Comactinia titan, Messing, 2003

Messing, Charles G., 2003, Three new species of Comasteridae (Echinodermata, Crinoidea) from the tropical western Pacific, Zoosystema 25 (1), pp. 149-162 : 150-154

Comactinia titan n. sp.

( Fig. 1 )

HOLOTYPE. — Philippines. MUSORSTOM 3, stn CP121, 12°08’S, 121°17’E, 73-84 m, 3.VI.1985 ( MNHN EcCh 186).

PARATYPES. — Philippines. MUSORSTOM 3 (no data) ( MNHN EcCh 185).

New Caledonia. SMIB 5, stn DW100, 23°23.9’S, 168°05.4’E, 80-120 m, 14.IX.1989 ( MNHN EcCs 10234).

ETYMOLOGY. — From the Greek titan , one of a family of mythological giants that ruled the earth until overthrown by the Olympian gods; now, more broadly, one of gigantic size or power, a reference to the great thickness of the arms of this species relative to those of other comatulids.

DISTRIBUTION. — Known only from the Philippines and New Caledonia in 73-84 m (possibly to 120 m). The specimen lacking data was found in a jar with a label for RV Coriolis stn 116. However, the depth at this station was 804-812 m and the accompanying specimens included Asterometra longicirra (Carpenter, 1888) , typical of 200-300 m, and Comatella nigra (Carpenter, 1888) , characteristic of <50 m. The correct label is thus considered lost. RV Coriolis occupied all 54 MUSORSTOM 3 stations in the vicinity of Mindoro Island.

DIAGNOSIS. — A species of Comactinia reaching extremely large size, with proximal arms bearing strong alternating articular tubercles and reaching a diameter of 5 mm; cirri up to XXXVI in number, up to 31.4 mm in length with 22 segments; proximal segments of proximal pinnules smooth and cylindrical or rounded rhombic; combs tapering to a point, present to P 5 in large specimens.

DESCRIPTION

Centrodorsal discoidal, up to 10.0 mm across; polar area flat or slightly concave, smooth, up to 7.6 mm across. Polar area of small specimen with crescentic traces of obsolete sockets.

Cirri of large specimens XXVII-XXXVI (up to X regenerating), 16-22, maximum length 31.4 mm, in crowded single and partly double marginal row. Proximal cirrals cylindrical; c1 short; following segments increasing in length to c5-7; L/W of longest cirral 1.0; following cirrals gradually shorter and slightly compressed with L/W becoming 0.8, sometimes wider than proximal cirrals. Distal 2-3 cirrals preceding penultimate slightly narrower and more elongated, L/ W 1.0 - 1.1; antepenultimate distally polished; penultimate cirral smaller than preceding, L/ W 0.9 -1.1, with erect conical opposing spine; claw curved, longer than penultimate cirral. Small specimen with cirri XXII, 14-15, up to 13.2 mm long; c4 longest, L/ W 1.4; antepenultimate cirral with a weak aboral tubercle.

Radials visible in interradial angles or completely hidden by centrodorsal. Single tip of basal ray possibly visible under edge of centrodorsal in one interradius of one specimen. IBr2 short, apposed laterally and flattened aborally, joined by close synarthry (possibly cryptosynarthry). Ibr 1 oblong with diverging lateral margins, partly hidden by centrodorsal in the two large specimens; W/L c. 5.0 in small specimen. Ibr 2 (axil) pentagonal with short diverging lateral margins, or triangular; W/L 1.9-3.0. Lateral aboral margins of brachitaxes ossicles and exterior lateral margins of proximal few arm ossicles thickened and covered with superficial pale reticulated stereom. Articulations between brachitaxes ossicles and proximal brachials also sometimes covered with pale yellowish tissue that obscures articulations.

Arms 10; anterior arms longer; small specimen with anterior ray length 145 mm and posterior 65 mm. Large paratype with posterior ray length 137 mm; anterior rays broken at 140 mm. Arms of holotype broken at 110 mm or less; longest arm fragment tapering rapidly near broken tip as in posterior arms of small specimen. An apparently anterior arm (remaining ray length 100 mm) is 2.5 mm across at its broken tip. A comparison with the small specimen suggests that the holotype’s intact anterior ray length may have reached 300 mm.

Arm ossicles (except brr 1-2 and slender distalmost ossicles) with convex lateral margins; middle brachials with thickened distal margins, the combination making each ossicle appear swollen. Brachials from brr 2-5 to brr 9-13 (br 2 to brr 5-7 in small specimen) with well developed alternating articular swellings. br 1 oblong (slightly longer exteriorly in small specimen), united interiorly; W/L 3.0-4.4. br 2 longer exteriorly and with P 1 articulation clearly visible in aboral view; W/L 2.6-3.1. Exterior lateral margins of both br 1 and br 2 thickened, apposed and flattened against ossicles of adjacent rays; midaboral surface of brr 1-2 with low synarthrial swelling. br 3+4 short, oblong; syzygial articulation usually sinusoidal; W/L 2.3-

C

3.0; diameter 2.5-4.0 mm. One to several following brachials short, oblong; W/L 2.8-3.8. Following few brachials cuneate, becoming triangular with smooth, thickened distal margins concave in aboral view (with fine short tooth-like spines in the small specimen). Middle brachials short, triangular, with distal margins as in preceding brachials; W/L 2.8-4.1. Some arms of larger specimens distinctly wider in middle than at base, up to 5.0 mm across. Brachials becoming cuneate distally, proportionally not as short as middle brachials; lateral margins not as convex; distal margins neither concave nor thickened; W/L 1.5- 2.5.

First syzygy at br 3+4 (br 4+5 on one arm of large paratype); second chiefly at br 11+12, but varying from br 8+9 to br 24+25. Following interval widely variable with no uniform pattern; chiefly 4-5 (rarely 3, 7 or 8) in small specimen. In the holotype, second syzygies between br 8+9 and br 12+13 chiefly followed by two to five intervals of 4-7 muscular articulations each, with intervals of chiefly 8-9 thereafter. In the large paratype, two to three intervals following second syzygies at br 10+11 or br 11+12 consist of four or five articulations and intervals of 6-10 thereafter. Intervals following a second syzygy at br 23+24 or br 24+25 are chiefly 11-12; arm with br 4+5 followed by intervals of 17, 17, 8 and 12 muscular articulations.

Proximal pinnules decreasing in length from P 1 to P 4 or P 5, robust proximally, slender and flagellate distally. P 1 of up to 52 segments, 33.4 mm long, with up to 13 low, separated, nonconfluent teeth with flat or rounded apical profiles; fully developed teeth often slightly displaced toward one lateral margin; two or three distal pinnulars with diminishing teeth, tapering to a terminal pinnular that lacks a tooth. Proximal pinnulars cylindrical (rounded rhombic in the small specimen), wider than long; middle segments cylindrical and about as long as wide; distal segments preceding comb slightly constricted with L/ W 1.5 -1.7. Large specimens with all segments smooth. P 1 of small specimen with 32 segments and six teeth, 16.1 mm long, with numerous very short spines on lateral margins of pinnulars facing arm tip.

P 2 similar to P 1, up to 51 segments, 32.4 mm long, with up to 16 teeth; the longest segments preceding the comb shorter than in P 1, L/ W 1.2. P 2 distinctly shorter than P 1 in small specimen. P 3 similar to P 2 but not quite as wide across the base, 44 segments, 26.9 mm, 15 teeth; proximal teeth short and flat-topped; more distal teeth rounded and proportionally taller than on preceding pinnules; distal three pinnulars tapering to point. P 3 on small specimen much shorter and less robust than P 2, 18 segments, 8.4 mm, six teeth (the first rudimentary). P 4 up to 36 segments, 21.5 mm, with 13 teeth (not including two rudimentary initial teeth); small specimen with P 4 of 12 segments, 6.8 mm long, no comb and with distal pinnulars compressed and longer than wide. P 5 with or without comb in large specimens; comb-bearing P 5 of up to 28 segments, 16.5 mm, with eight teeth (including tapering final three pinnulars); P 5 without comb of up to 23 segments, 16.5 mm; proximal pinnulars short and cylindrical as in preceding pinnules; middle segments squarish; distal segments longer than wide, compressed and with fine spines on lateral margin facing arm tip.

Middle pinnules longer than those immediately following oral pinnules, of up to 33 segments, 20.3 mm; basal few pinnulars short, following segments squarish with distal adambulacral margins thickened; distal segments slender and elongated, L/W to 2.4. Distal pinnules more slender than middle pinnules, up to 26 segments, 16.1 mm; pinnulars beyond basal few longer than wide; distal pinnulars in small specimen with L/W up to 3.0.

Mouth marginal; anus central; tegmen naked.

Color of rays (preserved) tan or pinkish tan with short bands of darker faded purple. Cirri and pinnules tan. One large specimen with distal cirrals dark brown; the other with the proximal parts of the rays faded purple. The small specimen is faded pink.

DISCUSSION

At a maximum diameter of 5 mm, C. titan n. sp. has thicker, more massive arms than any other comasterid. The arms actually appear wider because the distance from the left side of one brachial to the right side of the succeeding brachial is slightly greater than the diameter of each brachial. The species is placed in Comactinia because it shares with the other two members of the genus – C. meridionalis (Agassiz, 1865) and C. echinoptera (Müller, 1841) – the following diagnostic features: 10 arms; IBr2 series joined by synarthry; first brachial syzygy at br 3+4; mouth excentric, and oral pinnule combs consisting of nonconfluent, often off-center, single teeth flattened along the pinnule axis. C. titan n. sp. also shares with C. meridionalis terminal oral pinnulars that taper to a point, and short cirrals of similar length, almost completely lacking any aboral ornamentation. The small specimen of C. titan n.sp.

shares with some specimens of C. echinoptera a weak, rudimentary aboral spine on the antepenultimate cirral ( Messing 1978; Messing & Dearborn 1990). Apart from its longer cirri with more numerous segments and strongly developed alternating articular tubercles, both of which may derive simply from its much greater size, C. titan n. sp. differs from the other two in having the proximal segments of the oral pinnules smooth and cylindrical or rounded rhombic. In C. meridionalis , these ossicles are spinose, rhombic and sometimes strongly projecting; in C. echinoptera , the basal pinnulars of the oral pinnules bear rounded keels.

With the addition of C. titan n. sp., Comactinia becomes the only comasterid genus known from the tropical western regions of both Atlantic and Pacific oceans. Antedon de Freminville, 1811 (family Antedonidae Norman, 1865 ) is the only other comatulid genus known from shelf depths in both regions, but it is far more widespread, also occurring in European and West African waters. The possibility exists that C. titan n. sp. is convergent rather than congeneric with the two Atlantic species, especially given the relatively generalized features of the genus (i.e., 10 arms, excentric mouth, IBr2 with a synarthry, and first syzygy at br 3+4). However, C. titan n. sp. exhibits no characteristics that place it outside the genus as currently construed.

Figures

FIG. 1. — Comactinia titan n. sp.; A, B, P1 pinnule comb in aboral (A) and lateral (B) views (MNHN EcCh 185); C, cirrus (MNHN EcCh 186); D, cirrus (MNHN EcCs 10234); E, portion of centrodorsal and base of one ray (with abnormal br4+5 on right arm) (MNHN EcCh 186); F-H, pinnules (MNHN EcCh 186); F, P14; G, P5; H, P1. Scale bars: A, B, 1 mm; C-H, 5 mm.