Monomia calla, Koch, Milan, Nguyen, Thanh Son & Ďuriš, Zdeněk, 2015

Koch, Milan, Nguyen, Thanh Son & Ďuriš, Zdeněk, 2015, Monomia calla, a new species of swimming crab (Decapoda, Portunidae) from Madagascar and the Philippines, Zootaxa 3981 (3), pp. 405-412 : 406-411

Monomia calla sp. nov.

( Figs 1–4 )

Material. 1 male, holotype, CW 33.5 mm, MNHN-IU-2014-10105; South off Sainte Marie Cape, 26°08' S – 46°04' E, south of Madagascar; Atimo Vatae Expedition, 14 May, 2010, fishery vessel Nosy Be 11, stn CP3611, 106– 111 m.

Additional material. 1 male, CW 38.4 mm, ZRC 2001.0633; Philippines: Balicasag Island, Bohol, 28 Nov. 2001, coll. by local fishermen, tangle nets, 50– 500 m.

Description of male holotype. Carapace ( Figs 1 A, 2A) subcircular, CL/CW ratio 0.66. Front width 0.18 of CW, frontal region including inner orbital tooth 0.27 of CW, fronto-orbital width (between tips of outer orbital teeth) 0.55 of CW. Front subdivided into 4 distinct subequal triangular teeth, median pair distinctly narrower than lateral, with median notch slightly shorter than more lateral ones. Inner orbital angle reaching half of lateral frontal teeth, obtusely angulate, with lateral part of dorsal surface finely granular, median part smooth. Supraorbital margin granular, with 2 well-developed notches medially, on base of first anterolateral tooth. Infraorbital margin strongly granular, with narrow, very deep lateral notch, with tooth-like elevation on ventral side of first anterolateral tooth. Anterolateral margin convex, with 9 forward projecting teeth with granular margins; first tooth larger, with sinuous outer margin, rounded tip; second to eighth teeth subequal in size, sharp; ninth tooth about double size of preceding ones. Posterolateral margin slightly granular, concave, slightly shorter than anterolateral margin; posterolateral angle rounded; posterior margin finely granular, slightly convex.

Dorsal surface of carapace densely covered by short tomentum. Regions well defined, elevated, bounded by patches of distinct knob-like granules; anterior median elevation forming cross-like structure with mesogastric granular patches, connected by smooth area with granular metagastric regions; latter regions with transverse line of granules anteriorly; mesobranchial regions subdivided into 4 patches of granules; anterolateral regions fringed by groups of granules; cardiac, lateral postcardiac, median postcardiac regions each with simple granular patch. Epistome well defined, median tooth projecting beyond posterior angle of median frontal incision. Surface of male thoracic sternites ( Fig. 1 B) finely tomentose, sternites 2–5 roughly granular; sternite 6 granular along anterior, lateral margins; sternites 7, 8 smooth; sternites 3, 4 fused, without distinct sulcus; sternite 4 with deep median groove; sternites 5–8 well defined. Abdomen ( Figs 1 B, 2B) T-shaped, outer surface densely tomentose; posterior abdominal margin forming pair of subparallel tranverse laminar crests on each of somites 2, 3 slightly sinuous, with median concavity on somite 3, median convexity on somite 2; lateral margins of somite 3 almost straight, oblique, with subrectangular angles; somites 3–5 fused, sulcus between somites 4, 5 inconspicuous, sulcus between somites 3, 4 reduced to short central groove; elevated submarginal ridge posteriorly present on somite 4; somite 6 robust, subrectangular, 2 times longer than telson, 1.1 times longer than wide distally, lateral margins subparallel, slightly diverging distally, with rounded anterolateral angles distinctly elevated laterally, with pair of low but distinct distolateral swellings covering tips of male first gonopods, somewhat less elevated regions covering bases of male first gonopods on proximolaterally part of somite 4; telson narrowly triangular, 1.3 times longer than basal width, with rounded tip, posterior margin broadly rounded.

Third maxillipeds ( Fig. 2 C) distinctly granular on ischium, merus, exopodal peduncle, with densely setose margins; palp (dactylus, propodus, carpus) tapering distally, with segments subcylindrical; merus subquadrate, with lateral, mesial glabrous fields, anterolateral angle forming widely subtriangular projection; ischium about 2.0 times merus length, 1.7 times as long as wide, with longitudinal glabrous sulcus. Exopod relatively stout, about half of ischium width, with subdistal triangular projection on inner medial border; flagellum longer than merus width.

Chelipeds ( Figs 1 A, 2D) symmetrical, relatively robust, with chela length subequal to CW. Merus with 4 spines on anterior, one glabrous, depressed, spine on posterior border. Carpus with 1 sharp, long, inner spine, one flattened outer spine; 3 distinct carinae on dorsal surface, with 2 of latters terminating as spines (see above). Upper surface of palm with 2 granular crests, inner one ending by spine distally, outer surface with distinct spiniform proximal tooth over articulation with carpus, with 2 granular crests ending on level of finger joint; inner surface of palm with obtuse longitudinal keel dividing ventromesial, ventrolateral surfaces of squamiform transverse ridges; fingers straight, tapering, 0.7 of maximum palm length, distinctly carinate. Movable finger of right chela with distinct slightly elongated molariform tooth proximally on cutting edge, left chela with bilobed conical teeth on such position. Fingers otherwise with bi-, trilobed serial conical teeth separated by small single lobes.

Fifth ambulatory leg with merus finely serrate on both antero-, posterodistal angles. Dactylus oval, 2.4 times longer than maximum width, broadly rounded distally, with longitudinal median sulcus; upper surface finely pilose, with 4 longitudinal glabrous patches submedially, marginally.

Male first gonopod ( Fig. 1 C–E) with proximal part swollen but tapering distally, situated obliquely to median body plane, distal half slender, parallel to body plane, flattened in oblique plane facing ventrolaterally, apex bended laterally, subterminally widened to oblique funnel with ventrally opened longitudinal groove, dorsal margin membranous, tip recurved medially.

Variation in Philippine specimen ( Figs. 3 , 4 ). The Philippine specimen is very similar to the holotype and consistent in the majority of the characters. Most significantly, the male first gonopods of both the specimens are almost identical. The carapace of the Philippine specimen, however, is relatively broader, with the CW/CL ratio 1.7 (1.55 in the holotype); the frontal and anterolateral teeth are more slender, sharper, with the last (lateral) tooth a bit longer; the angle of the posterolateral margin posterior to the lateral tooth is more subquadrate (broadly rounded in the holotype); the chelipeds have the carpal and palmar teeth relatively more robust, with the merus shorter and stouter, and with 3 spines on the anterior border of the merus (4 spines in the holotype); the sixth pleomere of abdomen with more sinuous lateral margins (vs. more straight and angular); and the telson lightly shorter ( Fig 3 B).

Measurements [in mm]. Holotype: CW 33.5, CL 22.4, fronto-orbital length 18.1, frontal length 8.9, right/left chela length 27.6/27.9, right/left finger length 13.4/13.7.

Coloration. The holotype specimen was preserved for some time in ethanol but residual red spots are visible ( Fig. 1 A) on the tips of the anterolateral teeth of the carapace, on the front, on the anterior border of the manus and carpus of the chela, and on both the inner surface of the palm and the movable finger.

Etymology. This species is named after the flower of the calla lily, a plant of the genus Zantedeschia , family Aracea, to which the shape of the male first gonopod of the new species resembles. The name is used as a noun in apposition.

Remarks. The subgeneric name Monomia was established by Gistel (1848) as a substitution for De Haan’s (1833) name Amphitrite , which was established for a group of Portunus species (type species P. gladiator Fabricius, 1798 ). Amphitrite Mueller, 1771 , the senior homonym, is a genus of polychaete worms (Ng et al. 2008). Its subgeneric status has been accepted by most authors in recent years, except Barnard (1950), who used it as the generic name for two South African species, M. argentata (A. Milne-Edwards 1861) , and M. gladiator (Fabricius, 1798) . Ng et al. (2008) recognised 11 species in the genus (as a subgenus). Chertoprud et al. (2012: 312) more recently used the name at generic level for M. pseudoargentata ( Stephenson, 1961) , in addition to the two species by Barnard (1950), citing other studies that suggested the various subgenera of Portunus are all valid genera. We agree at least in as far as Monomia Gistel, 1848 , is concerned its member species can all be characterised by the following characters: moderately broad and dorsally slightly convex carapace with large orbits and large anterolateral teeth, and with rounded posterolateral angles; basal antennal segment forming a blunt lobiform process; epistome slightly produced into a median tooth; and merus of the third maxilliped with a produced anterolateral angle (cf. Alcock 1899; Barnard 1950).

Monomia calla sp. nov. can be distinguished from all other congeners by the unique shape of the male first gonopod, terminating into a widened, funnel-like tip. Compared to most congeners, the new species also differs by the presence of a single posterior meral tooth on the chelipeds, and by the front of the carapace subdivided into four subtriangular teeth of almost the same size. In contrast, the majority of congeners, i.e., M. argentata , M. australiensis ( Stephenson & Cook, 1973), M. curvipenis ( Stephenson, 1961) , M. euglypha ( Laurie, 1906) , M. gladiator , M. petrea ( Alcock, 1899) , M. pseudoargentata , and M. samoensis Ward, 1939 , possess two spines on the posterior margin of the merus of the cheliped, and have low submedian frontal teeth (cf. A. Milne-Edwards 1861: 332; Alcock 1899: 35-38; Ward 1939: Figs. 5, 6; Stephenson 1961: Pl. 2, Figs. 3 , 4 ; Stephenson & Cook 1973: Figs. 6-10).

Ng et al. (2008: 152) resurrected Portunus ponticus Fabricius, 1798 , as a distinct species, briefly commenting that it was close to M. gladiator . We examined photographs of the types of Monomia pontica in the Zoology Museum of the University of Copenhagen ( Jensen 2006) and it clearly differs from the new species by the presence of transverse crests (instead of patches of granules) on the dorsum of the carapace, the submedian frontal teeth produced beyond lateral teeth (subequal in the new species), distinctly elongate chelipeds with palms much more slender than the merus (with stout palm in the new species), and the presence of two sharp teeth dorsally on the distal part of the palm (one tooth in the new species).

Monomia rubromarginata ( Lanchester, 1900) and M. lecromi ( Moosa, 1996) are morphologically closest to M. calla sp. nov. due to the presence of one tooth on the posterior margin of the cheliped merus, with sharp and distinct frontal teeth, and with a similar shape of the merus of the third maxilliped. There are nevertheless some significant differences between these two species and the new species: males have the abdomen with a trapezoid penultimate segment (relatively quadrangular in the new species), with its lateral outline clearly continuing to the lateral borders of the telson, and an almost straight, distally simple, male first gonopod (twisted gonopod with a funnel-shaped tip in the new species) (cf. Lanchester 1900; Stephenson & Campbell 1959; Moosa 1996).

The closest congeners of M. calla sp. nov. are from the Western Pacific: M. lecromi was reported only from the Chesterfield Islands, Coral Sea ( Moosa 1996), whereas M. rubromarginata has been recorded from Singapore ( Lanchester 1900), the South China Sea and the Malay Archipelago ( Shen 1937), as well as the northern half of Australia ( Stephenson & Campbell 1959). The wide geographical distance between the localities of the new species, Madagascar and Philippines, together with some morphological distinctions reported above, is intriguing. While the observed morphological differences are not very major, the fact remains that only two specimens are known, and their male first gonopod structures are very similar. More specimens will need to be obtained to ascertain the degree the variation, perhaps also with additional genetic studies conducted.

The species name “ Portunus (Monomia) calla ” was first used by Nguyen (2013) in his thesis, but as the work is not published, the name is not available. With the description of Monomia calla sp. nov., 12 species are now known in the genus.

Distribution. Known from the type locality, south off Madagascar, the western Indian Ocean and Bohol Island, Philippines, the Sulu Sea.

Figures

FIGURE 1. Monomia calla sp. nov., male holotype, MNHN-IU- 2014 - 10105. A, overall habitus, dorsal. B, thoracic sternum and abdomen, ventral. C, male first gonopods, ventral. D, left male first gonopod, ventromesial. E, same, apex. Scale bars: A, 10 mm, B, 5 mm, C – E, 1 mm.

FIGURE 2. Monomia calla sp. nov., male holotype, MNHN-IU- 2014 - 10105. A, carapace, dorsal. B, abdomen, ventral. C, third maxilliped. D, right chela and distal carpus, lateral. Scale bars: A, D, 10 mm, B, C, 5 mm.

FIGURE 3. Monomia calla sp. nov., male (38.4 × 24.1 mm), ZRC 2001.0633. A, overall habitus of specimen. B, thoracic sternum and abdomen, ventral. C, front view. D, left chela.

FIGURE 4. Monomia calla sp. nov., male (38.4 × 24.1 mm), ZRC 2001.0633. A, left male first gonopod. B, apex of left male first gonopod. C, lateral view of left male first gonopod apex. D, left male second gonopod. E, basal antennal segment. F, third maxiliped. G, male abdomen. Scale bars: 1.0 mm (B, C, same scale bar).