Aquilonastra undetermined

Aquilonastra sp. Material examined: 11 specimens (ZMSBUK-1663/1 - ZMSBUK-1663/11) Holotype: (ZMSBUK-1663/1) Largest sampled specimen in this study: R: 22mm, r: 11mm. Description: (Figs. 32–34) Five equal or relatively subequal short arms (R /r ~2:1), arms broader towards the disc, tapering to a rounded end distally; abactinal carinal plates with up to 38 thick, short and columnar spinelets, some arranged in tight discrete clusters but not consistently so, other spinelets being dispersed over the entire plate surface, greater number of spinelets on plates towards the centre of disc and along midline of rays, lateral plates with smaller spinelets; pedicellariae and gonopores present in abactinal interradii; madreporite conspicuous, although partially obscured on edges by spines of abactinal plates; inferomarginals small, not forming conspicuous edge to body margin, typically with 21 spinelets per plate (at R = 22); actinal plates in interradii arranged in fine rows, baring up to 19 spinelets proximally and 10 spinelets distally, roughly arranged in a few compact series; tube feet cylindrical with central disc; colour in live specimens greyish with large red, mottled cluster in centre of disc, colouration not preserved in alcohol. Systematic notes: Four species of Aquilonastra are currently recognised from the Persian Gulf, A. burtoni, A. iranica, A. samyni and A. watersi ¸ but the microscopic nature of many of the characters used to differentiate between the species and the lack of much genetic data for the region makes definitive identification difficult. Morphologically, the Aquilonastra sp. described here can be readily separated from A. samnyi by the presence of abactinal pedicellaria and from A. burtoni by all specimens only having a single, conspicuous madreporite. It can further be separated from A. iranca by the far greater number of spinlets on the abactinal, inferomarginal and actinal plates (Table 2). Of the Persian Gulf species, it most closely resembles A. watersi, but again has more spines on each plate, particularly so abactinally (Table 2). The Aquilonastra sp. identified here, also somewhat resembles the Japanese species A. batheri (OʼLoughlin & Rowe 2006). Indeed, before the establishment of A. watersi as a distinct taxon, some specimens of A. watersi from the Omani coast were initially identified as A. batheri (O’Loughlin & Waters 2004). With some exceptions, most species of Aquilonastra have relatively localised ranges, presumably largely driven by their tendency to reproduce primarily through fission or through brooding (OʼLoughlin & Rowe 2006; O’Loughlin & Bribiesca-Contreras 2015), so it is unlikely that the range of A. batheri truly extends to the Persian Gulf. Although we therefore note clear morphological differences with other Persian Gulf species, we are currently unable to definitively identify Aquilonastra sp. as a new taxon here. Spinelet count has been used in previous studies as key diagnostic features for members of the genus Aquilonastra, but this appears to be a variable character within some species. Although the specimen of Aquilonastra sp. studied here have uniformally higher spinlet counts across the three plate series than do specimens of A. watersi and A. iranica of equivalent size, greater comparative effort across a wide range of specimens will be needed to determine whether these counts fall outside of the natural range of variation for A. watersi and A. iranica. Furthermore, although genetic data is almost universally lacking for Persian Gulf echinoderms, a recent study found that specimens morphologically identified as A. watersi and A. irancia could not be separated genetically using 16S markers (Adeli et al. 2020). Although this is evidence from only a single gene, and does not preclude the possibility that these two species have only very recently diverged, it suggests that morphological data alone may not be sufficicent to properly identify diversity within the genus, and that genetic data will be required to determine the status of the Aquilonastra species identified here. Observations: Bostaneh, Hormozgan Province, Iran. Intertidal area, tidal pool and subtidal 1.5 m depth.