![Thumbnail: [Volume 37, 1904 page 298]](/journals/rsnz/images/rsnz_37/thumbnails/rsnz_37_00_0324_0298_ac_02.gif)
Art. XX.—Earthworms from the Kermadecs.
[Read before the Otago Institute, 8th November, 1904.]
Plates XIII. and XIV.
Owing to the thoughtfulness of Mr. R. Shakespear, of Little Barrier Island, I am indebted to Captain Bollons, of the Government steamer “Hinemoa,” for the first samples of the Oligochæta that have been collected in the Kermadecs. Captain Bollons was good enough to take a considerable amount of trouble to obtain these worms. The soil forms, he tells me, a very thin covering of decayed vegetation upon pumice rock, and he was unsuccessful in his earlier efforts to find any earthworms, but finally, at Coral Bay, his persistency was rewarded. My best thanks are due to these gentlemen for their kindness.
I received the specimens alive, packed with soil and moss in a tin box: they consisted of three small earthworms and six Enchytræids. Of the earthworms, two were immature individuals of some species of the genus Allolobophora belonging to the family Lumbricidæ—the members of which are readily transported, and are, as a matter of fact, widely distributed by the agency of man. Though I am unable to identify the species to which these individuals belong, there can be little doubt but that they have been “introduced” by some means, though Captain Bollons states that this part of the island has never been inhabited; nevertheless, some parts have been occupied, and there can be no difficulty in explaining the presence of these worms here. The third worm is mature, and belongs to the genus Rhododrilus,* which, according to Michaelsen's most recent writings, has its headquarters in New Zealand, and is represented on both the main islands as well as on the outlying islands. The present species, however, differs from any hitherto described, and I propose to name it
Rhododrilus kermadecensis, n. sp.
Colour.—Pinkish, with transparent body-wall.
Dimensions.—Length, 65 mm.; diameter, 1.75 mm.; with 108 segments.
Chœtœ.—The eight bristles are wide apart, and approximately their arrangement in the midbody is ab =½bc; bc = cd = 2ab; aa = bc; dd = 2cd. But at about the 20th segment the lines
[Footnote] * It appears from a recent work by Michaelsen that he would fuse the species of Rhododrilus with those of Microscolex, the older genus. I have given reasons in a paper forwarded to the Zoological Society for distinguishing the two genera.
![Thumbnail: [Volume 37, 1904 page 299]](/journals/rsnz/images/rsnz_37/thumbnails/rsnz_37_00_0325_0299_ac_02.gif)
of c and d descend slightly, so that the gap bc is reduced, and dd increased, in the forepart of the body.
Prostomium epilobic, about one-half, without a posterior transverse groove.
Clitellum covers segments 13–18 inclusive. The ventral chætæ and intersegmental furrows are visible, though the skin is somewhat thickened across the ventral surface.
Genital Pores, &c.—A pair of large porophores on the 17th segment, in line with chætæ ab; and in front of the chætæ there is a single large median “copulatory tubercle,” in the form of an oval glandular pad, not very prominent, covering the whole of the ventral surface of segment 19, and the prechætal region of the 20th.
Dorsal pores are visible posteriorly.
Internal Anatomy.—In the bisected individual I made out the following points, sufficient to characterize the species: The dorsal blood-vessel is enlarged in segments 14, 15, and 16; the last hearts are in the 13th segment. The gizzard is quite minute, in segment 5. There is no œsophageal gland, though the tube is dilated in the 13th and 14th segments. The intestine commences in the 18th.
The Reproductive System.—The sperm-sacs lie in segments 9, 11, and 12. The prostate is a large, tongue-shaped gland, extending through the six segments 17–22, with a short muscular duct in the 17th. A couple of long chætal sacs underlie the prostate, extending back from the 17th to the 21st segment. Each sac contains three chætæ—a functional “penial chæta” and two smaller ones at different stages of development. The penial chæta (Plate XIV., figs. 4, 5) is long, delicate, and bent distally. The tip is curved, spoon-shaped, so that the side and top views differ. The surface is quite devoid of ornamentation.
There are three pairs of spermathecæ, in the segments 7, 8, and 9. Each (Plate XIV., fig. 1) is an ovoid sac, with a short muscular duct about half the diameter of the sac. It receives close to the body-wall a long cylindrical diverticulum, which in the specimen, studied is curved in an S-shaped manner. The tip is not dilated (till compressed), but the base is enlarged at its union with the duct.
Remarks.—In the possession of three pairs of spermathecæ this species resembles R. cockayni from Campbell Island, from which, however, it differs in its colour, dimensions, arrangement of copulatory tubercle, and form of penial chæta.