Coralaxius nodulosus

Coralaxius nodulosus (Meinert, 1877)

Axius nodulosus Meinert, 1877: 212.

Coralaxius abelei Kensley & Gore, 1981: 1278, figs 1–6.

Coralaxius abelei – Coelho & Ramos-Porto 1991: 68; Serejo et al. 2006: 312; Alves et al. 2008: 52.

Coralaxius nodulosus – Sakai & de Saint Laurent 1989: 11; d’Udekem d’Acoz 1999: 153; Ngoc-Ho 2003: 454.

Vitória–Trindade Seamounts specimens. 5 males, cl 2.3–2.5 mm, 9 females, cl 2.0– 3.2 mm, 1 ovigerous female, cl 4.4 mm (MZUSP 39503), R / V “Marion Dufresne”, TAAF MD55 / Brésil 1987 Expedition, Brazil, off Espírito Santo, Vitória-Trindade Seamount Chain, 20º41’S– 37º49’W, Vitória Bank, stn 10, DC24, 48 m, coll. M. Tavares, 13.v.1987. 1 male, cl 3.3 mm (MZUSP 39502), idem, 20º35.8’S– 37º27.4’W, Vitória Bank, stn 11, CP25, 65 m, coll. M. Tavares, 14.v.1987. 1 male, cl 1.9 mm, 1 female, cl 3.2 mm (MZUSP 39504), idem, 20º25’S– 36º42’W, Montague Bank, stn 14, DC27, 81 m, coll. M. Tavares, 14.v.1987. 1 male, cl 4.9 mm (MZUSP 39501), PS/ V “Astro Garoupa”, REVIZEE, Brazil, Espírito Santo, Vitória-Trindade Seamount Chain, 20º29’13.2”S– 36º06’10.8”W, Jaseur Bank, stn 23 R, DR, 50-60 m, 12.vii.2001.

Comparative material examined. Female, cl 4.0 mm (MZUSP 39500), PS/ V “Astro Garoupa”, REVIZEE, Brazil, Espírito Santo, 19º45’36.0”S– 39º31’37.2”W, stn 27 R, DR, 60 m, 28.vi.2001. male, cl 3.5 mm (MZUSP 39499), 19º16’19.2”S– 38º01’08.4”W, stn 20 R, DR, 67 m, 28.vi.2001.

Distribution. United States (South of Florida), Belize (Carrie Bow Cay, Curlew Cay), Jamaica, Costa Rica and Brazil (Rocas Atoll; Abrolhos Bank; Seamounts off coast of Bahia and Espírito Santo: Besnard, Eclaireur, Vitória, Montague, Jaseur, Davis, Almirante Saldanha; Martin Vaz Islands), 6–270m (Coelho & Ramos-Porto 1991; Kensley 1994; Serejo et al. 2006; present study).

Remarks. Kensley & Gore (1981) proposed the monotypic genus Coralaxius to accommodate a new species, C. abelei, from the western Atlantic (Florida and Belize). Sakai & de Saint Laurent (1989) transferred Axius nodulosus Meinert, 1877 to Coralaxius, a species originally described from the North Sea (off Nymindegab, Denmark). Upon examination of the holotype of A. nodulosus and abundant material previously assigned to C. abelei, Kensley (1994) considered that Meinert’s specimen was “unquestionably a mature male of C. abelei ” and merged it into the synonymy of A. nodulosus. His argument was summarised and supported by Ngoc-Ho (2003). Unfortunately, Kensley never illustrated the holotype of A. nodulosus.

Also based on abundant material of C. abelei and, supposedly, on the holotype of Axius nodulosus, Sakai (2011) argued that C. nodulosus differs from C. abelei in bearing no teeth arranged in a semi-circle (corona) on the gastric region of the carapace (whereas such a corona is distinct in C. abelei), and further differs from it in having simple appendix masculina on the second male pleopod (vs setose, distally bilobed appendix masculina in C. abelei) (cf. Sakai 2011: figs. 48, 49C, B, 50F; Kensley & Gore 1981: figs. 1, 6h). Based upon these morphological characteristics, Sakai (2011) erected the monotypic genus Meinertaxius for Axius nodulosus s. s.

However, it is not clear whether Sakai’s (2011) description and illustrations actually correspond to the holotype of Axius nodulosus examined by Poulsen (1940) and Kensley (1994). Sakai (2011) mistakenly referred to Meinert’s specimen as the “ lectotype ” and his illustrations and statement that the rostrum in A. nodulosus is “unarmed laterally” contradict Poulsen’s (1940) redescription and illustration of the holotype of A. nodulosus, in which he mentioned that “... one or two thorns are present on the carapace near the base of the rostrum.” (See also Poulsen 1940: fig. 2). Kensley (1994) agrees with Poulsen in describing the holotype of A. nodulosus as having a “single small lateral spine at [the] base of the rostrum”, but he never reported the rostrum to be damaged nor commented on Poulsen’s (1940: 210) statement that in the holotype the rostrum is “somewhat mutilated”. Sakai (2011: fig. 49B–C) illustrated the rostrum undamaged in A. nodulosus.

Furthermore, the differences between the type of A. nodulosus and species of Coralaxius are no more than would be expected between a post-larva and an adult: it lacks convincing gastric sculpture, has an extra maxilliped 3 flagellar article and has an undeveloped pleopod 2 (G.C.B. Poore, pers. comm.).

Axius nodulosus s. s., supposedly collected from off Nymindegab (Denmark), is known from the North Sea only from the holotype and has never been collected there again, or elsewhere in the North Sea, for over a century. Kensley (1994) suggested that the holotype of A. nodulosus actually came from the Caribbean Sea (perhaps from the Danish West Indies) where the species is very abundant. We follow Kensley (1994) in considering Axius nodulosus Meinert, 1877, a subjective older synonym of Coralaxius abelei Kensley & Gore, 1981. Therefore, Meinertaxius Sakai, 2011 is here synonymised with Coralaxius Kensley & Gore, 1981, as they have subjectively the same type species.

Further south, C. nodulosus has been reported as C. abelei from the Brazilian coast between 40 and 270 m depth. The present record from the Vitória-Trindade Seamount Chain partially fills the distribution gap between the continental shelf (Coelho & Ramos-Porto 1991; Coelho 1997; Coelho et al. 2007; present study) and the remote oceanic island of Trindade (Serejo et al. 2006; Tavares et al. 2017).