Tanaoa serenei

Tanaoa serenei (Richer de Forges, 1983)

(Figs. 1B, D, 4E, F, 5A)

Randallia serenei Richer de Forges, 1983: 634, Figs.1–4; Poupin & Richer de Forges 1991: 211. “ Randallia ” serenei — Paulay et al. 2003: 497.

Tanaoa distinctus — Galil 2003: 402 (part), Figs. 1B, 3 C, D.

Material examined. 1 male (32.9 x 33.2 mm) (ZRC 2000.565), Tumon Bay, Guam, 400 m, in fishtrap, coll. S. Annesbury, October 1999.

Comparative material. Tanaoa distinctus (Rathbun, 1894): 1 male (38.4 x 37.5 mm), 1 female (ZRC 2000.535), station 34, TC33, Hawaiian Islands, coll. Townsend Cromwell.

Colour. In life, the species is a dirty white overall with scattered orange granules (Fig. 5 A).

Remarks. Galil (2003) synonymised Randallia serenei Richer de Forges, 1983, with R. distincta Rathbun, 1894, and referred the latter to her new genus Tanaoa. She commented “Richer de Forges (1983: 638), distinguished R. serenei from R. distincta in having more rounded tubercules on the posterior margin of the carapace and pronounced branchio-cardiac grooves, though admitting “Pour mieux décrire chacune de ces espèces, il serait nécessaire d’examiner une gamme de taille de chaque espèce”. Examination of the type series of R. distincta and R. serenei, and numerous additional specimens, including the male first pleopod, has shown that the latter is a junior synonym of the former” (Galil 2003: 404). In her material examined, Galil (2003) listed not just the types but also extensive material from the U.S. National Museum of Natural History, Smithsonian Institution, Washington D.C. (USNM) and MNHN of both taxa.

We have examined adult male specimens of both Randallia serenei Richer de Forges, 1983, and R. distincta Rathbun, 1894 (now in the genus Tanaoa), and we do not agree with Galil’s (2003) decision about their synonymy. All specimens are similar in size and clearly mature. The size of the granules along the lateral carapace margins, particularly the anterolateral part, is distinctly more uneven in R. serenei (Fig. 1B), with that of R. distincta more entire and less prominently raised (Fig. 1A). The size of the cardiac spine is also prominently larger in R. serenei (Fig. 1B) than in R. distincta (Fig. 1A). The carapace features are quite different. While both have the dorsal surfaces granular, the granules on R. serenei are relatively larger and more beaded (Fig. 1B). The surface granules are much smaller and more squamiform in R. distincta (Fig. 1A) than in R. serenei (Fig. 1B). The surfaces of the sternum, abdomen, third maxillipeds and pereiopods are also different with regard to the form of their granules (Fig. 1A, C versus Fig. 1B, D). Very prominent is also the difference in the strength of the grooves around the gastric, cardiac and branchial regions. In R. serenei, the grooves are very deep and prominent (Fig. 1B) while they are very shallow in R. distincta (Fig. 1A). The G1 structures also differ. In R. serenei, the G1 is relatively more slender and the distal part has a distinct subdistal projection (Fig. 4 E, F). The G1 of the ZRC specimen of R. distincta is proportionately stouter and the distal part only has a small lobe just before the tip (Fig. 4 A–C). Dr. Bella Galil was kind enough to send us her unpublished figure of the G1 of the largest Hawaiian male of R. distincta (carapace width 43.0 mm, USNM 29882). The distal part of its G1 (Fig. 4 D) is interesting as it is dilated forming a broad triangular flap. The distal part of the G1 of the ZRC specimen (Fig. 4 B) has the inner margins somewhat folded and crenulated, and if expanded, it would probably resemble the condition of the USNM specimen (Fig. 4 D). Certainly the difference in the shape of the distal part of the G1 of the ZRC and USNM specimens can be accounted for by variation. The condition of the distal part of the G1 of the USNM specimen of R. distincta (Fig. 4 D), however, is still rather different from that of R. serenei, which has a subdistal finger-like projection (Fig. 4 F). Galil’s (2003: Figs. 1B, 3 C, D) figures of “ Tanaoa distinctus ” were based on a specimen from Tuscarora Seamount near Wallis I. in the southwestern Pacific Ocean; they agree in all respects with what is here defined as R. serenei. Galil (2007) also reports “ T. distinctus ” from the Solomon Islands. This material needs to be rechecked to ascertain which of the two species they belong to. For the moment, T. distinctus sensu stricto is known only from the Hawaiian Islands.

The first author has examined a good series of specimens of R. distincta from the type locality (Hawaiian Islands) in the Bishop Museum, Honolulu (from which the present pair in ZRC originated) and there are no major variations in carapace form. He also examined numerous specimens of R. serenei in the collections of the Marine Biology Laboratory of the University of Guam (from which the present specimen in ZRC came), and they are consistent in their diagnostic characters (see also Paulay et al. 2003). Similarly, the second author has examined a good series of R. serenei from French Polynesia (see also Richer de Forges 1983) which shows the consistency of the characters discussed above. Considering the differences, we believe that it is better to recognize R. serenei and R. distincta as separate taxa until more data becomes available.

The characters of R. serenei are consistent with Tanaoa as defined by Galil (2003) and it is here also referred to this genus, together with T. distinctus.