possess complex mechanisms for capturing prey. They are distinct from the Thecosomata, another order of pteropods, which have shells and feed using cilia and mucus. The Gymnosomata are sometimes referred to as "sea slugs".123

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gastropod
Classification
Order Gymnosomata Shell absent; no mantle cavity; complicated feeding mechanisms; pelagic carnivores; 7 families. Order Nudibranchia Sea slugs without shell, mantle cavity, osphradium, or internal gill; many feed on sessile animals; few swimmers (family Tethyidae); highly colourful, often conspicuous.
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Order Gymnosomata Shell absent; no mantle cavity; complicated feeding mechanisms; pelagic carnivores; 7 families. Order Nudibranchia Sea slugs without shell, mantle cavity, osphradium, or internal gill; many feed on sessile animals; few swimmers (family Tethyidae); highly colourful, often conspicuous.
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pteropod
…small animals constitute the order Gymnosomata; those having a shell and feeding by means of cilia and mucus constitute the order Thecosomata. The shell is delicate and translucent; contrasting forms are seen in the straight-needle pteropod (Creseis acicula), the coiled pteropod (Limacina species), and the long-snouted pteropod (Cavolina longirostris).
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…small animals constitute the order Gymnosomata; those having a shell and feeding by means of cilia and mucus constitute the order Thecosomata. The shell is delicate and translucent; contrasting forms are seen in the straight-needle pteropod (Creseis acicula), the coiled pteropod (Limacina species), and the long-snouted pteropod (Cavolina longirostris).
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