Teramnonotus, Santana, William, 2015

Santana, William, 2015, A new genus and two new species of hymenosomatid crabs (Crustacea: Brachyura: Hymenosomatidae) from the southwestern Atlantic and eastern Australia, Zootaxa 3905 (1), pp. 91-106 : 92-93

Teramnonotus n. gen.

Elamena (pro parte)— Monod 1956: 469; Lucas 1980: 170 –171; Ng & Chuang 1996: 6; Ng et al. 2008: 108; Guinot et al. 2013: 191 [not Elamena H. Milne Edwards, 1837 . Type species Hymenosoma mathoei Desmarest, 1823 ].

Type species. Elamena gordonae Monod, 1956 , by original designation. Gender masculine.

Included species. Teramnonotus gordonae ( Monod, 1956) n. gen., n. comb., eastern Atlantic (between Conakry, Guinea and Monrovia, Liberia), T. johnlucasi n. gen., n. sp., western Pacific ( Australia: Queensland), and T. monodi n. gen., n. sp., southwestern Atlantic ( Brazil: Ceará, Rio Grande do Norte, Sergipe, Bahia and Rio de Janeiro).

Comparative material. Elamena longidactylis Yang & Sun, 1998: 1 male cl 2.8 mm, cw 2.3 mm, 1 juvenile female cl 2.5 mm, cw 2.2 mm, Xiamen, Gu-Lang-Yu, Fujian Province, China, mud flat, under stones, 13.xii.1984 ( ZRC 2004.0736). Hymenosoma mathoei Desmarest, 1823 : Gesira, Somalia, coll. x.1981, reef, two females, one juvenile female ( ZRC 1994.4235). Gesira, Somalia, coll. x.1981, reef, young male ( ZRC 1994.4234). Trigonoplax spathulifera Lucas, 1980 : Western Australia, Woodside Dampier Expedition 2, Dampier Archipelago, Brigadier Island, 4.8 km E of East Point, stn DA2/99/85, between 20º26.38'S, 116º39.76'E and 20º26.09'S, 116º40.10'E, S. Slack-Smith & M. Hewitt coll., 26.vii.1999, 29 m, 1 ovigerous female ( WAM C27116); Woodside Dampier Expedition 3, Dampier Archipelago, Nelson Rocks, stn DA3/99/68, 20º27.99'S, 116º39.71'E, M. Hewitt coll., 7.ix.1999, 6 m, 1 juvenile female ( WAM C27685). Woodside Dampier Expedition 1, Dampier Archipelago, Angel Island, stn DA 1/98/09, 20º28.69'S, 116º47.95'E, M. Hewitt coll., 20.x.1998, 1 juvenile female ( WAM C25639), 1 male ( WAM C25640); Searipple Passage, Burrup Peninsula, 20º31'S, 116º51'E, D. S. Jones & B. Morton coll., 7.x.1999, 1 juvenile female ( WAM C33088). Trigonoplax unguiformis H. Milne Edwards, 1853 : Indonesia, Moluccas, Ambon, Hitu, Ambon Bay, outer bay, in front of Ruhmatiga, up to river Lela; Rumphius Biohistorial Expedition, stn 41, L.B. Holthuis coll., 10.xii.1990, dredge, 4–28 m, female ( RMNH).

Diagnosis. Carapace pear-shaped, moderately convex, dorsal carapace surface with faint longitudinal ridge, edges slightly upturned; rostrum triangular, upturned, continuous with carapace surface; ventral rostral keel absent. Epistome long, almost as long as broad; pterygostomial region with 2 prominent blunt teeth. No orbits, eyes-stalk immovable, short, stout, fused with carapace; most of eyes hidden beneath rostrum in dorsal view, only cornea visible dorsally; small post-ocular tooth present; cornea pigmented. Antennules fold beneath rostrum; interantenullar septum short, reaching to less than half-length of second antennular article. Antenna conspicuously slender, short, concealed by rostrum in dorsal view. Third maxillipeds broad, almost completely filling mouth square, ischium subequal to merus along lateral edge; merus heart-shaped; epipod lamella about same size as basal portion (operculum); palp articulating near merus anterolateral angle; exopod with distinct flagellum. Chelipeds slender, subequal, stouter than pereiopods; dactyli usually with 2 subterminal teeth. Thoracic sternite 4 extended laterally, conspicuously convex anteriorly distinctly separating Milne Edwards openings from chelipeds. Thoracic sternite 8 fully covered by carapace in dorsal and posterior views. Female abdomen very large, broader than cephalothorax width, soft; somites 1, 2 free, somites 3–5, fused; somite 6 separated from previous somites, fused with telson; Pl2–Pl5 articulated close to lateral edge of somites enlarging brood cavity. Vulvae located on medially fused part of thoracic sternites, oblique, slit-like, peripheral border swollen.

Remarks. Elamena H. Milne Edwards, 1837 (type species Hymenosoma mathoei Desmarest, 1823 ) is the second largest hymenosomatid genus in terms of species, 25 species (Ng et al. 2008). Elamena has been reviewed and partially revised in a number of occasions (e.g., Alcock 1900, Kemp 1917, Tesch 1918, Gordon 1940, Melrose 1975, Lucas 1980, Ng & Chuang 1996), yet its species composition is still in need of a reappraisal. Guinot (2011b), for instance, commented on the puzzling position of Elamena truncata (Stimpson, 1858) in Elamena , and Ng & Chuang (1996) stated that E. magna Ng & Chuang, 1996 , might actually belong in a new genus. Elamena longirostris Filhol, 1885 , also leaves doubt as to its generic position; Filhol (1885) stated that E. longirostris belong in the same genus as Elamena whitei Miers, 1876 , a species subsequently reallocated in the genus Halicarcinus White, 1846 (Ng et al. 2008) . A comparison between Elamena gordonae Monod, 1956 s . str. and representatives of Elamena (including its type species) revealed that E. gordonae can no longer be attributed to Elamena , nor to the closely related genus Trigonoplax H. Milne Edwards, 1853 . Elamena gordonae Monod, 1956 s . str. is therefore herein transferred to Teramnonotus n. gen. as its type species along with the two new species being described, one from the southwestern Atlantic and a second from eastern Australia.

The genus Teramnonotus n. gen. can be distinguished from Elamena H. Milne Edwards, 1837 s . str. in having: (i) an immovable ocular peduncle, completely fused to the carapace ( Figs. 1B, D , 5B, C ) (freely movable in Elamena , Fig. 5D ); (ii) rostral keel absent ( Figs. 5A–C , 6A, B ) (a distinct, vertical keel on the ventral surface of the rostrum in Elamena ; Figs. 5D , 6C ); (iii) subhepatic region with two strong lobes ( Figs. 1B, D , 4A–C , 5B, C ) (smooth in Elamena ; Figs. 2B , 5D ); (iv) thoracic sternite 8 concealed by the carapace in dorsal and posterior views ( Fig. 6 D) (thoracic sterni.te 8 partially visible in dorsal and posterior views between the carapace, the abdominal somites 1 and 2, and the P5 coxa in Elamena ; Fig. 6 F); (v) narrow thoracic sternite 8 so that the P5 coxae are close to each other ( Fig. 1A, B ) (wide thoracic sternite, so that the coxae of P5 are far from each other in Elamena ; Fig. 2A ); (vi) first female abdominal somite distinctly narrower than the second ( Fig. 6 D) (somites 1 and 2 of about the same size in Elamena ); (vii) female abdominal somites 1 and 2 free, somites 3 to 5 fused, lateral clefts still discernible even if minute, and a pleotelson ( Fig. 7 A –D) (somites 1–5 free and a pleotelson in Elamena ).

Trigonoplax H. Milne Edwards, 1853 [type species Ocypode (Trigonoplax) unguiformis De Haan, 1839 , by monotypy] share a number of characters with Elamena and, in the past, was even considered a subgenus of Elamena by many authors (e.g., Alcock 1900; Kemp 1917; Gordon 1940). Trigonoplax can be distinguished from both Elamena and Teramnonotus n. gen. by (i) the inhalant water openings being fused laterally for more than half of its length (see Lucas, 1980: 154) (not fused in Elamena and Teramnonotus n. gen.; Fig. 5 B, C ), and (ii) a large portion of the female thoracic sternite 8 is not dorsolaterally covered by the carapace ( Fig. 6 E) (thoracic sternite 8 fully covered by the carapace in Teramnonotus n. gen. and a small portion of thoracic sternite 8 dorsally exposed in Elamena in dorsal and posterior views respectively; Fig. 6 D, F). Trigonoplax also differs from Teramnonotus n. gen. in the presence of well-developed keel on the ventral surface of the rostrum (rostral keel absent in Teramnonotus n. gen.; Figs. 5A–C , 6A, B ).

Etymology. The generic name Teramnonotus is a combination of the Greek words teramnos (soft) and notus (back), in allusion to the soft and smooth dorsal surface of the carapace. Gender masculine.

Figures

FIGURE 1. A – D, habitus, dorsal and ventral views. A, B, Teramnonotus johnlucasi n. gen., n. sp., ovigerous female holotype cl. 2.8 mm, cw. 2.7 mm (AM P. 12208). C, D, Teramnonotus monodi n. gen., n. sp., ovigerous female paratype cl. 4.3 mm, cw. 3.6 mm (MZUSP 10273). Note (arrows) rostrum integrated into the carapace outline in A (versus rostrum well detached from the carapace outline in C). A – D, stained with methylene blue. Scale bars: A – D, 1 mm.

FIGURE 5. A – D, anteroventral view of the cephalothorax. A, Teramnonotus gordonae (Monod, 1956) n. gen., n. comb., holotype (after Monod 1956: fig. 630 bis). B, Teramnonotus johnlucasi n. gen., n. sp., ovigerous female holotype cl. 2.8 mm, cw. 2.7 mm (AM P. 12208). C, Teramnonotus monodi n. gen., n. sp., ovigerous female paratype cl. 4.3 mm, cw. 3.6 mm (MZUSP 10273). D, Elamena mathoei (Desmarest, 1823), female (ZRC 1994.4235). Arrows indicate the rostrum, which is integrated into the carapace outline in B (rostrum well detached from the carapace outline in C). Scales: A – D, 1 mm.

FIGURE 6. A – C, lateroanterior view of carapace. D, F, posterior view of the cephalothorax and abdomen. E, posterodorsal view of cephalothorax. A, Teramnonotus johnlucasi n. gen., n. sp., ovigerous female holotype cl. 2.8 mm, cw. 2.7 mm (AM P. 12208). B, D, Teramnonotus monodi n. gen., n. sp., ovigerous female paratype cl. 4.3 mm, cw. 3.6 mm (MZUSP 10273). C, F, Elamena mathoei (Desmarest, 1823), female (ZRC 1994.4235). E, Trigonoplax unguiformis H. Milne Edwards, 1853, female (RMNH). Arrows indicate the absence of the rostral keel in A – B (distinct vertical keel on ventral surface of rostrum in C). Ab 1, Ab 2, first and second abdominal somites. CxP 5, coxa of the pereopod 5. St 8, thoracic sternite 8 exposed. Scales: A – D, 1 mm. E – F, 2 mm.

FIGURE 4. A – D, habitus, dorsal view. A, Teramnonotus gordonae (Monod, 1956) n. gen., n. comb., holotype (after Monod 1956: fig. 629). B, Teramnonotus johnlucasi n. gen., n. sp., ovigerous female holotype cl. 2.8 mm, cw. 2.7 mm (AM P. 12208). C, Teramnonotus monodi n. gen., n. sp., ovigerous female paratype cl. 4.3 mm, cw. 3.6 mm (MZUSP 10273). D, Elamena mathoei (Desmarest, 1823), female (ZRC 1994.4235). Scales: A – D, 1 mm.

FIGURE 2. A – D, habitus, dorsal and ventral views. A, B, Elamena mathoei (Desmarest, 1823), female (ZRC 1994.4235). C, D, Trigonoplax unguiformis H. Milne Edwards, 1853, female (RMNH). Note (arrows) part of the thoracic pleurite 8 visible between the carapace, the abdominal somites 1 – 2, and the coxa of P 5 in A and C. A – D, stained with methylene blue. Scales: A, B, 1 mm; C, D, 2 mm.

FIGURE 7. A, C. Female abdominal somites and pleotelson, dorsal view. A, B, Teramnonotus johnlucasi n. gen., n. sp., ovigerous female holotype cl. 2.8 mm, cw. 2.7 mm (AM P. 12208). C, D, Teramnonotus monodi n. gen., n. sp., ovigerous female paratype cl. 4.3 mm, cw. 3.6 mm (MZUSP 10273). Ab 1, Ab 2, first and second abdominal somites. Ab 3 – Ab 5, third, fourth and fifth abdominal somites fused together. PlT, pleotelson (sixth abdominal somite and telson fused together). Scales: A – D, 1 mm.