Anaspidea |
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| ORDER : ANASPIDEA | ||
| Family : Aplysiidae | ||
Members of the Anaspidea are commonly known as Sea Hares because of the rabbit-Iike appearance of some members of this order.
They have an oral tentacle on each side of the mouth and smaller cylindrical rhinophores on the head.
Eyes as such are non-existent, only minute, black-pigmented, photo-receptors are present.
Anaspideans are exclusively herbivorous. They are most frequently found in shallow waters, where they feed on algae and sea grasses
Exept Akera, members of the order generally have large parapodia that are folded over the mantle cavity located on the back of the animal.
Akera retains a bulloid shell, whereas alI other anaspideans have a small internaI shell plate or no shell at all. If the shell is internal, it is located dorsally between enlarged parapodia, visible through a small gap.
Many species have acquired the ability to swim, correlated with their evolutionary reduction or loss of the shell. Most swimming aplysiids employ muscular movements of lateral parapodial lobes, but in Notarchus swimming is effected by a form of jet propulsion elsewhere the mollusca found only in the cephalopoda
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Sea Hares have two main secretory glands in their mantle cavity, one we call the Purple Gland lies on the roof of the cavity, above the gill. It usually produces a purple secretion but can also produce a white ink in some species. This is not to be mistaken for the white milky secretions of the Opaline Gland which lies beneath the gill on the floor of the mantle cavity There is a lot of evidence to show that Sea Hares store noxious chemicals from their algal food, particularly from red algae, in their skins, and when these chemicals are secreted, they provide a powerful defence against predation. Experiments have shown that fishes tend to avoid sea hares. For purple ink, the main ingredient of the pigment is phycoerythrin, and is derived from red sea weeds that the slug eats. |
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The Aplysiidae ( Lamarck, 1809 )
Exept Akera, Family: Akeridae Pilsbry, 1893 (absent from Reunion Island), all the Anaspidea are in fact Aplysiidae members.
Aplysia Linnaeus, 1767
Body and mantle : The head is elongated and bears enrolled antero-lateral oral tentacles (sometimes fimbriated), and antero-dorsal rhinophoral tentacles. The mantle is usually smooth, reduced, bearing the openings (sometimes numerous) of the opaline gland and the purple gland (whose secretion consists of a number of unstable chromoproteins). Mantle cavity greatly reduced, a small exhalant siphon for the respiratory stream is often detectable in life. The foot is expanded dorso-laterally to form substantial parapodial lobes.
Photo : A. dactylomela |
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Shell : Shell internaI, enclosed by the mantle, but visible through a pallial foramen of variable size. Central areas of the shell calcified, but periphery flexible.
Photo : A. dactylomela |
