Arcoscalpellum

Arcoscalpellum was first described in 1907 by Dutch zoologist Paulus P. C. Hoek as a section of the genus Scalpellum, in his account of barnacles found in an expedition to Sibolga. Hoek viewed the section, defined in part by a bowed carina, as less primitive than the species with a straight or angularly bent carina, which he put in the sections Protoscalpellum and Euscalpellum respectively.^[1] The type species is Scalpellum (Arcoscalpellum) velutinum by original designation, but that species is considered a junior subjective synonym of Arcoscalpellum michelottianum.^[2][3] The genus Holoscalpellum, described by Henry Augustus Pilsbry, is an exact synonym of Arcoscalpellum according to Pilsbry himself.^[2][4]

Arcoscalpellum was once used as a catch-all taxon for "most living and many fossil scalpellids" before being revised in the 1970s and 80s by Soviet zoologist Galina Zevina. In 2016, however, English paleontologist Andrew Scott Gale redefined the genus further, based on the morphology of the type species, as characteristics used for identification in a past paper were found by him to plesiomorphic for the Scalpellidae.^[3] Some species once placed in Arcoscalpellum have been moved into other genera, such as Graviscalpellum (created in 1980) and Regioscalpellum (created in 2016).^[5]

The 2016 paper by Gale examined the phylogeny of the Scalpellidae, and found the family could be grouped "into two sharply demarcated clades". Arcoscalpellum was placed into the more basal, or "primitive" group, a redefinition of the subfamily Scalpellinae.^[6] Gale noted that the redefined Scalpellinae were still "technically paraphyletic" but argued that they "can be readily identified".^[7] The study was supported with morphological and molecular phylogenetic techniques, with the proposed groups matching genetic groups independently proposed the previous year.^[6] The Arcoscalpellum species sampled were the most derived of the Scalpellinae on the consensus tree. (The genus Diotascalpellum was the most basal scalpelline.)^[8]

The World Register of Marine Species lists the following species (94):