Arenaeus Dana, 1851

Koch, Milan, Spiridonov, Vassily A. & Ďuriš, Zdeněk, 2023, Revision of the generic system for the swimming crab subfamily Portuninae (Decapoda: Brachyura: Portunidae) based on molecular and morphological analyses, Zoological Journal of the Linnean Society 197, pp. 127-175 : 145-147

= Arenaeus Dana, 1851 (type species Portunus cribrarius Lamarck, 1818, by monotypy; gender masculine) [ ICZN, 1922. Opinion 73]

KEY TO DISTINGUISH GENERA OF SUBFAMILY PORTUNINAE (CARUPELLA NOT INCLUDED) 1. Posterolateral junctions of carapace rounded ( Fig. 15A); dorsal surface of carapace finely granulate, with regions feebly demarcated, sometimes with narrow rows of granules …..................................................... 2

- Posterolateral junctions of carapace rounded; dorsal surface of carapace with well-defined granulated regions ( Figs 8A, 9A, 10A, 14A) …..................................................................................................................... 4

- Posterolateral junctions of carapace angular, pointed, often distinctly upturned; dorsal surface with well-defined granulated regions ( Figs 12A, 13A, 16A, 17A) ...............................................................................… 7

2. Supraorbital fissures broadly open, V-shaped ( Rathbun, 1930: pl. 58) ..........................................… Arenaeus

- Supraorbital fissures narrow or fused ........................................................................................................… 3

3. Merus of third maxilliped with anteroexternal angle rounded or subrectangular, not produced laterally; supraorbital fissures not broadly open ( Fig. 15A); male pleon narrowly triangular, almost smooth ( Fig. 15C) ….......................................................................................................................................... Portunus

- Merus of third maxilliped with anteroexternal angle strongly produced laterally; male pleon reverse T-shaped ( Rathbun, 1930: pl. 58) ….................................................................................................. Callinectes

4. Cheliped palm with two spines on upper face (excluding spine on articulation with carpus) ( Fig. 9A) …..... ..................................................................................................................................................... Cavoportunus

- Cheliped palm with a single spine on upper face (excluding spine on articulation with carpus) ( Fig. 14A) …....................................................................................................................................................................... 5

5. Frontal teeth distinct; carpus of chelipeds usually with a sharp spine on outer surface ( Fig. 8A, B) ............... ...................................................................................................................................................… Allomonomia

- Frontal teeth low, lobate; carpus of chelipeds with low spine or crest on outer face …................................. 6

6. Carapace semicircular or circular ( Fig. 10A), except for Cycloachelous euglyphus : hexagonal, inner convex carapacial part, excluding depressed lateral teeth semicircular; Serène, 1969: fig. 2) …...... Cycloachelous

- Carapace broadly hexagonal ( Fig. 14A) ….......................................................................................... Monomia

7. Frontal teeth low, indistinct ( Figs 12A, B, 13A, B) …..................................................................................... 8

- Frontal teeth distinctly produced, lobate or acute ( Figs 16A, B, 17A, B) ….................................................. 9

8. Merus of third maxilliped anterolaterally produced to elongate triangular projection; merus of chelipeds with two posterodistal teeth; anterolateral teeth of carapace sharp ( Fig. 12A) …........................... Eodemus

- Merus of third maxilliped without elongate distolateral projection; merus of chelipeds with single posterodistal tooth; anterolateral teeth of carapace blunt ( Fig. 13A) .............................................… Incultus

9. Three frontal teeth ( Fig. 16B); male pleon elongately trapezoid ( Fig. 16C); infraorbital margin deep, ‘V’-shaped notch .............................................................................................................................… Trionectes

- Four frontal teeth ( Fig. 17B); sixth male pleomere distinctly constricted subdistally ( Fig. 16C); infraorbital margin with narrow lateral notch …............................................................................................. Xiphonectes

= Euctenota Gerstaecker, 1856 (type species Euctenota mexicana Gerstaecker, 1856 , by monotypy; gender feminine)

Included species: Two.

Arenaeus cribrarius (Lamarck, 1818)

= Portunus cribrarius Lamarck, 1818

= Lupa maculata Say, 1818

= Arenaeus websteri H.G. Jones, 1968

Arenaeus mexicanus Gerstaecker, 1856

= Euctenota mexicana Gerstaecker, 1856

= Arenaeus bidens Smith, 1871

Diagnosis (modified from Williams, 1984): Carapace more than twice as wide as long, finely granulate. Front not so far advanced as outer orbital angles, with six teeth including inner orbitals; submedian pair of teeth at either side of central notch coalesced. Superior margin of orbit with two deep fissures dividing it into three lobes; inferior margin of orbit with wide external fissure, inner angle much advanced. Lower surface of carapace densely setose. Anterolateral margin with nine strong teeth, somewhat acuminate, heavily setose beneath; most posterior produced into strong lateral tooth. Chelipeds of moderate size; merus with three spines on anterior border and short tuberculiform one near distal end of posterior border; carpus with lateral ridges and inner spine, outer spine present or absent; palm with five longitudinal granulose ridges and two spines, one at articulation with carpus and another above base of dactylus. Walking legs rather short and broad, densely fringed with short setae. Swimming legs stout, unarmed. Pleomere 2 produced on each side into strong, sharp, slightly upcurved spine. Male pleon broadly triangular on segments 3–5, sixth segment elongate, telson narrowly triangular. First male pleopod long, slender, filiform, with short, swollen basal part.

Remarks: No specimen was analysed in this study. Spiridonov et al. (2014) suggested Arenaeus to be the closest relative of Portunus (in the present restricted extent, below) and Callinectes , all relatively large swimming forms with a lack of conspicuous granular patches on the carapace, slender gonopods and leaf-like walking dactyli. Evans (2018) subsequently confirmed their close, but somewhat unresolved phylogenetic relationship.

Size: Both males and females reach a width of 153 mm ( Camp et al., 1977; Williams, 1984).

G e o g r a p h i c a l r a n g e: We s t e r n A t l a n t i c, f r o m Massachusetts to Argentina; eastern Pacific, from Mexico to Peru ( Rathbun, 1930; Zupolini et al., 2017).