Thalassina is a lobster-like animal which grows up to 30 centimetres (12 in) long,[1] but is more typically 6–20 cm (2.4–7.9 in) long. Its colour ranges from pale to dark brown and brownish green.[2] The carapace is tall and ovoid, extends over less than one third of the animal's length, and projects forward into a short rostrum.[3] The tail is long and thin, and, like many burrowing decapods, the uropods are reduced in form, and do not form a functional tail fan with the telson.[4] Various rows of setae on the legs and gills are used to prevent sediment from reaching the gills and for expelling any which does reach them. Thalassina also makes use of "respiratory reversal" to keep the gills free of dirt.[5]
Fossils of Thalassina are encountered "in countless numbers",[8] and extend back as far as the Miocene. They are generally preserved in a hard phosphatic nodule which is believed to be the animal's moulting position. Storms may trap the animals in their burrows, and the mineral-rich nature of the sediments leads to very rapid fossilisation.[9] The presence of Thalassina, together with other warm-water species in the Miocene of Japan (outside the current range of the species) is taken as confirmation of a period of increased temperatures 16 million years ago.[10]
Thalassina is the only genus in the family Thalassinidae (=Scorpionoidae Haworth, 1825).[11][3] For many years, only a single species, Thalassina anomala, was recognised, but a 2009 revision by Nguyen Ngoc-Ho and Michèle de Saint Laurent increased the number of extant species to eight, including one fossil species.[12] Thalassinidae is classified in the infraorder Gebiidea, alongside the families Upogebiidae, Axianassidae and Laomediidae.[13][14]
^K. Sakai (2004). "The diphyletic nature of the Infraorder Thalassinidea (Decapoda, Pleocyemata) as derived from the morphology of the gastric mill". Crustaceana. 77 (9): 1117–1129. doi:10.1163/1568540042900268. JSTOR20107419.
