Pallenopsis rotunda, 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 : 521-524

Pallenopsis rotunda n. sp.

urn:lsid:zoobank.org:act:C7FDF5A4-B01C-467C-9D82-261ADF2146B8

( Fig. 3 , 4 )

Material examined. MNA (11029) holotype, one adult male, Victoria Land Transect cruise ( Italica XIX), Cape Hallett , stn. H-out 4 bis, 72°18.4' S 170°26.7' E, 234 m depth, Van Venn, 12 Feb 2004 . BECA (P.1500) one larvigerous male, Victoria Land Transect cruise ( Italica XIX), Cape Hallett , stn. H-out 4 bis, 72°18.4' S 170°26.7' E, 234 m depth, Van Veen, 12 Feb 2004 . MNA (11030), one adult female, Victoria Land Transect cruise ( Italica XIX), Cape Hallett, stn. H-out 3B, 72°17'.1 S 170°25'.8 E, Agassiz trawl, 255–261 m depth, 4 Feb 2004 .

Diagnosis. Proboscis cylindrical, slightly widened at the end. Lateral processes in contact proximally and along most of their length. Chelae fingers shorter than palm width, wedge-shaped and touching along their length when closed; movable chelae finger with setose pad. Palp in contact with oviger basal process. Legs with long setose setae mainly placed on dorsal and lateral surfaces, not arranged in rows. Auxiliary claws longer than half claw length.

Description of the holotype (male). Size moderate, leg span 94.5 mm. Proboscis mostly cylindrical, slightly up-curved, with a little narrowing in the middle and greatest diameter at the bulbous end, distally equipped with short spines.

Trunk fully segmented, with lateral processes in contact proximally, slightly separated distally, V-shaped. Tiny bilaterally paired dorsal tubercles on the three first segments with some scarce long setose setae. Lateral processes with dorso-distal small tubercles, with long setose setae. Cephalic segment tapering anteriorly at chelifores’ insertion.

Abdomen long, up-curved, with long setose setae on distal half, and slightly widened on its distal half.

Ocular tubercle at anterior part of cephalic segment, taller than wide, with a pointed cone. Four eyes of similar size, anterior pair slightly lower than posterior pair.

Chelifores large, with two-articled scape. First scape article longer than second one, both with dorsal and dorso-distal short spines; the second one wider distally. Chela palm longer than wide, with inner latero-distal fringe of short spines. Fingers shorter than palm width, wedge-shaped, smooth and touching when closed. Spinose pad present at base of movable finger.

Palps one-articled, rounded, in contact with oviger basal process.

Oviger ten-articled. Fourth article with an external pore on its proximal half, fifth article is the longest oviger article. Strigilis with higher density of setae than more proximal articles.

Walking legs with long setose setae mainly on the three longest articles, on dorsal and lateral surface, not arranged in rows. First coxa with dorso-distal ornamentation similar to lateral processes; second and third coxae with setae on ventro-distal surface. Second coxa longer than first and third coxae together. Second tibia the longest article, with ventro-distal long spines. Tarsus short, with ventro-distal long spines. Propodus with a row of five spines in the proximal half, increases in size from proximal to medial part; distal half with several spines not arranged in a row. Main claw longer than half propodus length; auxiliary claws longer than half main claw length. Cement gland tube shorter than half femur diameter. Sexual pores located ventrally on second coxa of third and fourth legs.

Measurements of holotype (mm). Length of trunk (tip of the cephalic segment to the tip of fourth lateral processes): 8.7. Width of trunk across second lateral processes: 7.1. Length of cephalic segment: 5.0. Length of proboscis: 4.0. Basal diameter of proboscis: 1.8. Greatest diameter of proboscis: 2.2. Length of abdomen: 3.6. Length of left chelifore scape: 5.1; length of scape articles: 2.9, 2.2. Length of left palm: 2.4. Length of left chelae: 0.5. Length of left palp: 0.8. Length of third left leg: 43.7; length of articles of leg 3: coxa 1 2.1, coxa 2 4.7, coxa 3 2.1, femur 1 9.5, tibia 1 8.7, tibia 2 11.8, tarsus 0.5, propodus 2.7, claw 1.6, auxiliary claws 1.0. Length of right oviger: 14.6; length of oviger articles (first to 10th): 0.63, 1.46, 1.67, 2.71, 2.92, 1.33, 1.25, 1.04, 0.83, 0.71.

Variability. The female specimen (MNA 11030) has fewer setae than the holotype (MNA 11029), and they are also shorter. In the female, the ovigers are shorter ( Fig. 4F ), less setose and straighter than those in the males. Sexual pores in the female are located ventrally on second coxa in all walking legs.

Distribution. At present, Pallenopsis rotunda n. sp. is known from Victoria Land, from Cape Hallett, at a depth of 234– 261 m.

Etymology. The species epithet derives from rotundum (L.) because of the general rounded and compact appearance of the body.

Remarks. Pallenopsis rotunda n. sp. is comparable to P. vanhoffeni Hodgson, 1915 , P. hodgsoni Gordon, 1938 and P. pilosa ( Hoek, 1881) as they share the following set of characters: (1) body and walking legs with long and short setae; and (2) chelae fingers wedge-shaped and touching when closed.

These four species are very setose but this ornamentation shows different arrangement on the surface of the walking legs. The long setae on the walking legs of P. pilosa are placed on dorsal, lateral and ventral surfaces ( Child 1995; Hoek 1881; Pushkin 1993), while in the three other species the long setae are mainly on dorsal and lateral surfaces. These long setae are arranged in rows in P. vanhoffeni , but random in P. hodgsoni and P. rotunda n. sp.

Gordon (1938: fig. 3) showed different microscopic structure of the long setae on the walking legs of P. pilosa , P. vanhoffeni and P. hodgsoni . She illustrated long setae with minute setules in P. vanhoffeni and P. hodgsoni (although both species showed different arrangements), but P. pilosa showed long setae without the tiny setules. Pallenopsis rotunda n. sp. also has long setae with similar minute setules.

The presence of a setose pad at the base of the movable finger in Pallenopsis rotunda n. sp. is a differential character between this species and the three other species closer morphologically.

The main additional differences between the species here compared have been summarized in Table 2 .

Figures

FIGURE 3. Pallenopsis rotunda sp. nov. Holotype, male. A Dorsal view (showing the relative size and distribution of spines); B lateral view. Scale bars: 3 mm (A, B).

FIGURE 4. Pallenopsis rotunda 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 Male oviger (due to fixed position of articles in this appendage, the number of articles and apparent proportions in the illustration could not reflect real relations, see text for full measurements and ratios); G Female strigilis. Scale bars: 3 mm (A); 1 mm (C, E, G); 0.5 mm (D); 2 mm (F).