People usually associate crabs with water bodies. Crabs require water to survive and reproduce. A few species of crabs, from different lineages, have evolved the ability to survive for long periods of time without water. However, none of them can lay eggs and produce young in the absence of water. Such crabs are called land crabs and most of them belong to the Family Gecarcinidae. Found in tropical regions of the world, land crabs are equipped with specialized blood vessels and gills to extract oxygen from the air. When it is time to mate, they travel back to the sea.
The females release their eggs into the water where they develop into larvae. Another group of crabs, of the Family Sesarmidae, has given rise to some land crabs that have overcome the need to visit the sea. An example is the species Metopaulias depressus of Jamaica. This highly unusual land crab lives in the water trapped inside the leaves of bromeliads (a group of plants from the Family Bromeliaceae). Not only do the larvae grow up in an environment far removed from the sea, they are also taken care of by the mother, a highly unusual case of parental care in a group notorious for cannibalism.
The Western Ghats of South India have given rise to a species of crab that is equally strange. It was identified in the year 2017, and is found only in a small patch of forest in the state of Kerala. The Kani maranjandu (of the Family Gecarcinucidae, ) can be identified by its long and dainty legs, an adaptation to its arboreal lifestyle. It too has no need to visit the sea as it evolved from a group of freshwater crabs. Like its Jamaican counterpart, it has moved away from its original habitat. Instead, it relies on the water trapped inside the hollows of the great trees of the Western Ghats’ lush forests. The species was named after the Kani tribe, a Dravidian-speaking ethnicity of the region who helped biologists capture and document it.
Given below is a description of the species’ discovery in the Science Daily:
During a two year survey of the freshwater crab fauna, which started in 2014 in Westerns Ghats in Kerala, India, the people of Kanikkaran (also known as Kani) reported sightings to the survey team of “long-legged” tree crabs in the area. Early attempts to capture them proved futile. On September, 5 2016, researchers with the help of the Kani tribe were finally able to capture a female specimen and later a large adult male.
The specimens examined are deposited in the Zoological Survey of India and in the museum collection of the Department of Aquatic Biology and Fisheries, University of Kerala, India. The new species is named Kani maranjandu after the Kani tribe in Kerala, who helped discover the tree crab. Maranjandu is the local Malayanam name for tree crab.
According to Dr. Biju Kumar, one of the study’s authors, the discovery of this crab is very important in the context of conservation of the Western Ghats Biodiversity Hotpot as they can serve as ecological indicators, reflecting the health of the ecosystem. “As water holding hollows in large trees are essential for the survival of this unique species, the discovery also stress the need for conservation of large trees in the degraded forest ecosystems of the Western Ghats,” Kumar said.
Image Attribution: The image above, sourced from Wikimedia Commons, is the photograph of a Kani maranjandu crab. It was uploaded by Biju Kumar.
- New Species of Tree Living Crab found in Western Ghats (dated April 3, 2017), Science Daily
- New Tree-Living Crab Species found in Kerala (dated April 4, 2017), The Hindu