Triacanthoneus toro Anker, 2010

Anker, Arthur, 2020, Taxonomic remarks on the alpheid shrimp genus Triacanthoneus Anker, 2010 with description of a second eastern Pacific species (Malacostraca: Decapoda), Zootaxa 4772 (3), pp. 450-468 : 463-466

Triacanthoneus toro Anker, 2010

Figs. 9–11

Triacanthoneus toro Anker 2010a: 49 , figs. 1–4, 10A–C.

Material examined. Triacanthoneus toro Anker, 2010: 1 ovigerous specimen (cl 3.8 mm), MZUSP 33674 , Panama, Caribbean coast, Bocas del Toro, Isla Popa , shallow sea grass flat, with rubble, sponges, sea plumes, and some corals, depth: 0.5–2 m, leg. A. Anker et al., 30 April 2015; 2 non-ovigerous specimens (cl 4.4 mm, 4.6 mm), MZUSP 33675 , Panama, Caribbean coast, Bocas del Toro, Isla Bastimentos, Cayo Coral , shallow subtidal sand flat with sea grass and coral rubble, in burrow, suction pump, depth: 0.5–1 m, leg. A. Anker et al., 28 April 2015 .

Tentative identification: Triacanthoneus cf. toro Anker, 2010: 1 ovigerous specimen (cl 4.5 mm), OUMNH. ZC. 2016-01-0087, Mexico, Yucatan Peninsula, Sisal , El Casquito , 21°12’28.15”N 90°3’18.25”W, under coral, leg. J. Duarte, 18 October 2016 .

Remarks. The three Panamanian specimens agree very well with the type series of T. toro , as described and illustrated by Anker (2010a). The variation in the position of the carapacial teeth seems to be minimal (cf. Figs. 9 , 10 ; Anker 2010a: figs. 1, 2B, 10A). Interestingly, the species is known with certainty only from Bocas del Toro in Panama ( Isla Colón, Isla San Cristobal, Isla Popa and Isla Bastimentos), where it inhabits subtidal sand flats with abundant rubble and sea grass, often near mangroves, at depths ranging from 1 to 7 m ( Anker 2010a; present study).

The specimen from Sisal, Mexico, herein tentatively identified as T. cf. toro differs in some aspects from the holotype of T. toro , for instance, in the development of the conical anteromesial tubercle on the eyestalks, which seems to be much smaller in the former specimen and not visible in lateral view (cf. Fig. 11 ; Anker 2010a: fig. 2B; this tubercle being also clearly visible in the close-up views of the cephalic region in Figs. 9B , 10B ). The Mexican specimen also has three pairs of very robust cuspidate setae inserted at approximately 0.3, 0.5 and 0.7 of the telson length, respectively (Dr. Sammy De Grave, pers. comm.). However, the presence of additional cuspidate setae, as well as additional posterior spiniform setae on the telson might be an aberrant condition, which is occasionally also seen in other genera, especially in Synalpheus Spence Bate, 1888 (e.g., Banner & Banner 1978, 1979; A. Anker, pers. obs.). Most of the other morphological characters of the Mexican specimen seem to be congruent with the description of T. toro in Anker (2010a) . Most importantly, in the specimen from Sisal, the mid-dorsal tooth is situated at about half of the carapace length, whilst the lateral teeth arise in the hepatic area, well below and well more anterior relative to the mid-dorsal tooth ( Fig. 11 ), exactly as in the holotype and the topotypical specimens of T. toro reported above ( Anker 2010a: fig. 2A, B; see also Figs. 9 , 10 ). Furthermore, in the specimen from Sisal, the postorbital margin margin is broadly rounded, without any trace of orbital teeth ( Fig. 11 ), as in T. toro ( Anker 2010a: fig. 2A, B). On the other hand, the general shape of the rostrum and the size of cornea of the Mexican specimen appear to be more like those of T. alacranes .

De Grave et al. (2017), while reporting T. alacranes from Isla de la Juventud, Cuba, noted some important differences between their single Cuban specimen and the holotype of T. alacranes from Alacranes Reef. In the Cuban specimen, which is noticeably smaller than the holotype, the dorsolateral carapacial teeth are much more advanced compared to those of the holotype ( De Grave et al. 2017: fig. 1A), almost approaching their position in T. toro . A further difference is that the postorbital margin of the Cuban specimen is much less pronounced and not as angular as in the holotype of T. alacranes (Dr. Sammy De Grave, pers. comm.), in which it forms subtriangular orbital teeth (cf. Anker 2010a: fig. 8A, B; De Grave et al. 2017: fig. 1A). However, the two pairs of the dorsal cuspidate setae of the telson of the Cuban specimen are small and situated in the posterior third of the telson, i.e. they agree in both their relative size and position with those of the holotype ( Anker 2010a: fig. 8L). Based on the evaluation of the above features, the Cuban specimen indeed is best assigned to T. alacranes , whereas the Mexican specimen seems to be morphologically much closer to T. toro .

With only three specimens of Triacanthoneus from the southern Gulf of Mexico and Cuba presently available, i.e. the holotype of T. alacranes from Alacranes Reef, the specimen from Sisal herein assigned to T. cf. toro , and the specimen from Isla de la Juventud identified as T. alacranes ( De Grave et al. 2017) , it is difficult to make more firm conclusions about the the above observed morphological differences. In the present study, they are considered as part of intraspecific variation within T. alacranes and T. toro , awaiting a thorough morphological + molecular analysis of this material and eventually, collection of new material.

Figures

FIGURE 9. Triacanthoneus toro Anker, 2010: non-ovigerous specimen (cl 4.6 mm) from Bocas del Toro, Panama (MZUSP 33675); living shrimp in dorsal [A] and lateral [B] views. Photographs by the author.

FIGURE 10. Triacanthoneus toroAnker, 2010: ovigerous specimen (cl 3.8 mm) from Bocas del Toro, Panama (MZUSP 33674); living shrimp in dorsal [A] and lateral [B] views. Photographs by the author.

FIGURE 11. Triacanthoneus cf. toro Anker, 2010, ovigerous specimen (cl 4.5 mm) from Sisal, Mexico (OUMNH.ZC. 2016- 01-0087), anterior portion of carapace and frontal appendages, lateral view.