New Zealand Amphipoda: No. 6.
[Read before the Philosophical Institute of Canterbury, 5th November, 1924, received by Editor, 31st December, 1924; issued separately, 26th April, 1926.]
Euthemisto antarctica Dana and Euthemisto gaudichaudi Guérin.
A species of Themisto is frequently washed up on the shores of New Zealand, but the identification of it has given rise to a considerable amount of uncertainty and difference of opinion. In 1879 specimens were examined by Mr. G. M. Thomson, and by him were referred to Themisto antarctica Dana. He quoted the description given by Spence Bate in his Catalogue of the Amphipoda in the British Museum, and added a description of the female and of the young taken from the incubator pouch. In the “Challenger” Report Stebbing identified one of the species collected with that described by Thomson, but gave it the new name of Euthemisto thomsoni, being of opinion that it was different from Dana's species. In the “Challenger” Report he also recorded specimens of E. gaudichaudii Guérin, and figured this as well as the species which he called Euthemisto thomsoni. The chief character which induced Stebbing to consider the New Zealand specimens distinct from Dana's species was that the body is usually dorsally carinated in the adult animals, while this carination is not mentioned by Dana. In 1889, however, Bovallius pointed out that the development of the carina is a varying character in all the species that he had examined, and is usually less distinct in an ovigerous female than in a male of the same size. For this and for other reasons he concluded that Stebbing was not correct in his identifications, but that his E. gaudichaudii was really the same as E. antarctica Dana, while his E. thomsoni was identical with E. gaudichaudii Guérin.
I have examined specimens washed up at different times on various parts of New Zealand coast, and, while there is not much doubt that they are the same as those described by Stebbing under the name E. thomsoni, I have been unable to determine whether this should be referred to E. gaudichaudii, as Bovallius thinks, or to E. antarctica. Of these two “species” Bovallius (1889, p. 295) says, “They are closely allied, and less easily distinguished from one another than the two northern forms; the best distinguishing mark being, however, the relation between the length of the first and second pairs of uropoda.” I have been unable to distinguish my specimens into these two groups by this character, and the last manuscript note that I had made about them was that the two species appeared to be identical.
Shortly afterwards I received Dr. K. Stephensen's final report on the Hyperiidea of the Danish Oceanographical Expedition, 1908–10, to the Mediterranean and the adjacent seas. In this he uses the generic name Themisto to include Parathemisto Boeck and Euthemisto Bovallius, and unites the two northern species T. compressa Göes and T. bispinosa Boeck under the name of T. compressa. He gives elaborate descriptions and comparisons of different specimens obtained by the Danish expedition,
grouping some of them under one or the other of the two forms compressa and bispinosa, while other specimens he considers intermediate between these two. The point of interest for New Zealand workers is that Stephensen unites Euthemisto antarctica Dana with E. gaudichaudii Guérin, and considers that both should be united with Themisto compressa of northern seas. His figures and descriptions leave little doubt that this conclusion is correct, and the result is that T. compressa must be looked upon as a bipolar species, being found in the Atlantic north of 40° N. lat., and in the southern seas south of 35° S. lat., while it appears to be altogether lacking in the intervening area.
It is interesting to note that in this case we have a species occurring with two forms in the colder northern seas and reappearing in two similar forms in the colder southern seas. I have drawn attention to a similar example in the case of the amphipods known as Ampelisca eschrichtii and A. macrocephala (1917, p. 75).
The New Zealand Species of Podocerus.
I have always been puzzled to distinguish the different species or forms of Podocerus found in New Zealand. P. cristatus (G. M. Thomson) was described by Mr. Thomson in 1879 under the name Cyrtophium cristatum, and it was easy to identify some of the forms found on the New Zealand coast with this species as described by him. In the same year Haswell independently described C. dentatum, an Australian form which Stebbing has—I think, rightly—considered to be the same as P. cristatus; in 1885 Haswell placed this species in the genus Dexiocerella.
The New Zealand species are common on the coast, frequently being found at the roots of seaweed, on the sea-squirt Boltenia, and on other organisms which they usually closely resemble in colour; as they are also somewhat sluggish in movement, they are sometimes hard to distinguish. They appear to show considerable variation in breadth of body, length of the appendages, colour, &c. Other specimens were at different times taken on sertularians, which they so closely resembled that on more than one occasion they were nearly being overlooked altogether, although it was known that they were frequently found on the hydroids. Some of these appeared at first sight narrower than the others, and it was thought they had probably formed a separate species. Closer examination, however, usually failed to reveal any striking or constant difference.
In 1885 Haswell had described another species, under the name Dexiocerella laevis, from Australian shores, differing from D. dentata mainly in having none of the segments dorsally produced.
In his Das Tierreich Amphipoda, published in 1906, Stebbing transferred these and other species to the genus Podocerus, recognizing ten species, two of them being P. laevis (Haswell) and P. cristatus (G. M. Thomson), the latter including Dexiocerella dentata Haswell. More recently I have examined and mounted numerous specimens, males and females, from different parts of Australia and New Zealand. Some of them it is easy to identify as P. laevis, and others as P. cristatus, in accordance with the descriptions given by Stebbing, and I think it is desirable to retain these two species distinct as a matter of convenience, though other forms are to a large extent transitional in one character or another. In P. laevis the body is usually smooth, without dorsal carination or with only slight indications of such. The gnathopoda are somewhat short and stout, in
the first the carpus being short and having a distinct rounded lobe fringed with setae extending along nearly its whole length. The second gnathopod has the propod short and stout, fully half as broad as long, the palm is nearly straight, and in fully-grown specimens bears two or three somewhat blunted teeth, and is irregularly dentate near the base of the finger. In the peraeopoda the propods bear three or four stout setules, the strongest of them being on the proximal portion of the propod.
On the other hand, P. cristatus usually has the body more or less carinate on the posterior segments of the peraeon and of the pleon. The gnathopoda are more elongated, the carpus of the first being more slender and having the lobe extending only along part of its length. The second gnathopod in general resembles that of P. laevis, but is more elongated, being more than twice as long as broad. The peraeopoda have the setules on the propods less stout, and those that are present more evenly distributed along the margin.
Fig. 1.—Podocerus laevis (Haswell): male specimen from Cape Maria van Diemen. a, first gnathopod; b, second gnathopod; c, propod of peraeopod.
In many respects P. cristatus shows an approach towards P. danae Stebbing from Kerguelen Land, but in that species all the segments of the body, including the head, bear carinate teeth or processes, and the appendages, especially the second antennae and gnathopoda, are much more elongate. I have specimens from China and Japan that I feel inclined to consider a variety of P. danae, the only appreciable difference being that the carinal processes are rounded, instead of being pointed as
in the Kerguelen Land specimen. P. brasiliensis Dana from the tropical Atlantic is in many respects similar to P. cristatus, but is described as having the body not carinate. I have only one specimen of P. variegatus Leach, the species commonly found in the North Atlantic, and this again shows very close approach both to P. laevis and P. cristatus, and it is not surprising that in 1893 Della Valle grouped most of these species under the name P. brasiliensis.
Fig. 2.—Podocerus cristatus (G. M. Thomson): male specimen from Cook Strait. a, first gnathopod; b, second gnathopod; c, propod of peraeopod.
Barnard (1916, p. 277) has recorded Podocerus cristatus (G. M. Thomson) from False Bay, South Africa.
The New Zealand Species of Allorchestes.
In his report of the Crustacea of the United States Exploring Expedition Dana gives two species of Allorchestes as occurring in New Zealand, both collected in the Bay of Islands.
A. brevicornis seems from the figure to be immature, and Stebbing (1906, p. 584) has rightly suggested that it is perhaps a young male of a Hyale; it is, I think, a specimen of Hyale grandicornis Kroeyer, a species found on the shores of all subantarctic lands. The genera Hyale and Allorchestes closely resemble each other, and are not easy to distinguish.
In young males of Hyale grandicornis, and perhaps of other species, the carpus of the second gnathopod is produced into a process lying between the merus and propod, similar to the one normally found in adult males of Allorchestes. This process is also present in the females of both genera; in many cases it cannot be demonstrated without dissction of the appendage, and its value as a generic character is accordingly reduced. The shape of the telson differs in the two genera, but this character again is one that is not always readily observed.
It is not surprising, therefore, that the identifications of Allorchestes novizealandiae made up to the present are somewhat uncertain. Fortunately I am able to give below a distinguishing character which is, I think, quite reliable, though it is well marked only in adult males.
Allorchestes novizealandiae Dana.
Allorchestes novizealandiae Dana, 1853 and 1855, p. 894, pl. 61, fig. 1 a–f (male), g–v (female). Allorchestes novizealandiae Stebbing, 1906, p. 581 (with synonyms). Hyale chiltoni G. M. Thomson, 1899, p. 206.
This species was described and very fully figured by Dana in 1852, and, though it has been referred to by both Mr. G. M. Thomson and myself
on various occasions, I have never quite felt sure about the correctness of our identifications. In 1899 Mr. G. M. Thomson described a new species, which he named Hyale chiltoni, well marked by the peculiar character of the first gnathopod of the male, the dactyl being long and curved and projecting far beyond the short palm. Subsequently to that date I have had specimens from different localities that I had no hesitation in referring to Thomson's Hyale chiltoni, and this was confirmed by comparison of them with mounted specimens so named in Mr. Thomson's own collection. Examination of them, however, showed that in the male the second gnathopod has the carpus produced into a narrow lobe as described by Stebbing for the genus Allorchestes, and in the telson and other points the specimens also agree with this genus, and I had accordingly labelled my specimens “Allorchestes chiltoni (G. M. Thomson).”
In comparing this species with the description and figures of Allorchestes novizealandiae as given by Dana, my attention was specially drawn to the figure he gives of the first gnathopod of the male, which differs considerably from that of the form found in some other species of Allorchestes, but proved to be a fairly accurate representation of the corresponding appendage of Hayle chiltoni G. M. Thomson; and a comparison of the other appendages leaves no doubt that the species described by Dana was the one subsequently described by G. M. Thomson under the name of Hyale chiltoni, a name which will therefore have to be reduced to a synonym.
The figures given by Dana agree very well indeed with those of my specimens, perhaps the only important point being that the joints of the peduncle of the second antenna are not very slender as he describes, but of fairly average breadth.
Dana's specimens were taken in the Bay of Islands on the shores of Parua Harbour, the animals being found in holes in wood that had been bored by teredos. I have specimens from Dunedin, Lyttelton, Timaru, Cape Campbell, Cape Maria van Diemen, and other parts of the New Zealand coast; also from Chatham Islands. Dana mentions that this species is near to A. australis Dana, an Australian species which Stebbing has considered to be the same as A. compressa Dana. In the localities given by Stebbing for A. novizealandiae, Valparaiso is given with a query, but so far I have been unable to ascertain the authority for this.
The figures illustrating this paper have been kindly drawn for me by Miss E. M. Herriott, M.A., Assistant in the Biological Laboratory of Canterbury College.
Barnard, K. H., 1916. Contributions to the Crustacean Fauna of South Africa: 5, Amphipoda. Ann. South African Museum, vol. 15, pp. 105–301.
Bovallius, C., 1889. Contributions to a Monograph of the Amphipoda Hyperiidea: Part I2. K. Svensk. Vet. Akad. Handl., vol. 22, No. 7.
Chilton, C., 1917. The Identity of the Two Amphipods Ampelisca eschrichtii Kröyer and A. macrocephala Liljehorg, considered from an Antarctic Point of View. Jour. Zool. Research, vol. 2, pp. 75–93.
Dana, J. D., 1853, 1855. United States Explor. Exped., vol. 13, Crustacea.
Della Valle, A., 1893. Gammrini del Golfo Napoli. Fauna und Flora des Golfes von Neapel. 20 Monographi.
Stebbing, T. R. R. S., 1888. The “Challenger” Amphipoda.
Stebbing, T. R. R. S., 1906. Amphipoda: 1, Gammaridea. Das Tierreich, 21 Lieferung.
Other references can be obtained from those here given.