Art. XIX.—A He-examination of Hutton's Types of New Zealand Earthworms.
[Read before the Otago Institute, 18th October, 1898.]
In the year 1876, Captain Hutton read before the Otago Institute a paper entitled “The New Zealand Earthworms in the Otago Museum,”* in which he described six new species of earthworms, four of which he locates in the genus Lumbricus and two in that of Megascolex. At that time—now more
[Footnote] * Trans. N.Z. Inst., vol. ix., p. 350.
than twenty years ago—very little was known of the internal anatomy of the group, or of the characters which serve to differentiate genera from one another. Indeed, up till 1872 the only extra-European genera that had received distinctive names—which are still retained—were Pontoscolex and Perichœta, Schmarda (1861). The anatomy of the latter had been studied by Vaillant (1869). Closely similar to it externally, and often confused therewith, is the genus Megascolex, described from external features by Templeton in 1844. Several other genera had, however, been named from external characters alone, but most of these are now unrecognisable, and have dropped out of zoological literature.
Now, Perichœta and its ally Megascolex differ from all other earthworms—with the exception of a genus to be mentioned below, and only defined in 1892—in having very numerous bristles or chætæ, and in having them arranged in a circle round each segment of the body, instead of possessing, as does Lumbricus, only eight bristles per segment, and in having these more or less in couples or pairs on the lower surface. Of course, this is only one out of many features, external and internal, in which the two genera differ, and it is mentioned here as being the chief reason which led Hutton to identify the worms as he did.
In 1872 a very important memoir on the exotic earthworms contained in the Paris Museum was published by E. Perrier,* in which he examined his material anatomically, and thereby distinguished among worms with eight chætæ a number of new genera; but it does not appear that Hutton was acquainted with this memoir at the time he wrote his paper in 1876, and hence arose some of the errors in his identification of the worms of the Otago Museum. Later on he became acquainted with the contents of Perrier's memoir, for in the “New Zealand Journal of Science” (vol. i., 1883, p. 586) he suggests, wrongly, that two of his species of Lumbricus may belong to Perrier's genus Digaster, while Mr. Smith speaks of some of them as Endrilus, which is probably a misprint for Eudrilus, but neither writer states the grounds for using either of these names.
During the last fifteen years the literature dealing with earthworms has assumed very large proportions, chiefly at the hands of half a dozen zoologists in Europe; and, as the number of species and genera have been increased, and the various continents and islands of the world have contributed their quota of material, thanks to the trouble taken by residents and travellers, we have been able to recognise that, just as certain birds and mammals have their special geographical
[Footnote] * Nouv. Archiv. du Museum d'hist. nat. de Paris, 1872.
limitation, so have earthworms. We know that certain genera have their home in certain definite portions pf the land or zoological regions, and that certain species of these genera are peculiar to certain definite areas of each region. Further, we have to recognise that a native fauna of worms may be interfered with by the introduction of foreign worms, in the same way that native birds tend to disappear at the hands of man, or his accompanying animals. From the Accumulated knowledge, then, of recent years we know that the worm Lumbricus is a characteristic European (and perhaps North American) genus, and that it does not occur in other parts of the world unless carried thither by man. We know this from the fact that no distinct species of Lumbricus (and its allied genera, which have recently been separated from it) occur outside Europe and North America; consequently, when Hutton described Lumbricus, n. sp., from New Zealand, lumbricologists felt pretty sure that an error had been made, and, moreover, the description, as given by him, served to show that the identification was impossible.*
Just as New Zealand has its special and peculiar birds, so it has peculiar species, and genera of earthworms. These genera belong to the family Acanthodrilidœ, which differ from Lumbricus in every possible way, except that they have generally eight bristles in each segment; and Hutton's diagnoses of his species of Lumbricus indicated that they belong to this family.
As to the Megascolex, too, this genus, though having a wide distribution, and occurring in Australia, has certainly not been recorded from these Islands; but there is a very deceptive similarity between Megascolex (a Perichœta) and a genus of the family Acanthodrilidœ to which I gave the name Plagiochœta some few years ago, and from Hutton's brief account of the Megascolex, n. sp., it seemed pretty certain that they belonged to this genus.
As I have for the last thirteen years spent a good deal of my time in the study of worms from all parts of the world, it was natural that I should wish to examine the New Zealand representatives at first hand. Our knowledge at present depends almost entirely on the able researches of my friend Mr. Beddard, who has been able to give a detailed account of the anatomy of our native worms, and to describe a considerable number of species, owing mainly to the kindness of the late Professor Parker and of Mr. W. W. Smith, of Ashburton, both of whom have from time to time sent specimens Home to him. There is, however, still some work to be done, especially in the biology of the group, though we already have some very
[Footnote] * For instance, Beddard, Proc. Zool. Soc, 1885, p. 812.
interesting and valuable contributions to this subject from the hands of Mr. Smith.* I hope to complete and extend the work along both lines of research, especially as Beddard's observations deal with preserved material, and with comparatively small numbers of specimens. I hope to examine large series in a comparative manner, to ascertain how far variation occurs, and especially to add details of colouration and habit to Beddard's accounts of anatomy. One of my first steps in this direction after my arrival at Dunedin was to examine the types of Captain Hutton's species, which I fortunately discovered in the store-room of the Otago University Museum. The following are the names of the types as given by him with certain remarks upon them :—
I was unable to find the type; but it is evident from Hutton's description that the worm belongs to the family Acanthodrilidœ, and may possibly be identical with Beddard's Acanthodrilus novœ-zelandœ or A. rosœ.
There are three bottles so labelled—(a) Collected in “Dunedin”; (b) “Water of Leith”; and (c) “From Wellington.”
[Footnote] * Trans. N.Z. Inst., vols, xix., xxv., and xxvi.
[Footnote] † For description, see Benham, Quart. Journ. Mioroso. Sci., xxxiii., 1892, p. 289; and for remarks, see Beddard, “Monograph of the Order Oligochœta”, p. 535.
There are two bottles so marked : (a) “From Hampden”; (b) “From Dunedin.”
[Footnote] * In the method of enumerating the segments we have to subtract one for Hutton's numbers, as he appears to have counted the prostomium as the first segment, as was the custom then.
One bottle, labelled “Dunedin,” contains four individuals, only one of which possesses a clitellum; the three others, though immature and badly preserved, show by their size and by the position of the first dorsal pore that they are the same species as the mature specimen, which is the common British brandling worm, Allolobophora fœtida. Hutton himself recognised the resemblances, and considered the possibility of the identity. I must correct his statement that the clitellum is “not tuberculated inferiorly”; the tubercles, indeed, exist on the usual segments—28, 29, 30, and partly 31—but they form a continuous though indistinct ridge. Again, the “male openings”—here he means the male pores, not, as usual, the spermathecæ—are on the 15th segment, not on the “16th.”
Now we come to his two species of Megascolex:—
One bottle, from Dunedin, contains two entire individuals and two portions. All are very poorly preserved, but are sufficiently in condition to show that the worm belongs to the genus Plagiochœta, Benham,* as Beddard has already surmised. †
At present only one species of Plagiochœta is definitely characterized—viz., P. punctata, which was collected by Mr. E. Vaughan Jennings at Maungatua, and sent to the British Museum, for the authorities of which I examined and named
[Footnote] * “Notes on Two Acanthodriloid Earthworms from New Zealand,” Quart. Juart. Micros. Sci., xxxiii., 1892, p. 289.
[Footnote] † Proc. Zool. Soc., 1892, p. 667.
it. This M. sylvestris, of Hutton, agrees very closely with P. punctata, but differs from it in the following points: (1.) It is not so depressed, being nearly circular; this may be due to its poor preservation. (2.) The dorsal and ventral gaps in the circle of chætæ are equal, and measure only twice the normal gap, whereas in P. punctata the dorsal gap is four times the normal. (3.) The prostomium is not entirely imbedded in the 1st segment; it is possible that my specimens of P. punctata, in which the prostomium appears to reach the 2nd segment, had shrunk in preservation, so that the two segments approach and hide the hinder edge of the 1st segment. (4.) There are only three pairs instead of four pairs of sperm-sacs; the first pair is on the septum between 9 and 10, and pushes into both these segments. (5.) The chætæ measure, on an average, 0.19 mm.; the ventralmost couple, in sections, reaching 0.22 mm; and the smallest are 0.165 mm.
From these facts it is difficult, at present, to determine whether M. sylvestris is or is not identical with P. punctata, for so long as only one species is known it is impossible to say what are specific characters, and we must wait till further information about the genus is to hand.
This was collected at Queenstown; the single bottle contains one entire individual and three broken specimens. All are so soft that they break on handling. The length of the complete individual is only 1 ½ in. (Hutton gives 2 in.—perhaps for the living worm). The drawing of the prostomium is wrong in representing it small; it is more like that of the preceding species. The chætæ are not in a continuous circle, but quite evidently in couples, as Hutton figures for M. sylvestris; in fact, the worm is an undoubted Plagiochœta.
If we may judge from the state of preservation, the present species was more deeply pigmented than M. sylvestris, for it is not so absolutely bleached by the spirit as that worm; it is, in fact, a very faint brown. The dorsal gap in the circle of bristles measures three times, and the ventral gap twice, a normal gap between two successive couples.
This worm differs from P. punctata in the following characters: (1.) The spermiducal pores are carried by papillae, and there is no defined ridge surrounding the ventral area on which the pores lie (this may, of course, be due to the preservation of the worm). (2.) The spermathecæ have two peculiar diverticula, instead of a single simple cylindrical diverticulum; of these, one is an oval pouch, the other is a three-lobed pouch with a narrow neck; the two pouches open close together into the duct of the main sac. This is a very definite specific character. (3.) The chætæ measure
0.22 mm., and are stouter and more strongly curved than in the preceding species.
Both these species of Hutton's agree with P. punctata in having 13 couples of chætæ on each side of each segment. Bach couple is inserted between two bundles of longitudinal muscles, which number therefore 12 on each' side, together with a broader dorsal and ventral bundle separating the uppermost and lowermost couples of each side. In the three species—or, perhaps, I ought to say three individual specimens—hitherto examined the chief difference visible in section lies in the width of the median muscle-bundles—i.e., the gap between the right and left couple of chætæ—as well as in the length and proportions of the chætæ. The position of the nephridiopores is identical, being between the 3rd and 4th muscle-bundles, or between the 9th and 10th muscle-bundles counting from below, for the pores alternate in position as in so many of the Acanthodrilids.*
With regard, then, to these two individuals described by Hutton, there is no doubt that M. lineatus is distinct from my species, while I am uncertain about M. sylvestris, and if further research—upon which I am now engaged—shows that it is identical with P. punctata, Hutton's specific name will have to replace that given by me.
For the present we may summarise the types as follows:—
1. (?) Acanthodrilus uliginosus, Hutton.
Syn. Lumbricus uliginosus, Hutton.
2. (a.) Neodrilus monocystis, Beddard.
Syn. Lumbricus campestris, Hutton (in part).
(b.) Lumbricus rubellus, Hoffmeister.
Syn. L. campestris, Hutton (in part).
3. (a.) Allolobophora caliginosa, Savigny.
Syn. Lumbricus levis, Sutton, (in part).
(b.) Octochsetus levis, Hutton.
Syn. Lumbricus levis, Hutton (in part).
4. Allolobophora fœtida, Savigny.
Syn. Lumbricus annulatus, Hutton.
5. Plagiochæta sylvestris, Hutton.
Syn. Megascolex sylvestris, Hutton.
6. Plagiochæta lineatus, Hutton.
Syn. Megascolex lineatus, Hutton.
[Footnote] * Vide pl. xv., fig. 17, loc. cit.