Dodecolopoda is a monotypic genus of sea spider (class Pycnogonida) in the family Colossendeidae.[1] The only species in this genus is Dodecolopoda mawsoni. This species is notable as one of only two species of sea spider with six pairs of legs (instead of the usual four leg pairs) and the first such species to be discovered.[2] [3]
This species was first described by the Scottish zoologists William Thomas Calman and Isabella Gordon of the British Museum (Natural History) in 1933. The original description is based on a male holotype found at a depth of 219 meters below the surface off the coast of MacRobertson Land. Calman and Gordon named this species for Sir Douglas Mawson, who obtained this specimen on his voyage to the Antarctic region in 1931.[4]
This sea spider is notable for not only its twelve legs but also its gigantic size, measuring from tip to tip of its legs when fully extended. The leg of the fourth pair on the holotype, for example, measures in length. The sea spider's long legs act as stilts, holding its body well above the seabed surface below.[5] This species is the only sea spider to combine giant size with six pairs of legs, as the only other species with twelve legs (Sexanymphon mirabilis) is small.
The twelve-legged sea spiders in the genus Dodecolopoda resemble the ten-legged species in the genus Decolopoda. For example, both genera feature long legs, a long proboscis that curves downward and is distally inflated, and a tarsus (third most distal article of the leg) that is much longer than the propodus (second most distal leg article). The sea spiders in Dodecolopoda, however, are larger, feature a longer tarsus and shorter claw (most distal leg article) compared to the propodus, and have more legs than the species in Decolopoda.
Both Dodecolopoda and Decolopoda resemble the eight-legged species in the genus Colossendeis (e.g., C. wilsoni) but retain chelifores as adults. Phylogenetic analysis based on molecular data indicates that both Dodecolopoda and Decolopoda are nested within the genus Colossendeis in a phylogenetic tree. Thus, Colossendeis is paraphyletic with respect to these two polymerous (i.e., extra-legged) genera. This paraphyly would normally make both Dodecolopoda and Colossendeis junior synonyms of Decolopoda, the oldest name, and require all three 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.[6]
This sea spider is found in the Indian and Atlantic regions of the Southern Ocean and is endemic to the Antarctic region.[7] [8] Specimens have been found off the South Shetland Islands, the Palmer Archipelago, and Enderby Land, and in the Ross Sea, captured at depths ranging from 146 to 549 meters below the surface. The distribution of this species is probably circumpolar.[9]