Euritmia Sarda-Borroy , 1987

Capa, Maria, Osborn, Karen J. & Bakken, Torkild, 2016, Sphaerodoridae (Annelida) of the deep Northwestern Atlantic, including remarkable new species of Euritmia and Sphaerephesia, ZooKeys 615, pp. 1-32 : 6-7

Taxon classification Animalia Phyllodocida Sphaerodoridae

Euritmia Sarda-Borroy, 1987

Euritmia Sardá-Borroy, 1987: 48; Capa et al. 2014.

Amacrodorum Kudenov, 1987a: 917-918.

Type species.

Euritmia hamulisetosa Sardá-Borroy, 1987.

Diagnosis.

Body short and ellipsoid. Macro- and microtubercles absent; papillae all over body surface and parapodia. Prostomial and peristomial appendages short, spherical or digitiform. Parapodia with simple chaetae, enlarged sub-distally, with serrated cutting edges; hooks absent.

Remarks.

This genus was erected to accommodate a small and atypical species with the body covered by numerous papillae and bearing simple chaetae, Euritmia hamulisetosa Sardá-Borroy, 1987, from southern Spain, and a species previously described as Sphaerodorum , Euritmia capense (Day, 1963), from South Africa ( Sardá-Borroy 1987). Euritmia capense is distinguished from Euritmia hamulisetosa in the number, arrangement and type of dorsal epithelial papillae, having two transverse rows of each large and small papillae per segment instead of four rows of similar papillae; and the chaetal morphology with a typical distal spine in Euritmia hamulisetosa , absent in Euritmia capense ( Day 1963, 1967; Sardá-Borroy 1987). A few months later, another genus was erected to accommodate a similar species, Amacrodorum bipapillatum Kudenov, 1987a. In addition to the absence of large tubercles and the presence of simple chaetae, this species was characterised by the presence of two kinds of epithelial papillae, spherical and ellipsoid. The latter author was probably not aware of the description of Euritmia and also did not notice the diagnostic features of the South African species, similar to Amacrodorum bipapillatum . Amacrodorum bipapillatum is distinguished from the two previously described species in the number of transverse rows of dorsal papillae and the arrangement of the ellipsoid and hemispherical papillae. The new species described herein shares with the other three species the absence of macro- and microtubercles, the presence of several rows of papillae over the body surface and the presence of distally hooked simple chaetae. For these reasons, all these species are considered as members of the genus Euritmia and united under this name. Being an older name than Amacrodorum and applying the Principle of Priority (Article 23, International Code of Zoological Nomenclature), Euritmia takes priority.

The genus currently gathers four species, distinguished mainly by the shape and arrangement of dorsal and ventral papillae, the number and arrangement of parapodial papillae and the shape of the chaetae (Table 2). This latter attribute has only been studied under SEM in Euritmia hamulisetosa , and therefore is the best known in the group; it is probable that the reported smooth chaetae in the other species would show some thin spinulation if observed under high magnification.

Moreover, a group of species to date considered belonging to Sphaerodoropsis (Group 4, according to Borowski 1994) also show these features, although the chaetae, instead of being simple, could be considered as pseudocompound. These are Sphaerodoropsis multipapillata ( Hartmann-Schröder, 1974), Sphaerodoropsis heteropapillata Hartmann-Schröder, 1987, and Sphaerodoropsis plurituberculata Capa & Rouse, 2015. Commensodorum commensalis ( Lützen, 1961) shares the type of chaetae with Euritmia , being typically simple. Nevertheless, Commensodorum commensalis has few and small macrotubercles, consisting of four macrotubercles arranged in a simple transverse row per segment. It is still unclear if these taxa are closely related and if the potential fusion of shafts and blades to form simple chaetae (like in Sphaerodorum , Commensodorum , and Euritmia ) occurred more than once within the group.