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Volume 15, 1882
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Art. X.—Additions to the Isopodan Fauna of New Zealand.

By Charles Chilton.

[Read before the Philosophical Institute of Canterbury, 6th April, 1882.]

Plate XVIII.

While staying for a few days at Timaru during the last Christmas holidays I contrived to collect a few small Crustacea from amongst the seaweed that is exposed at low tide, just at the north side of the breakwater.

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Among these was one belonging to the very remarkable genus Apseudes. Of this genus there are two species given in Bate's and Westwood's “British Sessile-eyed Crustacea,” and Mr. Haswell has lately described one from Australia,* but the animal I have does not belong to either of these three species.

For the sake of those who may not be able to consult Bate's and West-wood's book, I transcribe the generic characters.

Genus Apseudes, Leach.
(Bate's and Westwood's “British Sessile-eyed Crustacea,” vol. ii., p. 144.)

“Body elongated. Head and first segment of the pereion confluent. Upper antennæ longer than the lower, with the first joint of peduncle long and robust, the flagelluum consisting of two elongated articulated filaments. First pair of gnathopoda chelate; second pair having the propodos transversely dilated. Pleon terminated by a large segment bearing two long and two short slender filaments.”

Apseudes timaruvia, sp. nov. Pl. XVIII.

Front of cephalon broad, with a slight projection in the centre, and produced into a sharp point immediately in front of the eyes. Eyes small. Upper antennæ with the basal joint of peduncle very large and strong, with a prominence on the inside; second joint fully twice as long as the third. Flagellum not so long as peduncle, secondary flagellum rather more than half as long as the primary. First pair of gnathopoda very large and strong, fixed finger with a prominence on its inner surface, and having the end tipped with hairs. Propodos of the second pair of gnathopoda not dilated. Pleon short, sixth segment not longer than the rest together. Terminal tail-legs with thé outer branch half as long as the inner.

Colour, light brown.

Length, about ¼ of an inch.

Hab. Timaru.

Of this species I have obtained a single specimen only, but I have examined it with considerable care and made as much as I could out of it, because it belongs to a very remarkable genus of Crustacea. Bate and Westwood in their book on the British Sessile-eyed Crustacea say “this is one of the most interesting genera of Crustaceous animals.” This is because it possesses both Isopodan and Amphipodan characters, and also some that belong to the Macroura; the union of the head with the first thoracic segment into a “carapace,” and the great chelate gnathopoda make the dorsal view very like that of a Macrourous Decapod.

The animal I have described differs from the other species of the genus in some points, as will be seen from the fuller description given further on,

[Footnote] * Proceedings Linnæan Society of New South Wales, Vol. VI., Part the Second, p. 193.

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but it so evidently belongs to the same group, that I have thought it better that the genus should be widened than that matters should be complicated by the addition of a new genus.

In the upper antenna (pl. XVIII., fig. 2) the basal joint of the peduncle is very large, and on the inner side, at about one-third of its length from the base, there is a projection (p), the edge of which is crenulated. There is a somewhat similar structure in Apseudes talpa, but it is not so well marked. The two projections of the two antennæ appear to fit with one another and form a grasping organ of some kind. The second joint of the peduncle is only one-third the length of the first and is slightly expanded distally; it is followed by the third joint, half as long as the second, bearing the two flagella. It is, I believe, only in this genus of Isopoda that the upper antenna has two flagella, though it is common enough among the Amphipoda.

The secondary (inner) flagellum is half as long as the primary one, and consists of about six joints, the primary flagellum having about fourteen. On the primary one several of the joints bear longish simple setæ, and a single auditory cilium at their distal ends (fig. 2 a).

In the second antenna (pl. XVIII., fig. 3) four joints can be distinguished in the peduncle, possibly there is another joined to the head. From the first of these joints there springs a small projection ending in a very long seta; this may possibly correspond to the “olfactory denticle” of Spence Bate, which is so common among the Amphipoda. The last joint of the peduncle is about as long as the two preceding together and is followed by the flagellum, which contains about eight joints bearing long ciliated setæ. In other species of Apseudes the inferior antenna bears a small oval squamose plate on the peduncle, something like that found in the Macroura, but I have not been able to find any similar structure in my species.

The mandible (pl. XVIII., fig. 4) is large and powerful, besides the teeth on the fixed portion there are also some on the end of a large piece which projects from about the middle and appears to be movable. The appendage consists of two joints, though there may also be another close down to the mandible itself. The second last joint is the longest and bears several short setæ, the last joint narrows towards the end and bears several short and two or three long setæ.

As I have only had a single specimen I have not been able to make out all the mouth-parts satisfactorily; the one represented in fig. 5 I believe to be the second maxilla, or perhaps only part of it. It consists of two pieces, one narrows towards the distal end, which bears a crown of strong setæ; the other springs as an appendage from the base of the first, it also narrows towards the end, this is covered with very short hairs and bears four very

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long divergent setæ. This appendage to the second maxilla appears to be the homologue of a similar appendage to the second maxilla of Tanais, as described by Fritz Muller* and figured by Dr. MacDonald.†

The maxillipedes (pl. XVIII., fig. 6) are rather long: the first joint is short, the next is much larger and longer and, I believe, bears an appendage. The third joint is broader than long, while the fourth is much longer than broad and has the inner side fringed with setæ. The two terminal joints are seen partially in profile in fig. 6, but in fig. 6 a. they are seen full on; they both bear several long setæ, each of which is serrated on one side only.

The first thoracic segment is so closely joined to the head that the line of junction cannot be seen; the second thoracic segment is more closely united to the “carapace” thus formed than the other thoracic segments are to one another.

In the other species of Apseudes the eyes are pedunculated like those of the Podophthalmous Crustacea, but in this species they are very small, and there is no sign of any peduncle.

The first pair of gnathopoda (pl. XVIII., fig. 7) are very large. The carpus and propodos are the two largest joints, the propodos being espcially large; it is produced into a strong blunt finger, which has a rounded prominence at the middle of its inner side, and bears several short stiff-looking setæ at the end. The movable finger is strong, curved, tipped with brown at the end, and somewhat roughened on the inside. In conjunction with the fixed finger it forms a very powerful chela.

In all other species of Apseudes that I know of, the propodos of the second gnathopod is transversely dilated; this is, indeed, given by Mr. Spence Bate as a generic character, but in my species the second gnathopod (pl. XVIII., fig. 8) differs from the other thoracic legs only in being very slightly larger. The carpus is broader than the propodos; both bear stout spines on their inner edge, and there is one spine and two or three long hairs at the base of the terminal finger. The third pair of thoracic legs differ from the second only in being very slightly smaller and in having a few more spines and hairs. The hairs are plumose. Fig. 9a shows the arrangement of these spines and hairs. The succeeding legs are of the small general shape, but the spines gradually disappear, until in the last pair (fig. 10) there are none at all; the terminal finger also differs in having prominences on its inner edge.

The pleon is very short. I have not been able to make out the divisions between the segments, but it is evident that the first five segments must be

[Footnote] * “Facts and Arguments for Darwin,” p. 17.

[Footnote] † “On the External Anatomy of Tanais vittatus.”—Transactions of the Linnæan Society, Second Series, Zoology, vol. i., p. 67, pl. xv., fig. vi.d.

Picture icon

Additions to the Isopodan Fauna of New Zealand.

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very short, almost linear transversely, and although the sixth is larger, it also is, I think, broader than long and not so long as the others together. In other species of Apseudes the sixth segment of the pleon is longer than the preceding five together.

The tail-piece is triangular and is tipped with two or three short setæ. In the terminal tail-legs the outer branch is one-half as long as the inner and both bear long straggling setæ.

The other appendages of the pleon appear to be about midway in structure between the first three pleopoda of the Amphipoda and the branchial pleopoda of the Isopoda. They (pl. XVIII., fig. 11) are small and each consists of a narrow basal-joint followed by two equal branches, the whole bearing long ciliated setæ. They differ from the first three pairs of pleopoda of the Amphipoda only in the fact that the branches are not divided into many joints, in fact they resemble them so much and differ so much from the branchial sacs of the typical Isopoda that I think they cannot be used as respiratory organs. The possession of the appendage to the second maxilla points to the fact that respiration must be carried on at the sides of the head, as is stated by Fritz Muller to be the case with Tanais.

I have taken, both on the banks of the Avon, Christchurch, and at Eyreton, specimens of a small terrestrial Isopod that I at first took to be an Oniscus. I have however found that it cannot be distinguished in any specific character from Philongria rosea; I have therefore to record the occurience of this species in New Zealand.

I give the generic and specific descriptions.

Genus Philongria, Kinahan.
(Bate's and Westwood's “British Sessile-eyed Crustacea,” vol. ii., p. 454.)

Generic character.—“Ovate, subdepressed. Cephalon without frontal or lateral lobes. Outer antennæ 9- or 10-jointed, with the second joint cylindrical; terminal joints subulated. Coxæ of first and sixth rings of pleon obsolete. Uropoda entirely exserted; basal portion trigonate. Outer ramus elongate, pointed, and exserted obliquely. Inner narrow, extending beyond the middle of outer, pointed.”

Philongria rosea (loc. cit., p. 460).

Specific character.—“Ovate scabrous, covered with small tubercles. Eyes small. Inner antennæ conspicuous. Outer antennæ with the flagellum slender, with apparently only four articuli, which are very difficult to detect except under a strong lens; tipped with a pencil of hairs. Terminal segment of the pleon with the extremity truncated straight. Colour reddish, with whitish spots and dorsal line.

“Length, three-twentieths of an inch.”

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Hab. Christchurch and Eyreton. In damp situations, under decaying leaves, etc.

This species must, I suppose, have been introduced in some way from England, though there are difficulties in this belief, for I have found it abundantly at two places several miles apart, separated by rivers over which animals of this kind cannot easily cross, and, moreover, it does not appear to be widely distributed in England, for Bate and Westwood say (p. 461):—“We believe that this species has only hitherto been found in Mr. C. Spence Bate's courtyard and cellar, and that of the neighbouring houses, at Plymouth, where it is tolerably abundant.”

I have, however, no doubt that my specimens cannot be distinguished specifically from Philongria rosea, and we must therefore await further information before we can decide whether it has been introduced or not.

Explanation of Plate XVIII.

Apsedes timaruvia.

Fig. 1.

Dorsal view x 14.
  2.

Upper antenna x 34. p, the crenulated process on the basal joint, a, setæ and auditory cilium from one of the joints of flagellum, more highly magnified.
  3.

Lower antenna x 60.
  4.

Mandible x 34.
  5.

Second maxilla x 40.
  6.

Maxillipede x 60. a, last two joints seen full face.
  7.

First gnathopod x 14. a, part of the same showing the shape of the fingers.
  8.

Second gnathopod x 24.
  9.

Third thoracic leg x 19. a, end of the same x 40.
  10.

Last (seventh) thoracic leg x 19.
  11.

Pleopodum x 60.
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