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Tuatara: Volume 2, Issue 2, July 1949

Lyreidus australiensis Ward (Brachyura, Gymnopleura) from Cook Strait

Lyreidus australiensis Ward (Brachyura, Gymnopleura) from Cook Strait

The present record of Lyreidus australiensis is based on the fairly complete exoskeleton of the cephalothorax and its appendages from a single semi-digested female recovered by Mr. B. M. Bary from the stomach of a dogfish taken in the Wellington area. This is apparently the first record of a gymnopleuran for New Zealand, and is of interest in adding to our fauna a representative of a group of lesser Brachyura notable for a blending of brachyuran and macruran features. The abdomen is reduced; uropods, absent; epistome and pterygostomium, united; external maxillipeds, plate-like and covering a well-formed mouth-field, etc.; but with these crab-like features there are the macruran features such as the presence of a definite rostrum; the free basal segment of the antennae; narrow posterior thoracic sternites; and an astacuran pattern in the central nervous system. Bourne (1922, J. Linn. Soc. Zoo. xxxv., No. 231) views the Gymnopleura as arisen from Macrura independent of other Brachyura and strikingly convergent with the Oxystomata.

The majority of species live on the continental shelf, mostly on sandy bottom. Some are taken by hand-line in the vicinity of coral reefs. Their habits are little known; but the depressed dactyli of Lyreidus and some others indicate that these dig in sand, and possibly

This study has been assisted by a grant-in-aid of research from the Research Grants Committee of the University of New Zealand. page 70

burrow. Judging from the presence in the stomach of the fish of L. longipes and of a new species of Trichopeltarion both of which are known from sandy bottom, along with the present specimen, this Lyreidus was captured in a sandy area. The species has been trawled on several occasions off the eastern Australian coast, and is probably common in Cook Strait.

Lyreidus Australiensis. Ward, 1933.

The carapace elongate, the greatest width at the middle of the length where it is nearly two-thirds of the length; the dorsum, strongly convex transversely and slightly so longitudinally. The fronto-orbital margin is one-third, the anterolateral margin three-quarters, the postero-lateral margin equals, and the posterior margin just exceeds one-half, in each case of the greatest width of the carapace. The flat rostrum has a median ventral keel, and from above, the form of an equilateral triangle. The orbts are wide and deep, the lateral wall formed by the medially concave external orbital angles which are acute and equal in length to the rostrum. The anterolateral margins diverge, are weakly concave anteriorly and convex posteriorly. The lateral spine is wide-based, acute, and anteriorly directed. The posterolateral margins are initially subparallel but convergent posteriorly where they form an obtuse angle with the transverse, slightly concave posterior margin.

Lyreidus australiensis. Fig. 1, dorsal view of cephalothorax; Fig. 2, external face of right chela; Fig. 3, of left chela; Fig. 4, external maxillipeds.

Lyreidus australiensis. Fig. 1, dorsal view of cephalothorax; Fig. 2, external face of right chela; Fig. 3, of left chela; Fig. 4, external maxillipeds.

The wide, short peduncle of the eye fills the orbit which has a single orbital fissure, and there is a recess in the external orbital angle into which the peduncle fits. The basal segments of the antennules are short, rounded below, ridged above, and separated by a plowshare-shaped interantennulary septum. The basal segment of the antenna page 71 is short and depressed. The ischium and merus of the external maxillipeds are subequal in their greatest lengths.

The first sternite is flat, anteriorly trilobed, manubriform and in its greatest width slightly exceeds the fronto-orbital margin. The subsequent sternites are narrow and deeply grooved. The abdomen is lacking.

The chelipeds are increasingly compressed from the rounded arm to the thin fingers. The left arm has a small spine median to the dorsal margin. There is a recurved tooth median on, and a spine distal on, the dorsal margin of the wrist. The dorsal margin of the strongly compressed hand is keeled; the ventral margin of the left hand has three, of the right hand two, low but sharp-edged spines. There are no teeth on the occlusal surfaces of the fingers, which have sharp cutting edges. The movable finger is set at right angles to the palm, is long, tapering; but the fixed finger is broad, flat and short. The basal segments of the legs are triangular in section; the distal, compressed and keeled, excepting the dactyli which are elongate, tapering, and depressed so that their width is transverse to the width of other segments of the leg.

Length of the carapace, 37 mm.; greatest width, 20 mm. (both as measured with the carapace returned to a normal shape, not collapsed).

Haswell (1882, Catal. Austral. Crust.) recorded Lyreidus tridentatus de Haan 1841 from specimens collected at Port Stephens and Port Jackson in Australia. Ward (1933, Austral. Zool., 7 No. 5) considers the Australian material is distinct and has named it as L. australiensis, a species resembling L. tridentatus but with longer orbits, a broader carapace and sternum, longer and more slender chelae, etc. The present specimen fits well with Haswell's description from Australian specimens, agrees with Bourne's figures of the venter and of various appendages etc., of an Australian specimen; and other than in the hands which are not as heavy, with the photograph of Ward's holotype male. Accordingly the present specimen is recognised as L. australiensis although Ward's definition of this species is quite cursory. The other species of Lyreidus seem to be L. bairdii Smith 1881 which has the anterolateral margins indented and a broad angle between the anterior and the lateral margins; L. channeri Wood-Mason 1885 (syn. L. gracilis W.-M. 1887) having the external orbital angles produced beyond the rostrum, and a prominent anterior and a still larger posterior spine in the middle and at the end of the anterolateral margin; the doubtful L. elongatus Miers (? syn. L. tridentatus) was described by Miers as having the carapace barely equalling in width one-half of the total length, a narrow rostrum, four spines on the lower margin of the hand, and the greatest width level with the lateral teeth; and L. politus Parisi which is known to us only from Sakai's plate (1922, Sci. Rept. Tok. Bun. Daig. B) which shows a fronto-orbital margin not one quarter of the greatest width of the carapace, the anterolateral margin smoothly continuous with the posterolateral margin, and no lateral spine. None of these species agree with the present material.