Paratelecrinus orthotriremis, Messing, Charles G., 2013

Messing, Charles G., 2013, A revision of the genus Atelecrinus PH Carpenter (Echinodermata: Crinoidea), Zootaxa 3681 (1), pp. 1-43 : 35-39

Paratelecrinus orthotriremis , new species

Figures 15 , 16

Holotype. USNM E42705 , JSL II 1744, York Bay, St. Vincent, St. Vincent and Grenadines, 13°09’45”N, 61°16’59”W, 490 m, 24 Apr 1989.

Paratypes. Bahama Islands: USNM 1133481, JSL II 3691, NW Providence Channel, 26º25.361’N, 77º51.672’W, 704 m, 26 July 2009 (1 spec.); USNM E42650 , JSL II 808, off Great Abaco I., 25°52’12”N, 77°15’30”W, 696 m, 9 Apr 1984 (1). Caribbean Sea: USNM E42673 , JSL II 1733, Bridgetown, Barbados, 13°00’42”N, 59°39’32”W, 477 m, 18 Apr 1989 (1); USNM E42685 , JSL II 1740, York Bay, St. Vincent, 13°07’12”N, 61°17’02”W, 393 m, 22 Apr 1989 (2).

Other material examined. Strait of Florida: USNM 34820, Fish Hawk 7285, S of Key West, 24°15’00”N, 81°47’30”W, 560 m, 19 Feb 1902 (1 spec.). Bahama Islands: USNM E19280 , Gerda 242, SW of Bimini, 25°36’N, 79°21’W, 458–531 m, 30 Jan 1964 (1). USNM E17878 , Pillsbury 1441, N of Acklins I., 22°25’06”N, 73°52’00”W, 855 m, 23 Jul 1971 (1); USNM E17959 , Pillsbury 1478, NW of Mayaguana I., 22°27’18”N, 73°10’06”W, 770 m, 23 Jul 1971 (1); USNM E42651 , JSL I 1500, off San Salvador I., 24°02’25”N, 74°32’32”W, 521 m, 22 Oct 1983 (1); USNM E43084 , JSL II 811, off Eleuthera I., 26°35’00”N, 76°49’04”W, 608 m, 11 Apr 1984 (1); USNM E43085 , JSL II 817, off Whale Cay, 25°23’03”N, 77°47’15”W, 522 m, 15 Apr 1984 (1); USNM E43086 , JSL II 1497, off Andros I., 25°12’12”N, 77°59’56”W, 635 m, 18 Oct 1987 (1). Yucatán Channel: USNM E17832 , Gerda 889, 20°55’N, 86°28’W, 177–220 m, 10 Sep 1967 (2). St. Vincent and Grenadines (all York Bay, St. Vincent): USNM E42672 , JSL II 1744, 13°09’45”N, 61°16’59”W, 483 m, 24 Apr 1989 (1); USNM E42674 , JSL II 1740, 13°07’12”N, 61°17’02”W, 407 m, 22 Apr 1989 (1); USNM E42675 , JSL II 1745, 13°07’13”N, 61°16’46”W, 392 m, 24 Apr 1989 (1); USNM E42676 , JSL II 1745, 13°07’13”N, 61°16’46”W, 392 m, 24 Apr 1989 (1); USNM E42685 , JSL II 1740, 13°07’12”N, 61°17’02”W, 393 m, 22 Apr 1989 (2); USNM E42686 , JSL II 1747, 13°07’13”N, 61°16’46”W, 414 m, 25 Apr 1989 (1); USNM E42687 , JSL II 1740, 13°07’12”N, 61°17’02”W, 407 m, 22 Apr 1989 (1); USNM E42706 , JSL II 1740, 13°07’12”N, 61°17’02”W, 395 m, 22 Apr 1989 (1). Barbados: E42681 , JSL II 1727, 13º14’36” N, 59º44’90”W; 554 m, 15 Apr 1989 (1 dissociated for SEM); USNM E42682 , JSL II 1728, 13°14’56”N, 59°43’30”W, no depth, 15 Apr 1989 (1); USNM E42689 , JSL II 1733, 13°00’42”N, 59°39’32”W, 496 m, 18 Apr 1989 (1).

Diagnosis. A species of Paratelecrinus with 15 columns of cirrus sockets (3 per radial area); peripheral sockets small (0.4–0.8 mm tall) ( Figures 15 a–b); brachitaxes and proximal brachial pairs with moderately developed synarthrial swellings; Iax2 hexagonal with parallel sides in smaller specimens (e.g., Figure 16, top row), rhombic with narrower distal angle in large specimens (e.g., Figure 16, bottom row); no thin, wing-like, lateral flanges. Lateral margins of Ibr1 straight or slightly diverging.

Description of the holotype ( Figure 15 a). Centrodorsal conical, tapering from base; basal diameter ~ 3.6 mm (obscured by bases of cirri); height 5.0 mm; HD ~1.4; interradial margin weakly concave; radial margin weakly concave midradially, with or without weak midradial projection, convex over peripheral cirrus sockets. Apex blunt conical with weak ridges derived from obsolete sockets. Sockets in 15 crowded columns, three per radial area, with 5 sockets in midradial column, 5–6 sockets in lateral columns; narrow flat interradial strip separating columns in adjacent radial areas in proximal two-thirds of centrodorsal; no interradial ridge. Cirri compressed, too crowded to count precisely, ~LXXX; longest intact of 37 segments, 70 mm long (longest possibly ~41 segments, ~ 80 mm); c1–2 short; c3 squarish; longest cirrals with LW 5.0; distal adoral corner of distal cirrals spine-like in side view, producing serrate adoral profile; weak rounded aboral spine on penultimate cirral; weaker rudiment on antepenultimate cirral; terminal claw with slightly hooked tip; cirrus tapering toward tip.

Externally visible portion of basals almost straight, swollen interradially, thin laterally and with slightly expanded ends just touching midradially. Radials very short, concave distally; WL 6.4–6.6; lateral margins of radials visible between rays, separating adjacent brachitaxes; proximal corners slightly swollen over basals. Ray length 207 mm, including 25-mm incomplete distal filament. IBr2 and IIbr1–2 with moderately developed synarthrial swelling. Ibr1 with lateral margins parallel and distal margin moderately V-shaped; WL 2.6. Iax2 rhombic, wider than Ibr1; WL 1.0; distal portion parallel-sided. IIbr1 curved wedge-shaped, deeply concave distally; exterior margin long, straight, thickened and apposed against IIbr1 of adjacent ray; interior margin short, receding into distinct gap; WL 3.5. IIbr2 almost triangular, longer exteriorly and wider distally; WL 1.5. IIbr3+4 longer interiorly; 2.6 mm across; WL 1.4–1.6. Proximal brachials wedge-shaped, with weak alternating articular tubercles on IIbr8 and following ossicles; WL 1.8. Middle brachials almost triangular; WL 1.8. Distal brachials weakly wedge-shaped with the pinnule articulation on the longer lateral margin slightly projecting as a small shelf in aboral view; brachials beyond mid-arm with proximal aboral margin weakly everted and shelf-like, bearing a row of spines; distal aboral margin smooth; WL 0.8; becoming longer than broad (LW 1.5) with slightly expanded distal margin as arm tapers toward apinnulate tip. Elongated brachials of distal apinnulate filament with pair of weak distolateral spines; WL up to 2.7. Syzygies at 3+4, 6+7, 9+10 [3+4, 5+6, 8+9 on both arms of one ray (one followed by 11+12, 13+14, 15+16); 3+4, 7+8, 11+12 on another] and subsequently chiefly at intervals of 2 muscular articulations, many 3 distally (some 2, 4).

P1 on IIbr13 to IIbr17; all broken but with first segment short, wider distally; second squarish and slightly narrower distally; third squarish; fourth slightly longer than wide; following pinnulars of about equal length but becoming narrower distally; proximal pinnulars flattened, with blunt tooth at distal corners of proximal segments beyond basal two; pinnulars becoming cylindrical with expanded overlapping distal ends as pinnule tapers distally. Following pinnules to 13.7 mm long, of 27 segments; first pinnular short, widest distally; second short, widest proximally; third slightly longer than wide, flattened; pinnulars in proximal half (beyond basal two) flattened with blunt spine at distal corners; middle and most distal pinnulars of similar length but becoming narrower and more slender with expanded ends; distal pinnulars reaching LW>7.0. Pinnule and arm ambulacra (including apinnulate distal filament) with numerous saccules.

FIGURE 16. Paratelecrinus orthotriremis n. sp. Iax2 of 17 specimens showing the gradual change from hexagonal to rhombic with increasing size. Scale bar: 1 mm.

Description of other specimens. Centrodorsal conical, with convex sides or in larger specimens tapering from the base; basal diameter 1.8–4.2 mm (chiefly ≥ 2.3 mm); HD 1.0–1.4, chiefly ~ 1.1 in smaller specimens (diam. ≤ 2.5 mm) and 1.2–1.3 in larger specimens (diam. ≥ 2.8 mm); interradial margin often weakly projecting and swollen, sometimes flat or concave, never with a deep V-shaped excavation; radial margin usually with a pair of shallow concavities accommodating ends of adjacent basals, with a weak midradial triangular projection between them; centrodorsal base of smallest specimen (diam. 1.5 mm) with thin convex interradial ridges. Apex conical or blunt conical, often with weak ridges derived from obsolete cirrus sockets. Sockets in 15 crowded columns, three per radial area; larger specimens with 3–4 sockets in midradial column, 5–7 sockets in lateral columns, and with columns in adjacent radial areas sometimes separated by narrow interradial strip; smaller specimens with 1–4 midradial sockets, 3–5 sockets in outer columns, and no interradial separation; peripheral sockets 0.4–0.8 mm tall. One small specimen ( USNM E42674 ) with 2 columns of cirri per radial area but with an immature midradial peripheral socket forming an incipient third column. USNM E19280 with a fourth immature peripheral socket across a radial area.

Cirri ~XL– LXXXV, with at most 41 segments, ~ 85 mm long, compressed and distally tapering; delicate and thread-like in small specimens. Smaller apical cirri often retained, of 18–25 segments, 5.0–17.0 mm long. Up to first three cirrals short (fewer in smaller specimens); following segments increasing in length; c7–18 longest, with LW 3.5–5.4 (up to 8.1 in small specimens); middle cirrals with expanded distal ends; adoral distal corner sometimes projecting distally and spine-like ( Figures 15 c–d, top). Cirrals in distal half shorter, but remaining longer than wide; terminal few cirrals lacking distal expansion. Antepenultimate and penultimate cirrals with LW 1.3–2.0 and 1.2–0.8, respectively, usually bearing curved aboral spine (rarely absent or rudimentary). Claw slightly curved ( Figures 15 c middle, lower; 15d lower).

Externally visible portion of basals shallow chevron-shaped, gently arched or almost straight, usually forming a low complete ring separated interradially from centrodorsal by ligament bundle, but with lateral ends usually not as swollen and often not as well separated from centrodorsal as in P. cubensis . Basals rarely extremely narrow laterally and barely touching, or reduced to interradial triangles and not forming complete circlet. Radials short, with at least slightly concave distal margin and usually diverging lateral margins; WL 1.7–2.3 in smaller specimens, 2.3–3.6 in larger specimens, and 7.0 (extremely short) in USNM E42689 ; radial profile ~90–100º in large specimens, ~65–80º in small specimens.

Ibr1 oblong with straight or slightly diverging lateral margins; small specimens with shallow V-shaped distal margin; WL chiefly 2.0–2.4; two specimens with small distolateral triangular projections; larger specimens with distal margin often more deeply V-shaped; distolateral margins receding into interior, forming gaps between bases of adjacent rays; WL chiefly 2.4–3.3. Iax 2 in small specimens hexagonal with lateral margins straight or slightly convex, usually apposed against adjacent axil; no gaps ( Figures 15 b, 16 top row); larger specimens becoming rhombic with a longer narrow distal angle and proximal synarthrial swelling ( Figures 15 a, 16 bottom row); proximal angle broadly obtuse in small specimens, narrower in large specimens, but never <90°; WL 1.0–1.3. USNM E42673 bears one ray with an extra V-shaped ossicle between Ibr1 and Iax2.

Maximum ray length 207 mm, including a 25-mm regenerating distal filament without pinnules ( USNM E42705 ). USNM E42673 has rays 140 mm long to the distalmost pinnule plus a 60-mm distal filament similar to that of P. cubensis , suggesting that a complete ray in USNM E42705 might reach 260 mm. IIbr1 longer exteriorly, in contact interiorly over axil or separated; distal margin gently concave to deeply V-shaped; WL 1.9–2.7 (up to 3.5 in a large specimen); exterior lateral margin slightly thickened in some specimens. IIbr2 irregularly pentagonal or quadrate, longer exteriorly and wider distally; WL 1.3–1.5 (1.1 in one small specimen); larger specimens with strong proximal synarthrial swelling and with well-developed gap between adjacent IIbr2 on each ray. Exterior lateral margins of IIbr1 and IIbr2 rarely both flattened. IIbr3+4 longer interiorly; 0.75–1.9 mm across; WL 1.0–1.5. IIbr5 and following few brachials weakly to moderately wedge-shaped; WL 1.1–1.5 (up to 2.1 in large specimen). Middle brachials wedge-shaped to almost triangular, with one side much longer than the other; WL 0.9–1.5 (up to 2.0 in large specimen). Some larger specimens with low alternating articular tubercles on IIbr8 and following brachials. Distal brachials wedge-shaped (sometimes only weakly) and longer than wide, with proximal aboral margin at least weakly everted, shelf-like and bearing a row of spines; distal aboral margin smooth or slightly raised; WL chiefly 0.6–0.8; slender distalmost brachials of filament up to six times longer than wide. Syzygies at 3+4, 6+7 and 9+10; subsequently at intervals of 2 (occasionally 3, rarely 4 or 5) articulations. Two large specimens with distal intervals chiefly 3–4. Rarely 8+9; 7+8 and 10+11; 7+8 and 11+12, or 6+7 and 10+11.

P1 usually on IIbr17 (rarely IIbr12 to IIbr20), mostly broken; longest with 30 segments, 14.3 mm; first pinnular short and triangular; second trapezoidal; following pinnulars becoming more slender and much longer, initially flattened but becoming cylindrical with expanded overlapping distal ends as pinnule tapers distally; distal segments extremely slender. Several proximal segments beyond second often bearing a blunt or triangular distal aboral tooth. Longest distal pinnules up to 19.2 mm long, of 33 segments; proximal pinnulars flattened; those beyond basal two with strong aboral distal tooth or blunt spine; pinnulars becoming more slender distally with expanded distal ends; middle and distal segments of about equal length but shorter near tip; distal pinnulars with LW up to 9.0.

Distribution. South of Key West, FL, Bahama Islands, Yucatán Channel, Barbados and St. Vincent. The records from the Strait of Florida and Bahamas are from generally deeper water (seven records in 521–855 m; one trawl record in 458–531 m) than those from the Caribbean Sea (nine records in 392–496 m; one in 554 m). The much shallower record from off Arrowsmith Bank (177–200 m) reflects shoaling isotherms across the Yucatán Channel from the Cuban to Mexican sides associated with northward geostrophic flow of the Yucatán Current. Meyer et al. (1978) recorded similarly shallower records for other crinoid species here relative to their depth distributions along the Bahama margin of the Strait of Florida, where geostrophic flow of the Florida Current depresses isotherms ( Leaman et al. 1987).

Etymology. The name orthotriremis derives from Latin triremis, the ancient Mediterranean warship with three tiers of oars, after the three columns of cirrus sockets in each radial area, and Greek orthos, straight, in reference to the parallel sides of the Ibr1 ossicles and relatively straight interradial margin of the centrodorsal.

Remarks. Paratelecrinus conifer and P. telo , both from the Indo-West Pacific, are the only other atelecrinids with cirri in 15 columns, but P. orthotriremis differs as follows: no V-shaped notch in the interradial margin of the centrodorsal; lateral margins of Ibr1 straight or slightly diverging, and axil with a more rounded proximal angle. P. telo has proportionately larger cirrus sockets than either P. orthotriremis or P. conifer , and its axil has a distinctly different, triangular distal angle. P. conifer also occurs in substantially deeper water (1009–1479 m).

Figure 16 illustrates the gradual change in axil shape from hexagonal with more or less straight lateral margins in small specimens, to rhombic in larger specimens.

Figures

FIGURE 15. Paratelecrinus orthotriremis n. sp. a. Centrodorsal with cirrus bases and one brachitaxis in lateral view, USNM E 42705 (holotype). b. Centrodorsal and ray bases in lateral view, USNM E 43085. c. One middle cirral (upper) and tips of two cirri (middle, lower), USNM 42705 (holotype). d. Two middle cirrals (upper) and tip of one cirrus (lower), USNM E 43085. Scale bars: 1 mm.