Decolopoda is a genus of sea spider (class Pycnogonida) belonging to the family Colossendeidae.[1] This genus includes two valid species, D. australis and D. qasimi. As the name of this genus implies, these two species are among the seven species of sea spider with five pairs of legs instead of the usual four leg pairs.[2] The species D. australis is notable as the first polymerous (i.e., extra-legged) sea spider to be discovered.
The species D. australis was first described by the American naturalist James Eights based on specimens found in sea along the South Shetland Islands in the Antarctic region in 1834.[3] [4] [5] Naturalists mostly ignored his discovery, dismissing the description by Eights as erroneous or based on a monstrosity, until the discovery of more ten-legged species several decades later. The French zoologist Eugène-Louis Bouvier described one of these sea spiders as a new species, D. antarctica, in 1905, but authorities have since deemed D. antarctica to be a junior synonym of D. australis,
Another species in this genus, D. qasimi, was described by V. Jaya Sree, R.A. Sreepada, and A.H. Parulekar of the National Institute of Oceanography in India in 1993. The original description of this species is based on a male holotype found off the coast of Queen Maud Land in Antarctica. This species is named for the Indian marine biologist Syed Zahoor Qasim.
Sea spiders of the giant species D. australis have five pairs of legs and are bright scarlet. These sea spiders often weigh more than 10 g, and their legs span more than 20 cm.[6] The holotype for the species D. qasimi also has ten legs, is dark maroon (when preserved), and has even longer legs (184.7 mm in length, compared to 100 mm for D. australis). The species D. qasimi also differs from D. australis by having denticulate spines on its ovigers and hair only on its legs.
The ten-legged sea spiders in the genus Decolopoda resemble the twelve-legged sea spiders in the genus Dodecolopoda. For example, both genera feature long legs, a long proboscis that curves downward and is distally inflated, and a tarsus that is much longer than the propodus.[7] The species in Decolopoda, however, are smaller, feature a shorter tarsus and longer claw compared to the propodus, and have fewer legs than Dodecolopoda.[8]
The sea spiders in the genus Decolopoda also resemble those found in the genus Colossendeis (e.g., C. wilsoni) but are larger and retain chelifores in adults. Phylogenetic studies based on molecular data indicate that the genus Decolopoda is nested within the genus Colossendeis in a phylogenetic tree. Thus, Colossendeis is paraphyletic with respect to Decolopoda.[9] This paraphyly would normally make Colossendeis a junior synonym of Decolopoda, the older name, and require these genera to merge under the name Decolopoda. To avoid this disruption, authorities keep these genera under different names and retain Colossendeis as a paraphyletic genus.[10]
Both species in this genus are found in the Southern Ocean and are endemic to the Antarctic region.[11]