Pentanymphon antarcticum Hodgson 1904

“Pentanymphon antarcticum

(Plate V.)

Pentanymphon antarcticum, Hodgson (11), p. 458; Cole (7), p. 405; Bouvier (3), p. 294.

Specific characters: --

Body very slender, lateral processes long and widely separated, neck very long.

Chelifori: chelae long and slender, shorter than scape, with short, stout, uniform, close-set teeth.

Palps: terminal joint longer than preceding, which is in turn half the length of the third.

Ovigers: terminal claw pectinate, denticulate spines, with seven pairs of lateral teeth, the first being very small.

Legs rather long and slender, with a well-developed terminal claw and two auxiliaries; setae arranged in four rows on the last three joints.

The body is very slender, quite smooth, with very widely separated long lateral processes. Anteriorly it is slightly curved downwards.

The Cephalon is long and slender, longer than the second and third segments, and expanded distally into two dorsal lobes for the articulation of the chelifori.

The Ocular tubercle lies immediately in front of the first pair of lateral processes. It is short, merely a low rounded hump, in fact, bearing four well-developed eyes.

The Abdomen is very small, directed upwards, and not separated from the trunk by and articulation. It is rather conical and extends but little beyond the trunk, not nearly so far as the posterior lateral processes.

The segmentation of the trunk is distinct, the joints occurring immediately behind the lateral processes.

The Proboscis is directed downwards, cylindrical, with a slight swelling about the middle of its length; it is a long as the cephalon, and its extremity is rounded.

The Chelifori arise above the proboscis, each on a lobe of the cephalon, which is here rather more than twice the diameter posteriorly. The scape is single-jointed, longer than either the proboscis or the chela. A few delicate setae are scattered along its length, and there is an inconspicuous distal fringe. The chela is a little shorter, the palm and dactyli occupying equal halves; the former is covered with fine setae which also form a fringe round the base of the movable finger. The fingers are slender and much curved near the tips. Both are provided with a row of fairly stout teeth of nearly uniform size, rather closely set.

The Palps arise below the chelifori and at the sides of the proboscis; they are built on exactly the same plan as in the genus Nymphon (fig. 1a). The first joint is small and stout, the proportions of the remainder being 8 : 5 : 3 : 4. The second joint is sparingly setose except for a distal fringe; the other joints become more and more setose to the last, which is richly supplied. On the outer side they are more abundant than elsewhere.

The Ovigers are ten-jointed and present in both sexes. (Fig. 1b.) They arise from very short but conspicuous processes on the lower side of the cephalon immediately in front of the first pair of lateral processes. The details of this appendage are as in Nymphon. The first joint very small, the second is twice the size, and the third, which has a very oblique termination, is a little longer still; non of these bear setae. The fourth joint is very long, slender, and slightly curved; it carries a glandular aperture on its outer side about a quarter of its length; all the setae are small; very few occur except as a distal fringe. The first joint is longer still, the longest of the appendage, and its distal half is enlarged in diameter; it is covered throughout with fine setae. The sixth joint is rather more than half the length of the fifth, slightly curved, and on the outer side of the curve plentifully supplied with fine setae. Of the four terminal joints the first is little more than half the length of the preceding, the other three are shorter and sub-equal; very few setae occur, except distally. They carry a single row of denticulate spines (fig. 1c). These spines consist of a slender shaft with a swollen base; near the base is a pair of small teeth followed by two pairs of comparatively long slender ones; the remaining four pairs are more slender and blade-like, graduating to a mere trace. The terminal claw is furnished with about nine slender teeth. Both denticulate spines and terminal claw are frequently very much worn.

With regard to the Legs, all five are practically of the same size and proportions, and though there is a considerable amount of variation in this respect it is confined to narrow limits. They may attain a length of as much as 36 mm. Of the three coxae, the first and third are sub-equal and together about as long as the second; all, especially the third, bear a few minute setae, chiefly ventral. The proportions of the three following joints are approximately as 6.5 : 7 and 10; the tarsus and propodus are long and slender, the former being the longer. The limb is more or less covered with fine setae. On the femur they are scanty and for the most part small; a few longer ones are to be found along the shaft and distally. On the first tibia they are comparatively long and arranged in four indistinct rows, of which the lateral ones are not easy to observe. On the second tibia they become smaller and much more numerous, especially distally, and the distal fringe is strongly developed ventrally. The same arrangement holds a good for the two remaining joints, but the ventral row is very strongly developed, the setae becoming almost spinous and closely set. The terminal law is a powerful one, and is accompanied by two slender auxiliaries of about quarter its size.

The Genital apertures of the female are found on the second coxae of all the legs, and in the adult they are distinct enough. The apertures of the male are at all times difficult to observe, and I have only been able to distinguish them on the three posterior pairs of legs.

Nearly thirty specimens of this species were taken in Winter Quarters, at all times of the year, and in depths ranging from 12 to 125 fathoms. They very considerably in size, a variation obviously due to age, but in essential details they are in agreement except in one particular, and that is the articulation of the abdomen to the trunk; in certain cases among the more robust forms it is distinctly articulated. The trunk in all cases is seen to be very minutely scabrous when removed from spirit. The females are more robust than the males when the sexes can be separated, a feature which is most noticeable in the femora, but extends to the first tibiae. The males, as a rule, are rather more setose than the females.

A few of the eggs borne by one of the males are hatched. On emerging from the egg the body is ovoid, and possesses three pairs of appendages. The cheliforus comprises a stout scape with one very long seta, and a small but well-developed chela, without teeth on the dactili; a small proboscis lies below these. Details of the other two pairs of appendages cannot be seen without special preparation, which has not as yet been undertaken. Other specimens crawling about the egg-masses show the proboscis, chelifori, the palps not clearly jointed, and four pairs of appendages, having three stout sub-equal joints, followed by a fourth nearly as long as the three together, only a great deal more slender, and terminating in a very minute claw; a conical abdomen lies at the extremity of the trunk, the posterior part of which is provided with a small number of very long setae.” (Hodgson 1907, 36-39)