Alisometra owstoni (A. H. Clark, 1912 )

Obuchi, Masami, 2020, Shallow-water Comatulids (Echinodermata: Crinoidea: Comatulida) of the Ashizuri-Uwakai Sea, Shikoku Island, Southern Japan, Species Diversity 25, pp. 309-328 : 321

25. Alisometra owstoni (A. H. Clark, 1912) [Japanese name: Toge-shimofuri-umishida]

Morphology. Centrodorsal hemispherical, 4.0– 5.2 mm across; polar area flat, 0.7–0.8 times of centrodorsal diameter. Cirri robust, XXXVIII–XLII, up to 22 segments, 17 mm long, arranged in two, partly three rows; segments L/W up to 1.0, with aboral transverse bar near proximal end; distal segments sometimes with additional transverse bar near distal end. Radials concealed. IBr and IIBr series composed of 2 ossicles, with low synarthrial tubercle. Arms 20, up to 115 mm long; first arm syzygy at br 3+4; distal intersyzygial intervals 3–6. Comparative pinnule length P 1 =P 2 =P 3>P 4 =P 5; P 1–3 enlarged, stiffened, spine-like, with segments finely spinose on distal end. Disk flat, stellate, two times wide of centrodorsal.

Posture. Fully exposed on gorgonian perches, forming radial fan.

Coloration in life. Rays banded with dark brown and cream, with white and orange spots.

Distribution. Endemic to Japan: Sagami Bay ( Kogo and Fujita 2014) to the Ryukyu Islands ( Kogo and Fujita 2005).

Remarks. Genus Alisometra A. H. Clark, 1947 is characterized by small body sizes and spine-like proximal pinnules. This genus includes two species, which are bounded by morphologies related to body sizes, such as arm length and the number of cirri. The examined specimens fell into the larger form, A. owstoni , although the number and length of arms were larger than previous specimens with 10–12 arms of about 50 mm long (A. H. Clark 1912; Kogo and Fujita 2014).