Himerometra A.H. Clark, 1907

Mohammednowshad, B., Idreesbabu, K. K., Parameswaran, Usha V., Messing, Charles G. & Sureshkumar, S., 2020, The Shallow-water Crinoid Fauna of Lakshadweep Atolls, North-western Indian Ocean, Zootaxa 4789 (1), pp. 247-265 : 255-256

Himerometra A.H. Clark, 1907

Type species.— Antedon crassipinna Hartlaub, 1890 (a junior synonym of Actinometra robustipinna Carpenter, 1881 ).

Diagnosis.— A genus of Himerometridae with centrodorsal low hemispherical to discoidal with concave to deeply depressed aboral apex; cirrals with or without aboral spines; division series aborally rounded and well separated, and proximal pinnules much larger and thicker than those following; proximal most pinnule (PII on IIBr2 of IIBr4(3 + 4)) largest; following pinnules decreasing in size (from Taylor et al., 2017).

Remarks.— A.H. Clark (1913b, 1941) recognized six species in Himerometra distinguished by variations in robustness, length, ornamentation, and number of segments of proximal pinnules, numbers of arms, and size and robustness of cirri. However, Taylor et al. (2017) removed one species ( H. persica A.H. Clark, 1907 ) to Heterometra based on a re-examination of type specimens, and placed three species ( H. martensi ( Hartlaub, 1890) , H. magnipinna A.H. Clark, 1908b , and H. bartschi A.H. Clark, 1908b ) in synonymy under H. robustipinna based on

a combined molecular and morphological analysis. They maintained Himerometra sol as distinct due to its only known occurrence in the Maldives Is., well outside the then-known range of H. robustipinna . It is also included under H. robustipinna herein (see below).

Himerometra robustipinna ( Carpenter, 1881)

Actinometra robustipinna Carpenter, 1881:201 .

Antedon martensi Hartlaub, 1890:182 .

Antedon crassipinna Hartlaub, 1890: 185 .

Himerometra martensi: A.H. Clark, 1907:356 ; 1941:188, 203–09, pl. 17 (figs. 64, 65), pl. 18 (figs. 66, 67), pl. 19 (figs. 72-75).

Himerometra magnipinna A.H. Clark, 1908b:214 ; 1941:188–193, pl. 15 (figs. 54, 55), pl. 16 (fig. 56), pl. 17 (figs. 61, 62).

Himerometra bartschi A.H. Clark, 1908b:212–213 ; 1941:188, 209–212, pl. 14 (figs. 52, 53), pl. 16 (figs. 57–59).

Himerometra robustipinna: A.H. Clark, 1913b:286–287 ; 1941:188, 193–203, pl. 16 (fig. 60), pl. 17 (fig. 63), pl. 18 (figs. 68, 69); Taylor, et al., 2017:347–352.

Himerometra sol A.H. Clark, 1912:40 , 115; 1941:188–189; Taylor, et al., 2017:352–353.

Material examined: Western outer reef of Kavaratti I., 10.867N, 72.167E, 16 m, 12 Dec 2018, Saheerali and Mohammed Nowshad coll. (2, MTRLDST E0227, ZSI/ WGRC /IR.INV/13965); 18 m, 21 Dec 2017, Mohammed Nowshad, coll (1, MTRLDST E0229) .

Diagnosis.— Same as genus. With the inclusion of Himerometra sol as a junior synonym of H. robustipinna (see below), Himerometra is now considered monospecific.

Description of survey specimens ( Figure 2E ).— Both MTRLDST 0227 and ZSI/WGRC/IR.INV/13965 with robust cirri with articulations not expanded; few distal most cirrals ranging from smooth, through weakly carinate or with small median aboral tubercle to bearing strong, distally-directed triangular aboral spine; brachials discoidal, broader than long; syzygies irregularly spaced, occurring only at long intervals; pinnules on brachitaxes and PII on IIBr4(3+4) thick and stout; proximal pinnulars broader than long, distal ends of pinnulars of enlarged proximal pinnules everted or thickened, usually strongest on middle pinnulars, but sometimes restricted to more distal ones. MTRLDST E0227: 40 arms, 145 mm long; cirri XL, 29, 30 mm long; PII of 28 pinnulars, 18 mm long. ZSI/WGRC/ IR.INV/13965: 32 arms, 130 mm long; cirri XXIV, of 28 segments, 29 mm long; PII of 25 pinnulars, 15 mm long. MTRLDST E0229: arms 46, to 165 mm long. Centrodorsal thick discoidal, 4 mm across; aboral pole strongly concave. Cirri LII, 32, stout, 36–42 mm long; cirrals approximately subequal; longest segments, in basal third, nearly as long as broad; distal segments slightly broader than long; terminal 10–12 with small, low median dorsal tubercle; opposing spine well developed. IIIBr4 (3+4) developed externally, IIIBr2 internally. Proximal pinnules very stout, tapering distally to flagellate tip; PII 26 mm long, with pinnulars equally broad; distal margins of proximal pinnulars smoothly everted. Color: rays dark purplish-grey; cirri and pinnules bright red.

Habitat.— The specimens perched fully exposed on corals and rocks.

Distribution.— From Lakshadweep and the Maldive Is. in the west to New Caledonia in the east, including ANI and Admiralty Is., and from northern Australia (Port Hedland, WA, to Lady Musgrave I., QLD) to Okinawa, Japan (A.H. Clark, 1941; Rowe & Gates, 1995; Kogo, 1998; Sastry, 2007; Taylor, et al., 2017). Depth range: littoral to 57 m (Taylor, et al., 2017).

Remarks: This is the first record of this species from Lakshadweep. Taylor et al. (2017) maintained Himerometra sol A.H. Clark, 1912 , as distinct from H. robustipinna only because the holotype and paratype of the former were collected in the Maldive Islands, well outside the range of H. robustipinna —at the time known only as far west as Burma ( Myanmar). A.M. Clark (1972) attributed a third specimen from the Maldives to H. sol , but, as with the holotype, none of its morphological features distinguishes it from specimens attributed to H. robustipinna or its junior synonym H. magnipinna . Characters of the Lakshadweep specimens fall well within the range of H. robustipinna . Because this collection extends the range of H. robustipinna beyond Myanmar, we here treat H. sol as a junior synonym of H. robustipinna .

Figures

FIGURE 2. A‒D. Comaster schlegelii. A–B.MTRLDST E0225, aboral view showing centrodorsal, cirri, brachitaxes, and proximal arms (A) and in situ (B). C–D. MTRLDST E0224, aboral view showing centrodorsal lacking cirri, brachitaxes, and proximal arms (C) and in situ (D). E. Himerometra robustipinna, MTRLDST E0227, in situ. F. Phanogenia typica, MTRLDST E0223, aboral view showing centrodorsal, brachitaxes and proximal arms. G. Comanthus wahlbergii, MTRLDST E0231, oblique aboral view showing centrodorsal, cirri, brachitaxes, and proximal arms.