The fifth family is Tornatellidæ, types, Tornatina and Tornatella.
The third order is the Pulmonifera, and the fourth is the Prosobranchiata; we shall speak of them in the next chapter.
In this family we reach a group of Gasteropods much more numerous, both in species and in special types, which respire by the aid of branchiæ, or gills. Cuvier divides them into many orders, based chiefly upon their respiratory organs.
The Tectibranchiata have the gills attached either to the right side of the body or upon the back, arranged in the form of leaflets, more or less divided, but not symmetrical, and nearly covered by the mantle. Bulla and Aplysia are the two principal genera of the group, and may be considered as the type of two small families.
The Aplysiæ were known to the ancients under the name of sea-hares (Lepus marinus), from some fancied resemblance to the terrestrial hare. They were objects of profound horror, inspired either by their singular form, or from an acrid, caustic, and inodorous liquid which they secrete. A magic influence was attributed to them; they were supposed, for instance, to have influence over the female heart. It is not easy, however, to explain the evil renown acquired by an animal which is known to be gentle and even timid. They are naked and fat, somewhat resembling the Limnæa in their oval, elongated form, their thickness in the dorsal region, and their posterior locomotion. Their head, which is very indistinct, is furnished with four tentacles, the anterior two of which are the largest, and somewhat resemble the ears of a hare. The eyes are found at the base of the posterior tentacles. These characters are observed in Aplysia depilans (Fig. 180). Aplysia inca shows also the same arrangement (Fig. 181). In this family the mollusc is much more important from its volume than from its internal, rudimentary, and horny shell, which is contained in the branchial shield. In Fig. 182 we have the small and thin cartilaginous shell which exists in the interior of the animal.
Fig. 180. Aplysia depilans (Lin).
Fig. 181. Aplysia inca (D'Orbigny).
Fig. 182. Shell of Aplysia inca.
The Aplysiæ are found nearly in every region of the globe, not only upon the shores of the Continent, but on every island shore. They commonly inhabit sandy and muddy shores of small depths, or even the rocky recesses, or under shelter of the stones which have fallen from the cliffs. Their eggs consist of those long filaments which are discharged in immense numbers, and which fishermen call sea-worms.