Arenaeus mexicanus (Gerstaecker, 1856)

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 : 368-370

Arenaeus mexicanus (Gerstaecker, 1856)

( Figs. 3 , 4 )

Euctenota mexicana Gerstaecker 1856: 131 , pl. 5, figs. 3–4 (type-locality, Mexico; type in Museum für Naturkunde, Berlin, MFN 301, type photograph examined).

Arenaeus bidens Smith 1871: 90 ; Lockington 1877.

Neptunus mexicanus H. Milne Edwards 1879: 212 , pl. 42, figs. 3, 3A–3E.

Neptunus (Neptunus) mexicanus Miers 1886: 172 .

Neptunus cribrarius Cano 1889: 90 , 102, 213.

Arenaeus mexicanus — Faxon 1895: 22.— Rathbun 1910: 537, 577, pl. 37, fig. 2; 1930: 137, pl. 58, fig. 1, pl. 61.— Schmitt 1939: 9.— Garth 1948: 35.— Holthuis 1954a: 28.—1954b: 161.— Garth & Stephenson 1966: 53, pl. 5, fig. D, pl. 8, fig. D, pl. 10, fig. D, pl. 12, fig. B.

Type locality: Mexico.

Known range: from Baja California, Mexico to northern Chile (for detailed references see Rathbun 1930, Garth & Stephenson 1966, Retamal & Arana 2000).

Material examined. MEXICO (Pacific coast): 1 male (CL 28.22 mm—holotype photography), MFN 301 ; 1 female (CL 22.24 mm), NMNH 60003 : Ballena Bay , Baja California, 16.iii.1911, (US Fish Commission coll.) ; 1 male (CL 15.66 mm), NMNH 207834 : Magdelena Bay , Baja California, 02.xii.1931, (S.A. Glassell coll.) ; 1 male (CL 21.38 mm) and 2 females (CL 18.74 mm and 16.71 mm), UNAM 3513 : Perula Beach, Chamela Bay , Jalisco, 15.vi.1984, (J.C. Nates, J.L. Villalobos & A. Cantu coll.) . NICARAGUA (Pacific coast): 1 male (CL 25.61 mm), NMNH 29316 : Corinto, data not given, (coll. not given). COSTA RICA ( Pacific coast): 2 females (CL 23.03 mm and 23.41 mm), CCDB 5937 : Playa de Tamarindo , Tamarindo , 19.vii.2013, (E.A. Souza-Carvalho & F.L. Carvalho coll.) ; 1 male (CL 22.90 mm), UCR 2430-04 : Naranja Beach, Papagayo Gulf, Santa Elena, La Cruz , Guanacaste , 15.vii.2005, (R. Vargas coll.) ; 1 female (CL 42.40 mm) UCR 835-001 : Nicoya Gulf , 5.v.1981, (coll. not given), det. A. Dittel ; 1 female (CL 20.52 mm), CCDB 2936 : Puntarenas, 25.v.2010, (F.L. Mantelatto et al. coll.) ; 1 male (CL 29.60 mm) and 5 females (CL 28.90 mm, 26.70 mm, 27.40 mm, 28.40 mm and 24.20 mm), UCR 1382 : Organo Beach , Puntarenas, 16.v.1991, (coll. not given), det. A. Dittel ; 6 females (CL 40.20 mm, 37.80 mm, 35.70 mm, 36.10 mm, 37.80 mm and 37.40 mm) UCR 401 : Caldera , Puntarenas, 29.iv.1970, (R. Saenz coll.) ; 2 males (CL 47.60 mm and 55.40 mm) UCR 873 : Cano Island, 17.xii.1970, (V. Cruz coll.) ; 1 male (CL 12.04 mm), ULLZ 9113 : eastern Pacific Coast , 18.vii.2005, (F.L. Mantelatto coll.) ; 1 male (CL 14.76 mm), CCDB 1716 : Pacific , v.2005, (R. Vargas coll.) ; 2 males (CL 14.43 mm and 17.20 mm) and 1 juvenile (CL 11.03 mm), NMNH 20607 : Cocos Island , 28.ii.1891 (US Fish Commission coll.) . PANAMA: 1 female (CL 25.06 mm), NMNH 111712 : San Jose Island, Perlas Archipelago , 17.v.1944, (J.P.E. Morrison coll.) ; 2 males (CL 22.64 mm and 28.08 mm), NMNH 111673 : San Jose Island, Perlas Archipelago , 26.v.1944, (J.P.E. Morrison coll.) ; PERU: 1 male (CL 29.15 mm), NMNH 77097 : Paita , x.1926, (W.L. Schmitt coll.) ; 3 females (CL 22.12 mm, 21.59 mm and 21.33 mm) and 1 male (CL 18.47 mm), NMNH 111674 : Nanora Bay, Sechura Bay , 16.v.1941, (M.J. Lobell coll.) ; 2 males (CL 29.86 mm and 27.69 mm), NMNH 111853 : Chilca Bay , 16.iv.1941, (M.J. Lobell coll.) .

Diagnosis. Rostrum with 2 teeth; spine at the epistome region absent; sharp spine on the cheliped carpus.

Redescription. Dark yellowish orange, brownish yellow, or vinaceous brown, abundantly covered over dorsal surface with small, rounded white spots; spotted pattern faint on chelipeds. Front (frontal region) not having a spine in the epistome region, between antennules. Rostrum armed with 2 prominent teeth. Transverse sinus at distal end of cheliped merus shallow, marked; one spine at inner border of carpus; outer spine reduced to denticle leading to a developed carina. Male gonopods extended well beyond midpoint of telson.

Remarks. The holotype, preserved in dry conditions, was examined by the collection curator (C.O. Coleman, Museum für Naturkunde, Berlin), who sent us some detailed photos. From these records, the shape and the pattern of various structures, e.g. rostrum and carapace, connect with certainty the specimen to the description proposed above. Apart from the discrete characters in the descriptions, a myriad of other features subtly differs between the species. For instance, in A. mexicanus , the inter-regional furrows are more profound and marked, while the inner branchial lobule is more prominent; anterolateral teeth are apparently longer and narrower; the lateral horn and the merus of the swimming legs are proportionally longer; and the epistome region lacking a spine is more concave and profound. Another character that deserves attention is the supraorbital inner lobe (tooth sensu Rathbun 1930 and Garth & Stephenson 1966), which is narrower and nearly rectangular in shape or virtually similar to A. cribrarius , contrary to previous descriptions. Such character exhibited a variation in different populations of A. mexicanus . Analyzed specimens from Costa Rica possessed wider lobes, resembling the condition observed in A. cribrarius . Conversely, analyzed specimens from the Mexican Pacific, presented narrower structures, in accordance to previous descriptions for the genus. Further, the description of the male gonopods in Garth & Stephenson (1966) is imprecise, as it does not consider the basal ornamentation.

An illustrated, simplified key for the species of the genus Arenaeus is given in Fig. 5 .

Figures

FIGURE 3. Arenaeus mexicanus (CCDB 2936) and diagnostic features. A, dorsal view; B, carpus view, with the inner spine (black arrow) and an outer denticle (white arrow) at the carpus; C, frontal view and the absence of a spine in the epistome region, note the concavity instead.

FIGURE 4. First left gonopod of Arenaeus mexicanus (UNAM 3513). A, ventral view; B, tip morphology, ventrolateral view; C, tip morphology, dorsal view; D, subterminal armature, lateral view; E, basal armature, lateral view. Distal margin bent during the preparation (B and C).

FIGURE 5. An illustrated and simplified taxonomic identification key for the species of the genus Arenaeus.