Lamellibranch sentence example
Many Gastropoda deposit their eggs, after fertilization, enclosed in capsules; others, as Paludina, are viviparous; others, again, as the Zygobranchia, agree with the Lamellibranch Conchifera (the bivalves) in having simple exits for the ova without glandular walls, and therefore discharge their eggs unenclosed in capsules freely into the sea-water; such unencapsuled eggs are merely enclosed each in its own delicate chorion.
In other respects the anatomy of the cockle presents no important differences from that of a typical Lamellibranch.
Walcott has described a tiny lamellibranch (Modioloides) from the inferior Cambrian, and he reports the gastropod (?) genus Chuaria from the preCambrian.
As an example of the organization of a Lamellibranch, we shall review the structure of the common pond-mussel or swan mussel (Anodonta cygnea), comparing it with other Lamellibranchia.
It is on this account that the valves of a dead Lamellibranch always gape; the elastic ligament is no longer counteracted by the effort of the adductors.Advertisement
The phenomenon of " concrescence " which we have already had to note as showing itself so importantly in regard to the free edges of the mantle-skirt and the formation of the siphons, is what, above all things, has complicated the structure of the Lamellibranch ctenidium.
If we were to make a vertical section across the long axis of a Lamellibranch which had the axis of its ctenidium free from its origin onwards, we should find such relations as are shown in the diagram fig.
At the anterior end of the test is the apical plate from the centre of which projects a long flagellum as in many other Lamellibranch larvae.
Ostrea is a genus of Lamellibranch Molluscs.
The organization of the oyster, as compared with that of a typical lamellibranch such as Anodon, is brought about by the reduction of the anterior part of the body accompanying the loss of the anterior adductor, and the enlargement of the posterior region.Advertisement
Instead, the soft clam, Mya arenaria, a Lamellibranch not used by English or Norwegian fishermen, though abundant on their shores, is employed as bait by the fishermen to the extent of 14 million bushels per annum, valued at £120,000.
At the mouth of the river Conway in North Wales the sea mussel is crushed in large quantities in order to extract pearls of an inferior quality which are occasionally found in these as in other Lamellibranch molluscs (Gwyn Jeffreys).
The fresh-water Mussels, Anodonta cygnea, Unio pictorum, and Unio margaritiferus belong to the order Eulamellibranchia of Lamellibranch Molluscs, in which the anterior and posterior adductor muscles are equally developed.
The state of closure of the valves of the shell is not, therefore, one of rest; when it is at rest - that is, when there is no muscular effort - the valves of a Lamellibranch are slightly gaping, and are closed by the action of the adductors when the animal is disturbed.
That the condition of gaping of the shell-valves is essential to the life of the Lamellibranch appears from the fact that food to nourish it, water to aerate its blood, and spermatozoa to fertilize its eggs, are all introduced into this gaping chamber by currents of water, set going by the highlydeveloped ctenidia.Advertisement
The organization of the oyster, as compared with that of a typical lamellibranch such as Anodon (see Lamellibranchia), is brought about by the reduction of the anterior part of the body accompanying the loss of the anterior adductor, and the enlargement of the posterior region.