Arenaeus Dana, 1851

Zupolini, Lucas L., Magalhães, Tatiana, Pileggi, Leonardo G. & Mantelatto, Fernando L., 2017, Taxonomic revision of the speckled crabs, genus Arenaeus Dana, 1851 (Brachyura: Portunidae) based on morphological and molecular data, Zootaxa 4273 (3), pp. 362-380 : 365-366

Arenaeus Dana, 1851

Arenaeus Dana 1851: 130 (type species Portunus cribrarius Lamarck, 1818 , by monotypy)

Euctenota Gerstaecker 1856: 131 (type species Euctenota mexicana Gerstaecker, 1856 , by monotypy)

Diagnosis. Palate smooth, without longitudinal ridge. Carapace more than twice longer than wide, with 2 strong lateral horns (spines), 9 pairs of anterolateral teeth, including external orbital teeth and lateral horns; carapace finely granular, with yellowish-orange, brownish-yellow, or vinaceous brown, covered over dorsal surface with reticulum of abundant, small rounded white spots; inter-regional sulci present but not conspicuous. Rostrum narrow, short, 2 or 4 teeth; superior orbit border divided by 2 large, V-shaped incisions. Spine at epistome region present or absent. 1 or 2 spines at carpus of chelae; manus bearing 5 longitudinal carinae. Fifth leg segments flattened, unarmed. Spiniform borders at the second abdominal segment; sixth segment narrow in males (not as narrow, “T”-shaped as in Callinectes ), with sinuous margins, attenuated tip.

Redescription. Light yellowish-orange, brownish-yellow, or vinaceous brown, with reticulum of white, rounded spots on dorsal carapace. Spots not evenly distributed on carapace; anterior area, especially gastric region, with smaller spots; spots sparser, larger in chelipeds. Ventral surface light yellow or light cream, spots absent. Dactyl tip of ambulatory legs yellow. Color may not persist in long ethanol preservation.

Carapace more than twice longer than wide, produced laterally into strong horns (spines); fine granulate texture, visible under magnification. Inter-regional sulci detectable, mainly in mesogastric region, but not too deep. Posterolateral angle spiny or nearly rounded. 9 pairs of anterolateral teeth, including external orbit teeth and lateral horns, densely fringed beneath; first 3 anteriormost teeth similar in shape, size, fourth wider; sixth and seventh the sharpest; lateral horn very prominent, longer than the sixth, seventh together; lateral horn, sixth, seventh lateral teeth slightly curved forwards, with white tips. Front (frontal region) commonly hirsute. Rostrum narrow, short, much less advanced than outer orbit angles; 2 or 4 teeth. Supraorbital border with 3 teeth, a lobe on each side; inner orbit tooth less prominent than outer; superior orbit border with 2 V-shaped incisions, inner deeper, more open than outer, intervening lobe subtruncate, fairly wide; inner tooth relative to orbit small, little prominent, less advanced than others; rostrum: inferior orbit border with wide, triangular incision between inner, outer teeth.

Chelipeds short, stout. Basis and ischium short, flattened; ischium with short tooth at distal end. Merus elongated, nearly pyramid-shaped, attenuated towards basis; 3 spines on inner face, generally larger in size outwards; tooth near distal end relatively obsolete; transverse sinus more marked near distal end; obsolete tooth on outer border near distal end. Carpus short, cylindrical, armed with 1 or 2 sharp spines; 2 denticles on dorsal face, both leading proximally to fairly developed carinae. Palm elongated, cylindrical, attenuated towards both ends; 5 longitudinal carinae; 2 spines, 1 at the proximal end, near the carpus joint, second at distal end, above dactyl base; 2 poorly developed distal prominences near dactyl, dorsal prominence relatively denticular, lateral prominence shorter and stouter.

Articles of ambulatory and swimming legs wide, flattened. Tip of ambulatory legs yellow; merus arcuate on external border, unarmed.

Second abdominal segment laterally produced into 2 strong spines; sixth segment narrower distally, with sinuous margins; telson attenuated.

First male pleopods elongated, slender; base fringed below; extended well beyond midpoint of telson; outer, ventral faces densely covered with small bristles on nearly the entire basal portion, absent on dorsal surface; terminal portion with single row of bristles located on ventral face; tip rather flattened, spoon-shaped.