The Early Post-larval Stages and Systematic Position of
Eurynolambrus australis M. E. and L. (Brachyura)
[Read before Wellington Branch, November 29, 1950; received by Editor, February 19, 1951]
This study is part of a series assisted by a grant-in-aid of research from the University Research Grants Committee.
This paper identifies and describes the early-settled, post-larval stages of the crab, Eurynolambrus australis M-E. and L., which is a common endemic species found at the lower tidal levels on stony and rocky coasts. These post-larval stages are of the greatest value in the determination of the systematic status of this species, which was originally (1841) placed in the Parthenopidae and accepted as a member of this family by Dana, Miers (1876), and by Filhol (1885). In 1879, Miers transferred the species to the “Cancerinae”, as being intermediate between the latter and the Parthenopidae, since while there is marked resemblance to Cryptopodia as in the expanded triangular form of the carapace, etc., Miers considered that the orbital and antennal regions show affinity with Cancer—the front being bilobate, the flagellum excluded from the orbital hiatus, the anterior legs not trigoniform, and essentially the legs not concealed by the carapace.
Flipse (1930) reviews the Parthenopidae, and apparently accepts Miers’ conclusion, for he quotes Miers (1879) and makes no further reference to Eurynolambrus in this review. The adult E. australis has a superficial cancroid facies. The oxyrhynchous characteristics are minimised by this adoption of this cancroid form, and meticulous examination of even the adult brings the status of the species as a parthenopid into doubt. The chelipeds, though long only in the largest specimens, are reasonably mobile and the fingers not markedly bent on the hand. Hooked hairs are present. As Miers determined, the second joint of the antenna is actually large, firmly attached to the epistome, and providing an incomplete floor to the orbit so that the orbits are relatively well-formed; but all of these characters refer more to the Majidae than the Parthenopidae and still less so to the Cancridae. In the Cancridae, as known to me in Cancer novae-zealandiae, the orbit is floored largely by an infraorbital plate from below and the second segment of the antenna forms only a small portion of the floor.
The post-larval stages described below remove all doubt from the status of E. australis as an oxyrhynch. The well-developed, divergent rostra; the incomplete orbit consisting of a supraocular eave, a cupped postocular process, and an intervening spine; the open ventral aspect of the orbit; dorsal turbercles; hooked hairs, used for masking; the enlarged second segment of the antenna carrying an anterior and an anterolateral spine; all these features and the general facies are
Fig. 1—First post-larval stage. Dorsal view of carapace. Chatham Islands.
Fig. 2–Second post-larval stage. Dorsal view of carapace. Island Bay.
Fig. 3—Third maxilliped, left side, of second post-larval stage.
Fig. 4—Anterior portion of carapace in ventral view, second post-larval stage.
Fig. 5—Fourth leg of second post-larval stage in posterior view.
Fig. 6—Abdomen of second post-larval stage.
Fig. 7—Chela of second post-larval stage, outer aspect.
Fig. 8—Male pleopod, left side, dorsal aspect.
Fig. 8a—Apex of pleopod, dorsal aspect.
Fig. 9—Anterior portion of carapace in ventral view, adult male.
Fig. 10—Lateral view of anterior portion of carapace to show subhepatic excavation.
Fig. 11—Dorsal view of carapace of adult male. Wellington.
Fig. 12—Abdomen and sternum of adult male.
All scales = 1 mm. excepting Fig. 11.
oxyrhynchous (Rathbun, 1925). There is no resemblance to the brachyrhynch post-larval stages as known to me.
The position of E. australis in the Oxyrhyncha is difficult to establish, since I have been unable to obtain data on the early settled stages of these crabs. The Parthenopidae are not otherwise known for New Zealand, but the Majidae are represented here by several species. The many features of both adult and post-larval stages compared, with our maioids indicate that E. australis is more correctly a member of the Majidae, and should probably be placed in the Pisinae, where it represents an advanced condition in completion of that type of orbit since there is the large, blunt, cupped post-ocular process into which the eye can be retracted, but with the cornea still visible from above and definitely more so from below; a supraocular eave; short eye-stalks; proximally wide, distally toothed second segment of the antenna; bilobed rostrum; subequal width to the merus and ischium of the external maxillipeds; and a long slender first male pleopod, while the second is short (Stephenson, 1945).
The first received, the larger of these post-larval specimens, was sent by Mr. J. T. Morton, who collected it from the holdfast of Macrocystis washed up at Island Bay, December, 1948. This was originally recognised as a maioid, but was unassignable to any of our species until the conformation of the posterolateral margin was recognised as suggesting E. australis, and subsequently the sub-hepatic cavern was seen as common to the young and the adult of the species. The smaller specimens were then found in a collection from Chatham Island (September, 1948) in company with Galathea pusillus and a post-larval specimen of Pilumnus sp. Fortunately, the smaller and larger specimens appear separated by at least one moult, giving an indication of the slow assumption of the specific form. The detailed morphology is drawn from the larger specimen, which differs in no significant respects, other than proportionally, from the smaller. Both specimens were liberally masked with sand-grains when first received.
4 mm. Post-larval Stage (Fig. 1)
The carapace is longer than wide, and characterised by two flattened lateral expansions, one hepatic, the other branchial, separated by a deep semicircular notch bordered with hairs. The rostrum is formed by two triangular divergent, flattened horns, the inner margin of each being straight, and fringed with hairs; the outer margin toothed.
Posterior to the rostrum the margin is extended laterally to form a supraocular eave, of which the antero-lateral angle is minutely bispinate and the posterior angle produced into a laterally directed spine. The eye is retractile into a postocular cup, which is the hollowed-out anterior part of the hepatic expansion, though never to such an extent as to entirely conceal the cornea in dorsal or ventral view. The supraocular eave and the postocular cup are separated by a small fissure containing the small mesocular tooth at its base.
The margins of the hepatic region are entire, broadly indented, the posterior angle acuminate. The margins of the branchial expansion are obtusely toothed with three subequal teeth projecting laterally,
and two posterior smaller teeth directed posterolaterally. The posterior margin of the carapace is rounded and carries two posteriorly directed paramedian spines submarginal in position.
Anterior to the orbits the carapace is deflexed, so that the tips of the rostra are ventral to the cornea. The carapace is convex antero-posteriorly and is armed in the midline with four tubercles—two mesogastric, which are spinate, a small urogastric, and one intestinal. In addition, there is a pair of cardiac tubercles, and a large branchial one which forms the apex of a triangle with smaller ones at the other angles. A slightly divergent row of hooked hairs extends from the rostrum on to the protogastric, each rising from a small spine, of which the second—the post-frontal—and the four and fifth—protogastric—are the largest.
The second antennal article is broad and forms the floor of the orbit. Its anterolateral angle projects at the side of the rostrum beyond the supraocular eave as a forwardly directed spine, followed on its outer margin by three or four small spinules. The spine bears a small accessory spinule on its medial border, and there is another spine close to the origin of the third antennal article. The second and third antennal articles are visible at the side of the rostrum. The flagellum outreaches the rostrum by about half its length.
The antennules are set almost longitudinally; the fossa is divided into two by a large interantennular spine, and by a median anterior spiniform process from the epistome. The epistome is well developed, and is divided into two parts by a shallow, transverse groove which connects the two prominences upon which the antennal glands open.
The third maxillipeds completely close the buccal cavern; the ischium and merus are finely dentate along their inner margins which are sparsely provided with hairs. The merus is expanded at its anteroexternal angle into a rounded lobe which bears four or five well-spaced denticles. There is a small spine at the anterointernal angle by the origin of the palp.
The subhepatic region is bluntly swollen, and carries three small tubercles, the posterior and outer one being the largest. The large branchiohepatic suleus is slightly hollowed out beneath, and a groove runs from this point anteriorly between the subhepatic and pterygostomial regions to the inferior orbital border between the postocular cup and the basal antennal article.
The abdomen consists of seven distinct segments; it is almost straight except for a slight widening of the sixth segment distally. It is ridged in the midline and provided with a series of long, straight hairs. The sternal segments are distinct, and slightly excavated on each side of the sutures.
The chelipeds are weak, being only slightly longer than the first ambulatory legs; they are equal in size. The palm is bluntly carinate above and below; the fingers are half the length of the palm, and meet only at their tips. The carpus is triangular and unarmed. The merus is also triangular in section with the apex of the triangle forming the sharp lateral margin, while of the other two margins which are medial, the dorsal carries two sharp spines, and the ventral a tubercle
at about the middle of its length. The ambulatory legs decrease in size from the first to the last. They are almost smooth, and carry a row of hooked hairs dorsally and a row of simple hairs ventrally. The ischium bears a large spine below, almost terminal in position; the inferior border of the merus carries a small spine at the middle of its length. The most characteristic feature of the ambulatory legs is the extension of the posterior distal margin of the propodus as a lobe which covers the insertion of the dactylus.
5·6 mm. Post-larval Stage (Figs. 2 to 7)
This stage shows some combination of both juvenile and adult features. The form of the carapace is still essentially the same as in the preceding, but the branchial expansion has become further produced laterally and the teeth reduced to rounded lobes. Juvenile features retained include the divergent rostral horns, the open orbit, the presence of an open notch between the branchial and hepatic expansions, the sharp spines on the basal antennal article, which in the adult become reduced to blunt tubercles, and the presence of hooked hairs on the carapace and legs. The ambulatory legs have acquired the adult form and are now flattened and carinate. The ischium is armed below with two spines, one median, the other almost terminal in position. The inferior border of the merus is armed in its proximal third with a short median carina which divides distally into two divergent carinae; the carpus fits into the V-shaped groove thus formed when the legs are bent. In the mid-dorsal line the merus bears a row of low tubercles; the carpus is short with a posterolateral carina, which is raised into a tooth at its distal end and an anterolateral carina which is bidentate. The propodus has a median dorsal carina, and along the middle of the internal surface are three or four small tubercles each carrying two very long hairs. The lobe covering the insertion of the dactylus is present as in the younger form. The dactylus is shorter than the propodus and tapers to a curved horny tip; it is provided with long scattered hairs.
The Adult (Figs. 8 to 12)
The lateral expansions of the carapace in the adult of E. australis are greatly increased in size so that the breadth of the carapace is greater than the length. The largest specimen in our collection is a female 26 mm. long and 39 mm. wide, with arm length of 28 mm. Filhol's specimen included a male 36 mm. long and 60 mm. wide with arm length 50 mm, and a female 36 mm. long, 70 mm. wide, length of arm 38 mm.
The rostrum appears bilobed, though on closer examination a closed fissure is visible in the midline. In a small female, 14 mm. long and 18 mm. wide, the rostrum is still distinctly bifid, though it is fused for more than half its length. The wide fissures which were a feature of the juvenile carapace are scarcely visible in the adult. The notch between the branchial and hepatic regions is almost obliterated, and because of the great development of the branchial region now lies anterior to the mid-point of the carapace, which is its position in the juvenile. The spine at the anterolateral angle of the basal antennal article is represented by a tubercle, and the other spines are not acute.
The fissure betwen the supraocular eave and the postocular cup disappears, but the mesocular spine remains, though very much reduced. A feature of the adult carapace is the four large, outwardly directed depressions, two placed where the hepatic, branchial and gastric regions unite, the others over the middle of each branchial region.
The male abdomen differs little from that of the juvenile, but the two lateral tubercles on the sixth segment have disappeared. The abdomen of the adult female is seven-jointed. It occupies the whole space between the legs, and reaches right to the base of the mouth field. On either side of the midline is a shallow longitudinal groove; the last segment is broadly triangular. The first pleopod of the male (Fig. 8) is slender, and apically divided into three (Fig. 8a); the inner portion projects beyond the end of the pleopod and is armed on its internal surface with short spinules; the median portion takes the form of a ventral lobe bearing long setae which seen from beneath are arranged in two rows, only the anterior row being visible from above; the outer, or sternal portion is bent inwards at its tip into a hook-like structure, the outer surface is provided with setae, the marginal ones being long and continued almost to the base of the pleopod. The second pleopod is short and composed of three distinct segments.
Chilton, C., and Bennett, E. M., 1928. Contributions for a Revision of the Crustacea Brachyura of New Zealand, Trans. N.Z. Inst., 59, 731–778.
Flipse, H. J., 1930. Die Decapoda Brachyura der Siboga-Expedition. VI. Oxyrhyncha: Parthenopidae; XXXIX C2: 1–96.
Miers, E. J., 1876. Catalogue of the Stalk and Sessile-eyed Crustacea of New Zealand. London: 1–136.
—— 1879. On a Collection of Crustacea, etc. 1. Podophthalmata. Proc. Linn. Soc. Zool., v. 14.
Rathbun, M. J., 1925. The Spider Crabs of America. U.S. Nat. Mus. Bull., 129, 1–613.
Stephensen, K., 1945. The Brachyura of the Iranian Gulf, etc. Dan. Sci. Investig. in Iran, (IV), 57–237.