Art. IV.—On a New Zealand Fresh-water Leech (Glossiphonia (Clepsine) novæ-zealandiæ, n. sp.).
[Read before the Philosophical Institute of Canterbury, 4th July, 1900.]
The specimens upon which this communication is founded were collected by Mr. Henry Suter, who discovered them living attached to the underside of stones near the margin of Lake Takapuna, in the North Island of New Zealand, in company with fresh-water Mollusca and sponges. Exceptional interest attaches to this discovery because it is generally supposed that leeches are absent from the land and fresh-water fauna of New Zealand. Thus in Parker and Haswell's “Textbook of Zoology” (vol. 1, p. 481) we find the statement, “Hitherto no member of the class has been found in New Zealand, with the exception of the marine Branchellion.”
It should be pointed out, however, that a land-leech (Geobdella limbata) has been recorded from New Zealand. The only literature upon this species which we have been able to obtain is Moore's paper on the leeches of the United States National Museum,* in which two specimens collected by the United States Exploring Expedition are stated to have come from New Zealand. It seems highly improbable that so aggressive an animal as a land-leech should remain unknown to the numerous local collectors who have explored the New Zealand bush, and we prefer to believe that some mistake has been made in the labelling of the two specimens in the United States National Museum.
Owing to the extremely small size of our species, the irregularity of the annulation in front, and the absence of any papillæ or colour-markings on the integument, we have found it impossible to determine the segmental arrangement of the various organs with that exactness which has of late years been customary with that describers of leeches.†
Our observations have been made upon both living and preserved specimens, and the internal anatomy has been investigated by means of transverse and longitudinal vertical serial sections, as well as by dissection and the examination of
[Footnote] * “Proceedings of the United States National Museum,” vol. xxi., p. 563.
[Footnote] † Compare Whitman, “The Segmental Sense-organs of the Leech,” American Naturalist, October, 1884; and “Description of Clepsine plana,” Journal of Morphology, vol. iv., No. 3, 1891.
entire specimens stained and cleared. From the point of view of the comparative anatomist the results obtained are hardly sufficient to compensate for the large expenditure of time and trouble, as in most respects the anatomy seems to agree very closely with that previously known for other species of the genus. The structure and arrangement of the nephridia, however, appear to be very peculiar, though we have not succeeded in working them out in detail, and the presence of only two annuli in the typical somite appears to distinguish our species not only from others of the same genus, but from all other Rhynchobdellidæ.*
In contracted specimens the body is ovoid; emarginate and somewhat broader behind; strongly convex above and concave beneath, so that there is a large hollow space below the body which serves as a brood-pouch; with no distinct head. The length of a spirit-preserved specimen was 6 mm., and the width 4 mm., with posterior sucker 1.5 mm. in diameter. Another specimen, when extended in life, measured as much as 18 mm. in length. The animal in life is of a very pale dull orange or flesh-colour, semitransparent, with no papillæ nor colour-markings except microscopic pigment-cells. In spirit the colour is almost white, opaque.
The posterior sucker (disc) is flat, and usually nearly circular in outline; in contracted specimens scarcely visible from above. The much smaller anterior sucker appears to be made up of from five to eight annuli† (it is impossible to determine the exact number), and its anterior margin, forming the extreme anterior end of the body, bears a slight median notch.
On the dorsal surface of the body about fifty-five annuli may commonly be counted, but the annulation is not sufficiently distinct and regular to make an exact count practicable. In the middle region of the body it is evident, from the arrangement of the nephridial apertures and various internal organs, that each somite is composed of two annuli.
The eyes are four in number, placed two on each side of the middle line, those of the same side very close together, sometimes touching one another, so as to appear as one in contracted specimens, but separated from those of the opposite side by a fairly wide interval. Their position is about on a level with the hinder margin of the anterior sucker. Those of one side may be distinctly in advance of those of the other side, and the position as regards the annuli of the head seems
[Footnote] * See Postscript, however.
[Footnote] † In counting the annuli we assume throughout this paper that the head (anterior sucker) is made up of eight.
to be slightly variable, owing probably to the irregularity of the annulation. In a young specimen no eyes were visible at all. The form of the eye, when viewed from above, is crescentic, and on each side the two eyes lie back to back, with the concavities of the pigment-cups facing away from one another, one looking forwards and the other backwards.
The mouth is placed well in front of and above the middle of the anterior sucker, only a short way behind the marginal median notch.
The anus lies dorsally a short way in front of the posterior sucker; it may be separated from the sucker by two annuli.
The male genital opening lies in what we count as the thirteenth annulus behind the anterior sucker, so that if we assume that the anterior sucker is composed of eight annuli the male aperture may be located in annulus 21. The aperture itself has tumid lips, and the annulus in its neighbourhood is much swollen. Probably this annulus is composed of two fused together, between which the aperture lies,* but we have thought it desirable not to attempt a theoretical analysis. Some three or four of the annuli behind and in the neighbourhood of the male aperture may exhibit a well-marked longitudinal wrinkling.
The actual female aperture was unrecognisable in our specimens, but sections show that it must lie close behind the male aperture, apparently in the groove between the 21st and 22nd annuli. Nephridial apertures could not be recognised externally, but longitudinal sections showed seven pairs, lying on annuli 31, 33, 35, 37, 39, 41, 43.
Some specimens carried a number of eggs attached to the ventral surface of the body in the brood-chamber before mentioned. These eggs are ovoid in shape, and about 0.5 mm. in longer diameter.
The general anatomy agrees very closely with that of other species, as described, for example, by Oka in his “Beitr äge zur Anatomie der Clepsine.”†
Alimentary Canal.—The mouth appears as a narrow transverse slit in the cup-like anterior sucker. It leads into a narrow tubular buccal cavity, through which the long muscular proboscis can be protruded. When the proboscis is retracted the buccal cavity extends back to about the 11th annulus. The proboscis, or pharynx, is long and cylindrical, and in a state of retraction extends from about the 11th to about the 25th annulus, lying in the middle of the body. From the posterior end of the pharynx the narrow œsophagus runs for-
[Footnote] * Compare Clepsine plana, Whitman, loc. cit.
[Footnote] † “Zeitschrift für wissenschaftliche Zoologie,” band 58, 1894.
wards dorsally (when the pharynx is retracted) to about the 22nd annulus, and then turns backwards to open into the large thin-walled crop. The crop gives off six pairs of lateral diverticula, increasing in size from in front backwards, the 1st pair being very small and lying at the sides of the pharynx, while the 6th pair are large, sacculated on the outer sides, and turn backwards so as to run almost longitudinally to the level of the posterior sucker. The lateral diverticula of the crop spring from the median portion opposite to annuli 25, 27, 29, 31, 33, and 35. Following the crop there comes a curious sacculated portion of the alimentary canal, which we propose to consider as the stomach, and which consists of a median portion giving off four pairs of crowded lateral diverticula opposite to annuli 36, 37, 38, and 39. Then follows the intestine, the front half of which is greatly dilated to form a pear-shaped sac, tapering off behind into a narrow portion, which opens posteriorly at the anus.
Nervous System.—The cerebral ganglia lie above the alimentary canal about opposite to the 13th annulus. The nerve-collar runs round the anterior portion of the pharynx and connects the cerebral with the subœsophageal ganglia. The subœsophageal ganglia and the three succeeding pairs of the ventral chain lie in front of the male genital aperture. The 5th pair (counting the subœsophageal as the first of the chain) lies immediately behind the male aperture, opposite the 21st annulus. The 6th to the 17th pair inclusive lie in alternate annuli from the 23rd to the 45th. The remaining ganglia, about six in number, are fused together, and extend from about the 47th annulus into the posterior sucker.
Circulatory Organs.—The arrangement of the vessels and sinuses in the genus Clepsine has been very fully worked out by Oka,* and we have not thought it worth while to investigate it in detail in the species under discussion.
Nephridia.—The nephridia seem to exhibit great peculiarities, and we regret that owing to the difficulties of the investigation we are unable to give a complete account of them. We have found in sections seven funnels, with corresponding capsules, on each side; these lie opposite to annuli 23, 25, 27, 29, 31, 33, and 35, and seem to agree closely with the corresponding structures as figured by Oka.* We have also found seven pairs of external openings in the integument, but these are placed on annuli 31, 33, 35, 37, 39, 41, and 43. We do not doubt that these are the nephridial apertures, but we have been unable to trace any connection between them and the internal funnels, and it seems strange that they should be so widely separated from the latter.
[Footnote] * Loc cit.
Each external aperture appears to be eight annuli or four somites behind the corresponding internal funnel. Of course, it is quite possible that some mistake has been made here, but the coincidence of the numbers on both sides of the animal (investigated by longitudinal sections) is very remarkable. It may be that the external apertures have been overlooked in the anterior four pairs of nephridia and the internal portions in the posterior four pairs, and perhaps this is the most likely explanation. If it be so, then we have indications of eleven pairs of nephridia.
Reproductive Organs.—There are normally six pairs of testes, opposite annuli 24, 26, 28, 30, 32, and 34, but they are not always regular, and may even differ in arrangement on the two sides of the same animal. The testes lie between and below the diverticula of the crop, and are vertically compressed from in front backwards, so that in the adult animal they form flattened plates. The vasa deferentia in the adult animal are very long and coiled. Each commences in front of the testes amongst the copious glands at the sides of the pharynx, and, passing backwards, coils about, finally turning forwards and inwards to meet its fellow of the opposite side at the male genital aperture, each duct ending in a conspicuous round swelling.
The ovaries are contained in two elongated sacs which pass gradually into the oviducts, the latter uniting together in the middle line just behind the point of union of the vasa deferentia. In the young animal the two ovaries and their ducts lie tranversely across the body in the same straight line. In older animals they turn backwards, extending about as far as the fifth division of the crop and then turning aside.
[Postscript.—A copy of this paper, with illustrations, was sent to the Melbourne meeting of the Australasian Association for the Advancement of Science in January, 1900, but want of funds has prevented its publication. Meanwhile a paper has appeared, by J. P. Moore,* describing a biannulate Glossiphonid from North Carolina, for which he proposes the new genus Microbdella. Microbdella biannulata, Moore, very closely resembles our species, and its discovery in America adds greatly to the interest attaching to the New Zealand form, which is, however, evidently specifically distinct. It appears† that Oka, in 1895, had already described a biannulate leech, but this was an Ichthyobdellid belonging to the genus Ozobranchus.]
[Footnote] * “A Description of Microbdella biannulata, with Especial Regard to the Constitution of the Leech Somite” (“Proceedings of the Academy of Natural Sciences of Philadelphia,” 1900).
[Footnote] † Compare Moore, “Note on Oka's Biannulate Leech” (“Zoologischer Anzeiger,” 3rd September, 1900).