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IntroductionThe heteropods are a group of pelagic snails (Class Gastropoda) that are found in moderate to low abundances, primarily in tropical to subtropical latitudes. Among the gastropods, they have four striking adaptations to the open ocean environment. First, the bodies and shells are largely transparent; only the buccal mass, eyes and viscera are opaque. Because of this transparency, one can view internal structures in the head region (see first photograph below). Second, the foot, which in bottom-dwelling snails is the sole-like structure used for crawling along substrates, is laterally-compressed to form a ventral swimming fin. Because of the weight of the dorsal visceral mass, heteropods swim "upside-down", with the fin directed upward. Third, they possess image-forming eyes, with a large, spherical lens and a basal, ribbon-like retina (see second photo below). And, fourth, the radula has elongate, sickle-shaped lateral and marginal teeth that are used to snare prey after the radula is protruded from the mouth, which is located at the tip of their mobile proboscis. The presence of a trunk-like proboscis is responsible for their common name, "sea elephants."
DiagnosisGastropod mollusks with:
- Bodies that are largely transparent
- Paired image-forming eyes with large, spherical lenses
- Laterally-flattened ventral swimming fin
- Radula with elongate, sickle-shaped teeth that are used to snare prey