Concept

Anaspidea

Résumé
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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