The clade Anaspidea, commonly known as sea hares (Aplysia species and related genera), are medium-sized to very large opisthobranch gastropod molluscs with a soft internal shell made of protein. These are marine gastropod molluscs in the superfamilies Aplysioidea and Akeroidea.
The common name "sea hare" is a direct translation from lepus marinus, as the animal's existence was known in Roman times. The name derives from their rounded shape and from the two long rhinophores that project upward from their heads and that somewhat resemble the ears of a hare.
Many older textbooks and websites refer to this suborder as "Anaspidea". The original author Paul Henri Fischer described the taxon Anaspidea at unspecified rank above family. In 1925 Johannes Thiele established the taxon Anaspidea as a suborder.
Since the taxon Anaspidea was not based on an existing genus, this name is no longer available according to the rules of the ICZN. Anaspidea has been replaced in the new Taxonomy of the Gastropoda (Bouchet & Rocroi, 2005) by the clade Aplysiomorpha.
The scientific name for the order in which they used to be classified, the Anaspidea, is derived from the Greek for "without a shield" and refers to the lack of the characteristic head shield found in the cephalaspidean opisthobranchs. Many anaspideans have only a thin, internal and much-reduced shell with a small mantle cavity; some have no shell at all. All species have a radula and gizzard plates.
Jörger et al. (2010) have moved this taxon (named as Anaspidea) to Euopisthobranchia.
The name "Aplysiomorpha" was preferred by Bouchet and Rocroi (2005) over "Anaspidea Fischer", 1883, but the authors now agree that there is a consistent usage for Anaspidea in the recent literature and that the older name must be preferred.
Sea hares are mostly rather large, bulky creatures when adults. Juveniles are mainly unobserved on the shoreline. The biggest species, Aplysia vaccaria, can reach a length of and a weight of and is arguably the largest gastropod species.
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Mollusca is the second-largest phylum of invertebrate animals, after the Arthropoda; members are known as molluscs or mollusks (ˈmɒləsk). Around 85,000 extant species of molluscs are recognized. The number of fossil species is estimated between 60,000 and 100,000 additional species. The proportion of undescribed species is very high. Many taxa remain poorly studied. Molluscs are the largest marine phylum, comprising about 23% of all the named marine organisms. Numerous molluscs also live in freshwater and terrestrial habitats.
The clade Anaspidea, commonly known as sea hares (Aplysia species and related genera), are medium-sized to very large opisthobranch gastropod molluscs with a soft internal shell made of protein. These are marine gastropod molluscs in the superfamilies Aplysioidea and Akeroidea. The common name "sea hare" is a direct translation from lepus marinus, as the animal's existence was known in Roman times. The name derives from their rounded shape and from the two long rhinophores that project upward from their heads and that somewhat resemble the ears of a hare.
Sea snail is a common name for slow-moving marine gastropod molluscs, usually with visible external shells, such as whelk or abalone. They share the taxonomic class Gastropoda with slugs, which are distinguished from snails primarily by the absence of a visible shell. Determining whether some gastropods should be called sea snails is not always easy. Some species that live in brackish water (such as certain neritids) can be listed as either freshwater snails or marine snails, and some species that live at or just above the high tide level (for example, species in the genus Truncatella) are sometimes considered to be sea snails and sometimes listed as land snails.