On the pelagic mollusc Phyllirrhoe, attached to it by the subumbral surface, and its tentacles have become rudimentary or absent.
1, A), and agrees with the method of coiling of a mollusc without lateral torsion, such as Nautilus.
This circlet of gill-lamellae led Cuvier to class the limpets as Cyclobranchiata, and, by erroneous identification of them with the series of metamerically repeated ctenidia of Chiton, to associate the latter mollusc with the former.
This organ has, without reason, been supposed to represent the second ctenidium of the typical mollusc, which it cannot do on account of its position.
Still, Lake Baikal has a seal (Phoca vitulina, Phoca baikalensis of Dybowski) quite akin to the seals of Spitsbergen, marine sponges, polychaetes, a marine mollusc (ancilodoris), and some marine gammarids.
The mollusc itself is often eaten, and dried for consumption in China and Japan.
Similarly Karl Hoffmann of Wiirzburg wasted his appreciations of the newer schools of developmental biology in fanciful notions of human diseases as reversions to normal stages of lower animals; scrofula being for him a reversion to the insect, rickets to the mollusc, epilepsy to the oscillaria, and so forth.
In most cases this is a mollusc, and the larvae bore their way into the most diverse organs, often accumulating to such an extent as to give a distinctly orange colour to an otherwise colourless tissue, and to cause the demolition of particular structures e.g.
In dry localities or in the absence of the intermediate host (usually a mollusc) this larva soon dies.
The cercaria swims freely for a time and either encysts directly on grass or weeds or it enters a second host which may be another mollusc, an insect, crustacean or fish, and then encysts.
The ciliated larva escapes from the egg into the water and enters an intermediate host (leech, mollusc, arthropod, batrachian or fish) where it undergoes a metamorphosis into a second stage in which most of the adult organs are present.
It presents a characteristic feature in its mollusc fauna, which contains many species not found in the neighbouring regions, and only found in the Alpine region.
COCKLE, in zoology, a mollusc (Cardium) of the class Lamellibranchia.
A medusa with a remarkable habit of life is Mnestra parasites, which is parasitic on the pelagic mollusc Phyllirrhoe, attaching itself to the host by its subumbral surface; its tentacles, no longer required for obtaining food, have become rudimentary.
Both ctenidia, right and left, are invariably present, the axis of each taking origin from the side of the body as in the schematic archi-Mollusc (see fig.
19, B, a) and connected in front of it by a commissure, are the representatives of the cerebral and pleural ganglia of the typical Mollusc, which are not here differentiated as they are in Gastropods.
Thus in the primitive mollusc the mantle-cavity contains a symmetrical group of structures at the posterior end of the body, and this group of structures is called the pallial complex.
It was present in the ancestral mollusc, occurs in nearly all archaic types, and is only absent in the most specialized forms, in which it has evidently been lost; these forms are certain Neomeniomorpha, all the Lamellibranchia, various degenerate Gastropoda, and the Cirrhoteuthidae among Cephalopods.
So far the young mollusc has not reached a definitely molluscan stage of Xviji.
They invariably disappear before the adult stage is reached, but their presence in the larva is evidence that the ancestral mollusc possessed a pair of true nephridia quite distinct from the coelomic excretory organs, which are so characteristic of existing forms in the adult condition.
Mollusca, and it is possible to construct a diagrammatic mollusc, as was first done by Lankester, which will possess these primitive features.
- Diagram of a primitive Mollusc, viewed from the left side.
The Cephalopoda can be derived without much difficulty from the schematic Mollusc, if we assume that some metameric repetition of organs has occurred, as explained above in reference to the coelom.
The suckers of a mollusc, the socket of the thigh-bone, &c.; and in botany for the receptacle of Fungi.
It is held by some morphologists that the mollusc body is unsegmented, and therefore is to be compared to a single segment of a Chaetopod or Arthropod.
(iv.) Phascolion, '10 ' species, small, living in mollusc-shells and usually adopting the coiled shape of their house; only one kidney, the right, persists.
The Pliocene deposits contain a mollusc fauna more arctic than that which exists at the present time, indicating probably that the connexion between the Pacific and Arctic Oceans was broader than it is now.
To this he added the account of Thule (which he placed six days' voyage north of Britain) and the adjoining regions, in which there was no longer any distinction between air, earth and sea, but a kind of mixture of all three, resembling the gelatinous mollusc known as pulmo marinus, which rendered all navigation and progress in any other mode alike impossible.
That pagurids must have the usually soft pleon or abdomen protected by the shell of a mollusc is now known to be subject to a multitude of exceptions.
The advantage that this group has derived from the adoption of mollusc xvrr.
The mollusc reciprocates by throwing off its embryos on the parent fish, in the skin of which they remain encysted for some time, the period of reproduction of the fish and mussel coinciding.