Pallenella smithi, Staples, 2025

Staples, David A., 2025, Pycnogonids, ‘ sea-spiders’ (Arthropoda, Pycnogonida) selected from the collections of the South Australian Museum with descriptions of new species and review of the genus Pallenella., Memoirs of Museum Victoria 84, pp. 1-47 : 36-39

Pallenella smithi sp. nov.

Figure 12a–h. Plate 14a–f u r n:lsid:z o oba n k.org:a ct:4E8 4 C D07-B52D - 423F-9 070 -

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Material examined. Holotype. Male, egg-bearing ( SAM E9451 ). Backstairs Passage (35° 35´S, 137° 55´E), 41 m, Dr. Verco, 19 Jan 1896.

Diagnosis. Pre-ocular cephalon dorsal surface low, rounded, hardly raised, longitudinal cuticular division best-defined on anterior surface, neck short. Eyes rather small for genus, eight lenses. Anal tubercle horizontal. Chela palm conspicuously inflated, fingers robust, shorter than palm, moveable finger slightly shorter than immoveable finger, strongly curved, cutting margins heavily chitinized, touching near tips, gap widening proximally, moveable finger cutting edge recessed proximally. Propodal heel low, with three or four strong spines, sole gently curved, spines random and abundant, claw evenly curved along both margins, reaching to middle heel spine when closed. Second coxa three-times the length of coxa 1.

Description. Leg span about 39 mm. Trunk (plate 14a) smooth, lateral processes 1 and 2 separated by about half own diameter, spacing between subsequent processes diminishing posteriorly, length of lateral processes more than 1.5 times basal width. Pre-ocular surface of cephalon low, rounded, mid-region hardly raised in anterior view, longitudinal cuticular line most evident on anterior surface, fading distally, neck well-defined, shorter than width.

Eye tubercle height about equal to basal width, eight eye lenses, sense organs prominent.

Proboscis (plate 14b) with shallow constrictions at about one-third and two-thirds length, distal-most inflated part with obscure dorsomedian swelling, jaws fringed with setae partly hidden by dark staining, basal arthrodial membrane extended and broad in this specimen.

Figure 12. Pallenella smithi sp. nov., male, holotype (SAMA E9451): a–c, trunk, dorsal, anterior (proboscis extended) and lateral view; d, right chela; e, f, leg 3 and propodus; g, h, right oviger and claw.

Chela (plate 14d) palm bulbous, tips of chela fingers dark, fingers much shorter than palm, immoveable finger slightly longer, outer margin of moveable finger strongly curved, fingers touching near tips, gaping for most of length when closed, spacing increasing proximally, cutting edges both fingers heavily chitinized, without protuberances on inner or outer margins, moveable finger cutting edge strongly recesses at base.

Oviger bases originating immediately in front of first lateral processes but not in contact, directed ventrally, oviger typical of male, segment 5 longest, distal apophysis bearing about eight tiny surface spines, segment 4 next longest, compound spine formula, segments 7–10, 16:14:13:11 (54 spines), distal-most and proximal-most spines off-set, terminal claw little more than half length of segment 10, slightly angled Plate 14. Pallenella smithi sp. nov. male, holotype ( SAMA E9451 ): a–c, trunk, dorsal, lateral and anterior views showing extended proboscis with stained tip; d, chelae; e, leg 3; f, propodus .

outwards, narrow, pointed, both distal margins serrated but difficult to interpret, possibly worn.

Anal tubercle horizontal, inflated, not quite reaching ends of first coxae.

Legs (fig. 12e, plate 14e) with thickened lateral cuticular line running full length to tarsus. Coxa 2, almost three times length of coxa 1, with small inconspicuous subterminal cone on dorsal surface, tibia 2 longest segment, femur slightly curved, longer than tibia 1, tarsus with distal group of about four sharp spines on ventral surface and many scattered smaller spines, propodal heel low, three strong linear spines, proximal-most spine shortest, sole weakly curved, with random and crowded field of sharp spines, claw curved similarly along both margins, reaching to middle heel spine when closed. Gonopores ventral, coxa 2, legs 3 and 4.

Measurements of holotype (mm). Trunk length (frontal margin of cephalic segment to tip of fourth lateral processes), 5.80; width across second lateral processes, 2.67; proboscis length (dorsal), 2.01; greatest diameter proboscis, 0.95; scape length; 1.66; anal tubercle length, 1.08. Oviger (segs 4–10): seg. 4, 2.43; seg. 5, 2.55 (across chord of arc); seg. 6, 0.53; seg. 7, 0.63; seg. 8, 0.46; seg. 9, 0.44; seg. 10, 0.39; claw, 0.18. Leg 3 (anterior side): coxa 1, 0.68; coxa 2, 1.92, coxa 3, 0.61; femur, 4.07; tibia 1, 3.74; tibia 2, 4.90; tarsus, 0.09; propodus, 1.11; claw, 0.76.

Etymology. This species is named for the late Dr Brian J. Smith, Senior Curator, Division of Zoology, Museum of Victoria who actively encouraged and mentored researchers to work on the museum collections.

Remarks. A single group of eggs is held on each of oviger segments 4 and 5. Most eggs are of uniformly dark colouring, but some are bi-coloured (plate 14d). The longitudinal division of the cephalon is most evident on the anterior margin and fades towards the mid-region of the crop (plate 14a). However, the extent of the longitudinal cuticular line can be ambiguous as shown in plate 14a, b). The proboscis has shallow constrictions at about one-third and two-thirds its length and is strongly stained distally, obscuring the presence of setae that may be lining the jaws. In part, the staining, highlights the presence of a dorsomedian swelling on the anterior surface (plate 14c).

This species belongs to a group of five that share robust chela fingers, a strongly curved moveable finger, a horizontal anal tubercle, a low propodal heel with spines arranged linearly and a weakly-curved sole. The other four species in this group are P. ambigua , P. harrisi , P. pachycheira and P. watsonae . Two species are immediately recognized by distinctive characters P. pachycheira by strong annular constrictions at about one-third and two-thirds the lengths of the longer segments of the legs (plate 16d) and P. watsonae by the short, chela fingers with rounded tips and extremely large protuberances on the cutting edges (plate 21a, b). Brenneis et al. (2020) designated several specimens from Eaglehawk Neck, Tasmania as P. cf. ambigua . Pallenella cf. ambigua was recovered as the genetically closest congener to P. harrisi but the authors cautioned that morphological and genetic analyses of both species remain under investigation. The type locality of P. harrisi is Bass Point, NSW and whilst it is easiest to distinguish live specimens by colour markings, morphological differences are less apparent. The authors observed strong morphological similarities with P. cf. ambigua (and the P. ambigua holotype) but noted that the P. harrisi specimens have a proportionately shorter scape, a more inflated chela palm and exceed P. cf. ambigua in chela height and robustness of the fingers ( Brenneis et al. 2020). Considering morphological uncertainties, the authors chose not to distinguish P. cf. ambigua and P. harrisi in their key which can be followed down to couplet 11. Based on available images, the proboscis of P. cf. ambigua ( Brenneis et al. 2020: plate 13B) also appears to be wider, and with a less tapered tip than either the P. ambigua holotype (plate 19c herein) or P. harrisi ( Brenneis et al. 2020, plate 13B´). Apparent differences in proboscis shape aside, the pre-ocular surface of P. harrisi is distinctly divided by what appears to be a conspicuous median cuticular division extending to at least the somewhat cleft apex of the pre-ocular surface (see Arango and Brenneis 2013, Fig. 13C) as opposed to the P. ambigua holotype which has a low, evenly rounded pre-ocular surface with the cuticular division restricted to the anterior surface. The spine counts of the P. harrisi holotype is 51, and the P. ambigua holotype is 44, which further supports their independent status. The oviger spine count of P. cf. ambigua was not recorded. It is interesting to observe that the chela moveable finger of P. harrisi is described with a mid-point lobe on the cutting edge and Stock (1956) described the moveable finger of P. ambigua as having an insignificant, central, rounded protrusion on the inner side, but in neither case was this figured by the authors. Additional images of the P. ambigua holotype are provided for comparison (plate 19a–f).

A compelling argument for assigning this specimen to P. harrisi could be mounted based on the sharing of a bulbous chela palm and the similarity in the number of oviger spines ( P. harrisi , 51 spines versus P. smithi sp. nov., 54 spines). There are however, a number of differences that support their independent status: (1) the propodus of P. harrisi is more elongate and has a broader claw, with a more rounded and swollen outer surface (compare Arango and Brenneis 2013, fig. 13D with plate 14f), (2) the proboscides are dissimilar (compare Brenneis et al. (2020, fig. 13B’) with plate 14c herein, (3) no mid-point lobe or protuberance is present on the cutting edge of the moveable finger (in outer or inner view) of this specimen, (4) the pre-ocular surface mound of P. harrisi appears to be elevated and more acute, compared to the rounded surface of P. smithi (compare Arango and Brenneis 2013 fig. 13C with plate 14b herein). There is no record of the distinctive colour form of P. harrisi south of Montague Island on the south coast of NSW and it is reasonable to assume that in the absence of notes on the label, this South Australian specimen lacked the striking colours and body markings of the NSW specimens. Of course, that species may be present in other colour forms. This male agrees with the P. ambigua male holotype in the shape of the proboscis and chela (compare plate 19c, d; with P. smithi plate 14c, d herein). There are however, a number of differences that distinguish the species and which can be summarized as follows: (1) the total number of oviger compound spines in P. smithi is greater (54 spines versus 44 spines in P. ambigua ), (2) the propodus of P. smithi is more strongly curved and with longer, more slender heel spines (compare plate 14f with P. ambigua plate 19F), (3) the propodal claw of P. smithi is more slender and with inner and outer margins equally curved, versus outer margin more strongly curved and inner margins straight for most of its length in P. ambigua , (5) based on Stock’s measurements, coxa 2 of P. ambigua is slightly more than twice the length of coxa 1 (2.1 times) versus coxa 2 of P. smithi is closer to three times (2.8 times) the length of coxa 1. Considering more recent observations, Bamber’s (2005) record of P. ambigua from Esperance Bay will require confirmation.