Tricarina

''Tricarina'' is an extinct genus of crustaceans in order Isopoda, known from a single incomplete fossil specimen from the Cretaceous of western Iran. It has a flattened body with three longitudinal ridges, which give it its name.

Sources

The single known specimen of ''Tricarina'' was discovered in a well core that had been bored at a site on the Khuzestan Plain in south-western Iran, at , and at a depth of . The rocks that contain it are calcareous shales, which form part of the Gadvan Formation, and are part of the main sequence of rocks for the production oil and gas around the Persian Gulf. Examination of the foraminiferan fossils show that the shales are Barremian to Aptian in age.

Description

The fossil of ''Tricarina gadvanensis'' is known from a part and counterpart from a core drilled to make an oil well. It has been deposited in the Carnegie Museum of Natural History, Pittsburgh, Pennsylvania, as specimen number CM 54197. A segment of the cylindrical core was cut away before the fossil was discovered, and the fossil is accordingly incomplete: the front of the carapace extends over the cut edge, and much of the pleon is outside the edge of the core. Most of the carapace is visible, and shows a flattened form, with three distinct longitudinal carinae or ridges. The bases of the antennae are preserved, but no eyes are apparent. A single pereiopod (walking leg) is visible, and it ends without a chela (claw).

Systematics

Feldmann ''et al.'' (2007) classified ''Tricarina gadvanensis'' as a decapod crustacean. According to Feldmann ''et al.'', ''T. gadvanensis'' cannot be accommodated in any of the previously known families of Decapoda. The few families which contain species with flattened bodies, such as Scyllaridae and the various families of Polychelida, all have very different ridge patterns. They therefore erected a new family, Tricarinidae, to accommodate this single genus and species. The lack of claws suggests affinity to slipper lobsters and spiny lobsters, and the new family is therefore placed in the inraorder Achelata. The genus name ' refers to the three ridges on the carapace, while the specific epithet ' refers to the area from which the fossil was recovered.

Subsequent restudy of the fossil led Hyžný ''et al.'' (2020) to conclude that ''T. gadvanensis'' was not a decapod, but rather an isopod, probably closely related to the family Serolidae.

Ecology

The lack of eyes in ''Tricarina'' suggests a deep-water organism, a feature also seen in Polychelidae and Thaumastochelidae. This is also corroborated by the rocks it was found in, which are thought to have been deposited in a deep, offshore setting. It is probable that ''Tricarina'' burrowed into the sediment, as was also inferred for '' Eryon'', and as seen in some slipper lobsters.

References

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{{Taxonbar, from=Q7840589, from2=Q20899243, from3=Q20899245

Early Cretaceous crustaceans
Monotypic isopod genera
Fossils of Iran
Fossil taxa described in 2007
Early Cretaceous arthropods of Asia
Cretaceous Iran