Zygometra cf. comata AH Clark, 1911

Goh, Shawne, Quek, Randolph Z. B., Foo, Sze Hui, Tay, Teresa Stephanie, Messing, Charles G. & Huang, Danwei, 2023, Phylogeny and morphology of Himerometroidea (Echinodermata: Crinoidea) feather stars in Singapore, Raffles Bulletin of Zoology 71, pp. 92-105 : 97-98

Zygometra cf. comata AH Clark, 1911

( Fig. 3 )

Zygometra comata AH Clark, 1911: 762 .

Holotype. USNM 35137 .

Material examined. Sta. DR 125, Sister’s Island , start 01°12.416′N, 103°49.858′E, end 01°12.433′N, 103°49.817′E, 30.8– 25.3 m, 30 May 2013 (n = 1; SS-3643-6, ZRC. ECH.1975); sta. DR174, Next to Boarding Ground A, start 01°12.202′N, 103°52.178′E, end 01°12.141′N, 103°52.078′E, 135– 79.6 m, 4 June 2013 (n = 1; DR174, ZRC.ECH.1967); sta. SUB07 , SE of St. John’s Island , start 01°12.671′N, 103°51.232′E, end 01°12.607′N, 103°51.145′E, 53.7– 34.8 m, 19 April 2016 (n = 3; TR0316i, ZRC.ECH.1626; TR0316ii, ZRC.ECH.1627; TR0318ai, ZRC.ECH.1625); sta. SUB18 ,

SE of St. John’s Island , start 01°12.682′N, 103°51.222′E, end 01°12.646′N, 103°51.135′E, 59.9– 45.2 m, 2 June 2016 (n = 1; TR0966, ZRC.ECH.1634); sta. SUB36 , SW of St. John’s Island , start 01°12.649′N, 103°50.659′E, end 01°12.617′N, 103°50.613′E, 40.6– 38.3 m, 30 June 2016 (n = 5; TR2143, ZRC.ECH.1629; TR 2144i, ZRC.ECH.1678; TR 2151i, ZRC. ECH.1630; TR 2151ii, ZRC.ECH.1633; TR2160b, ZRC. ECH.1631) .

Diagnosis. Zygometra with 12–35 arms in both adults and juveniles, with adult longest arm lengths between 40–135 mm but as short as 10 mm in juveniles; cirri between 15–32 cirrals, longest cirri between 28–45; first two brachials of undivided arms and proximal and distal edges of brachitaxes plain, not thickened or everted and scalloped (modified from Messing & Tay, 2016; AH Clark, 1941).

Description. Aboral surface of centrodorsal flattened and smooth; radials smooth; cirri X–XXXII (XIII and XXV in examined juvenile and adult respectively); proximal and distal cirrals broader than long; middle cirrals as broad as long; middle to distal cirrals bearing sharp, prominent aboral spine that begins abruptly ( Fig. 3C ). Laterally everted brachials observed on specimen (DR174, ZRC.ECH.1967), differing from the diagnosis above ( Fig. 3A ); specimens examined all possess IBr(1+2) ( Fig. 3B ) and IIBr4(3+4). Proximal pinnules generally thin and slender, and taper to a blunt point. Pinnulars smooth and weakly carinate ( Fig. 3D ). Remarks. Among AH Clark’s (1941) examined specimens, those from Singapore are the smallest, with 12–25 arms that are 40–70 mm long and cirri bearing 25–30 cirrals. As noted in AH Clark’s (1941) monographs, Z. comata is variable in size-related characteristics such as the number of arms and cirrals. Given that the differences between Z. comata and other Zygometra species may be ontogenetic ( Messing & Tay, 2016), the species identity of examined specimens here cannot be confidently ascertained (see Discussion). This species is distributed from the Mergui Archipelago to north-western Australia, Indonesia, Philippines, and Hong Kong (AH Clark, 1941). Depth range in Singapore 135– 27 m, inhabiting substrates comprising laterite gravel, sand, reddish marine clay, or dead shells.

Figures

Fig. 3. Zygometra cf. comata morphological characters. A, middle brachials everted at distal margins (red arrow); B, syzygy perforation between first and second ossicles of IBr (red arrow), and synarthry (yellow arrow); C, cirri with middle to distal cirrals bearing sharp aboral spines (red arrow) that begin abruptly (yellow arrow); D, smooth and weakly carinate proximal pinnules.