First record of a freshwater crab , Maydelliathelphusa masoniana ( Henderson , 1893 ) ( Decapoda : Brachyura : Gecarcinucidae ) from West Bengal , India

The genus Maydelliathelphusa Bott, 1969 includes five species, M. masoniana (Henderson, 1893), M. edentula (Alcock, 1909), M. falcidigitis (Alcock, 1910), M. harpax (Alcock, 1909), and M. lugubris (Wood-Mason, 1871), and is endemic to India. Out of the five species, only Maydelliathelphusa lugubris (Wood-Mason, 1871) was reported from West Bengal previously. Present study reports the second species, M. masoniana (Henderson, 1893), from West Bengal, India for the first time.


OPEN ACCESS
Freshwater crabs belonging to infraorder Brachyura of order Decapoda are important in terms of nutrient cycles, bio-indicators of environments, disease transmission and small scale fisheries (Cumberlidge et al. 2009;Valarmathi 2017;Harhoglu et al. 2018;Kotwal & Sharma 2020). They are characterized by a broad carapace-covered cephalothorax having five pairs of thoracic legs or pereiopods (one pair of chelipeds, four pairs of walking legs) and a reduced abdomen (Deb 1999;Yeo et al. 2008). These crabs complete their entire life cycle in freshwater environments without moving to saltwater (Yeo et al. 2008).

Materials & Methods
During an ichthyological survey, two specimens of M. masoniana were collected from a small stream (26.229 0 N, 89.255 0 E, elevation 32m) of the Brahmaputra River system in Cooch Behar district, West Bengal, India (Image 1). The collected specimens were immediately photographed; morphometric measurements were taken and preserved in 70% alcohol after anaesthetized. The specimens were identified as per the standard identification keys of Henderson (1893), Alcock (1910a,b), andNg et al. (2008). The specimens were deposited in the Aquatic Animal Biodiversity Museum of the Department of Industrial Fish & Fisheries, Asutosh College, Kolkata (Reg. No. AABM/IFF/ AC/CRUSTACEA/CRAB-1 to 2).  Table 1).

SHORT COMMUNICATION
Diagnosis: The carapace is broader than long, slightly depressed; epigastric cristae distinct, rugose, located somewhat anterior to postorbital cristae without merging with the latter ( well defined towards the sides; a wide gap between frontal margin and postorbital cristae; external orbital tooth prominent; anterolateral margin with prominent epibranchial tooth; wide frontal margin, frontal median triangle incomplete (Image 2B & 3B); cervical groove well developed; mesogastric furrow deep, slightly bifurcated posteriorly; chelipeds asymmetric and massive (Image 2 E), carpus with a strong spine, propodus and dactylus with strong teeth which can meet only at the tips creating a wide gap between them (Image 2E); 6 th pleonal somite of adult male slightly longer than breadth with concave lateral margin (Image 2F).
Description: The morphometric measurements of the identified species are presented in Table 1. The carapace enlarged, broader than length (cw/cl= 1.36), slightly depressed, dorsal surface smooth; epigastric cristae distinct, rugose, located anterior to postorbital cristae without merging with the latter; postorbital cristae well defined towards the sides, a wide gap between frontal margin and postorbital cristae (Image 2A, 3A); orbits large, external orbital tooth prominent; wide frontal margin (fw/cw= 0.18); anterolateral margin with prominent epibranchial tooth; cervical groove well defined; mesogastric furrow deep, slightly bifurcated posteriorly; eyes smaller than orbital space, eyestalk short, narrow (Image 2B, 3B ); mandibular palp three-segmented; 1 st , 2 nd maxilliped with long flagellum on exopods; 3 rd maxilliped almost cover buccal cavity when closed (Image 2B, 3B); ischium subrectangular, longer than broad, with a narrow medial groove; merus nearly pentagonal, broader than long; exopod slender, longer than ischium, reaching the base of merus, with a long flagellum (Image 2D ). Chelipeds smooth, asymmetrical and massive, right cheliped larger than the left (Table 2, 3) carpus, with strong spine, propodus and dactylus with 12 to 13 strong teeth which can meet only at the tips creating a wide gap between them (Image 2E); ambulatory legs (P2-P5) stout, shorter than chelipeds; P3 longest and P5 shortest, dactylus longer than propodus with four rows of spines on the margins.
Colour: Dark brown in fresh condition.
Habit & Habitat: M. masoniana creates small burrows at the adjoining areas of soil and water of the stream for living and breeding purpose (Image 4A-C). Their preferred habitat is the small or narrow canals or streams with slowmoving water. They are nocturnal in habit.
Conservation status: As per the IUCN Red List of threatened species, the species belongs to the Least Concern (LC) category (Cumberlidge 2008).

Discussions
The freshwater crab, M. masonia was originally described as Telphusa masonina in the year 1893 by Henderson using type locality of river Jumna, North-West Provinces, India. Alcock (1910) transferred the species to the sub-genus Barythelphusa Alcock, 1909 of the Genus Parathelphusa Edwards, 1853 using a specimen from northern to central India. Bott (1970) created the subgenus Maydelliathelphusa and placed the species in that subgenus in a revisionary work. Specimen collected in the present study is in agreement with the original description of M. masoniana. In an earlier study, Krishnamurthy (1995), reported the species from Uttar Pradesh, India. Recently, the species has been reported from Jammu & Kashmir (Kotwal & Sharma 2020).

Conclusion
The present study extends the distribution of M. masoniana to West Bengal. As all the five species of the genus Maydelliathelphusa are similar morphologically, molecular taxonomy to confirm the morphological taxonomy of the species is warranted. Further studies are needed to investigate the biology, threat and conservation of this species, and to evaluate the potentiality of the species for commercial fisheries in that region.

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