| Sea Hares | |
|---|---|
| Aplysia californica, a typical sea hare displaying inking behavior | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Gastropoda |
| (unranked): | clade Heterobranchia clade Euthyneura clade Euopisthobranchia[1] clade Aplysiomorpha P. Fischer, 1883 |
| Families | |
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The clade Aplysiomorpha, commonly known as Sea hares or Sea Bags (Aplysia species and related genera), are medium-sized to very large Opisthobranchia with a soft internal shell made of protein. These are marine gastropod molluscs in the superfamilies Aplysioidea and Akeroidea.
The common name "sea hare" derives from their rounded shape and from the two long rhinophores that project upwards from their heads and that somewhat resemble the ears of a hare.
They are also referred to locally in their natural coastal habitat of Southern California as the "Sea Bag" This is due to their appearance resembling a tan grocery shopping bag floating in the water upon initial glance.
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Many older textbooks and websites refer to this suborder as Anaspidea. The original author P. Fischer described the taxon Anaspidea at unspecified rank above family.[2] In 1925 Johannes Thiele established the taxon Anaspidea as a suborder.
However, 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)[1] have moved this taxon (named as Anaspidea) to Euopisthobranchia.
Sea hares are mostly rather large, bulky creatures. The biggest species, Aplysia vaccaria, can reach a length of 75 centimetres (30 in) and a weight of 2 kilograms (4.4 lb) and is arguably the largest gastropod species.
Sea hares have soft bodies with an internal shell, and like all opistobranch mollusks they are hermaphroditic. Unlike many other gastropods, they are more or less bilaterally symmetrical in their external appearance. The foot has lateral projections, or "parapodia".[3]
Sea hares are herbivorous, and are typically found on seaweed in shallow water. It seems to be the case that some young sea hares are capable of burrowing in soft sediment leaving only their rhinophores and mantle opening showing. Sea hares have an extremely good sense of smell. They can follow even the faintest scent using their rhinophores, which are extremely sensitive chemoreceptors.
Their color corresponds with the color of the seaweed they eat: red sea hares have been feeding on red seaweed. [4] This camouflages them from predators. When disturbed, a sea hare can release ink from its ink glands, providing a potent deterrent to predators. This release acts as a smoke screen, while at the same time, adversely affecting the smell sensors of their predators. In a small environment, this ink could be toxic to the inhabitants. The color of the ink is white, purple or reddish, depending on the color of the pigments in their seaweed food source. Their skin contains a similar toxin that renders sea hares largely inedible to many predators.
Some sea hares can employ jet propulsion as a locomotory method, although without the sophisticated cognitive machinery of the cephalopods their motion is somewhat erratic.[5][6]
Aplysia californica is a typical example of a sea hare, and is noteworthy for its usefulness in studies of neurobiology because of the unusually large size of the axons that are a part of its nerve cells.