Capillaster multiradiatus (Linnaeus, 1758)

(Fig. 4A, B, D)

Diagnosis. Capillaster with usually 15–25 arms and 15–28 (usually 20–24) cirrals; middle and distal cirrals short, broader than long (modified from A. H. Clark, 1931).

Remarks. Capillaster multiradiatus differs from C. sentosus (below) in being smaller with fewer arms, and having shorter, less robust cirri of fewer cirrals. The two are easily distinguished wherever they have been observed in situ together (Messing, 1998b), but it is not clear how smaller, incompletely developed specimens of C. sentosus can be distinguished from C. multiradiatus. A. H. Clark (1931) noted several “typical” C. sentosus specimens from Singapore with 57 to 100 arms, but also described a smaller specimen with 35 arms as “practically intermediate” between the two species. Specimens collected in Singapore were chiefly small, with at most 27 arms (chiefly 19–23) and ray lengths 55 mm at most. Several small specimens have 10 arms with ray length as little as 15 mm.

Colour. Entirely white or with proximal rays pale yellow, or entirely pale yellow with white pinnules and dark brown or black ambulacra. Elsewhere, colors are widely variable (Messing, 1994, 2007, unpublished data).

Local depth range. 22.7–125 (possibly 22.4–136) m.

Ecology. All specimens were collected during the SSBW via beam trawl or rectangular dredge. Habitats recorded included laterite rock, rocky, gravel, mud, or sandy, with two stations recording mud, two recording clay and one with wood, charcoal, rock and mud. Capillaster multiradiatus is a common reef-dweller elsewhere in the tropical Indo-Western Pacific. At Madang, Papua New Guinea, it is cryptic or semicryptic during the day with arms extended from sponges or foliaceous or branching corals and occurs no shallower than 8 m. In> 25 m, it may be completely exposed on octocoral fans or whips and usually forms an irregular radial fan with several arms curled. At Palawan Island, Philippines, it was found during the day in 17–20 m exposed on corals with arms coiled, and semicryptic in a sponge with arms in a multidirectional posture. Pinnules along each arm orient in a single plane rather than in a multidirectional posture (Messing, 1994, 2007). At Palau, however, it is cryptic during the day and semicryptic at night among coral branches or in crevices with arms forming monoplanar arm fans in as little as 1 m (Meyer & Macurda, 1980; Messing, 2007). This distinctive habit suggests that specimens identified as C. multiradiatus should be treated as tentative pending revision.

Material examined. Sta. 5314-TB1, start 01°14.730'N, 103°53.870'E, end 01°14.944'N, 103°53.890'E, 27.8-33.8 m, 17 May 2013 (SIO-BIC E6563); sta. TB16, outside Eastern Boarding Ground A, 01°13.537’N, 103°53.793’E, 89.5–98.0 m, 21 May 2013 (1; ZRC.ECH.0357); sta. TB28, Singapore Port Limit, Eastern Boarding Ground A, 01°13.181’N, 103°52.900’E, 94.3–97.6 m, 22 May 2013 (2; SIO-BIC E6534, ZRC.ECH.0370); sta. TB58, around Tanah Merah, 01°16.808’N, 103°58.246’E, 38.7–39.9 m, 24 May 2013 (1; ZRC.ECH.0374); sta. TB73, South of Pulau Semakau, 01°11.282’N, 103°46.632’E, 24.6–29.8 m, 25 May 2013 (specimen discarded); sta. TB97, near Eastern Bunkering A, 01°18.425’N, 104°04.607’E, 22.4–22.7 m, 28 May 2013 (4; SIO-BIC E6545); sta. TB98, Eastern Bunkering A, 01°18.938’N, 104°05.312’E, 30.2–33.6 m, 28 May 2013 (4; SIO-BIC E6543); sta. TB109, Eastern Boarding Ground A, 01°13.045’N, 103°52.943’E, 111–114 m, 29 May 2013 (1; ZRC.ECH.0446); sta. DR111, outside Eastern Boarding Ground A, 01°12.989’N, 103°53.062’E, 125–136 m, 29 May 2013 (1; ZRC.ECH.0447, 4; ZRC.ECH.0456); sta. TB141, East Johor Strait, 01°17.725’N, 104°04.363’E, 28.3–28.4 m, 31 May 2013 (3; ZRC.ECH.0471); sta. TB142, East Johor Strait, 01°17.838’N, 104°04.157’E, 28.7–28.8 m, 31 May 2013 (10; ZRC.ECH.0474).

Material previously collected at Singapore. USNM 35026 (1), E.1086 (1), ZMC (26), Svend Gad (in A. H. Clark, 1931); MNB 2455 (1), Prof. Eduard von Martens (in A. H. Clark, 1931); NHM[?] (1), Prof. Charles Stewart (in Carpenter, 1888, A. H. Clark, 1931).