Apograpsus, Komai & Wada, 2008

Komai, Tomoyuki & Wada, Keiji, 2008, A Revision Of The Estuarine Crab Genus Ilyograpsus Barnard, 1955 (Crustacea: Decapoda: Brachyura: Macrophthalmidae), With Descriptions Of A New Genus And One New Species, Raffles Bulletin of Zoology 56 (2), pp. 357-384 : 379

Apograpsus , new genus

Type species. – Ilyograpsus paantu Naruse & Kishino, 2006 . Present designation by monotypy. Gender: masculine.

Diagnosis. – Carapace ( Figs. 17A, B ; 18A ) longer than wide; regions on dorsal surface well defined with gastric, cardiac, intestinal regions markedly elevated; cardiac region with 2 rounded prominences; intestinal region with low median ridge; lateral margin with 3 teeth including external orbital tooth, of which second tooth rudimentary; margin between external orbital tooth and third lateral tooth concave, thus carapace weakly constricted. Front broad, markedly bilobed, not constricted at base. Postfrontal ridges longitudinal, with few long setae anteriorly. Orbit large; upper orbital margin oblique; lower orbital margin ( Fig. 17C ) fairly oblique, smooth or faintly granular, mesial angle produced into prominent projection; inner orbital tooth small. Ocular peduncle ( Figs. 17A, B ; 18A ) slightly constricted; cornea large. Antennules ( Fig. 17B ) transverse or slightly oblique; basal segment inflated; inter-antennular septum narrow. Antennae ( Fig. 17B ) in orbital hiatus; flagellum relatively long. Central region of epistome strongly convex ( Fig. 17B ). Third maxilliped ( Fig. 17E ) similar to that of Ilyograpsus . Cheliped ( Figs. 16A, B ; 17G ; 18C, D ) small in male and female; merus ( Figs. 17F ; 18B ) narrowed distally, without subdistal spine on dorsal margin; carpus without prominent tooth or spine on inner surface; dactylus without differentiated teeth on cutting edges in male; fingers spoon-shaped at tips, not crossing when closed. Ambulatory legs ( Fig. 16A, B ) slender; meri ( Figs. 17I, J ; 18E, F ) each with sharp subdistal spine on anterior margin; propodi unarmed at posterodistal angles. Pleon generally similar to that of Ilyograpsus ; first somite with rounded lateral margin in male ( Fig. 17D ). First gonopod ( Fig. 17H ) stout, nearly straight in ventral view, slightly constricted at midlength; terminal process ( Fig. 17I ) very short, roundly truncate. Female gonopores close to suture between fifth and sixth sternite.

Remarks. – As already noted by Naruse & Kishino (2006), this species markedly differs from other species of Ilyograpsus in many characters. In particular, the carapace being longer than broad, the longitudinal postfrontal ridges with peculiar long setae anteriorly, the conspicuously projecting anteromesial angle of the lower orbital margin and the slightly constricted male first gonopod are unique for Apograpsus . In Ilyograpsus , the carapace is wider than long; the postfrontal ridges are transverse with procurved lateral parts; no setae is present at the anterolateral angle of the front; the anteromesial angle of the lower orbital margin is not markedly produced; and the first gonopod is not constricted at the middle. Furthermore, Apograpsus differs from Ilyograpsus in having three anterolateral teeth on the carapace, of which the second is rather obsolete. In Ilyograpsus , there are four anterolateral teeth. The meri of third and fourth pereopods in females (second and third ambulatory legs) are narrowed distally in Apograpsus , but in Ilyograpsus , the meri of these legs are not narrowed. The sister group of Apograpsus is still unclear, although the structure of the front and orbit of the carapace and the armature of the ambulatory meri link Apograpsus to Ilyograpsus , Enigmaplax and the hypothetical ancestor of Macrophthalmus (see Barnes, 1967). It is interesting to note that juveniles of Ilyograpsus species show some superficial resemblance to Apograpsus paantu , particularly in the carapace shape and the development of the anterolateral teeth (see Sawada et al., 2005, Fig. 4B ). This would seem to suggest a possibility that Apograpsus paantu was perhaps derived through a process of neoteny.

Etymology. – The name is derived from the Greek prefix “ Apo- ”, meaning remote, in arbitrary combination with the genus name “ Grapsus ”, in reference to the non-close relationship of the type species and closely related Ilyograpsus species to the Grapsidae or other related families.

Figures

Fig. 17. Apograpsus paantu (Naruse & Kishino, 2006), new combination. A–E, H, I, male (cl 3.9 mm), CBM-ZC 8834, Yagaji Port, Yagaji Island, Okinawa Islands, Japan. F, G, male (cl 3.4 mm), paratype, RUMF-ZC-238, Tima River estuary, Nago, Okinawa Island. A, carapace, ocular peduncles, and antennae, dorsal view (setae partially omitted); B, cephalothorax and cephalic appendages, frontal view; C, right lower orbital margin, ventral view; D, pleon, ventral view; E, left third maxilliped, ventral view; F, left fourth pereopod, dorsal view; G, left fifth pereopod, dorsal view; H, left first gonopod, ventral view; I, same, distal part, dorsal view. Scale bars: A, B, D = 1 mm; E–I = 0.5 mm.

Fig. 18. Apograpsus paantu (Naruse & Kishino, 2006), new combination. Female (cl 6.4 mm), paratype, CBM-ZC 8493, Yanma, Sumiyo, Amami-ohshima Island, Japan. A, carapace, ocular peduncles and antennae, dorsal view; B, merus of left cheliped, outer view; C, chela and carpus of left cheliped, dorsal view; D, left chela, outer view; E, left fourth pereopod, dorsal view; F, left fifth pereopod, dorsal view. Scale bars: A = 2 mm; B–F = 1 mm.

Fig. 16. Apograpsus paantu (Naruse & Kishino, 2006), new combination.A, male (cl 3.4 mm), RUMF-ZC-238, paratype, Tima River estuary, Nago, Okinawa Island, Japan; B, female (cl 6.4 mm), paratype, CBM-ZC 8493, Yanma, Sumiyo, Amami-ohshima Island, Japan.

Fig. 4. Ilyograpsus rhizophorae Barnard, 1955. A, male (cl 5.0 mm), paratype of Ilyograpsus vannini Sawada, Hosogi & Sakai, 2005, RMNH-D 26501, south of Massawa, Gulf of Zula, Ethiopia; B–E, male (cl 3.8 mm), MNHN-B 12846, Nozy Bé, Madagascar. A, left part of carapace, left ocular peduncle and antenna, dorsal view; B, left cheliped, dorsal view; C, same, chela, outer view; D, right first gonopod, dorsal view; E, same, ventrolateral view. Scale bars: A, B, D = 1 mm; C, E = 0.5 mm.