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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.
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Fig. 3.—Allorchestes novizealandiae Dana: male, a, first antenna; b, second antenna; c, first gnathopod; d, second gnathopod; e, third peraeopod.
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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.
Fig. 4.—Allorchestes novizealandiae Dana: female. a, first gnathopod; b, second gnathopod.
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
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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.