Clarkcoma canaliculata (Lütken 1869)

Clarkcoma canaliculata (Lütken)

Ophiocoma canaliculata Lütken, 1869, p. 46; Lyman, 1882, pp. 168, 177; Koehler, 1904, p. 75, figs. 30–32; 1922, p. 314; H. L. Clark, 1921, pp. 123, 128; 1928, p. 437, figs. 130a,b; 1938, p. 332; 1946, p. 244; A. M. Clark, 1966, pp. 291, 294, 327.

Ophiocoma canaliculata var. pulchra H. L. Clark, 1928, p. 439, figs. 131a,b.

Ophiocoma punctata Koehler, 1931, p. 205, pl. 14, figs. 2–5.

Ophiocoma pulchra H. L. Clark, 1938, p. 333; 1946, p. 244.—Dakin, Bennett, and Pope, 1960, p. 324, pl. 85 (bottom).—A. M. Clark, 1966, pp. 291, 327.

MATERIAL EXAMINED.—New South Wales: Newport, MCZ 6726 (1); Port Jackson, MCZ 5905 (paratype, Ophiocoma punctate Koehler); USNM 38638 (1); Shell Harbor, MCZ 5237 (1). South Australia: St. Vincent Gulf, MCZ 3462 (3), 5905 (1); Spencer Gulf, MCZ 4664 (2 paratypes, Ophiocoma pulchra H. L. Clark). Western Australia: Bunkers Bay, MCZ 5218 (2); Cape Naturaliste, BPBM, no number (5); Cheyne Beach, BPBM, no number (2).

DIAGNOSIS (for Clarkcoma bollonsi and C. canaliculata).—Disc diameter (d.d.) of both species to 24 mm; arms between three and four times as long as disc diameter. Granules in both species covering aboral surface of disc and extending into oral interradial area to variable extent. Specimens of C. canaliculata from New South Wales having more extensive granulation interradially than those from South and Western Australia. Aboral surface of longest arm spines of both species often showing evidence of a slight central depression (“canaliculate”); more evident for specimens of C. canaliculata examined. Longest spines frequently widened at tip (Figure 11). Mortensen (1924, p. 121) noted the outer part of a few of the arm spines in C. bollonsi was swollen. He suggested that a “parasitic organism” might be the cause of this condition, and in sectioning these spines, he found a “peculiar radiating structure.” No evidence of a foreign organism could be detected, however, but Fell (1952, p. 24) noted “the presence of three kinds of spines on otherwise similar material” and concluded that “this would confirm Mortensen’s opinion that club-shaped spines are pathological.”

Sequence of spines on each side of first ten proximal arm segments for an 11-mm (d.d.) specimen of C. bollonsi: 3-4-4(or 5)-5-6-6(or 7)-6(or 7)-6-6-5(or 6); number of spines decreasing distally, with four and five spines beyond 25th segment. Farther out on the arm, four, and finally three spines.

Three specimens of C. canaliculata (d.d. 7–18 mm) with following spine sequence: each side of first four proximal segments with 3-3(or 4)-3(or 4)-4(or 5) spines; beyond segment 3, an increase in number of spines on each segment with increasing size of specimen determined by comparing spine sequence of small and large specimens (see Table 1).

An evident specific difference between C. bollonsi and C. canaliculata appears in the shape of the dental plates, and this is reflected externally by the extent of the dental papillae. In C. bollonsi a greater proportion of the plate is occupied by dental papillae tubercles, and the overall length to breadth ratio of the plate is greater than for C. canaliculata (compare Figure 8, 14). This difference appears in similar-sized specimens of each species.

Disc diameter Number of spines Segments

7 mm 6 segment 6

18 mm 6 segments 5–15

7 mm 7 none

18 mm 7 segments 6–10

7 mm 5 out to segment 12

18 mm 5 out to segment 35

7 mm 3 segments 21 to end

18 mm 3 segments 47 to end

Clarkcoma bollonsi has dental papillae arranged regularly in several transverse rows, their number reduced toward the teeth; papillae in the lateral columns are larger than those of center. Clarkcoma canaliculata has papillae occurring in nearly the same number above and below (near teeth); irregularly placed in three or four columns; relatively larger and less extensive than for bollonsi of similar size. Number of papillae varying according to size of specimens. C. bollonsi with dental papillae area slightly wider than area occupied by teeth (Figure 14); length-to-breadth ratio of plate, 2.9–3.1 : 1. For C. canaliculata dental papillae area about same width as tooth area (Figure 8); length-to-breadth ratio, 2.0–2.7 : 1.

There is greater evidence of the canaliculate shape of the upper surface of the longer arm spines in C. canaliculata than in C. bollonsi, but the presence of these spines on C. bollonsi makes the character difficult to use as a means for species differentiation.

In his key to the species of Ophiocoma, H. L. Clark (1921, p. 123) distinguished canaliculata and bollonsi by differences in disc granules: those of bollonsi “at least near the disc-margin, higher than thick, becoming more or less markedly spiniform”; those of canaliculata “nearly or quite spherical and of more or less uniform size.” The spiniform nature of the granules at the disc margin as originally reported by Farquhar (1908) for the type of bollonsi has not been apparent, however, in the specimens I have examined. In these specimens the marginal disc granules do not appear to differ from those on either the oral or aboral surface of the disc. It must be assumed that there is a certain amount of individual variation in this character and that such variation does not reflect a constant specific distinction between the two species.

HABITAT AND DISTRIBUTION.—Clarkcoma bollonsi was first taken from a depth of 16 meters in Cook Strait, New Zealand (Farquhar, 1908). Mortensen (1924) recorded specimens collected from a “hard bottom” in depths ranging from 5 to 120 fathoms at several New Zealand localities and, later (1936), a single specimen from 128 meters in Cook Strait. Hurley (1959) gave an interesting report on the habitat and apparent density of C. bollonsi through the use of underwater photography. He noted the ophiuroids occurring in gregarious masses, and related this to their manner of feeding, suggesting that this species formed part of “a typical filter or detritus feeding community in an outer sublittoral cobble bottom where there is considerable seafloor current” (Hurley, 1959, p. 145). Fell (1958) reported this species from a number of New Zealand stations ranging in depth from 3 to 350 fathoms. Pawson (1965) reported specimens from the holdfasts of the algae Lessonia and Durvillea apparently collected intertidally at the Snares Islands. McKnight (1967) listed C. bollonsi from the Chatham Rise off eastern New Zealand collected in 210 meters.

Clarkcoma bollonsi, therefore, apparently is restricted to waters along the coast of New Zealand and on the Chatham Rise. The southern limit of this species appears to be the Snares Islands at latitude 48° South (Pawson, 1965).

Dakin, Bennett, and Pope (1960, p. 324) mention the occurence of C. canaliculata (as Ophiocoma pulchra) from Australian low water level on rocky coasts, “especially where there are rockpools and large stones resting upon pockets of sand or gravel. The ophiuroids lie under the stones and keep strictly in the shade under such conditions.” Koehler (1931) obtained his specimens (as Ophiocoma punctata) in depths of 5 to 8 meters off Port Jackson, Australia, and A. M. Clark (1966) reported specimens (as Ophiocoma canaliculata) from two stations at depths of 1.5 and 4.5 fathoms at Port Phillip, Victoria.

Clarkcoma canaliculata is known from temperate Australian waters. Its range extends from the vicinity of Shell Harbor, New South Wales (lat. 34° S), along the South Australian coast to Rottnest Island, Western Australia (lat. 33° S); it has not yet been reported from Tasmania.