Pallenopsis (B.) tritonis, Bamber, 1983

Bamber, Roger N., 2002, Morphological variation in and a redescription of Pallenopsis (Bathypallenopsis) tritonis Hoek, 1883 (Arthropoda: Pycnogonida), Journal of Natural History 36 (2), pp. 157-172 : 164-171

Redescription of Pallenopsis (B.) tritonis

Male. (Predominantly based on male of 4.48 mm trunk length from Discovery sample 10105#13; Registration No. NHM.Z.2000.941. Measurements as in table 3.) Trunk (®gure 5A, B) glabrous, fully segmented; lateral processes separated by little less than their own diameters, less than twice as long as their own diameters, normally bearing two or three small dorsodistal spinules. Cephalon as long as second and third segments combined; ocular tubercle anterior, dome-like, bearing four eyes of which posterior pair are smaller, and two small laterodistal papillae. Abdomen not articulating, elongate, erect, with one or two pairs of setae on anterior face; abdomen elongating exponentially with size of animal.

Chelifora overreaching proboscis; scape of two articles, subequal, second article commonly shorter, both with few dorsolateral setae, second article with four or ®ve dorsodistal setae. Chela (®gure 5C) of Bathypallenopsis - type, ®ngers subequal to or slightly longer than palm, curved, gaping, tips crossing, cutting edges with slight crenulations; palm sparsely setose.

Proboscis of tydemani - type, glabrous, elongate, generally parallel, widest at midlength, between 0.6 and 0.9 times as long as trunk.

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Palps adjacent to ventrolateral base of proboscis, small, single-articled, slightly curved in larger animals (®gure 5A).

Oviger (®gure 6A, C) ten-articled, second, fourth and ®fth articles subequal, these and third article with rows of setae pointing proximally; strigilis of distal ®ve articles, heavily setose; sixth article with three or four larger spines, these and many setae pointing proximally; no distal claw.

Legs similar; third leg (®gure 7) coxa 1 slightly shorter than coxa 3, coxa 2 more than 2.5 times length of coxa 3 with distoventral spur and sparse setae. Femur 14

at of by elongate, with sparse dorsal and ventral setae and few spines; slightly swollen at cement gland, cement gland tube simple, slightly shorter than femoral diameter. Tibia 1 shorter but more setose than femur, elongate, with few larger lateral spines; tibia 2 longer than femur, with numerous dorsal and ventral setae and spines, and lateral spines longer than tibial diameter. Tibial spines show distal denticulation

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at of by (®gure 8E). Tarsus small, with few dorsal and ventral setae and two ventrodistal spines. Propodus elongate, heel with two or three spines, sole normally with ®ve but up to eight shorter spines, the distal pair laterally parallel on the sole. Main claw elongate, two-thirds to three-quarters as long as propodus, auxiliary claws dorsal, 0.22±0.43 as long as main claw.

One teratological male from sample 7709#17 had only two right legs (®gure 8F).

Female. (Predominantly based on gravid female of 4.02 mm trunk length from 14

at of by Discovery sample 10105#1.) Generally similar to male, but without cement gland or tube; oviger (®gure 6B, D) much smaller and less developed (note comparative male and female ®gures in ®gure 6 are to the same scale), without strigilis, proximal four articles naked, distal articles sparsely setose, the setae all directed distally. Gravid females with numerous eggs, predominantly in legs but also occasionally in lateral processes, within chelifora and within abdomen.

Protonymphon larva. (Removed from male of 2.74 mm trunk length from Discovery sample 9801#61; ®gure 8G.) Flaccid, with elongate chela ®ngers, simple spines distally on chelifora, distally on larval legs and at base of larval legs. No elongate ®laments distally on larval legs (as characteristic of Phoxichilidiidae ).

Comparisons with other species

Pallenopsis profundis is known only from the poor-condition holotype, drawings of which were prepared by C. Allan Child of the Smithsonian Institution, and are reproduced herein (®gures 9, 10) with his generous permission. The morphometrics of this species are entirely compatible with the data and variation described for P. tritonis , although it is a larger animal; it is described (e.g. Hilton, 1942; Hedgpeth, 1949) as having a particularly long abdomen, but, as shown above, the abdomen of P. tritonis elongates exponentially with the size of the animal, so this feature would also be compatible. However, the spines on the tibiae are not denticulate (C. Allan 14

at of by

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at of by Child, personal communication), so it would appear inappropriate to synonymize Hilton’s species without more material of this size or from this locality.

Of the other members of the `tydemani -group’, Pallenopsis tydemani Loman, 1908 has a vestigial ocular tubercle without eyes, a proboscis not more than half as long as the trunk, more than ten propodal sole spines, and a more slender main claw; the specimen of `P. tritonis ’ recorded by Bamber (1983) can now be attributed to P. tydemani . Pallenopsis californica Schimkewitsch, 1893 has a proboscis less than half as long as the trunk length, chela ®ngers about twice as long as the palm, auxiliary claws about 0.15 times the slender main claw, and a proximal propodal heel spine more than twice as long as the propodal diameter (see Stock, 1975). Pallenopsis stylirostris Hedgpeth, 1949 is in most respects very similar to P. tritonis , but has a long, tapering proboscis more than 0.8 times the trunk length but which is not swollen centrally, nor is it overreached by the chelifora ( Hedgpeth, 1949: 278 ± 280). Pallenopsis richeri Bamber (in press) has a relatively shorter proboscis, a chelifore scape ratio>1.3, less spinose leg articles with the spines not denticulate, and a distinct conformation of the female oviger (male unknown) (Bamber, in press, ®gure 1E).

Conclusions

Pallenopsis (Bathypallenopsis) tritonis is a species showing a wide range in its morphometrics, not related to size or gender. It is widespread, occurring throughout the north Atlantic and north Paci®c, and at depths ranging from 344 to 7280 m (the deepest recorded depth for a pycnogonid), where it associates with gelatinous members of the plankton. Pallenopsis holti , P. paci W ca and P. stschapovae are junior synonyms of P. tritonis , as P. profundis may also prove to be.

The proximal orientation of spines and setae on the male oviger has been reported in other species of Pallenopsis (e.g. Bamber, in press) and, together with a welldeveloped strigilis, would appear to be an adaptation for retaining the eggs and/or larvae.

This analysis reēcts the advantage s of collections of material, in that samples covering some 20 years have been necessary to gather enough specimens for a su cient analysis of intraspeci®c variation, which is commonly poorly known in pycnogonids (but see also Bamber, 1982).

Acknowledgements I am very grateful to Dr C. Allan Child for correspondence over these species,

14 and for kindly supplying his drawings of the Pallenopsis profundis holotype; also to Dr John Mauchline for kindly donating the Rockall Trough material, to Mike Thurston for sample site details, and the o cers and crews of RRS Discovery and at staOE at IOS, who were involved with the collection and sorting of the samples from which the material analysed here derived .