Thecosomata

gastropod order

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July 14, 2026

Quick Summary

Thecosomata are a division of pteropods, which are small marine gastropods. Pteropods are characterized by a foot modified into winglike flaps used for swimming.1

Thecosomata specifically refers to pteropods that possess a shell. These shells are typically delicate and translucent, with varied forms such as straight-needle, coiled, or long-snouted shapes. In contrast, pteropods without shells belong to the order Gymnosomata. Thecosomata feed using cilia and mucus.12

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gastropod
Classification
Order Thecosomata Shell present; pelagic ciliary feeders; no gill; 6 families. Order Gymnosomata Shell absent; no mantle cavity; complicated feeding mechanisms; pelagic carnivores; 7 families. Order Nudibranchia Sea slugs without shell, mantle cavity, osphradium, or
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Order Thecosomata Shell present; pelagic ciliary feeders; no gill; 6 families. Order Gymnosomata Shell absent; no mantle cavity; complicated feeding mechanisms; pelagic carnivores; 7 families. Order Nudibranchia Sea slugs without shell, mantle cavity, osphradium, or
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pteropod
…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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…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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