Ophiarachnella Ljungman 1872
Creators: name: Boissin, Emilie
name: Hoareau, Thierry B.
name: Paulay, Gustav
name: Bruggemann, J. Henrich
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Echinodermata
Ophiuroidea
Ophiurida
Ophiodermatidae
Ophiarachnella

description: Genus Ophiarachnella Ljungman, 1872
Of the 23 recognized species of Ophiarachnella, 12 are recorded from shallow IWP waters (Clark & Rowe, 1971; Stöhr et al. 2016). Three of these IWP species are peculiar in showing a number of naked dorsal plates in addition to the naked radial shields: O. sphenisci (Bell, 1894), O. infernalis (MÜLLER ET TROSCHEL, 1842) and O. similis (Koehler, 1905). The remaining can be divided into two distinct groups: O. gorgonia (MÜLLER ET TROSCHEL, 1842), O. parvispina HL Clark, 1925, O. ramsayi (Bell, 1888), and O. elegans (Bell, 1894) have eight to 12 oral papillae and lowest arm spines are hardly longer than other spines; while O. macracantha HL Clark, 1909, O. paucigranulata H.L. Clark, 1938, O. septemspinosa (MÜLLER ET TROSCHEL, 1842), O. stabilis (Koehler, 1905) and O. snelliusi AH Clark, 1964 present only five to seven leaf-like oral papillae, have small circular radial shields and the lowest arm spines are distinctly longer than the rest, exceeding the length of the segment.
Ophiarachnella gorgonia (MÜLLER ET TROSCHEL, 1842) complex (UF-6578, Fig. 5 c,d, KC760012)
Material. 2 spms, St. 2; 1 spm, St. 3; 2 spms, St. 7
Remarks. Specimens have eight to nine oral papillae, elongate radial shields, and large supplementary oral shields. These characters identify them as O. gorgonia. Several colour morphs co-occur on Réunion: the two specimens from Cap La Houssaye (St. 2) are dark grey, while those from Pointe des Aigrettes (St. 3) and St-Leu (St. 7) are banded with three or four white segments alternating with three or four dark grey segments. One specimen from St-Leu also displays some pink/red on the disc. These colour patterns differ from the well known green and white colour pattern exhibited by this species elsewhere, including Madagascar (personal observation), Mayotte (Comoros; personal observation), Rodrigues (Rowe & Richmond, 2004), Mauritius (de Loriol 1893a) and throughout the IWP region (Clark & Rowe 1971). However, there is no other obvious differentiation compared to other O. gorgonia specimens. The dorsal and ventral disc and arm plates have the same size, shape or arrangement in both dark and green specimens. These Réunion morphotypes were, however, recently confirmed to represent a cryptic species, genetically closely related to the more general green morphotype found elsewhere (Hoareau et al. 2013). The type locality of O. gorgonia is unknown. Abundance: 2.
Distribution. Ophiarachnella gorgonia as presently understood is widespread across the IWP from East Africa to the West Pacific, but is absent from southeastern Polynesia (Devaney 1974). Hoareau et al. (2013) found substantial genetic differentiation across this range. Previously recorded from the Mascarenes at Rodrigues (Rowe & Richmond 2004), this is the first record for Réunion.
Ophiarachnella septemspinosa (MÜLLER ET TROSCHEL, 1842) (UF-6636, Fig. 5 e)
Material. 1 spm, St. 7
Remarks. The specimen shows the characteristic five to six leaf-like oral papillae. The radial shields are small and circular, distinctly darker than the rest of the disc. The arm spines are distinctly shorter than the segment, unlike in O. macracantha that displays longer middle and upper arm spines. The specimen is uniformly chocolate brown all over the body. In contrast some Pacific specimens (e.g. from Okinawa) display lighter segments on the arms that create a banding pattern. Abundance: 1.
Distribution. This species ranges from the SWIO to the Philippines and China / Japan (Clark & Rowe 1971). The species was previously recorded from Mauritius (de Loriol 1893a); this is the first record for Réunion.
description: Published as part of Boissin, Emilie, Hoareau, Thierry B., Paulay, Gustav & Bruggemann, J. Henrich, 2016, Shallow-water reef ophiuroids (Echinodermata: Ophiuroidea) of Réunion (Mascarene Islands), with biogeographic considerations, pp. 273-297 in Zootaxa 4098 (2) on pages 288-289, DOI: 10.11646/zootaxa.4098.2.4, http://zenodo.org/record/255654