Sometimes this gland is found in the young and not in the adult (Anodonta, Unio, Cyclas).
- Diagrams of the external form and anatomy of Anodonta cygnea, the Pond-Mussel; in figures I, 3, 4, 5, 6 the animal is seen from the left side, the centro-dorsal region uppermost.
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.
In this way the notches d, e of the hinder part of the mantle-skirt of Anodonta are in the siphonate forms converted into two separate holes, the edges of the mantle being elsewhere fused together along this hinder margin.
Aa, ae, af, ag, ah, ak, al, am, an, ap, aq, ar, as, at, au, av, aw, ax, ay, az, bb, In Anodonta these pallial tentacles are confined to a small area surrounding the inferior siphonal notch (fig.
The centro-dorsal point a of the animal of Anodonta (fig.
It is the approximate equality in the size of the anterior and posterior adductor muscles which led to the name Isomya for the group to which Anodonta belongs.
In removing the valves of the shell from an Anodonta, it is necessary not only to cut through the muscular attachment of the body-wall 4 ?"
The shell of Anodonta does not present these parts in the most strongly marked condition, and accordingly our figures (figs.
These notches are known in Anodonta as the afferent and efferent siphonal notches respectively, and correspond to the long tube-like afferent inferior and efferent superior " siphons " formed by the mantle in many other Lamellibranchs (fig.
Whilst the valves of the shell are equal in Anodonta we find in many Lamellibranchs (Ostraea, Chama, Corbula, &c.) one valve larger, and the other smaller and sometimes flat, whilst the larger shell may be fixed to rock or to stones (Ostraea, &c.).
Let us now examine the organs which lie beneath the mantle-skirt of Anodonta, and are bathed by the current of water which circulates through it.
The foot thus exposed in Anodonta is a simple muscular tongue-like organ.
I [I] ) so as to issue from the shell, and by its action the Anodonta can slowly crawl or burrow in soft mud or sand.
The labial tentacles or palps of Anodonta (n, o in fig.
The gill-plates have a structure very different from that of the labial tentacles, and one which in Anodonta is singularly complicated as compared with the condition presented by these organs in some other Lamellibranchs, and with what must have been their original condition in the ancestors of the whole series of living Lamellibranchia.
12) and in those of Anodonta (fig.
And in Anodonta (fig.
In Anodonta, besides being thickened, the skeletal substance of the filament develops a specially dense, rod-like body on each side of each filament.
Although the structured of the ctenidium is thus highly complicated in Anodonta, it is yet more so in some of the siphonate genera of Lamellibranchs.
In Anodonta, as in many other Lamellibranchs, the ova and hatched embryos are carried for a time in the ctenidia or gill apparatus, and in this particular case the space between the two lamellae of the outer gill-plate is that which serves to receive the ova (fig.
This is difficult to see in Anodonta, but if the mantle-skirt be entirely cleared away, and if the dependent lamellae which spring from the ctenidial axis be carefully cropped so as to leave the axis itself intact, we obtain the form shown in fig.
In Arca this can be seen with far less trouble, for the filaments are more easily removed than are the consolidated lamellae formed by the filaments of Anodonta, and in Arca the free axes of the ctenidia are large and firm in texture (fig.
The actual condition in Anodonta at the region where the gills begin anteriorly is shown in fig.
Affixed to the foot Passing still farther back behind the foot, we find in Anodonta the condition shown in the section D, fig.
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.
- Diagram of a view from the left side of the animal of Anodonta cygnaea, from which the mantle-skirt, the labial tentacles and the gill-filaments have been entirely removed so as to show the relations of the axis of the gill-plumes or ctenidia g, h.
- Vertical Section through there is least modification by concrescence of the primary an Anodonta, about the mid-region filamentous elements of the of the Foot.
The alimentary canal of Anodonta is shown in fig.
The coil of the intestine in Anodonta is similar to that of other Lamellibranchs.
The food of the Anodonta, as of other Lamellibranchs, consists of microscopic animal and vegetable organisms, brought to the mouth by the stream which sets into the sub-pallial chamber at the lower siphonal notch (e in fig.
The heart of Anodonta consists of a median ventricle embracing the rectum (fig.
In Anodonta the blood is driven by the ventricle through the arteries into vessel-like spaces.
The ventricle and auricles of Anodonta lie in a pericardium which is clothed with a pavement endothelium (d, fig.
The pair of renal organs of Anodonta, called in Lamellibranchs the organs of Bojanus, lie below the membranous floor of the pericardium, and open into it by two well-marked apertures (e and f in fig.
In Anodonta there are three well-developed pairs of nerve ganglia (fig.
The sense-organs of Anodonta other than the osphradia consist of a pair of otocysts attached to the pedal ganglia (fig.
Anodonta has no eyes of any sort, and the tentacles on the mantle edge are limited to its posterior border.
The gonads of Anodonta are placed in distinct male and female individuals.
In Anodonta the eggs pass into the space between the two lamellae of the outer gill-plate, and are there FIG.
The development of Anodonta is remarkable for the curious larval form known as glochidium (fig.
The early larva of Anodonta is not unlike the trochosphere of other Lamellibranchs, but the mouth is wanting.
Other Lamellibranchs exhibit either a trochosphere larva which becomes a veliger differing only from the Gastropod's and Pteropod's veliger in having bilateral shell-calcifications instead of a single central one; or, like Anodonta, they may develop within the gill-plates of the mother, though without presenting such a specialized 210 1P -' 1 °* larva as the glochidium.
Mushketov [1850-1902 ]) Cardium edule, Dreissena polymorpha, Neritina liturata, Adacna vitrea, Hydrobia stagnalis, in the Kara-kum desert, and Lithoglyphus caspius, Hydrobia stagnalis, Anodonta ponderosa and the sponge Metchnikovia tuberculata, in the Kizilkum desert.
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 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.
Unio differs in no important point from Anodonta in internal structure.
Anodonta cygnea, the Pond Mussel or Swan Mussel, appears to be entirely without economic importance.
The genital papilla of the female acquires a great development during the breeding season and becomes produced into a tube nearly as long as the fish itself; this acts as an ovipositor by means of which the comparatively few and large eggs (3 millimetres in diameter) are introduced through the gaping valves between the branchiae of pond mussels (Unio and Anodonta), where, after being inseminated, they undergo their development, the fry leaving their host about a month later.