Tropiometridae A. H. Clark, 1908b

Obuchi, Masami, 2020, Shallow-water Comatulids (Echinodermata: Crinoidea: Comatulida) of the Ashizuri-Uwakai Sea, Shikoku Island, Southern Japan, Species Diversity 25, pp. 309-328 : 321-322

Family Tropiometridae A. H. Clark, 1908b 27. Tropiometra afra macrodiscus ( Hara, 1895) [Japanese name: Oh-umishida]

Morphology. Centrodorsal thick discoidal, 7.3 mm across; polar area flat, 0.7 times of centrodorsal diameter. Cirri stout, XXXIV, up to 37 segments, 37 mm long, arranged in two, partly three rows; segments broader than long, without aboral ornamentation excepting opposing spine. Radials exposed at distal corners. IBr series composed of 2 ossicles. Arms 10, 210 mm long, remarkably massive, 5 mm at first syzygy; brachial short, with distal ends almost parallel; first arm syzygy at br 3+4; distal intersyzygial interval 14–23. Comparative pinnule length P 1 <P 2 <P 3>P 4 =P 5; proximal pinnules with ridge on basal segments; distal pinnules with aboral ridge, making profiles triangular. Disk stellate, three times as wide as centrodorsal.

Posture. Hiding on underside of overhangs, but sometimes fully exposed, forming simple arm fans.

Coloration in life. Uniformly dark brown or dark orange.

Distribution. Sadogashima Island, Japan ( Honma and Kitami 1978) to eastern Malay Peninsula ( Lane et al. 2000). Ogasawara Islands (A. H. Clark 1947).

Remarks. This large species is easily recognized by its massive 10 arms. Within the species, subspecies macrodiscus is regarded as a northern form, however there is no clear morphological difference to distinguish it from the nomenotypical subspecies, Tropiometra afra afra ( Hartlaub, 1890) which is distributed southward from the Philippines.