Melothelphusa, Pedraza, Manuel, Tavares, Marcos & Magalhães, Célio, 2016

Pedraza, Manuel, Tavares, Marcos & Magalhães, Célio, 2016, A new genus of freshwater crab of the tribe Kingsleyini Bott, 1970 (Crustacea: Decapoda: Brachyura: Pseudothelphusidae) with description of a new species from Mato Grosso, Brazil, Zootaxa 4173 (1), pp. 94-100 : 95-96

Melothelphusa n. gen.

Included species. Melothelphusa dardanelosensis n. comb. ( Magalhães & Türkay, 2010) [Formerly in Brasiliothelphusa ]; Melothelphusa apiaka n. gen., n. sp.

Type species. Melothelphusa apiaka n. sp. by present designation.

Distribution. Brazil, northern of Mato Grosso State, Aripuanã River, Apiacás and Juruena.

Diagnosis. Marginal process of G1 short, strongly curved toward spermatic channel, apex truncated; apical plate provided with strong, keel-like process, arranged transversally in abdominal view. Apical field of spines of G1 open, almost as wide as long. Opening of spermatic channel delimited by both the crest of abdominal lobe and the marginal process.

Description. Carapace distinctly wider than long, dorsal surface smooth, slightly convex, regions barely defined; gastric pits almost obsolete. Post-frontal lobules obsolete; median groove indistinct; fronto-orbital region width less than half maximum width of carapace. Branchial region markedly expanded laterally, moderately swollen; molting suture well distinct, ending between P4-P5 coxae. Frontal region strongly deflexed downwards. Supraorbital margin lined with small granules laterally. Subhepatic region smooth. Pterystogomial regions covered by short pubescence. Mxp3 merus subcircular, distinctly shorter than ischium, about 0.75 times its length; posteromesial border expanded mesially, grooved to receive folded dactylus, dentate. Opening of efferent branchial channel large; upper margin triangular in outline; channel closed ventrally by large lamellar scaphognathite. Epistome distinctly short, wide, deeply grooved transversally.

Chelipeds noticeably heterochelous, similarly armed, right cheliped largest. P2–P5 similar in shape, slender, P3 longest, P5 shortest.

Thoracic sternum rather longer than broad; sternal sutures 4/5 to 6/7 interrupted medially; sternal suture 7/8 uninterrupted. Sterno-abdominal cavity deeply excavated.

Male abdomen with 6 somites, telson; third somite widest, sixth longest. Penis noticeably long, emerging from nearby coxo-sternal condyle articulation, located in shallow depression on sternite 8, proximally thick, abruptly tapering distally.

Marginal process of G1 short, strongly curved toward spermatic channel, apex truncated; apical plate provided with strong, keel-like process, arranged transversally in abdominal view. Apical field of spines open, almost as wide as long; opening of spermatic channel delimited by crest of abdominal lobe and marginal process. G2 straight, almost as long as G1, distinctly slender, distal 3/4 tapered; tip flattened, with numerous short spinules on sternal surface.

Etymology. The generic name is a masculine patronym in honor or our colleague and friend Gustavo A. S. de Melo (the prefix ‘Melo’) with the suffix "thelphusa" (for ‘freshwater crab’).

Remarks. Melothelphusa n. gen. is established here for M. apiaka n. sp., its type species, and M. dardanelosensis n. comb. ( Magalhães & Türkay, 2010), originally described in the Kingsleyini genus Brasiliothelphusa Magalhães & Türkay, 1986 . Likewise, Melothelphusa n. gen. is herein assigned to the tribe Kingsleyini , with which it shares two diagnostic characters of the G1, namely the presence of an apical plate located above the opening of the spermatic channel, and base of G1 widened.

Melothelphusa n. gen. differs from Brasiliothelphusa Magalhães & Türkay, 1986 , as follows: (i) the marginal suture of G1 is straight (whereas the marginal suture of G 1 in Brasiliothelphusa is sinuous); (ii) the opening of the spermatic channel of G1 is delimited by both the crest of the abdominal lobe and the marginal process (whereas the opening of the spermatic channel is delimited by the crests of the sternal and the abdominal lobes of the apical plate in Brasiliothelphusa ); (iii) the sternal and the abdominal lobes of the apical plate of G1 subequal in size (whereas the sternal lobe of the apical plate is at least four times larger than the abdominal lobe in Brasiliothelphusa ); (iv) the apical plate of G1 provided with a strong, keel-like process arranged transversally in abdominal view (whereas the apical plate is smooth, devoid of any process in abdominal view in Brasiliothelphusa ).