The royal natural history . chiata, Poly-branchiata, and Pellibranchiata. A fifth group, Parasita, has also been proposed fora very curious mollusc (EntoconcJia), which lives parasitic within an echinoderm{Synapta). Nudibranchs are found in all parts of the world, and are mostabundant in depths where seaweeds and corallines flourish, although they are alsofound at low water or even between tide - marks. A few species have beendredged at great depths. Some even pass their life in the open sea, attached tofloating seaweeds, or swim about freely like Pteropods or Heteropods. The animals belonging
The royal natural history . chiata, Poly-branchiata, and Pellibranchiata. A fifth group, Parasita, has also been proposed fora very curious mollusc (EntoconcJia), which lives parasitic within an echinoderm{Synapta). Nudibranchs are found in all parts of the world, and are mostabundant in depths where seaweeds and corallines flourish, although they are alsofound at low water or even between tide - marks. A few species have beendredged at great depths. Some even pass their life in the open sea, attached tofloating seaweeds, or swim about freely like Pteropods or Heteropods. The animals belonging to this group are characterised by theirsymmetrical form, and the position of the vent. This is placed uponthe posterior or central part of the back and surrounded by the branching gills,which are more or less contractile. The body is protected above by a large dorsalshield of a spongy texture, and made more or less rigid by calcareous spiculeswhich are embedded in it. The tentacles are dorsal, and retractile through holes. Acanthodoris pilosa (magnified). in the mantle some distance from the anterior extremity of the bod}, They are smooth at the base, but lamellated towards the tip. The eyes are minute and situated in the skin behind the tentacles. „ . m . A large number of species from all parts of the world, at one Dons Tribe. L L . time considered forms of the old genus Doris, are now placed in thedistinct group Doridopsidce, on account of differences in the oral organs. Thegeneral aspect of the animals of this family is the same as that of Boris, the gillsbeing arranged in a circle around the vent on the posterior part of the back. Thebuccal mass or eating apparatus is small, without jaws or raclula, and organised forsuction. The extensive family Dorididai, contains a considerable number ofgenera and subgenera, characterised by differences in the branchiae, the relativeproportion of the mantle in regard to the foot, and variations in the radula andjaws The general aspec
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Keywords: ., bookcentury1800, booksubjectnaturalhistory, booksubjectzoology
