Pallenella Schimkewitsch, 1909

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 : 19-20

Genus Pallenella Schimkewitsch, 1909

Discussion. Brenneis et al. (2020) identified two Tasmanian forms which they designated P. cf. chevron , and P. cf. ambigua . Both forms shared ambiguous characteristics and in the absence of molecular data for P. ambigua and P. chevron it was not possible to arrive at unequivocable species determinations for those specimens. The status of P. cf. ambigua remains under investigation pending additional material. The points of difference between P. chevron and P. cf. chevron have not been clearly established. The pattern of red lines in P. cf chevron were discussed in detail and were described as an “invariable” feature of the Tasmanian specimens although, the pattern was also observed to be slightly deviating. The authors also had difficulty separating P. baroni and P. chevron due to overlapping ranges of diagnostic characters and placed greater attention to comparing P. baroni with P. cf. chevron . The variation in the length-toheight proportions of the chela amongst the collection was cited as a striking feature of P. cf. chevron and in some cases, specimens featured a “palm almost as elongated as in P. baroni ”. The authors documented extensive intraspecific variations within the P. baroni collection some of which were consistent with ontogenetic and allometric changes but insufficient attention was devoted to the identification of characters that distinguish P. baroni from its congeners. Pallenella baroni seems to share a closer relationship with the P. chevron holotype than it does with P. cf. chevron . Brenneis et al. (2020, in key) noted that the leg length of P. cf. chevron can be> 18 mm, which is considerably longer than the leg lengths of either the P. chevron or P. baroni holotypes ( P. chevron 13.02 mm and P. baroni 14.2 mm) and although the oviger spine count of P. cf. chevron was not recorded, the difference in the spine count of P. baroni (49 spines) and the P. chevron holotype (45 spines) is not significant. The oviger claw in both P. baroni and P. chevron (and P. cf. chevron ) share a rounded tip. Differences in live colour markings appears to be the only reliable characteristic that distinguishes P. chevron from P. baroni . The dark crust covering the distal proboscis and chelae of P. baroni is not regarded as diagnostic. The authors found that the presence of a “small protruding bump” half-way along the cutting edge of the moveable finger of P. baroni ( Brenneis 2020 Fig. 10D) is a variable character, but suffice to say, a bump is not evident on the cutting edge of the P. chevron holotype (plate 20d). Based on Brenneis et al. (2020 Figs10A–A”’, 11B–B”) the pre-ocular cephalon mound of P. cf. chevron and P. baroni is more prominent (but not acute), than appears to be the case in the P. chevron holotype (fig. 20b herein) and may be a point of difference, but not easily defined in a key. Based on Staples’ figures of P. chevron ( Staples 2007, Fig. 2G, H) and the images of P. cf. chevron ( Brenneis et al. 2020, Fig. 11C), the moveable finger is more strongly curved and the gap at the base of the fingers is wider in P. cf. chevron . The descriptions of the propodal heel spination of P. baroni and P. cf. chevron agree closely, particularly the presence of a smaller pair of distal spines. Presumably the paired spines sit side-by-side rather than in a linear arrangement as clearly illustrated by Staples (2007, Fig. 2J) but unfortunately, the images provided by Brenneis et al. (2020) do clarify the arrangement. At a time of diminishing taxonomic expertise and a greater reliance on molecular analyses, the unambiguous identification of voucher specimens is critical when selecting a particular specimen for molecular analysis but the unresolved variability noted in the P. baroni collection challenges that objective considerably. The morphological boundaries that define P. baroni are unclear. To construct a key here, the arrangement of the propodal heel spines and the presence or absence of a raised section, or “bump”, on the cutting edge of the chela moveable finger have been selected on a provisional basis to distinguish P. chevron and P. baroni . Additional images of the P. chevron holotype are attached to assist with comparison (plate 20a–f).

The possibility of hybridization within this genus should not be arbitrarily dismissed. Aside from the sharing of arborescent bryozoans as host substrates, sexual characteristics such as the placement and number of genital pores, oviger shape, and probable mating position, are remarkably consistent amongst congeners and suggest a low barrier to crossbreeding within the genus.

Arango, (2009) assigned a single female from Albany Western Australia to P. chevron but the distinctive chevron markings were not evident. That specimen had 38 oviger spines opposed to 45 spines in the holotype .

The number of eye lenses is easily over-looked and consequently it is not appropriate to use the lenses as a diagnostic character until all species recorded with four lenses have been re-examined. In the meantime, the number of lenses (either four or eight) confirmed by this analysis are recorded in the key to assist with discussion and identification rather than for use as a reliable systematic character generally. Hopefully, future workers can fill in the gaps. Where the number of lenses is not recorded, four lenses are assumed to be present pending review. For the key, the anal tubercle is regarded as being horizontal if it is not inclined upwards.

Live colour observations (where known) are recorded in the key.