Art. XVIII.—On the Anatomy of the Limpet (Patinella radians, Quoy).
[Read before the Philosophical Institute of Canterbury, 7th October, 1886.]
The following paper is an attempt to compare the structure of the New Zealand Limpet (Patinella radians) with that of the European Patella vulgata, L., as described in Cuvier's “Memoires,” page 15.
Patinella was made a genus by Professor Dall. The genus was founded upon Patinella magellanica (Gmelin), but that definition has been slightly extended, and made to include all the Patellas of New Zealand.*
It will be seen that the most important differences (as they will be shown in their proper places), between Patinella radians and Patella vulgata are—
1. That in Patinella radians the branchiæ do not extend all the way round the head, as they do in Patella vulgata, but
[Footnote] * “Proceedings of the Linnean Society of New South Wales, 1884,” p. 374.
end at the sides of the head, in about a straight line with the disc of the mouth.
2. The convolutions of the intestine are somewhat different to those shown by Cuvier, Fig. 12; but I have not been able to distinguish any expanded part of the intestine representing the stomach, further than that containing the coils of the odontophore.
3. The nervous system in Patella vulgata consists of a large ganglion, as shown in Cuvier, Fig. 16, from which nervefibres go off to all parts of the body. In Patinella radians it will be shown that there are three separate ganglia, connected to one another by thick commissures. There are the pedal ganglia, consisting of two thick masses on the upper surface of the foot. There are two parieto-splanchnic ganglia connected by a commissure going over the back, and by two other commissures connecting them with the pedal ganglia. These ganglia give off nerves to the somatic cavity, mantle, and branchiæ. The cerebral ganglia are situated in the head, and are connected with the parieto-splanchnic ganglia by commissures, and there are small ganglia on their course where the nerves go out to the tentacles. This nervous system shows that our southern species (as most southern forms are) is a more primary and older form than the northern species. This, I think, is the distinguishing characteristic of Patinella radians.
The shell is ovate and moderately convex; the apex is situated about a third of the length of the shell from the anterior end. The ribs in it are small, slightly rounded, and radiate out from the apex to the margin of the shell. They are intersected round the margin with short ribs extending only about half-way up the shell. The ribs are of a dark-brown colour, and the interspaces are of an ash colour. In the interior of the shell, the upper part, above the circular muscle, is of a dark-brown colour; below the circular muscle it has a nacreous appearance, having small grooves corresponding to the ribs on the outside, which at the margin are slightly flattened out, giving the rim of the shell a slightly serrated appearance.
The head consists of a large fleshy mass (shown in Fig. 2, a, b,) slightly narrowed at the neck; at the sides of the head are two well-marked tentacles, thick at their bases and tapering towards the points, very much of the shape of horns (x, y, Fig. 3). I have not been able to recognise the eyes, at the bases referred to by Woodward, page 278. The mouth opens on the lower surface of the body (it is shown, c, Fig. 1), it is simply a large oval-shaped sucking-disc.
The foot is a large olive-coloured oval disc, covering the lower surface of the body; by means of this muscular foot, the animal attaches itself to rocks; the free edge of the mantle hangs down round it.
The odontophore is armed with four tooth-like processes arranged in a series. Those of the inner series are of a brown horny colour at the apex, and transparent round the base.
The odontophore is about four times the length of the body of the animal, it is shown in position, (d, e, Fig. 2), after removing the foot. The teeth in the body of the coil are much sharper than those near the mouth, showing that they are replaced from behind as fast as they are worn out by friction in triturating the food. The muscular system round the odontophore is shown in Fig. 2
The branchiæ are numerous lamellar processes like ampullæ, lying between the fringe of the mantle and the foot; they do not extend all the way round the edge of the mantle, but only up to the sides of the neck; in Patella vulgata, figured by Cuvier, they extend round the whole body.
Nervous System.—As the nervous system seems to be the distinguishing feature between Patinella radians and Patella vulgata, I have dissected it out with great care. In P. vulgata the nervous system is simply a ganglionic ring, giving out nervefibres to the whole body. But in P. radians there are three different pairs of ganglia: (1.) Pedal ganglia are two ganglionic masses on the surface of the foot, connected together by a short thick commissure (ab, Fig. 5); they are connected to the parietosplanchnic ganglia by two very short commissures (ca, and bd, Fig. 5), and to the cerebral ganglia by two long commissures (ae, and bf, Fig. 5). These pedal ganglia give off two nerve-fibres to the surface of the foot (ah, and bh, Fig. 5), nearly meeting at their posterior ends. (2.) The parieto-splanchnic are not so large as the pedal ganglia; they are situated outside of and above the pedal, and connected to them by short commissures, to one another by a long commissure passing round the neck (cd, Fig. 5), and to the cerebral ganglia by two commissures (df, and ce, Fig. 5). These ganglia give off nerves (m, m, Fig. 5), to the mantle, and nerves (k, k', Fig. 5), to the sides of the somatic cavity, and the nerve g, Fig. 5, to the visceral cavity. (3.) The cerebral ganglia are situated in the top of the head at e,f, Fig. 5; they give off nerves to the tentacles, and one going round the top of the head (erf, Fig. 5).
Reproductive Organs.—There is a large ovary shown in Fig. 2 (lm), but I have not been able to trace the openings to the surface. I noticed that this ovary is much larger in summer time.
Muscular System.—The chief muscular organ is the foot; it covers the whole of the lower surface of the body, and acts like a sucker, attaching the animal to a rock. The circular muscle attaches the mantle to the upper rim of the foot. Its position is shown in Fig. 2 (pq). From this muscle the mantle hangs free round the foot. The muscles surrounding the head, and
working the odontophore, are shown in Fig. 2 (ab); they end in two globular-ended rods.
Alimentary System.—The mouth is situated on the lower surface at the anterior end of the body; it is simply an oval-shaped sucking-disc, and has a serrated appearance. It opens into a large œsophagus, surrounded by strong muscles; in it lies the odontophore with its three coils lying on the left side of the body when examined from below (shown Fig. 2, de). I have not been able to distinguish clearly an enlarged part, representing the stomach. The intestine has a great number of coils. I have traced them all out; they are shown in Fig. 4 (a to b). The coils differ from those in the European P. vulgata. The rectum is slightly swollen, and the anus opens on the left side of the head, under the mantle (shown k, Fig. 3, and b, Fig. 4). The liver is very large, occupying nearly the whole of the body cavity; it covers the whole of the intestines (shown Fig. 2, xy, and Fig. 3, fg).
I have not been able to make out the salivary glands referred to by Professor Ray Lankester in the “Annals of Natural History.”
Explanation of Plate XI.
Fig. 1 Represents the animal, seen from below; ab, the foot; c, mouth; de, fringe of the mantle round the shell; fg, branchiæ.
Fig. 2 A drawing of the animal after removing the foot; ab, muscles round the head; de, odontophore (in situ); f, g, h, k, parts of the intestines; pq, circular muscle; lm, ovary; st, free fringe of the mantle; xy, liver, filling up the interspaces.
Fig. 3 A drawing of the animal after removing the shell and outer coverings, seen from above; abc, coils of the intestine; d, anal end; e, oral end; fg, liver; pq, circular muscle; lm, mantle; xy, nerve commissure.
These three figures are enlarged six times.
Fig. 4 The coils of the intestines, magnified about eight times; a, oral end; b, anal end.
Fig. 5 Represents the nervous system; ab, are pedal ganglia; cd, the parieto-splanchnic ganglia; ef, cerebral ganglia; h, h1, pedal nerves; k, k1, nerves of somatic cavity; g, nerve going to the intestines.