Neosarmatium africanum, Ragionieri & Fratini & Schubart, 2012

Ragionieri, Lapo, Fratini, Sara & Schubart, Christoph D., 2012, Revision Of The Neosarmatium Meinerti Species Complex (Decapoda: Brachyura: Sesarmidae), With Descriptions Of Three Pseudocryptic Indo-West Pacific Species, Raffles Bulletin of Zoology 60 (1), pp. 71-87 : 73-78

Neosarmatium africanum , new species

( Figs. 1a , 2a , 3a,e , 4a,e , 5a , 6a,b )

Sesarma tetragona: Krauss, 1843: 44 ; Hilgendorf, 1869: 90, pl. 3, Fig. 3d ; 1879: 809; A. Milne-Edwards, 1868: 71; Hoffmann, 1874: 23; Lenz & Richters, 1881: 425 [not Cancer tetragona Fabricius, 1798: 341 ].

Sesarma africana (?): Bianconi, 1869: 341 [fide Hilgendorf, 1879: 809; Tesch, 1917: 171] [not Sesarma africana H. Milne Edwards, 1837 = Perisesarma huzardi ( Desmarest, 1825) ].

Sesarma tetragonum: Stebbing, 1910: 321 ; 1917a: 438; 1917b: 10 [not Cancer tetragona Fabricius, 1798: 341 ].

Sesarma meinerti De Man, 1887: 648 , 668–669 (in part); Pfeffer, 1889: 31; Ortmann, 1894a: 720 (in part); Lenz, 1905: 372; Gravier, 1920: 472; Cott, 1930: 679–692, pl. 1; Fourmanoir, 1953: 89; 1954: 5; Vannini & Valmori, 1981: 57; Pereyra Lago, 1989: 199; Emmerson & McGwynne, 1992: 41; Emmerson, 1994: 568.

Sesarma (Sesarma) meinerti: Tesch, 1917: 171–174 (in part); Chace, 1942: 201; 1953: 441; Bernard, 1950: 125–26, Fig. 25e, f; Crosnier, 1965: 61, Figs 81, 90, 91, 96, 103.

Neosarmatium meinerti: Davie, 1994: 35 (in part); Dahdouh- Guebas et al., 1997: 83; 1998: 345; Skov & Hartnoll, 2002: 1–7; Gillikin et al., 2004: 93; Skov et al., 2005: 1164; Fratini et al., 2005: 222, 225; Schubart et al., 2006: 195, 197; Berti et al., 2008: 101; Cannicci et al., 2008: 186; Ragionieri et al., 2009: 825–834, 2010: 179–188.

Material examined. — Holotype: male (42.83 × 38.33 mm) ( MZUF 678 ), Jumbo River , Somalia, coll. M. Vannini, Dec.1976 . Paratypes: SOMALIA: 2 males (24.07 × 20.17 mm; 40.42 × 34.48 mm) ( MZUF 677 ), Jumbo River , coll. M. Vannini, Dec.1976 ; KENYA: 1 male (37.65 × 32.36 mm) ( MZUF 3666 ), Mida Creek , coll. M. Vannini, Jul.1997 ; 1 male (27.38 × 23.89 mm) ( MZUF 2731 ), Mida Creek , coll. S. Fratini, 7 Feb.2005 ; 2 males (46.17 × 41.50 mm; 37.55 × 32.81 mm) ( MZUF 1025 ), Gazi Bay , coll. M. Vannini, Jul.1997 ; 1 male (27.38 × 23.89mm) ( MZUF 2731 ), Mida Creek , coll. S. Fratini, 7 Feb.2005 ; 3 males (36.72 × 34.03 mm; 38.31 × 33.09 mm; 34.09 × 29.57 mm) ( MZUF 2967 ), Mida Creek , coll. S. Cannicci, Oct.1997 ; SOUTH AFRICA: 1 male (45.53 × 40.14mm) ( MNHN-B31275 ), Natal , coll. B. Newman , 1997; AFRICAN COAST: 1 male, 1 female ( ZRC 1968.1.22.6–7), coll. MacNae, Apr.1967 ; MADAGASCAR: 1 female (34.0 × 29.0 mm) ( RMNH D171 ), Nosy Bé (former syntype of Sesarma meinerti De Man, 1887 ), coll. F. P. L. Pollen & D. C. van Dam , 1963–1966; 4 males (37.15 × 31.67 mm; 34.56 × 29.60 mm; 38.50 × 33.63 mm; 31.26 × 25.88 mm) ( MNHN-B30342 ), Tuléar , coll. A. Crosnier 8 Oct.1961 ; 1 male (40.7 mm carapace width) ( ZMB 12679) northwest Madagascar , coll. J. M. Hildebrandt , 1879.

Diagnosis. — Carapace narrowing towards posterior with slight concavity medially ( Fig. 2a ), without any indication of second anterolateral teeth. Male chela characterised by presence of single prominent line of tubercles along inner palm surface ( Fig. 3e ) with palm height 1.55 (± 0.12) times maximum chelar width. Descending slope of palm (with parallel prominent ridge) oblique at articulation with dactylus ( Fig. 3a ). Lower margin of chela straight. Dorsal surface of dactylus covered with tubercles until three-quarters of length ( Fig. 4a, e ). Male abdomen triangular; somite 6 with proximal width 1.35 (± 0.071) times length; telson length 1.24 (± 0.127) times width ( Fig. 5a ).

Description. — Carapace: smooth, bearing short setae in tufts on anterior half. Carapace ca. 1.14 (± 0.031; n = 19) times broader than long. Maximal carapace width ca. 1.23 (± 0.028; n = 19) times posterior carapace width. Carapace width ca. 1.61 (± 0.063; n = 19) times body height. Anterolateral tooth triangular. Lateral margin narrowing towards posterior slightly concave medially ( Fig. 2a ). Frontal border straight with front ca. 0.50 (± 0.021; n = 19) times carapace width. Postfrontal margin separated into 4 well-defined lobes, median lobes more prominent, than external ones, separated by deep concavity ( Fig. 1a ). Cardiac region with deep Hshaped gastro-cardiac groove. Branchial ridges prominent; other ridges arise laterally, near lateral margin of carapace ( Fig. 2a ).

Third maxilliped: Suture between merus and ischium of third maxilliped oblique. Ischium with shallow submedian sulcus; slender exopod with tip reaching half length of outer margin of merus. Inner margin of both ischium and merus with dense setae ( Fig. 1a ).

Chelipeds: Merus of chela with tubercles on inner face and along dorsal margins. Carpus with row of short setae on dorsal margin and weak tubercles along anterior and posterior margins. Outer surface of palm glabrous with microscopic granules ( Fig. 3a ). Chela length ca. 1.39 (± 0.09; n = 19) times dactylus length. Inner surface of palm with single prominent row of tubercles that forms angular structure ( Fig. 3e ). Descending slope of palm (with parallel prominent ridge) at articulation with dactylus oblique, especially visible from outer side ( Fig. 3a ). Proportion of chelar length to maximum chelar width ca. 2.61 (± 0.27; n = 19). Dactylus strongly curved, forming wide gap with pollex ( Fig. 3a, e ). Dorsal surface of dactylus with minute granules extending towards two-thirds of length ( Fig. 4a, e ). Immovable finger moderately curved inwards, ventral border straight ( Fig. 4a ).

Ambulatory legs: Third and second legs (pereiopods 3 and 4) longest. Length of merus of third walking leg ca. 2.1 (± 0.17; n =19) times its width. All legs with bristles along ventral margins of coxae, basis-ischia and meri. Outer surfaces of meri strongly rugose. Carpi and propodi with short mat of soft setae on dorsal and ventral margins of pereiopods 2 and 3, only present on dorsal margin of fourth pereiopods. Bristles present on both margins along carpi and propodi. Dactyli shorter than propodi with 6 longitudinal lines of setae proximally.

Male abdomen: Width of somite 3 ca. 2.24 (± 0.098; n = 19) times carapace width. Somite 6 elongated with proximal width 1.35 (± 0.071; n = 19) times length. Telson shorter than somite 6; ca. 1.24 (± 0.127; n = 19) times longer than wide ( Fig. 5a ).

Gonopods: First male gonopods almost straight, distally curved inward with outer margins convex. Distal part of stem straight, broad, with setae around apex ( Fig. 6a ); apex moderately fold towards medial plane of body ( Fig. 6b ).

Etymology. — The species name Neosarmatium africanum makes reference to the geographical distribution of this species along the East African coast, from Somalia to South Africa, including parts of Madagascar.

Colour. — This species occurs in East Africa with exclusively red-orange chelae, the colouration extending onto two-thirds of the proximal part of the palm and the fingers fading to yellow distally.

Habitat. — Neosarmatium africanum , new species, lives in burrows in the dry and muddy area of the upper intertidal belt associated with mangroves and estuaries. Burrow entrances usually are surrounded by a mound of mud. The burrows have secondary channels, with a mean length of around 80 cm usually extending to the water table ( Berti et al., 2008).

Ecology. — Neosarmatium africanum , new species, as many other species of Sesarmidae , plays an important role in the biochemical cycle of mangrove leaves degradation. Analysis of stomach content showed that its diet mainly consists of mangrove leaves, especially of Avicennia marina , completed with little animal matter ( Dahdouh-Guebas et al., 1997). Nevertheless, Skov & Hartnoll (2002) showed that the mangrove leaves are unlikely to fulfil the nitrogen requirements of crabs. Leaf fragmentation may enrich the nutritional quality of the substrate detritus, with the sediment detritus being a richer source of nitrogen, regularly ingested by crabs (Skov & Hartnoll, 2002). Moreover, this species seems to be a strong mangrove propagule consumer and may even affect the regeneration potential of mangroves ( Dahdouh-Guebas et al., 1998). As the density reached by N. africanum in most of East African mangroves can be high (see Fratini et al., 2011), bioturbation due to its excavation activity contributes to a rapid nutrient enrichment of soil and as a consequence, enhances mangrove primary production. These observations lead Cannicci et al. (2008) to review the ecological function of many crab species inhabiting the mangal ecosystem and highlighted the importance of crab bioturbation in producing a rapid enrichment of the primary production of mangroves. From a physiological point of view, N. africanum is able to resist large salinity fluctuations as congeneric species, like N. smithi , and this appears to be typical of species living along the landward fringe of the East African mangal ( Gillikin et al., 2004).

Breeding and larvae. — The breeding season of Neosarmatium africanum , new species, varies according to its latitudinal distribution along the East African coast. In Kenya and Tanzania, the highest occurrence of ovigerous females is during the dry season (between February and April), while in sub-temperate areas such as South Africa, most ovigerous females occur during the summer season (between January and February) ( Emmerson, 1994; Skov et al., 2005). Pereyra Lago (1989) described five zoeal stages and one megalopa stage of N. africanum (as N. meinerti ), highlighting important morphological characters useful for distinguishing their larvae from those of other sesarmid species sympatric in the same mangal and estuary areas.

Distribution. — East African coast from middle of Somalia to Natal in South Africa. It is also present in Madagascar, at least along the north-western coast of Madagascar close to Nosy Bè. We have not been able to study material from other parts of the island.

Figures

Fig. 1. Frontal view of four species of Neosarmatium: a, N. africanum, new species, holotype male (42.83 × 38.33 mm) (MZUF 678), Somalia; b, N. meinerti (De Man, 1887) paratype male (40.26 × 35.60 mm) (MZUF 2931), Seychelles; c, N. asiaticum, new species, holotype male (38.52 × 33.11 mm) (NMNS-6327-001), Taiwan; d, N. australiense, new species, holotype male (39.85 × 34.77 mm) (QM- W29085), Australia.

Fig. 2. Dorsal view of carapaces of four species of Neosarmatium: a, N. africanum, new species, holotype male (42.83 × 38.33 mm) (MZUF 678), Somalia; b, N. meinerti (De Man, 1887), paratype male (40.26 × 35.60 mm) (MZUF 2931), Seychelles; c, N. asiaticum, new species, holotype male (38.52 × 33.11 mm) (NMNS-6327-001), Taiwan; d, N. australiense, new species, holotype male (39.85 × 34.77 mm) (QM-W29085), Australia.

Fig. 3. Outer and inner surfaces of the right chelae of four species of Neosarmatium: a, e, N. africanum, new species, holotype male (42.83 × 38.33) (MZUF 678), Somalia; b, f, N. meinerti (De Man, 1887), paratype male (40.26 × 35.60) (MZUF 2931), Seychelles; c, g, N. asiaticum, new species, holotype male (38.52 × 33.11 mm) (NMNS-6327-001), Taiwan; d, h, N. australiense, new species, holotype male (39.85 × 34.77 mm) (QM-W29085), University of Darwin, Darwin, Australia.

Fig. 4. Dorsal view of distal chelipeds and dactyli: a,e, Neosarmatium africanum, new species, holotype male (42.83 × 38.33 mm) (MZUF 678), Somalia; b,f, N. meinerti (De Man, 1887), paratype male (40.26 × 35.60 mm) (MZUF 2931), Seychelles; c, g, N. asiaticum, new species, holotype male (38.52 × 33.11 mm) (NMNS-6327-001), Taiwan; d, h, N. australiense, new species, holotype male (39.85 × 34.77 mm) (QM-W29085), Australia.

Fig. 5. Male abdomens: a, Neosarmatium africanum, new species, holotype male (42.83 × 38.33 mm) (MZUF 678), Somalia; b, N. meinerti (De Man, 1887), paratype male (40.26 × 35.60 mm) (MZUF 2931), Seychelles; c, N. asiaticum, new species, holotype male (38.52 × 33.11 mm) (NMNS-6327-001), Taiwan; d, N. australiense, new species, holotype male (39.85 ×34.77 mm) (QM-W29085), Australia.

Fig. 6. Male left first gonopods and corresponding distal parts: a, b, Neosarmatium africanum, new species, holotype male (42.83 × 38.33 mm) (MZUF 678), Somalia; c, d, N. meinerti (De Man, 1887), paratype male (40.26 × 35.60 mm) (MZUF 2931), Seychelles; e, f, N. asiaticum, new species, holotype male (38.52 × 33.11 mm) (NMNS-6327-001), Taiwan; g, h, N. australiense, new species, holotype male (39.85 × 34.77 mm) (QM-W29085), Australia.