Maydelliathelphusa edentula Alcock, 1909

Shashi, Shibly Sadique, Pan, Da, Emu, Nusrath Jahan, Roy, Mishal, Sadek, Md. Abu, Sharifuzzaman, S M & Sun, Hongying, 2023, Two new records and an updated checklist of freshwater crabs (Arthropoda, Malacostraca, Decapoda, Potamidae and Gecarcinucidae) from Bangladesh, ZooKeys 1167, pp. 211-222 : 211

Maydelliathelphusa edentula Alcock, 1909

Figs 3 , 4c, d

Potamon lugubre edentulum Alcock, 1909: 247.

Paratelphusa (Barytelphusa) edentula - Alcock 1909: 376; Alcock 1910: 84, fig. 19.

Barytelphusa (Maydelliathelphusa) edentula - Bott 1970: 34.

Maydelliathelphusa edentula - Ng et al. 2008: 68.

Material examined.

1 male, 65.89 × 49.16 mm (Table 1 ), Kangsa River , Netrokona, Mymensingh, Bangladesh, 25°00'45"N, 90°38'54"E, 10 August 2021, collected by Shibly Sadique Shashi and Nusrath Jahan Emu.

Description of the male.

Carapace slightly depressed, ca 1.34 × broader than long; epigastric cristae distinct, epigastric and postorbital cristae on either side united (Fig. 3a ); postorbital cristae distinct, sharp, subparallel to frontal margin; frontal region deflexed, relatively wide; external orbital tooth prominent, epibranchial tooth present, prominent; frontal margin bilobed, frontal median triangle not complete; cervical groove well developed; mesogastric furrow very distinct, deep, slightly bifurcated posteriorly. Anterolateral and posterolateral regions rugose. Eyes smaller than orbital floor; eyestalk short. Third maxilliped with ischium subrectangular, longer than broad, with distinct narrow medial groove; merus pentagonal, broader than long; exopod slender, longer than ischium, reaching base of merus, with long flagellum (Fig. 3c ). Epistome lateral margins slightly sinuous, medial lobe triangular (Fig. 3c ).

Chelipeds surface smooth, unequal, right cheliped larger; carpus with distinct spine on inner angle; fingers longer than palm, movable finger strongly curved downward, immovable finger smoothly curved upward, wide gap between dactyl and pollex when closed, movable finger comparatively larger than immovable finger, inner margin of fingers lined with numerous round and blunt teeth (Fig. 3d ); ambulatory legs stout; second pair of ambulatories longest while the fourth pair shortest (Fig. 3b ); dactylus slender, longer than propodus, with 4 rows of spines on the margin (Fig. 3b ).

Male thoracic sternum smooth, pitted. Sternites s1/s2 completely fused forming triangular structure; suture between s3/s4 shallow; suture between s4/s5, s5/s6, s6/s7, s7/s8 distinct (Fig. 3b ).

Male pleon T-shaped, somites 5 and 6 constricted medially. Telson tongue-shaped, length and width almost equal (Fig. 3b ).

G1 stout, straight; terminal segment tapering gradually, almost 2 × shorter than subterminal segment (Fig. 4c, d ). G2 elongated, shorter than G1.

Remarks.

Maydelliathelphusa edentula was originally described as Potamon lugubre var. edentulum Alcock 1909 from Assam, India and subsequently transferred to Barytelphusa (Maydelliathelphusa) Bott, 1969 ( Bott 1970). The present record is the first report of the genus Maydelliathelphusa from Bangladesh. Previously, M. edentula was documented in India (Assam, Nagaland, Mizoram) and Bhutan (Samchi) ( Cumberlidge 2008b; Valarmathi 2017; Ray et al. 2018; Das 2021). Suitable habitats include freshwater rivers and streams ( Cumberlidge 2008b). Therefore, it is not surprising that M. edentula occurs in eastern Bangladesh, near its known distribution range.

The IUCN conservation status of M. edentula is Near Threatened (NT) because of its limited distribution range and vulnerable habitat ( Cumberlidge 2008b). Although the current study has expanded its known geographic distribution, the conservation status of this species is still not optimistic. In western Bangladesh, some local people, especially fishermen, eat this crab on a limited scale. In addition, various types of human activities, like pollution, urbanization and sand mining are impacting freshwater habitats in that area and, consequently, are threats to the population of M. edentula .

Until now, five species belonging to the genus Maydelliathelphusa have been recorded from India, Bhutan, and Nepal ( Cumberlidge 2008c; Valarmathi 2017; Das 2021). The morphology of the carapace of M. edentula is superficially similar to that of other four species. However, M. edentula can be easily distinguished externally by its large, distinctively asymmetric chelipeds and its united epigastric and postorbital cristae ( Bott 1970; Das 2021).

Figures

Figure 3. Maydelliathelphusa edentula a dorsal view b ventral view c frontal view d major chela and e minor chela. Scale bars: 2 cm.

Figure 4. G 1 a, b Acanthopotamon fungosum c, d Maydelliathelphusa edentula. Scale bars: 2 mm.