(b) Bivalvia (= Conchae): Mya, Solen, Tellina, Cardium, Mactra, Donax, Venus, Spondylus, Chama, Arca, Ostrea, Anomia, Mytilus, Pinna.
In the case of the pearl oyster this parasite is a cestode larva, but in the less valuable but no less genuine pearl produced by Mytilus, &c., the nucleus is a Trematode-larva (Jameson).
In Mytilus the foot is reduced to little more than a tubercle carrying the apertures of these glands.
II, A a portion of four filaments of a ctenidium of the sea-mussel (Mytilus) is represented, having precisely the same structure as those of Arca.
The filaments of the gill (ctenidium) of Mytilus and Arca thus form two closely set rows which depend from the axis of the gill like two parallel plates.
This is the condition seen in Arca and Mytilus, the so-called plates dividing upon the slightest touch into their constituent filaments, which are but loosely conjoined by their " ciliated junctions."
Complications follow upon this in other forms. Even in Mytilus and Arca a connexion is here and there formed between the ascending and descending rami of a filament by hollow extensible outgrowths called " interlamellar junctions " (il.
Then let us suppose that the inter-lamellar junctions already noted in Mytilus become very numerous, large and irregular; by them the two trellis-works of filaments would be united so as to leave only a sponge-like set of spaces between them.
- Filaments of the Ctenidium of Mytilus edulis.
It is important, because such a concrescence is by no means universal, and does not occur, for example, in Mytilus or in Arca; further, because when its occurrence is once appreciated, the reduction of the gill-plates of Anodonta to the plume-type of the simplest ctenidium presents no difficulty; and, lastly, it has importance in reference to its physiological significance.
Such a subdivision of the pallial chamber, and direction of the currents set up within it do not exist in a number of Lamellibranchs which have the gill-lamellae comparatively free (Mytilus, Arca, Trigonia, &c.), and it is in these forms that FIG.17.
The organs are developed as invaginations of the epidermis of the foot, and in the majority of the Protobranchia the orifice of invagination remains open throughout life; this is also the case in Mytilus including the common mussel.
In Mytilus the two apertures are on a common papilla, in other cases the two apertures are as in Anodonta.
" Anomia " (1854), " Mytilus " (1856), " Dentalium " (1856-1857), " Purpura " (1859), " Haliotis (1859), " Vermetus " (1860).
That the level of Lake Aral was much higher in postPliocene times is proved by the discovery of shells of its characteristic species of Pecten and Mytilus in the Kara-kum Desert, 33 m.
This was manufactured from the Mytilus californianus, a mussel which abounds there.
Musculus, diminutive of mus, mouse, applied to small sea fish and mussels), a term applied in England to two families of Lamellibranch Molluscs - the marine Mytilacea, of which the edible mussel, Mytilus edulis, is the representative; and the fresh-water Unionidae, of which the river mussel, Unio pictorum, and the swan mussel, Anodonta cygnea, are the common British examples.
The sea mussel (Mytilus edulis) belongs to the second order of the class Lamellibranchia, namely the Filibranchia, distinguished by the comparatively free condition of the gillfilaments, which, whilst adhering to one another to form gillplates, are yet not fused to one another by concrescence.
Mytilus possesses no siphonal tube-like productions of the margin of the mantle-skirt, nor any notching of the same, representative of the siphons which are found in its fresh-water ally, the Dreissensia polymorpha.
Mytilus edulis is an exceedingly abundant and widely distributed form.
The readiness with which the young Mytilus attaches itself to wicker-work is made the means of artificially cultivating and securing these molluscs for the market both in the Bay of Kiel in North Germany and at the mouth of the Somme and other spots on the coast of France.
It is a curious fact, illustrative of the ignorant procedure and arbitrary fashions of fisher-folk, that on the Atlantic seaboard of the United States the sea mussel, Mytilus edulis, though common, is not used as bait nor as food.
Mytilus edulis is considered of fair size for eating when it is 2 in.
Mytilus edulis is occasionally poisonous, owing to conditions not satisfactorily determined.
- For an account of the anatomy of Mytilus edulis the reader is referred to the treatise by Sabatier on that subject (Paris, 1875).