Environment

Meet the Western Ghats’ Wonderful New Freshwater Crabs

Five new species of brightly coloured freshwater crabs have been found in the Western Ghats, India’s wildlife haven. Of these, two species belong to the genus Ghatiana (discovered in 2014) and the remaining to Gubernatoriana (known since 1970).

Behind the discoveries are an undergraduate student and researchers from the Zoological Survey of India and the Indian Herpetological Society. They described the five new species, named Ghatiana atropurpurea, Ghatiana splendida, Gubernatoriana thackerayi, Gubernatoriana waghi, and Gubernatoriana alcocki, in the journal Zootaxa on February 23.

Prior to this, 36 species belonging to 14 different genera were known from the Western Ghats in the family of freshwater crabs called Gecarcinucidae. So the latest discoveries bring the total species count to 41. These crabs, which have adapted to a terrestrial or semi-terrestrial mode of life, need a freshwater pool for breeding – unlike their marine counterparts that breed in vast, salty water-bodies.

Freshwater crabs also produce fewer, yet larger, eggs than marine crabs. And their eggs hatch into fully-developed juveniles, which are cared for by the females over the coming few weeks.

Ghatiana atropurpurea

Ghatiana atropurpurea. Credit: Arjun Kamdar

Ghatiana atropurpurea. Credit: Arjun Kamdar

This is a tree-living crab with a preference for the jamun tree, whose fruit colour it resembles. It was found in July 2015 from rainwater-containing tree holes in Amboli, Maharashtra. Mature and immature adults were also sighted at ground-level tree holes in Hathipal, Goa, where younger crabs were seen foraging in the undergrowth or resting under rocks.

G. atropurpurea gets its name from the Latin for ‘dark purple’ (atropurpureus). This crab has a broad, deep purple shell that distinguishes it from the other newfound species. Before its scientific discovery, the crab was known to the locals as the ‘purple tree crab’; they had also observed it scavenging on millipedes and snakes that were accidentally killed by vehicles on roads.

Its claw-bearing legs or pincers are differently sized – one is larger than the other. Fingers of the larger claw have four or five large teeth, leaving a gap when their tips meet. This gap in the pincers helps in gripping food and competing for mates. (However, researchers don’t think there is a single reason why they are larger in some species and smaller in others, or differently sized between males and females. This could be due to foraging, sexual selection and defence).

Ghatiana splendida

Ghatiana splendida. Credit: Arjun Kamdar

Ghatiana splendida. Credit: Arjun Kamdar

Named for its splendid looks – pink coloured shell and pincers, and orange legs – this species was found feeding and hiding among cracks in basaltic rocks of a plateau near Amboli, Maharashtra. It was seen during the monsoon season, when rainwater collects in rock crevices. Its claw-bearing legs are unequal in size with left one much larger than the right. Additionally, in males, fingers of the larger claw have six or seven blunt teeth and they meet at the tip leaving a large gap while those of the females have nine or ten teeth and a smaller gap in between.

“The locals knew about the two Ghatianas and photographers had clicked them, too, but no one really thought what genus or species they were,” says Tejas Thackeray, who discovered the two species, along with Gubernatoriana thackerayi, when he was on a project photographing the endemic reptiles and amphibians of Kokan, Maharashtra, in 2015.  

“They would just call them the purple tree crab or the pink forest crab,” adds Thackeray, who is a 19-year old BA student at Jai Hind College in Mumbai and a wildlife photography enthusiast.

“On the third day of the trip we decided to go on a plateau nearby looking for the rare olive forest snake. After hours of searching and no signs of the snake, we decided to climb down the slope and explore the area. It was raining heavily and the area was full of leeches and suddenly I see this absolutely stunning, brilliant pink crab getting out of a hole and I couldn’t believe it; I had never seen a crab this beautiful. Hence, we decided to name it Ghatiana splendida,” Thackeray told The Wire.

Gubernatoriana thackerayi

Gubernatoriana thackerayi. Credit: Shailesh Bhosale

Gubernatoriana thackerayi. Credit: Shailesh Bhosale

Named after its discoverer, G. thackerayi is active during the day and feeds on worms. It was found during monsoon among horizontal cracks in sloping rock formations of Ratnagiri district in Maharashtra. Its shell and walking legs are a striking red while the two pincers are orange-red. Thackeray had suggested the name Gubernatoriana rubra (Latin for ‘red’) but his co-workers decided otherwise.

G. thackerayi’s pincers are broadly rounded or spoon tipped. They are slightly unequal in males; larger claw fingers are dotted with small, rounded teeth and the gap between them is small. In females pincers are of the same size. The crab’s long walking legs are adorned with fine brown bristles.

Gubernatoriana waghi

Gubernatoriana waghi. Credit: Rachit Shah

Gubernatoriana waghi. Credit: Rachit Shah

This orange crab with ivory coloured legs was discovered in Ahmednagar district of Maharashtra in October 2014 by zoologist Prashant Wagh, after whom it is named. It was observed under small rocks on the edge of a cliff in Harishchandragad.

Like other newly discovered species, G. waghi has unequal pincers with the right one being larger. Claw fingers have two or three large teeth and leave a big gap when their pointed tips come in contact.  

Gubernatoriana alcocki

Gubernatoriana alcocki. Credit: B.V. Jadhav

Gubernatoriana alcocki. Credit: B.V. Jadhav

G. alcocki was first seen in 2014 in the Satara district of Maharashtra. It was found under small rocks in short-lived streams on a mountain plateau. This species is restricted to high altitudes (at least a kilometre above sea level) of the Western Ghats because of its preference for such habitats and their isolation from other landscapes.

The crab lives alongside Bombay swamp eels (Monopterus indicus) in a strange predator–prey relationship: adult swamp eels feed on crabs and crabs feed on juvenile eels. The crabs are commonly sighted during monsoons (from June to September) but they are also abundant during the dry season.  

Crabs are olive-brown with orange-brown and hairy appendages. Pincers are of nearly the same size in females – their fingers have 12-14 small, blunt teeth; a relatively small gap is formed where the digits touch. In males, the right pincer is larger and smoother, and its fingers have two or three large teeth and leave a large gap in between.

G. alcocki is named after Indian-born British naturalist Alfred William Alcock, who contributed immensely to the study of ten-legged crustaceans (such as crabs) and “suggested the establishment of an Indian Zoological Survey” (PDF; p. 122) in a letter to the Secretary, Government of India, in 1906. The Zoological Survey of India (ZSI) was born a decade later.

Sameer K. Pati, a senior zoological assistant at the Pune centre of the ZSI, who was also behind the discovery of the genus Ghatiana in 2014, says that the finds are just tip of the iceberg. According to him, there are still as many undiscovered species and even new genera of freshwater crabs out there.   

An elated Thackeray adds, “With DNA analysis, what we think of as one species could turn out to be three or four different species [sharing] similar morphological characteristics. Genetically, they could be different.”  

However, freshwater crabs are endemic to the Western Ghats and have adapted to some specific habitats. With little tolerance for change, they face several human-induced threats like water pollution, deforestation and habitat transformation for agriculture, Pati explains. Cutting down trees, for instance, will directly affect Ghatiana atropurpurea, which is a tree-living crab. These problems are compounded by other factors such as the low number of eggs produced by freshwater crabs and a limited home range.

Richa Malhotra is a freelance journalist. She reports on science, wildlife and the environment.