Geonemertes pantini, a New Land Nemertine from the Dunedin District
[Read by title before Otago Branch on October 13, 1953: received by Editor, October 21, 1953.]
Geonemertes pantini, a new species of land Nemeitine from the Dunedin district is described. It is compared with two closely related species, G. novae-zealandiae Dendy, 1894, and G. spirospermia Darbishire 1909; and the differences established.
Description of the Species
Geonemertes pantini n.sp. of the phylum Rhynchocoela, order Hoplonemertea.
For New Zealand the following terrestrial nemertines have been described: Geonemertes novae-zealandiae Dendy, 1894; G. spirospermia Darbishire 1909; and G. caeca Darbishire 1909; though Pantin (unpublished) considers that the description of only the first of these is adequate.
Material: Two specimens were gathered near the Centennial Memorial, Signal Hill, Dunedin, under the bark of rotting wood, the larger by Mr. L. O. Simpson, in July, 1951, the other by the author's elder son, in May, 1952. The smaller specimen was observed alive.
External Characters: In spirit the body of the larger worm showed numerous contraction wrinkles, and the “head” was almost entirely invaginated. The length was 75 mm., the greatest breadth which occurred at a distance of 4 mm. from the anterior end was 5 mm. and the thickness was 2 mm. This dorso-ventral flattening, however, is not to be regarded as significant in speciation as it was produced in fixation.
The proboscis, which had been completely everted and autotomised consisted of an anterior portion 22 mm. long by 2 mm. in diameter, a tapering medial portion 8 mm. in length, and a posterior portion 30 mm. long and 5 mm. in diameter.
The smaller specimen while in motion was 65 mm. in length and had a greatest diameter of 2 mm. at about 4 mm. from the anterior tip of its sub-cylindrical body, from which region it tapered gradually to the posterior end, where it terminated in an obtuse point.
In spirit the proboscis 1.5 mm. in diameter, was extruded to a distance of 14 mm. The body of this specimen was also flattened during fixation.
The colour of the head, which it moved continuously from side to side, as noted also by Dendy for G. novae-zealandiae, was a translucent reddish brown with a slightly darker median portion between its two pairs of ocelli, the anterior pair of which were the larger and the more widely spaced. The body had a median dorsal stripe of a light orange to pink colour separating two slightly wider stripes of chocolate brown which commenced abruptly just behind the
cephalic slits and extended to the extreme posterior tip, these three stripes covering almost the entire dorsal and dorso-lateral surfaces. The remainder of the dorso-lateral and ventral surfaces were a pale salmon pink. In spirit these colours were bleached to a very pale slate grey, with the exception of the chocolate brown, which lost most of the reddish tinge from the pigment.
There are relatively small cerebral organs which open into the bases of almost vertical slightly curved cephalic slits at the lateral posterior margins of the head. As is normal with Hoplonemertini, the oesophagus opens into the rhynchodeum.
Internal Characters: The general internal characters are typical of the Hoplonemertines. Until, however, the outlets to the exterior of the numerous frontal glands are demonstrated in this species they cannot be considered as constituting a frontal organ in conformity with Hyman's definition (1951). Probably the secretion of these glands is discharged to the exterior by temporary canals through the basement membrane and epithelium of the head as Pantin suggests is the case with the Australian species.
On the lower surface of the rhynchocoel just anterior to and above the gut and just posterior to the level of the ventral cerebral commissure there are two distinct vascular plugs which the same author considers may act to prevent the blood from flowing from the anterior bifurcation of the dorsal vessel into the rhynchocoel.
No accessory lateral nerve—i.e., a smaller nerve running just dorsally to the lateral nerve, is present, though this nerve may exist in G. novae-zealandiae and does exist in G. spirospermia. The number of proboscis nerves in the sectioned specimen is sixteen. Darbishire (1909) has shown that the number of these nerves is not constant within a given species, however, so that it is not significant in speciation.
The type of nephridia and the state of the excretory system is as yet undetermined as the fixative used prevented their being observed.
G. pantini is characterised externally by its fairly large size, by its sub-cylindrical cross-section, by its vertical cephalic slits which define the postero-lateral margins of the “head”, and by its possession of only two dorsal stripes, these being continuous from just behind the slits to the posterior end.
G. spirospermia, the only other two-striped species, is markedly much flatter and broader, is cream in colour, and has a marked constriction anterior to the tail. The stripes which do not begin as abruptly as those of G. pantini do not continue to the end of the animal but thin out and disappear after the constriction. It also shows an anastomosis of these stripes which, however, may not be specific. G. spirospermia has an accessory lateral nerve, whereas G. pantini has not.
The author was given an opportunity to examine a specimen of G. novae-zealandiae in the Otago Museum collection (Tokanui, pr. R. Browne A.05.23.) This species differs from G. pantini in having four dorsal stripes. In spirit, the specimen showed quite definitely in addition to the two wide dorsal stripes, two very narrow dark stripes at about the junction of the dorsal and ventral surfaces which Dendy notes in his description and Darbishire illustrates. The median light band was comparatively wider than in G. pantini, and the specimen was
also much more flattened as well as being wider in comparison with its length. It exhibited a diminution in intensity of colour from the anterior to the posterior though this effect may have been due to differential bleaching.
As G. caeca is eyeless and is of a uniform cream colour entirely without markings, it should be readily distinguished from G. pantini.
Type: One preserved specimen in the collection of the Department of Zoology of the University of Otago.
The very sincere thanks of the author are due to Professor B. J. Marples and the staff of the Department of Zoology of the University of Otago for co-operation and assistance during the preparation of this paper, and to Dr. C. F. Pantin, after whom the species is named, for access to unpublished material.
Darbishire, A. D., 1909. A description of two new species of land Nemerteans from the Auckland Islands, Sub-Antarctic Islands of New Zealand, (Phil. Inst. of Canterbury). vol. 2, p. 674.
Dendy, A., 1894. Notes on a New Zealand Land Nemertine, Trans. N. Z. Inst., vol. 27. p. 191.
— 1895. Note on the Discovery of Living Specimens of Geonemertes novae-zealandiae, Trans. N. Z. Inst., vol. 28, p. 214.
Hyman, L. H., 1951. The phylum Rhynchocoela, The Invertebrata, vol. 2, Platyhelminthes and Rhynchocoela (McGraw-Hill Book Company, New York), p. 469.
Pantin, C. F. A., (unpublished). The Genus Geonemertes.