Caromiobenella helgolandica ( Claus, 1863 )

Caromiobenella helgolandica ( Claus, 1863) View in CoL

( Fig. 7 View FIGURE 7 )

Monstrilla nichollsi Davis, 1949: p. 247

M. dakinensis Davis, 1949: p.247

Diagnosis of Australian specimens. Diagnosis based on unscaled illustrations of individuals from New South Wales by Dakin & Colefax (1940), and on individuals from an unspecified site in South Australia by Nicholls (1944). Body with long, cylindrical cephalothorax, the latter 58% of total body length. Pedigerous somites 2–5 tapering posteriorly. Urosome comprising fifth pedigerous somite, genital double-somite, preanal somite, and anal somite carrying pair of caudal rami. Fifth pedigerous somite as long as genital double-somite. Anal somite about half as long as preanal somite. Caudal rami short, subquadrate, armed with 5 subequally long setae. Antennules 5-segmented, segments 1–3 clearly divided. Some identifiable setal elements (sensu Grygier & Ohtsuka, 1995) depicted, as follows: first segment with short, spiniform element 1; segment 2 with long element IId and 2–3 elements of the 2v group; third segment with elements 3 and IIId; fourth segment carrying elements 4v1, Vd, Vv, and 4aes; apical elements 6 1 and 6 2 present, latter apparently short, spiniform. Fifth leg represented by thick subrectangular exopodal lobe armed with two subequally long distal setae; inner margin of lobe with weak, smooth proximal expansion.

Remarks. In his preliminary revision of the Monstrilloida, Davis (1949) introduced two new names, Monstrilla dakinensis Davis, 1949 and M. nichollsii Davis, 1949 based on the incomplete drawings by Dakin and Colefax (1940) and Nicholls’ (1944) reports on Australian monstrilloids, respectively. We examined the available data and illustrations and propose to synonymize these two names with C. helgolandica . There are several points supporting our decision, i.e.: (1) the widespread distribution of C. helgolandica , known from all geographic regions ( Thomas et al. 2022; Zavarzin & Suárez-Morales 2024), including adjacent areas of the East Indies (see Scott 1909; Sewell 1949); thus, its occurrence in Australian coastal systems is expectable, (2) the body proportions, with a moderately elongate and slender cephalothorax more than 55% of the total body length, and antennules between 30 and 40 % of cephalothorax length, (3) the ovigerous spines are relatively short in C. helgolandica , not reaching beyond the distal end of the caudal setae (see Scott 1909; Sars 1921; Sewell 1949; Zavarzin & Suárez-Morales 2024) similar to depictions of the Australian specimens ( Dakin & Colefax 1940; Nicholls 1944), (4) fifth leg represented by a single lobe armed with two distal, subequally long setae with an inner protuberance likely representing a residual endopodal lobe. The fifth leg has some variation in the different reports of this species, with a very weak inner protuberance in some instances (see Scott 1909; Sewell 1949) and more defined in others, as in the depiction for M. dakinensis ( Dakin & Colefax 1940, fig. 205Fb) and M. nichollsii ( Nicholls 1944) ( Fig. 7B View FIGURE 7 ). It appears that Dakin & Colefax (1940) did not have access to Scott’s (1909) or Sars’ (1921) illustrations of C. helgolandica , which included illustrations of the fifth leg ( Fig. 7D, E View FIGURE 7 ). Sewell’s (1949) report from the East Indies was not yet available for comparison. They argued that their only female specimen remained as Monstrilla sp. because “… it does not appear to fit in any of the species described ” ( Dakin & Colefax 1940, p. 117). There are only three other species of Monstrilla with this armature pattern on the fifth leg: the females of the recently described M. annulata Suárez-Morales, 2024 , from a Mexican Caribbean reef system (see Suárez-Morales 2024), M. leucopis Sars, 1921 from Norway and the Gulf of California ( Suárez-Morales 2010; Suárez-Morales & Velázquez-Ornelas 2023), and M. wandelii Stephensen, 1913 from Groenland ( Park 1967). Other species with a fifth leg carrying only two subequal setae are the Indian Ocean M. conjunctiva , the Caribbean M. elongata Suárez-Morales, 1994 and the recently described M. annulata Suárez-Morales, 2024 .

Furthermore, Nicholls (1944) stated that the two female specimens examined by him were most similar to M. mixta T. Scott, 1914 , due to the structure of the fifth leg but the latter carrying three setae vs. two setae in the Australian individuals. In our opinion, the Australian Monstrilla females depicted by Nicholls (1944) could hardly be confused with M. mixta because it has a clearly different leg 5 structure and a much longer set of ovigerous spines (T. Scott 1914, pl. XVI, figs 8–12), different from the illustrated Australian specimens. It is reasonable to assume that Sewell’s (1949) report was not available to these Australian researchers to compare their material with his figures of the female of M. conjunctiva ( Sewell 1949, fig. 38C), in which case the resemblance (at least of the fifth leg setation) would have been noticed. Because of the evident lack of comparative data, Nicholls (1944, p. 56) decided against naming a new species. Furthermore, Davis (1949) did not provide further comments or comparisons to validate the names M. dakinensis and M. nichollsii , both of which should be considered as junior synonyms of C. helgolandica . With this analysis we can conclude that C. helgolandica occurs in unspecified localities of South Australia and coastal waters of New South Wales. It is likely that C. helgolandica will be revealed as a species group comprising distinct species with restricted distributional patterns in Australia, an idea shared by previous authors ( Grygier & Ohtsuka 1995; Suárez-Morales 2010, 2011). New sampling attempts in southern Australia are expected to obtain additional material to expand the knowledge about this species in Australian coastal systems.

Genus Monstrilla Dana, 1849