Pallenopsis gracilis, Cano-Sánchez & López-González, 2019

Cano-Sánchez, Esperanza & López-González, Pablo J., 2019, Two new species and new findings in the genus Pallenopsis (Pycnogonida: Pallenopsidae) with an updated identification key to Antarctic and Sub-Antarctic species, Zootaxa 4585 (3), pp. 517-530 : 518-521

Pallenopsis gracilis n. sp.

urn:lsid:zoobank.org:act:175B8998-91C7-47A7-9497-09F3F00C49F0

Figures 1 , 2

Material examined. MNA (11028) holotype, one ovigerous male, Victoria Land Transect cruise ( Italica XIX), Cape Russell, stn. SMN 1E, 74°43.4’S 164°14.1’E, 338–350 m depth, Agassiz trawl, 20 Feb 2004 .

Diagnosis. Proboscis cylindrical, slightly up-curved. Lateral processes separated by their own diameter (Ushaped). Ocular tubercle pointed forward, with the anterior pair of eyes larger than the posterior one. Chelae fingers subequal or shorter than palm width, wedge-shaped and touching when closed along its entire length; movable chelae finger with setose pad. Palps elongated stumps, arising from the sides of the neck at about half of its length (not in contact with oviger basal process). Auxiliary claws about half claw length.

Description of the holotype (male). Size moderate, leg span 142 mm. Proboscis mostly cylindrical, slightly up-curved, about half trunk length, distally equipped with short spines.

Trunk fully segmented, with lateral processes widely separated, about their own diameter. Segmentation ridge with fine short spines on tiny, bilaterally paired dorsal tubercles. First, second and third segments ventrally slightly inflated. Lateral processes with fine short dorsal and dorso-distal spines. Fourth segment shorter than third segment. Cephalic segment tapers toward the anteriorly positioned ocular tubercle.

Abdomen long, angle ca. 45° upward but slightly down-curved, with short spines on entire surface, and slightly widened on its distal third.

Ocular tubercle taller than wide, and topped by a pointed slightly forward-tilted cone. Four big eyes, anterior pair slightly larger and lower than posterior pair.

Chelifores large and with two-articled scape. First scape article longer than second one, both with short spines throughout but longer on the distal one. Chela palm longer than wide, spinose with a fringe of short setae along the inner side of the palm. Fingers shorter than palm width, placed more or less perpendicular to palm, wedge-shaped, smooth and touching when closed. Setose pad present at base of movable finger.

Palps one-articled, longer than wide. Inserted distinctly separated from oviger basal process.

Oviger ten-articled. Fourth and fifth articles curved, fifth article is the longest oviger article. Strigilis with short setae (most of them shorter than article diameter). Tenth article short, cone-like.

Legs with short spines along entire length. Second coxa longer than first and third coxae together. Second tibia the longest article, with spines increasing in length and density distally, with long spine ventro-distaly. Tarsus short, with ventro-distal long spines (medial thicker and taller than the others). Propodus slightly curved, broader proximally with one short and three long heel spines in a row, followed by heterogeneous random spines along the distal two thirds of the sole. Main claw longer than half propodus length; auxiliary claw about half main claw length. Cement gland tube shorter than half femur diameter. Sexual pores located ventrally on second coxa in third and fourth legs.

Measurements of holotype (mm). Length of trunk (tip of the cephalic segment to the tip of fourth lateral processes): 10.9. Width of trunk across second lateral processes: 6.8. Length of cephalic segment: 5.3. Length of proboscis: 5.1. Basal diameter of proboscis: 2.5. Greatest diameter of proboscis: 2.5. Length of abdomen: 4.6. Length of left chelifore scape: 5.6; length of scape articles: 3.0, 2.6. Length of left palm: 2.0. Length of left chela: 1.1. Length of left palp: 1.2. Length of third left leg: 67.6; length of articles of leg 3: coxa 1 2.0, coxa 2 6.0, coxa 3 2.2, femur 16.6, tibia 1 13.9, tibia 2 21.3, tarsus 0.6, propodus 3.0, claw 2.0, auxiliary claws 1.0. Length of left oviger: 13.7; length of oviger articles (first to 10th): 0.93, 1.8, 1.26, 2.33, 2.66, 1.26, 1.2, 1.2, 0.66, 0.4.

Distribution. At present, Pallenopsis gracilis n. sp. is only known from its type locality at Victoria Land, at a depth of 338– 350 m.

Etymology. The species epithet derives from gracilis (L.) because of its slender and stylized body shape.

Remarks. Pallenopsis gracilis n. sp. is only comparable to P. hiemalis Hodgson, 1907 , P. boehmi Schimkewitsch, 1930 and P. buphtalmus Pushkin, 1993 as they share the following set of characters: (1) chela fingers wedge-shaped and touching when closed; (2) movable chelae finger with setose pad; (3) palp longer than wide; and (4) slender body, with similar separation of lateral processes on proximal and distal part, U-shaped.

In P. hiemalis , the propodus has spines of similar length along the entire sole and the lateral processes are equipped with dorso-distal processes ( Gordon 1932; Pushkin 1975), while in the other above listed three species the propodus has heel spines longer than soles spines and there are no tubercles on the lateral processes.

Proboscis morphology is a differential character between P. boehmi on the one hand, and P. buphtalmus and Pallenopsis gracilis n. sp. on the other. In the first species the proboscis has a flat mouth area, giving a truncated end, and it is slightly widened in the middle and at the end, while in P. buphtalmus and Pallenopsis gracilis n. sp. the mouth area is rounded and the proboscis has a similar diameter along its entire length. Moreover, the anterior and the posterior pairs of eyes overlap along the proximo-distal axis of the ocular tubercle in P. boehmi (see Stock 1973a: 350, figs. 3 and 4), partially overlapping in two other species (see Pushkin 1993: 243, fig. 215; and Fig. 1 , this paper).

Although Pallenopsis buphtalmus and P. gracilis n. sp. are closer morphologically, Pushkin’s species has a dorsally flattened neck that does not taper distally and its ocular tubercle is as tall as it is wide and obliquely truncated, while in P. gracilis n. sp. the neck is convex dorsally, tapering distally, and the ocular tubercle is taller than it is wide and is pointed forward. Moreover, the dorsal area of short spines on the segmentation ridge of the three first segments are more or less rectangular in P. bupthalmus , but on two dorsal tiny tubercles in P. gracilis n. sp. (see also Table 1 for additional differences between these two species).

The main differences among the four species here compared have been summarized in Table 1 .

* Pallenopsis hiemalis has been a controversial species. The contributions of Child (1994), checklist of Munilla & Soler

(2009), or databases of Bamber et al (2018) included without further discussion this species as a synonym of P.

patagonica. Authors as Gordon (1932; 1944) or Pushkin (1975; 1993) consider P. hiemalis as a valid species. Indeed,

Gordon (1932) examined a high number of specimens attributed to P. patagonica (about 62) and she considered that only

the type specimen of P. hiemalis has differential characters to those of P. patagonica : the size and arrangement of

propodus spines, and the tubercle of the lateral processes and the relatively palps’ development. Later, in the same way,

this author ( Gordon 1944) pointed out that the propodus of P. hiemalis has not “heel”, but has spines along entire ventral

surface. Pushkin (1975; 1993) described this species using newly collected specimens, adding the structure and armature

of the walking legs 7th and 8th articles as different from all members of the genus.

** Stock (1973b) redescribed this species due to the fact that the original description was based on Böhm’s (1879)

imperfect notes, but this information is not provided by Stock.

Figures

FIGURE 1. Pallenopsis gracilis sp. nov. Holotype, male. A lateral view; B Dorsal view (showing the relative size and distribution of spinules). Scale bars: 0.5 mm (A, B.)

FIGURE 2. Pallenopsis gracilis sp. nov. Holotype, male. A Third leg, right; B Cement gland tube (detail from A); C Palm + Chela of chelifore; D Palp; E Distal third leg articles; F Oviger (due to fixed position of articles in this appendage, apparent proportions in the illustration could not reflect real relations, see text for full measurements and ratios). Scale bars: 6 mm (A); 0.5 mm (C, D); 1 mm (F, E).