Achelous ordwayi Stimpson, 1860

In, First Published, 2022, Brachyuran crabs (Crustacea, Decapoda) from the remote oceanic Archipelago Trindade and Martin Vaz, South Atlantic Ocean, Zootaxa 5146, pp. 1-129 : 51

Achelous ordwayi Stimpson, 1860

( Fig. 27A, D )

Achelos ordwayi Stimpson, 1860: 224 [Type locality: Key Biscayne and Tortugas, Florida].

Trindade specimens. 1 male ( MZUSP 21204 ), Trindade Island , R /V “Marion Dufresne”, TAAF MD55/ Brésil Expedition, stn 36 DC61, 20°29.2’S, 29°18.2’W, 22.v.1987, 63 m .

Size of largest male: cl 16.8 mm, cw 29 mm.

Comparative material examined. Achelous ordwayi : Brazil: Ceará: 1 juvenile female ( MZUSP 16948 ), Canopus Bank, 120 miles off the coast of Fortaleza, J. Coltro coll., viii.2005, depth not informed. Espírito Santo: 1 juvenile ( MZUSP 41472 ), Vitória – Trindade Seamount Chain, R /V “Marion Dufresne”, TAAF MD55/ Brésil Expedition, Davis Bank, stn 23 DC40, 20°39’S, 34°41’W, 15.v.1987, sandy shell, 60 m.

Distribution. Massachusetts to Florida, Gulf of Mexico, Antilles, Colombia, Venezuela, Guyana, and Brazil (Amapá to Rio Grande do Sul) ( Türkay 1968; Rodriguez 1980; Lemaitre 1981; William 1984; Melo 1996; Felder et al. 2009). Brazilian oceanic islands and seamounts: Fernando de Noronha ( Coelho & Ramos 1972), Canopus Bank, Vitória–Trindade Seamount Chain (Davis Bank) and Trindade Island (this study).

Ecological notes. Achelous ordwayi is benthopelagic ( Felder et al. 2009), living in association with calcareous algae and also found in a variety of soft sediments including mud, sand, sandy shell, rubble and detritic organogenic bottoms between the tide mark down to depths of 366 m ( Coelho & Ramos 1972; Melo 1996). It is preyed by the scorpionfish Scorpaena plumieri Bloch and porcupinefish Diodon hystrix Linnaeus (Randal 1967) , the triglid fish Prionotus rubio Jordan ( Reyes et al. 2020) and by the invasive lionfish Pterois spp. in western Florida waters ( Santamaria et al. 2020). Achelous ordwayi has been found to be infested by the parasitic ciliate Synophrya sp. ( Lee et al. 2019).

Remarks. A second species of Achelous , A. tumidulus , is found in Trindade (see below). The differences between A. ordwayi and A. tumidulus include: 6 deeply cut, acuminate frontal teeth (inner orbital included) and the carapace anterolateral teeth equal in size (vs frontal teeth not deeply cut, tip rounded and carapace anterolateral teeth unequal, alternating large and small in A. tumidulus ) ( Fig. 27A, B, D, E ).

Figures

FIGURE 27. A, D, Achelous ordwayi Stimpson, 1860, male, cl 16.1 mm, cw 28.1 mm (MZUSP 21204). B, E, Achelous tumidulus Stimpson, 1871, ovigerous female, cl 10.5 mm, cw 16.5 mm (MZUSP 41419). C, F, Cronius ruber (Lamarck, 1818), juvenile male, cl 7 mm, cw 10 mm (MZUSP 40173). Note in (B, C) carapace anterolateral teeth unequal, alternating large and small (arrows). Scales: D–F, 0.5 mm.