Art. XX. — The New Zealand Sand-hoppers belonging to the Genus Talorchestia.
[Read before the Philosophical Institute of Canterbury, 16th October, 1916; received by Editors, 30th December, 1916; issued separately, 24th August, 1917.]
The sand-hoppers or shore-hoppers that are so abundant on the shores of New Zealand are Amphipoda belonging to the family which Stebbing has named the Talitridae, though it was long formerly known, and is perhaps better known even now, as the Orchestidae. They present many interesting points in structure, and are specially worthy of study because they are undoubtedly forms that have arisen from marine ancestors and have gradually become adapted to a life on the seashore. Some members of the family are still almost entirely marine, spending the greater part of their life in the sea-water; others live at or above high-water mark almost beyond the reach of ordinary tides. Between these two extremes we have numerous transitional stages in structure and in habits, so that the family offers a favourable opportunity for studying the effects of altered conditions on the structure of the animals. One member of the family, Parorchestia sylvicola (Dana), has become quite terrestrial in habits, and is found all over New Zealand far from the coast
Similarly the terrestrial Isopoda belonging to the Oniscidae and allied families, commonly known as slaters, woodlice, &c, are descended from marine ancestors and present a series of transitional forms strikingly parallel to the Talitridae, though with the isopods the terrestrial forms are much more numerous and more perfectly adapted to terrestrial conditions. In their antennae and mouth-parts these isopods show many resemblances to the shore-hoppers, and a detailed comparison of the two groups, as an example of convergent evolution, would be instructive and fruitful in results. It is possible also, as I pointed out in 1884 (p. 156),* that forms now included in the same species or genera may have arisen independently in different places from the same widely distributed marine ancestor
The New Zealand sand-hoppers are grouped under several genera, such as Talorchestia, Orchestia, &c. Their classification is difficult owing to the close general resemblance of all of them and the consequent use of minute and apparently trivial characters in distinguishing the genera and species, and particularly owing to the fact that nearly all show marked sexual dimorphism, the females of different species being very much alike while the fully grown males may be quite different Again, the sexual characters of the male appear in most cases to be fully developed only at a late stage, the immature males being more like the females, and in the absence of a mature male it may be very difficult to say to what species any particular specimen belongs.
The Orchestidae of New Zealand have already received a good deal of attention. The species were originally described by Milne-Edwards,
[Footnote] * The references are made by the year of publication to the bibliographic list at the end of this article.
Dana, Spence Bate, and others. In 1881 (p. 208) G. M. Thomson gave a critical review of some of the species, and in 1899 he published a “Synonymy of the New Zealand Orchestidae.” In 1906, in Das Tierreich Amphipoda, Mr. Stebbing included the New Zealand species and gave brief diagnoses of them. In preparation for his paper Mr. Thomson had made many drawings of the different species, but these were not published, nor is Stebbing's list illustrated. Mr. Thomson has since handed over to me all his specimens, drawings, and notes. Some of these have been used in the preparation of this paper, and the others will be of great use when it is possible to compile a complete and critical list of the New Zealand Orchestidae.
At present, however, I deal only with the species of the genus Talorchestia. Of these there are three, and for them I accept the names as given by Stebbing in 1906, adding figures and notes on their distribution and habits which will, I hope, be sufficient to enable local collectors to identify their specimens.
All three species, with the possible exception of P. tumida, are endemic to New Zealand, and appear to be pretty distinct from the species of the genus found in other countries.
Genus Talorchestia Dana, 1852.
Talorchestia Stebbing, 1906, p. 543.
Stebbing defines Talorchestia by its differences from Orchestia, which he places before it in the list, and Orchestia is defined by reference to Talitrus. The three genera are very close to one another and to Talitroides and Orchestoidea, the five together forming a fairly well defined group of the Orchestidae.
The following definition of the genus will perhaps be sufficient for the New Zealand species; I omit, of course, the characters common to the family.
Antenna 1 shorter than peduncle of antenna 2; antenna 2 often strongly developed, especially in adult males. Gnathopod 1 small, simple in the female, subchelate in the male owing to the production of the propod into a narrowly rounded pellucid lobe, a similar lobe being usually present on the hind margin of the carpus near the distal end. Gnathopod 2 small and feeble in the female, the propod being produced into a rounded pellucid lobe beyond the minute chela-forming finger. Gnathopod 2 in the male very large and powerfully subchelate. Peraeopod 2 with the finger notched or otherwise modified and differing from that of peraeopod 1.
While the three genera are undoubtedly very closely related, Talitrus is distinguished by having the second gnathopod small and feeble in the male and similar to that of the female. In Orchestia the first gnathopod is usually subchelate in the female as well as in the male, and in the male the pellucid lobes on the carpus and propod are broader than in Talorchestia and differently shaped; in Orchestia, again, the finger of the second peraeopod is usually the same as that of the first.
The genera Talitroides and Orchestoidea are ill defined; the first should probably be united with Talitrus, and it is difficult to distinguish Orchestoidea from Talorchestia. Another genus, Talitriator, was established in 1913 (p. 109) by Methuen, who says in his diagnosis, “Like Talitrus except for the fifth side-plate …” The type is a truly terrestrial species
widely distributed in South Africa. In 1916 (p. 222) Barnard adopts the genus, transfers to it the Australian species Talitrus sylvaticus Haswell and T. kershawi Sayce, and gives a fresh diagnosis.
It seems probable that Talitriator will be found to be identical with Talitroides Bonnier, and this name has priority if the genus is retained as separate from Talitrus.
All the New Zealand species of Talorchestia, and, so far as I know, all the foreign species also, are confined to sandy beaches, where they may be found under decaying seaweed or driftwood, or burrowing into the sand about high-water mark. Some species of Orchestia may occur in similar situations, but many are found under stones, &c., on rocky shores.
Owing to the differences between the sexes and to the changes passed through by the males in attaining the adult form it is very difficult to give any artificial key for readily distinguishing the species, but perhaps the following will be useful:—
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
|1||Antenna 2 as long or longer than the head and first three segments of the peraeon, fourth and fifth peraeopoda not modified in male||T quoyana.|
|Antenna 2 shorter than the head and first three segments of peraeon, fourth or fifth peraeopod modified in male||2|
|2||Body very broad; carpus of fourth peraeopod irregularly dilated in male, fifth peraeopod normal.||T tumda|
|Body rather compressed; carpus of fifth peraeopod dilated in male into a large, rounded plate concave on inner side, fourth peraeopod normal||T telluns|
Talorchestia quoyana (Milne-Edwards). (Figs. 1 to 5.)
Talitrus brevicornis and Orchestia quoyana H. Milne-Edwards, 1840, vol. 3, pp. 15, 19. Orchestia quoyana G M. Thomson, 1899, p. 202. Talorchestia quoyana Stebbing, 1906, p 547 (with synonymy).
Specific Diagnosis.—Back broad. Antenna 1 reaching a little beyond end of penultimate joint of peduncle of antenna 2. Antenna 2 in female as long as head and first three segments of peraeon, in male becoming longer
and stouter, often more than half the body-length and with last joint of peduncle twice as long as the preceding. Gnathopod 1 in male with carpus much longer than propod, not lobed, propod very spinose, with small postero-distal lobe, palm transverse, finger reaching beyond it. Gnathopod 1 in
female similar but with propod narrowing distally so that the end is scarcely broader than the base of the finger. Gnathopod 2 in male with basal and ischial joints channelled in front, propod very large and massive, palm
Fig 2 —Talorchestia quoyana, female.
Fig. 3.—First gnathopod of adult male.
Fig 4—Second gnathopod of adult male (less enlarged than fig. 3).
oblique, spinose, with broad rectangular tooth near the finger, and prominent acute defining tooth. Gnathopod 2 in female not presenting characteristic features, basal joint elongate-oval, carpus longer than propod. Peraeopoda normal.
Length of male reaching 29 mm.; females smaller.
Occurrence.—On sandy beaches all round the coasts of New Zealand.
Remarks.—This is the largest and commonest sand-hopper in New Zealand; it occurs in great abundance on all sandy beaches under decaying seaweed or burrowing in the sand about high-water mark, usually a little below extreme high-water mark. It is probably somewhat nocturnal in
Fig 5b —Second gnathopod of older but immature male
Fig 5b —Second gnathopod of older but immature male
habit, seldom being seen in large numbers during the day unless disturbed from its burrows, when it leaps about with great agility. The colour is usually a light-yellowish brown with marbled markings of a darker brown, generally assimilating to the appearance of the sand.
Immature males have the second antenna shorter and more slender, resembling those of the females, and the second gnathopod small and feeble like that of the female except that the carpus is shorter and the propod broader. Two transitional stages are shown in figs. 5a and 5b.
Talorchestia tumida (G. M. Thomson). (Figs. 6 to 13.)
Talorchestia tumida G. M. Thomson, 1885, vol. 2, p. 577, and 1899, p. 203; Chilton, 1892, p. 259, Stebbing, 1906, p. 550 (with synonymy).
Specific Diagnosis—Back broad and body swollen, especially in old males. Antenna 1 reaching to end of penultimate joint of peduncle of antenna 2, short, flagellum shorter than peduncle Antenna 2 less than one-third the length of the body, last joint of peduncle about twice as long as the preceding, flagellum rather shorter than the peduncle. Gnathopod 1 in male spinose, carpus much longer than the propod, its hind margin with a narrowly rounded lobe near the distal end, propod with a similar lobe at distal end forming a transverse or slightly projecting palm. Gnathopod 1 in female similar but without the lobes, though the postero-distal
angle of the propod forms a slightly projecting blunt tooth. Gnathopod 2 in male varying much in appearance at different stages of development; invold males propod much swollen, widening distally, palm transverse or slightly oblique, spinose, not defined but forming at the junction with the
hind margin a broadly rounded projecting lobe, near the base of the finger on the inner side is a stout tooth-like projection; in younger males this process is nearer the middle of the palm and divides it into two deep excavations, finger stout, with a rounded projection on concave side, end
curved and fitting closely on to the curved end of palm. Gnathopod 2 in female normal. Peraeopod 4 with merus and carpus modified, merus expanding distally, carpus abruptly widening from a narrow base and then narrowing but with apex much wider than the propod, whole limb very spinose. Fifth peraeopod rather stout but otherwise normal.
Length of largest specimens about 15 mm.
Occurrence.—On sandy beaches at numerous points on the New Zealand coasts, and at Chatham Islands.*
Remarks.—This species is smaller and less common than T. quoyana, but is found at suitable spots all round the coast. Mr. Thomson says that it occurs “on sandy beaches and sandhills, usually at some distance from the sea.” Most of my own specimens, however, have been taken near high-water mark; at Moeraki, on the east coast of Otago, I found it burrowing in the sand in places similar to those where T. quoyana is usually found. It closely resembles that species in colour, but may be readily distinguished by the short antenna and the greatly swollen body.
In young males the second gnathopoda have the propod small and the palm regularly rounded as in some species of Orchestia; in older males the form differs very much at various stages, and it is possible there may be more than one adult form, though I think not. Fig. 13 is taken from a large specimen collected at Moeraki; other specimens have the palm more like that shown by Stebbing (1887, pl. 39, fig. A, gn. 2); it has the basal joint very long, and its anterior surface channelled to fit the large propod when reflexed.
Talorchestia telluris (Bate). (Figs. 14 to 18.)
Orchestia telluris Bate, 1862, p. 20, pl. 3, fig. 6; pl. 4, fig. 4: G. M. Thomson, 1899, p. 200. Talorchestia telluris Stebbing, 1906, p. 551 (with synonymy).
Specific Diagnosis. — Body rather compressed. Antenna 1 reaching rather beyond penultimate joint of peduncle of antenna 2. Antenna 2 variable, in first form short, about as long as head and first segment of peraeon, flagellum rather shorter than peduncle; in second form longer, especially in adult males. Gnathopod 1 in male with carpus longer than propod and bearing a small rounded pellucid lobe near middle of its free hind margin, propod with a rather larger lobe at distal angle forming a transverse palm; whole limb rather spinose. Gnathopod 1 in female similar but without the lobes, propod narrowing distally. Gnathopod 2 in the male of two forms. In the first form (fig 16) with propod large, oval, palm oblique, spinose, concave between the base of the finger and an acute
[Footnote] * In Mr G. M Thomson's collection are one large female and three smaller ones from Pirates' Bay, Tasmania, which appear to belong to this species, but without a male the identification is somewhat uncertain.
triangular tooth near the middle of palm, not defined, the end passing insensibly into the convex hind margin, finger with concavity near the hinge, then a broad protuberance, extremity curved to fit the end of the palm.
Fig. 14.—Talorchestia telluris, male
Fig 15 —First gnathopod of male.
Fig 16—-Second gnathopod of male, fast first (less enlarged than fig 15)
In the second form the palm is oblique but well defined by a stout tooth on the outer side, while on the inner side there is a short blunt thumb-like process, the end of the finger fitting in between the two, near the base of
P. 301: For “Fig 17—Second gnathopod of male,” &c., read “Fig. 18—Fifth peraeopod of adult male,”
P. 302: For “Fig, 18—Fifth peraeopod,” &c., read “Fig, 17—Second gnathopod of male, second form (less enlarged than fig. 15),”
[Face p. 301
the finger the palm bears a rounded spinose process which is followed by a long flat spinose protuberance separated by a concavity from the defining tooth, finger thickened on inner side near the base (fig. 17). Gnathopod 2 in the female normal. Peraeopod 5 in male with merus triangular, widening distally, carpus expanded posteriorly into an enormous oval plate, concave on the inner side (fig. 18).
Length.—About 12 mm.
Occurrence.—Sandy shores of New Zealand and Chatham Islands about high-water mark.
Remarks.—This species is smaller than the other two, and appears to be less common, though it has been taken at several widely separated places from the North Cape of New Zealand to Stewart Island. In Chatham Islands it seems to be relatively more abundant, as it occurs in most of the few collections I have had from those islands. In a few cases I have taken it not far from the mouth of a fresh-water stream, but this may be purely accidental.
The male can be easily recognized by the extraordinary process on the fifth peraeopod; all stages may be found between a slight flat expansion of the hind margin of the carpus and the huge process shown in fig. 18. A somewhat similar process is found in Talorchestia scutigerula (Dana), but in that species it arises as an expansion of the second or basal joint.
I have described this species as having two forms of the male, so far as the second gnathopods are concerned. It is possible, of course, that the second form should be considered a separate species, as its second gnathopod in the male differs very markedly from that of the first form. The animal has, however, the greatly expanded carpus of the fifth peraeopod, and in most other points agrees so closely both in structure and in habits that I prefer to group both forms under the one species. The description and figure of the gnathopod of this second form is taken from a Chatham Island specimen, and apparently all the Chatham Island specimens belong to this form. I have one specimen also, from Ross Beach, Westland, which has the second gnathopod like the Chatham Island form, particularly in the small thumb-like process on the inner side of the defining tooth, but it has the rounded protuberance on the palm near the base of the finger much broader than in the Chatham Island specimens. In the Ross specimen the fifth peraeopod is not fully developed, the carpus being considerably expanded but not having developed into the great oval plate characteristic of the species. In the first gnathopod of the Ross specimen the pellucid lobe on the propod is moderately well defined, but there is no sign of the similar small lobe on the carpus, and apparently this lobe on the carpus
and the full expansion of the carpus of the fifth peraeopod are not developed until after the characters of the second gnathopod have been attained. In the Ross specimen the second antenna is much longer than in form 1. or than it is in the Chatham Island specimens of form 2, being longer than the second gnathopod, while in the Chatham Island specimen it is distinctly shorter. It was this difference in the length of the second antenna, combined with the differences in the first and second gnathopods and in the fifth peraeopod, which made me first think that the Ross specimen must be a different species, but comparison with the Chatham Island specimen as above described forced me to the opposite opinion. From the
Kaiapoi Beach, near the mouth of the Waimakariri, I have several specimens similar to the Ross one, but all more immature and having the special characters of the second gnathopod less marked. I have also one specimen from Waiwera, Auckland, which appears to belong to this form, though the palm of the second gnathopod is not precisely the same as that figured; the rounded spinose process near the base of the finger is present as in form 2, but the palm is without the defining tooth, in this respect resembling form 1; pellucid lobes are present on the carpus and propod of the first gnathopod, and the carpus of the fifth peraeopod is more expanded than in the Ross Beach specimen, while the second antennae are short. This Waiwera specimen thus shows intermediate characters, and affords an additional reason for retaining forms 1 and 2 in the same species.
Barnard, K. H, 1916. Contributions to the Crustacean Fauna of South Africa, 5, Amphipoda, Ann. South Africa Mus., vol. 15, pp 105–302, pls. 26–28.
Bate, C. Spence, 1862. Catalogue of the Specimens of Amphipodus Crustacea in the Brit. Mus, London.
Chilton, C., 1884. The Distribution of Terrestial Crustacea, N.Z. Journ Sci., vol. 2, pp. 154–57.
— 1892. Notes on some New Zealand Amphipoda and Isopoda, Trans. N.Z. Inst., vol. 24, pp. 258–69.
Dana, J. D., 1852. The United States Exploring Expediton, vol. 13, Crustacea, Part II.
Methuen, P. A., 1913. Proc. Zool. Soc. 1913, p. 109.
Milne-Edwards, H., 1840. Histoire naturelle des Crustacés, vol. 3.
Stebbing, T. E. E., 1887. Trans. Zool. Soc. London, vol. 12, p. 202, pl. 39.
— 1906. Amphipoda, 1 Gammaridea, Das Tierreich, Lieferung 21-Berlin
Thomson, G. M., 1881. Recent Additions to and Notes on New Zealand Crustacea, Trans. N.Z. Inst., vol. 13, pp. 204–21, pls. 7, 8.
— 1885. New Crustacea, N.Z. Journ. Sci., vol. 2, pp. 576–77.
— 1899. Synonymy of the New Zealand Orchestidae, Trans. N.Z. Inst., vol. 31, pp. 197–207.