Redescription of Arabella iricolor (Montagu, 1804) with descriptions of two new species from the United Kingdom and South Africa

Abstract

Arabella iricolor (Montagu, 1804) was described with no diagnostic information for the characters used today to distinguish species within the genus. An updated description, together with genetic data, is provided using the holotype in conjunction with additional specimens collected at or near the type locality, to facilitate comparative analysis of other Arabella species and improve taxonomy within the genus. Arabella iricolor can be distinguished primarily through the long notopodial cirri that reach to or beyond the prechaetal lobes on chaetigers 1–9, in combination with unidentate maxilla I on both sides, four short digitiform pygidial cirri and gradually tapering ventralmost chaetae. The updated description and molecular information enabled the identification of a new species co-habiting with A. iricolor at the type locality and elsewhere. The new species, Arabella ampulliformis sp. nov., is characterised by two lateral pygidial lobes that extend into short cirri, appearing ampulliform in lateral view, in combination with a bifid left maxilla I, short left and long right maxilla II, short notopodial cirri and gradually tapering ventralmost chaetae. A new species from South Africa is also described, Arabella umgazanae sp. nov., distinguished through a bifid left maxilla I, short left and long right maxilla II, short notopodial cirri, two large lateral pygidial lobes and gradually tapering ventralmost chaetae along with additional characters relating to the chaetae, mandibles and maxillary apparatus. Problems surrounding the identification of Arabella species in South Africa are discussed in conjunction with details of the other species reported from the region.