Callichimaera Perplexa: Earliest Known Arthropod That Can Swim

In a recent international research, a team of researchers led by Yale paleontologist Javier Luque announced the discovery of hundreds of exceptionally well-preserved specimens from Colombia and the United States that belong to the mid-Cretaceous period of 90-95 million years ago. The cache consists of hundreds of tiny comma shrimp fossils, several true shrimp, and a totally new branch of the evolutionary tree for crabs.

One of the most interesting and fascinating research according to the researchers, is that of Callichimaera perplexa. Callichimaera perplexa are the earliest known arthropod that can swim with paddle-like legs since the extinction of sea scorpions more than 250 million years ago. Its name has been derived from a chimera, which is a mythological creature that has body features from more than one animal. The meaning of Callichimaera in English is "perplexing beautiful chimera." Luque observed that Callichimaera's "unusual and cute" appearance, such as its small size – which is approximately about the size of a quarter. It has very huge compound eyes with no sockets, bent claws; leg-like mouth parts, exposed tail, and long body are the common features that are typical of pelagic crab larvae. This clarifies that a large number of the larval traits that are visible in the "perplexing chimera" might have been retained and amplified in miniaturized adults by the changes in the timing and the rates of development. This process is termed as "heterochrony", which might lead to the growth of new body plans. Luque stated that “Callichimaera perplexa is extremely unique and strange and can be referred to as the platypus of the crab world”. It depicts the process that how novel forms evolve and become so dissimilar through time. In common, generally we consider crabs as big animals with broad carapaces, strong claws, small eyes in long eyestalks, and a small tail tucked under the body. Callichimaera disobeys all of these 'crabby' features and believes that re-thinking of the definition of what make a crab a crab. A study concerning the discovery is visible in the April 24 online edition of the journal Science Advances. Luque stated that it is immensely exciting that on the present day we find totally new branches in the tree of life from a distant past, especially from regions like the tropics, which despite being hotspots of diversity on the present day, are places that are known to be the least about in terms of their past diversity.

By: Anuja Arora

Content: https://www.sciencedaily.com/releases/2019/04/190424153732.htm