Comanthus parvicirrus ( Müller, 1841 )

Obuchi, Masami, 2020, Shallow-water Comatulids (Echinodermata: Crinoidea: Comatulida) of the Ashizuri-Uwakai Sea, Shikoku Island, Southern Japan, Species Diversity 25, pp. 309-328 : 312

4. Comanthus parvicirrus ( Müller, 1841) [Japanese name: Koashi-umishida]

Morphology. Centrodorsal thin, slightly raised from level of radials, 3.0–4.0 mm across; polar area flat, 0.7–0.8 times of centrodorsal diameter. Cirri weak, III–XIII, up to 14 segments, 8.5 mm long, arranged in single row with gaps; c5–7 longest, L/ W 1.2; distal 4–5 segments with aboral transverse ridge. Radials exposed, length 30% of centrodorsal diameter. IBr series composed of 2 ossicles, and II–IVBr of mostly 4(3+4), rarely 2. Arms up to 41; anterior arms up to 180 mm long, 2.1–2.3 times longer than posterior ones; brachials shorter than broad, with distal ends everted; first arm syzygy at br 3+4; distal intersyzygial intervals 4. Comparative pinnule length PD > P 1 >>P 2 <P 3 <P 4 =P 5; PD and P 1 enlarged; distal pinnules on anterior arms remarkably slender, with middle segments L/ W 4.0 . Terminal combs present to near arm tips at intervals, but sometimes to two third of arms, consisting of 7–13 segments; teeth confluent with lateral margins of pinnule segments, curved inward, basally contacted with adjacent one; small secondary teeth occasionally present on some segments; terminal segment with discrete large tooth; proximal segment with transverse saucer-shaped tooth. Disk three to four times as wide as centrodorsal.

Posture. Dwelling within cracks or crevices, or between stony corals, with anterior arms in multidirectional posture.

Coloration in life. Arms green to greenish yellow with dark articulations; pinnules dark green, often with yellow tips.

Distribution. Toyama Bay, Japan ( Kogo 1998) to New South Wales, Australia ( Rowe et al. 1986). Tonga (A. H. Clark 1931) to Mozambique (A. M. Clark 1972). Ogasawara Islands ( Gislén 1922) and Guam ( Kirkendale and Messing 2003).

Remarks. Genus Comanthus A. H. Clark, 1908 is characterized by the first arm syzygy at br 3+4, and the terminal combs with large and confluent teeth and saucer-like proximal teeth. Comanthus parvicirrus is recognized by the terminal combs distributed to almost the arm tips, and the distal pinnules with smooth and slender segments. During this research, some unfamiliar forms of Comatulidae were collected, which were similar to this species in general morphology, but had intermediate characters between Comanthus and Clarkcomanthus Rowe, Hoggett, Birtles, and Vail, 1986 . They appeared to consist of at least two groups by the shape and distribution of terminal combs. Here, these specimens were excluded from the examined materials. They need further study to identify the genus to which they belong, and to determine the boundaries between each form.