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Volume 75, 1945-46
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An Earthworm With Four Penes Conicodrilus genus novum.

By W. B. Benham, K.B.E., F.R.S.

[Presented to the Otago Branch, October 10, 1944; received by the Editor. October 20. 1944; issued separately, June, 1945.]

With 7 Figures.

During the period of my professorship I got into communication with various people in all parts of the Dominion requesting them to collect earthworms for me. Some of the animals received have already been described by me, but there had accumulated a large number of tubes and bottles containing others which I had had no time to examine while occupied with the work of teaching and superintending the work of the Museum, hence it was only after my retirement that the opportunity was afforded of overhauling the contents of some 200 receptacles.

Most of them contain specimens belonging to known genera, but I found one bottle with worms collected by Mr. J. McKenzie in 1901 at Lake Kanieri, Westland, in which, in addition to species of the genera Maoridrilus and Octochaetus, I found five individuals for which I find it necessary to add another genus to the nineteen genera already recorded as occurring in New Zealand, most of them being peculiar to this region.

The generic name, Conicodrilus, refers to the unique form of the papillae which carry the apertures of the prostates, the “porophores” as they are termed. In all the known genera of Acanthodrilines these porophores have the form of low, rounded prominences (Fig. 5), but in this new genus they have a remarkable form as quite prominent, relatively long, pointed cones, which are non-retractile. Such an unusual condition of these organs is unknown in any other of the genera of earthworms of which about 130 are recorded, with several hundred species. Nevertheless, several genera are known from various parts of the world in which retractile and intromittent penes have been described.

The present worm is nearly allied to Beddard's genus Dinodrilus in that it possesses six couples of chaetae instead of the usual four couples—that is, twelve per segment in place of the familiar eight.

It might be supposed that this arrangement of chaetae should be a good generic character, and that this worm should be placed in this genus. But there is a precedent for overlooking the chaetal arrangement; for example, I described in 1892 a small earthworm from Maungatua, near Dunedin, which, while presenting the usual Acanthodriline features, possesses a ring of some 50 chaetae round each segment, which led me to name it Plagiochaeta.

Some ten years later, in 1902, I ascribed to the same genus certain large worms from the mountains and forest of the West Coast, which I placed in four species. Some are meganephric, others micronephric, and of the former, some have the pores alternately situated dorsally and ventrally, others have the pores in a single row. Therefore Michaelsen (1909) removed them from the original genus, in which the pores alternate. The matter was discussed in a paper by Miss Cameron and myself in 1912.

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The fact, then, that so accomplished an oligochaetologist as the late W. Michaelsen neglected the more obvious chaetal arrangement for the less noticcable nephridial condition is a precedent for my making use of other structures.

Genus Conicodrilus nov.

Genotype: Dinodrilus gracilis Ude.

Conicodrilus kanieriensis, n.sp.

Five individuals were examined: they are slender, of a dark brown colour (in formaline) and the longest reaches 170 mm., with diameter of 4 mm.

The prostomium is Epilobic, being embedded in the first segment for about three-quarters the length of the latter.

The preclitcllar segments are, as is very usual, shorter than the postclittellar, being about one half their length. The elitellum encircles the body in segments ½ xiii to xvi; it is darker brown than the body generally, and of rather less diameter than the neighbouring segments, probably due to the greater contraction of this glandular region.

The most noticeable feature about this earthworm is, as has been noted above, the prominent prostate porophores, which are conical, pointed, pale in colour; those of the segment xvii curve backwards and nearly meet those of the xix, which curve forwards (Figs. 1 and 2). The two porophores of one side are carried by a longitudinal ridge which bears the spermatic groove, passing from the terminal aperture of one porophore down its side and so up the other one, thus putting the two pores into communication as in other Acanthodrilines. This lateral ridge forms also the boundary of a depression of the segment xviii due to the presence of the muscles within the body. There are no penial chaetae, which so often occur in this family.

In segment xiv, near the intersegmental groove, between segments xiii and xiv in the median line of the ventral surface, is a transversely oval area of paler tint than the surroundings, occupying about one-fifth of the width of the body. In this area lie the pair of oviducal pores, closer together than is usually the case, though Beddard figures them as close in Dinodrilus benhami.

The spermathecal pores are not evident but are in the usual position, vii/viii and viii/ix. Certain “sexual markings” are visible as transversely extended oval areas of a granular appearance and of rather darker tint than the general body on each of the segments, vii, viii and x, which last are larger than the other two pairs (Fig. 1). These glandular areas no doubt secrete a material which helps to hold the two worms together during copulation, and such glands or “markings” are present in many genera. These are present in three of the four individuals, but are not yet developed in the fourth.

The chaetae are very small, and difficult to detect in these formaline-preserved animals, but by cutting down one side of the body wall, clearing out the gut, etc., and mounting the flattened body wall in a clearing agent, the chaetae were studied under the microscope and the spacing measured.

In the preclitellar segments there are the typical EIGHT chaetae per segment, in couples (Fig. 3A) the ventral couple (a-b) are separated by 1 mm., the dorsal couple (b-c) by 1.25 mm.; the dis-

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tance between the two couples—that is b-c, is 2. The ventral gap, between (a-a) 2; 5 mm. and the dorsal gap (d-d) is 3.5 mm. There is, then, nothing unusual about these anterior segments. But in the post clitellar segments there are, as I have noted, about TWELVE chaetae (Fig. 3B); the six on either side are equidistant, being 1.5 mm. apart, while the ventral gap and the dorsal gap are 2 mm. wide—that is, less than in the case of the anterior segments.

Though Ude does not refer to the chaetal condition in the anterior segments, yet the formula he gives for the twelve in the posterior agrees with what is found in these specimens. It is quite likely that he did not think to examine the conditions anteriorly, as it is unusual for the arrangement to differ here from that of the general body.

The worm is micronephric, and dissection shows a series of minute tubules in a row near the anterior septum of each segment, but there is no concentration of such tubules as occurs in many species.

The gizzard in segment vi is somewhat urn-shaped, being wider near the anterior end and tapering posteriorly to about half its anterior diameter. Oesophageal glands are represented by an enlargement of the tube in xviii, where the walls are thicker than elsewhere, but there is no definite “pouching” such as often occurs.

The intestine commences in xix.

Enlarged “hearts” occur in segments xii, xiii, xiv, and xv. The Sperm sacs are three pairs, a small sac in segment ix, larger ones in xi and xii.

The spermathecae, two pairs as usual in the Acanthodrilines, in segments viii and ix. The “ampulla” is an elongated oval somewhat pointed at its end, with four club-shaped “diverticula,” opening into the duct (Fig. 4). In one spermatheca I noted only two diverticula, and such variation has been recorded by Ude, who found 3–6.

The prostate has the usual Acanthodriline structure.

The genus Dinodrilus of Beddard (spelt originally Deinodrilus, and altered by Michaelseu) was founded in 1880 for a species D. benhami “from New Zealand,” but the locality is given by Michaelsen in his monograph of 1900 as “Lake Brunner.” I have not been able to discover any statement by Beddard as to this, possibly it was in a letter to Michaelsen. The genus was founded on the fact that—although an Acanthodriline—the worm had twelve chaetae per segment. Beddard shows in the figure that the porophores have the usual form, low rounded mounds. The animal was “about five inches” long—that is, 125 mm.

A second species was established by Ude (1905), in which the porophores have precisely the same character as in the present species. His came from Stephens Island, in Cook Strait. He named it “gracilis.”*

A third species allotted to the genus is D. suteri, Benham (1905), collected at Swanson, near Auckland. It was only 40 mm. in length, and was manifestly immature, but in externals agrees with D. benhami—that is, it shows no sign of the conical porophores.

[Footnote] * I have endeavoured to obtain specimens from this island from the lighthouse keeper, but have been unsccessful.

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Hence we have, it seems, two genera presenting 12 chaetae per segment—Dinodrilus and Conicodrilus.

I append a tabular statement of the leading characters of these four species:—

[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

Tabular Statement of Differences.
L. Clit. Spth. Sp. sac. Gizz. Loc. Sexual Marks.
D. benhami. 125 mm. 14–16 3 div. 11, 12 6 and 7 L. Brunner ?
D. suteri. 40 mm. ? 1 div. ? 5 Swanson
C. gracilis 90 mm. (13) 14–16 3–6 div. 11–12 6 and 7 Stephens Is. xi, xii, xiii
Present worm 170 mm. 13–16 2–4 div. 9, 11, 12, 6 L. Kanieri vii, viii, x

There is a close similarity to Ude's species Conicodrilus gracilis, and at first I allotted the present worm to that species, but a more detailed study shows that it differs in a number of small features, the accumulation of which entitles it to specific differentiation. Thus in externals:—Ude makes no mention of the fact that on the preclitellar segments the chaetae number only eight. He may easily have overlooked that fact even if it occurred, but the form and position of the “sexual markings” are quite different. In the first place his figure (viii a, pl. xvii) shows them as pits surrounded by a raised ridge, so as to look like suckers; moreover, they are differently arranged, there being a pair of them in segment xi and a single median “sucker” in each of the segments xii and xiii.

Internally he makes no mention of the sperm sac in segment ix (which may easily have been overlooked); the number of diverticula of the spemathecae is also as many as six. In the present state of our lack of knowledge as to “variation” in the whole group of earthworms such small differences are by most authors regarded as specific.

Suggestion as to the Use of the Conical Porophores.

Very little is known as to the details of coition, or if you will, “copulation,” in the group of earthworms. We know the procedure in Lumbricus and in Eisenia, its near ally, and in these the two partners engage one another head to tail with the ventral surface closely in contact. Some apparatus or method is employed for the conveyance of the sperm from the male pores of the one into the spermatheca of the other, and this is assumed to be mutually contemporaneous.

In these two genera the two partners are wrapped together in a “slime sheath” derived from the secretion from the clitellum, but this is exceptional, and in other cases where the process has been studied such an envelope is absent. In several genera an extroversible “penis” is present and is inserted into the spermatheca.

One reason for the detailed account of the procedure in the family Lumbricidae is that the copulation takes place on the surface of the ground. This is also the case with Eutyphaeus waltoni, an Indian earthworm of the family Megascolecidae (as described by Bahl), but there is no “slime sheath” and the sperm-pore becomes, during copulation, everted and raised on a papilla which is inserted into the spermatheca: thus it is a penis. Whereas the Acanthodrilines and probably other families are more modest and pursue their amours in their own burrows out of sight of the enquiring zoologist,

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which may account for the lack of information available as to the preedure of the exotic worms.

As to the Acanthodrilines, nothing so far as I can ascertain has been recorded. But many years ago an observation was made by one of my students, Mr. James Grant, who reported it to me. While digging in his garden, he had come across a couple of worms engaged in their amours. He noted that they were temporarily attached to one another—not by any secretion, but by the protruded “penial chaetae,” which were, however, quickly withdrawn from the spermatheca. I append a conjectural figure of what probably occurs (Fig. 6).

In the group of Acanthodrilines the male ducts do not open into the duct of the prostate as in most Megascolecidae, but have independent openings in segment xviii, whereas the two pairs of prostates open in xvii and xix respectively. In the process of copulation the two partners adopt the usual “head-to-tail” position in such a way that the two prostate pores of a side are opposite the two spermatheca pores of the other worm. The difference in the length of the segments allowing this to take place in spite of the fact that the two spermathecal pores are in consecutive segments while those of the prostates are separated by a complete segment (Fig. 6). The penial chaetae, developed in special sacs communicating with the prostate duct, are exserted and are inserted into the main sac of the spermatheca—i,e., the “ampulla”. There is no “slime sheath” such as is present when coition of Lumbricus or Eisenia takes place.

The apertures of the sperm duct are in segment xviii opening into a “seminal groove,” which passes from one prostate pore to the other of the same side. The spermatozoa then passes along this groove, both in an anterior direction and a posterior. It is probably not propelled by repeated muscular contractions as has been described by Grove and Cowley in Lubricines, where, however, the seminal groove is much longer and its relations are totally different. Here in the Acanthodrilines the spermatozoa pass forwards and backwards to reach the penial chaetae projecting, as said above, into the ampulla, and these form a bridge or guide as it were for the sperm cells to enter the “diverticulum” of the spermatheca (Fig. 6). But it may be supposed that as the two porophores are not in consecutive segments, whereas the two spermathecae are, that the two sets of organs would not be really opposite. I have measured the distances involved and have noted further that the post-elitellar segments are small—that is, shorter than those in front, may even be but half the length. I have measured the spaces under consideration in species of Maoridrilus, Octochaetus and Hoplochaetina, and find that the distance between the two porophores is equal to that separating the two spermathecae. Hence, when the two worms are in contact, the two sets of pores are precisely opposite to one another.

Probably—for we know nothing about the secretion of the large prostate glands—this secretion affords a means of conveyance for the sperms as they pass along the groove and wash them into the spermatheca. For several authors have noted that they are to be found only in the diverticulum, while the ampulla is filled with a mucus-like material. In Fig. 6 I have endeavoured to display the course of the spermatoza by a series of large dots.

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And I suggest that in Conicodrilus these conical pointed porophores serve as “penes,” and are inserted into the ampullae (Fig. 7) in the same way as are the penial chaetae, which are absent in this genus. In the case of Maoridrilus, as of the Acanthodriline and other genera with penial chaetae, these serve not only to hold the two worms together, but serve as a bridge by which the sperm travels to enter the diverticula at the same time.

Literature.

Bahl,—, 1927. On the Reproduction Process of Earthworms: I. Copulation in Eutyphaeus waltoni. Q. J. Mic. Sci., vol. lxxi.

Beddard, F. E., 1880. On the Structure of Three New Species of Earthworms, etc. Q. J. Mic. Sci., xxix.

Benham. W. B., 1890. An Attempt to Classify Earthworms. Q. J. Mic. Sci., xxxi.

—— 1892. Notes On Two Acanthodrilid Earthworms from New Zealand. Q. J. Mic. Sci., xxxiii.

—— 1902. On the Old and Some New Species of Plagiochaeta. Trans. N.Z. Inst., xxxv.

—— 1905. Additional Notes on the Earthworms of the North Island. Trans. N.Z. Inst., xxxviii.

—— and Cameron, G., 1912. Nephridia of Perieodrilus. Trans. N.Z. Inst., xlv.

Grove and Cowley. Reproductive Process in Eisenia foetida. Q. J. Mic. Sci., vol. lxx.

Michaelsen, W., 1907. Die Fauna S. W. Australiens—Oligochaeta. Jena.

—— 1909. Oligochaeta of India, Nepal, Ceylon, etc. Mem. Indian Museum, vol. i.

—— 1910. Oligoch. v. verschiedenen Gebieten. Mittheil., a.d. Naturhist. Mus. Hamburg, xxvii.

—— 1920. Oligoch. v. westliche Vorderindien, etc. Jahrbuch d. Hamburg Wiss. Anst., xxxvii.

Ude, H., 1905. Terricole Oligocheten v. d. Inseln. d. Sudsee. etc. Zeit. f. Wiss, Zool., lxxxiii.

[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

Explanation of Lettering on the Figures.
amp.—ampulla. pr.—prostate.
cl.—clitellum. r.—ridge bounding the depression.
d.p.—depressed area between the penes. s.d.—sperm duct.
div.—diverticulum. s.g.—seminal groove.
ov.—aperture of oviduct. s.o.—aperture of sperm duct.
p.—penis or porophore. sx.m.—sexual markings.
p.ch.—penial chaetae.

Explanation of Plate 1.

Fig. 1.—Ventral view (enlarged about four times) of the genital region of Conicodrilus kanieriensis, showing the characteristic features, a.b. the ventral couple of chaetae.

Fig. 2.—Side view of the two penes of one side.

Fig. 3.—The arrangement of chaetae in A, a preclitellar and in B. a postclitellar segment. The relative length of the segments in the two regions is indicated. D, the dorsal, and V, the ventral, median lines. The eight chaetac in A and the 12 in B are in their true spacings as measured on the body wall under a microscope.

Fig. 4.—Spermatheca.

Fig. 5.—The genital region of a normal Acanthodriline (Maoridrilus) with low, rounded, dome-like porophores and penial chaetae, shown on one side only.

Fig. 6.—Diagrammatic longitudinal section of a couple of Acanthodrilines in copulation. The penial chaetae are inserted into the ampulae of the spermathecae. The difference in length of the segments is indicated, though the second spermatheca of B is placed too far from its true position. The course taken by the spermatozoa is indicated by the coarse granules entering the diverticulum. The position of testes and sperm ducts and their common exit are also shown.

Fig. 7.—Diagram of the assumed corresponding arrangement in Conicodrilus for one set of organs. … Here the porophore. acting as a penis, is inserted into the ampulla.

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Trans. Royal Society of N Z., Vol. 75
Plate 1.
Description on Page 28.
[Facing page 28.]

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