Art. XXVII.—On a Large Pterotrachœid from the Pacific Ocean.
[Read before the Otago Institute, 10th October, 1905.]
Hitherto only a single species of the pelagic group of Gastropods, the Heteropoda, has been recorded from the seas that wash our coasts. This is Carinaria australis,* Q. and G., which was obtained in 1827, during the voyage of the “Astrolabe,” between Australia and New Zealand. We may now add Firola (Pterotrachea) coronata, Forskål, to our marine fauna.
The specimen upon which this identification rests was washed ashore during January, 1905, at Long Beach, a few miles north of the Otago Harbour. Luckily for zoology, it was observed lying on the sandy shore and secured by Mr. W. Fels, of Dunedin, who transmitted it to me at the Museum. Unfortunately, it had been somewhat damaged by the tossing of the surf and by rolling on the sandy beach; thus the epidermis and underlying tissue was in great part rubbed off. The posterior end (metapodium) had been broken away behind the visceral hump. The visceral mass itself was a good deal damaged—only three or four gill-filaments remamed of the gill—and part of the male copulatory organ was broken away. The ventral fin (or mesopodium) is also a good deal damaged, at least half of it being absent; but I believe that so much as remains suffices to establish the specific identity with F. coronata.
An examination of the literature available showed me that the specimen is much larger than the majority of species of Pterotrachea (Firola), though P. adamastor, Lesson, from the
[Footnote] * Quoy and Gaimard, Voy. de l'Astrolabe, vol. ii, p. 394.
Cape of Good Hope, attains a length of 15in.* But this species differs from mine in the proportions of the parts.
The “Report of the ‘Challenger’” Heteropods did not enable me to carry the matter further; but my friend Mr. Charles Hedley, of the Australian Museum, to whom I applied for information on the matter, most kindly loaned me his copy of Vayssiére's “Mollusques Heteropodes.”† From a comparison of the account and figures of F. coronata contained therein I think there is little doubt but that the present specimen is either that or a closely allied species. My only reason for doubt is a small difference in the detailed structure of the median teeth of the radula. Vayssiére remarks (p. 37) that the form of the median teeth constitutes the most reliable character for distinguishing the different species of the genus. But, in spite of the small difference to which I refer, I refrain, in the absence of an entire specimen, from creating a new species.
In the Mediterranean specimens of F. coronata the median denticle of the median tooth of the radula is trifid; in the Pacific specimen this denticle is, throughout the radula, single-pointed (see Plate XLIII, fig. 2). I note the same asymmetry of the smaller denticulations as he figures (pl. iii, fig. 36), though these are rather fewer in number than he gives; and in all other respects—such as shape, proportions of median tooth and of its denticulated area—this tooth agrees with Vayssiére's account and figures, as do the other teeth.
There are twenty-one or twenty-two rows of teeth (Vayssiére gives twenty-three). Possibly the tip of the radula was torn in my specimen, as the buccal mass was ruptured, and protruded from the head, and probably for this reason I was unable to find the “palatal chitinous hooklets” which Vayssiére describes. Although there are no “thorn-like” processes remaining on the body, as in F. coronata, yet they persist on the head, where there are two parallel rows of four, as described for that species, and below the gills.
The following measurements were taken shortly after the animal had been placed in formalin.
Body.—Total length, probably 320mm.; length from preocular “thorns” to broken surface of visceral hump, 230mm.; vertical diameter about midway between ventral fin and base of snout, 30mm.; circumference of ditto, 90mm.; distance from base of fin to base of snout, 100mm.; distance from base of fin to level of genital pore, 60mm.
[Footnote] * Voy. de Coquille, p. 249, pl. ui, fig. 1.
[Footnote] † Vayssiére, Moll. Heteropodes, 1904 (pt 26 of “Les Resultats des Campaignes Scientifiques, par Albert ler, Prince Souverame de Monaco”).
Snout.—Length from preocular “thorns” to mouth, 110mm.; diameter at base, 20mm.; diameter just above buccal swelling, 10mm.
Ventral Fin.—Length of base, 45mm.
A comparison of proportionate sizes in my specimen and that figured by Vayssiére, which measures 260mm., shows a close agreement. In the Pacific specimen the length of the snout is contained two and a half times in the distance from preocular thorns to genital fin, and in the Mediterranean specimen twice. In the Pacific specimen the base of sucker is contained twice in distance between it and snout, and in the Mediterranean specimen twice. In the Pacific specimen the snout-diameter to length is one-fifth, and in the Mediterranean specimen one-fourth.
Since these proportions agree pretty well, we may estimate the total length of the uninjured specimen. Vayssiére states that the distance from the visceral hump to the tip of the “tail” (metapodium) is about twice the length of the finbase. Applying this to our specimen we should add 2x45=90mm. to the above figure of 230mm., giving a total length of 320mm. In the same way we may estimate the size of the uninjured fin. Vayssiére's figure shows the length to be rather more than twice the base-length, and height one and a half times the base-length. So that the fin in our specimen was probably about 90mm. in length (i.e., a quarter of the total length of the body), and 67 mm. in height.
I have been unable to find any statistics as to the size of the different species of Firola (Pterotrachea); neither in Bronn's “Thierreichs” nor in the “Cambridge Natural History” do any data exist. The “‘Challenger’ Report” gives only a list of hitherto-described species, without details; and, as I have remarked above, the only species to a description of which I can refer that approaches this one in size is P. adamastor, with its 15 in., which measurement includes the length of the snout.
As figures of the genus are not readily accessible in ordinary text-books, I have deemed it advisable to give an outline of my specimen, but with the missing portions represented in dotted outline, copied from Vayssiére. I hope that people interested in natural history will keep a look-out for this and other unusual marine animals, and forward them, preserved in formol, to me at the Otago University Museum. Formol is obtainable at any chemist's, and should be used in a diluted condition, by adding ten volumes of water to one volume of formol. Animals placed in a bottle filled with this fluid, carefully corked, and packed in a small wooden box, or in shavings, &c., and properly wrapped up, can be sent for a few pence by
sample post. Each such sending should be accompanied by the name and address of finder, and the locality at which the specimen was obtained.
Explanation of Plate XLIII.
Fig. 1. Outline of a damaged specimen of a male Firola coronata; x½: the missing parts added from Vayssiére's drawing, in a broken line.
Fig. 2. A median tooth of the radula; × 60.
Fig. 3. The base of the snout, viewed from in front, showing the eight preocular “thorns.” a, anus; f, ventral fin; g, gemtal pore; m, mouth; v, visceral hump.