Comatella stelligera ( Carpenter, 1888 )

Obuchi, Masami, 2020, Shallow-water Comatulids (Echinodermata: Crinoidea: Comatulida) of the Ashizuri-Uwakai Sea, Shikoku Island, Southern Japan, Species Diversity 25, pp. 309-328 : 310-311

1. Comatella stelligera ( Carpenter, 1888) [Japanese name: Futoude-ogasawara-umishida]

Morphology. Centrodorsal hemispherical, 9.5 mm across; polar area concave, 0.5 times of centrodorsal diameter. Cirri XXXVIII, up to 24 segments, 25 mm long, arranged in two rows; c6–8 longest, L/ W 1.4; distal segments polished, with aboral spine gradually developing. Radials invisible. I–IIIBr series composed of 2 ossicles; IIIBr arising both sides of IIBr. Arms 39, 200 mm long, arrayed in single plane; brachials rugose, shorter than broad; first arm syzygy at br 1+2, rarely br 3+4; distal intersyzygial intervals 3 or 4; single arm of examined specimen with brachials slender and smoother, besides difference of coloration. Comparative pinnule length P 1>P 2>P 3>P 4>P 5; P 1 and P 2 enlarged; P 2–4 with round- ed keel on side toward arm tip of proximal two segments. Terminal combs present as far as P 4, consisting of 15–20 segments; teeth single, confluent with lateral margins of pinnule segments closest to arm, with base separated from neighboring one; terminal segments with discrete teeth. Disk regenerating.

Posture. Hiding under overhangs or between foliose corals, with arms in multidirectional posture to multilayered arrays.

Coloration in life. Two basic patterns: one uniformly reddish brown, and another dark red wholly spotted with yellow. The examined specimen corresponding to the former, but a single arm of it to the latter.

Distribution. Sagami Sea, Japan ( Kogo and Fujita 2014) to Western Australia and Great Barrier Reef ( Rowe and Gates 1995). Tonga to Sri Lanka (A. H. Clark 1931). Ogasawara ( Gislén 1922) and Guam ( Kirkendale and Messing 2003).

Remarks. Genus Comatella A. H. Clark, 1908 is characterized by all division series of 2 ossicles, the first arm syzygy at br 1+2, the terminal combs confluent with lateral margins of the pinnule segments closest to the arm. According to A. H. Clark (1931), a form with IIIBr series arising from both sides of IIBr axillaries, like the examined specimen, could be identified as Comatella nigra ( Carpenter, 1888) . However, this symmetric bifurcation seems commonly found in large specimens of this genus (Obuchi, personal observation). Here, the identification followed Messing’s (2001) concept that the axillaries beyond IBr with distal facet asymmetrical and oblique so that the rays are twisted in C. nigra , whereas the arms are arrayed in a single plane in C. stelligera .

The examined specimen had the one arm remarkably different from others in terms of the slenderness and smoothness of the brachials, and the coloration. It indicates intra-specific variation or alternation with growth, which supports Messing’s (2001) view that small forms of Comatella with spotted arms, formerly identified as Comatella maculata ( Carpenter, 1888) by coloration, are the young of C. stelligera .