Discolocrinus iselini, Mironov, Alexandr N. & Pawson, David L., 2014

Mironov, Alexandr N. & Pawson, David L., 2014, A new species of Western Atlantic sea lily in the family Bathycrinidae (Echinodermata: Crinoidea), with a discussion of relationships between crinoids with xenomorphic stalks, Zootaxa 3873 (3), pp. 259-274 : 261-269

Discolocrinus iselini new species

Figures 1–6

Etymology. This new species is named in honor of the late distinguished physical oceanographer Columbus O. Iselin (1904–1971), after whom the University of Miami’s research ship, the R/V Columbus Iselin was named.

Diagnosis. Large species. Calyx conical with distinct sutures between BB. High tegmen with tube-like upper region. Most frequent proximal free arm pattern 1+2 3 4+5 6 7+ 8 9 10 (32 of 40 cases) with first pinnule on Brs 10–14. Pinnules in cross-section from V-shaped to crescentic, with overgrowth soft tissue containing numerous perforate plates and perforate and imperforate rods of different size and form. Rudimentary synarthrial characters remaining visible in pinnular articulations beyond pinnular 2. Proximal columnals circular, without thorns.

Material examined. Holotype: R/V. Columbus Iselin, Cruise 80-07, St. # 0 56, 18 September 1980, NE of Abaco Island, Bahamas, the Atlantic Ocean, 28°18' N, 74°12' W, 4383–4558 meters, collectors: K. Sulak, R.S. Carney and S. Robert; National Museum of Natural History, Washington DC, USNM E00048150. Paratypes: USNM 1229429, same locality data as holotype, four specimens and four fragments of arms. USNM Catalog number E00048151, R/V. Columbus Iselin, Cruise 80-07, St. # 0 57, 19 September 1980, NE of Abaco Island, Bahamas, The Atlantic Ocean, 29°20' N, 73°19'W, 4243–4253 meters, two specimens,

Description of holotype ( Figures 1 A, 2, 3, 4B–C, C, 5B–D): aboral cup with proximal arms and proxistele, total length 75.3 mm. Aboral cup conical, upper radial ring diameter 10.4 mm, diameter at base of basal ring 3.5 mm. Cup height 7.1 mm; ratio of BB and RR height 0.38 ( Figure 1 A, 2). Tegmen high, rising interradially to top of Brs 7–9, and bearing small plates and spicules ( Figure 3 C). Anal sac not found. IBr1 and IBr2 long, much longer than RR. Heigth of primibrachitaxis (IBr1+2ax) 17.8 mm; ratio of IBr1 to RR height 1.79; ratio of IBr1 to IBr2 height 1.06; ratio of IBr1 height to width 1.55; ratio of IBr2 height to width 1.50. Expanded proximal ends of IBr1 contiguous, whereas other areas of division series separated from each other. IBr1 and IBr2 with smooth surface and longitudinal median convexity; their sides flattened into lateral flanges continuing on to free arms; wide knobby processes on inner side.

All arms incomplete; secundibrachials 7 to 25 in number. Profile of arms smooth ( Figure 4 B). Lateral flanges in Brs 1–5. Proximal free arm pattern1+2 3 4+5 6 7+ 8 9 10 +11 (5 cases), 1+2 3 4+5 6 7+8 9+10 (1 case), 1+ 2 3 4 5+6 7 8+ 9 10 11 +12 (1 case), 1+2 3 4+ regenerate Brs 5–12 (1 case), Brs less than 10 in number (2 cases). Successive brachial pairs in median and distal arms. Muscular synathries with classical feature and fulcral ridge never oblique ( Figure 5 B). In some Brs, fulcral ridge disrupted in median aboral area ( Figure 5 D). Transverse synarthry with symmorphy and relatively wide fulcral ridge at IIBr1+2 like in paratype 6 ( Fig.5 A), symmorphy less developed and fulcral ridge much narrower in more distal IIBrs ( Figure 5 C).

All pinnules incomplete ( Figure 4 B, C); best preserved pinnule (P1 on Br14) comprises 14 pinnulars. Maximum length estimation of complete pinnule 20 mm. P1 on IIBr12 (2 arms), Br13 (1 arm), or Br14 (3 arms). Pinnule length variable; pinnular 2 longer than pinnular 1 (ratio 1.05–1.37); pinnular 3 about 1.4–1.8 time longer than pinnular 1. Cross section of proximal pinnulars asymmetrical V-shaped, and cresent-shaped in distal pinnulars. Outer side larger than inner side in pinnular 1 and pinnular 2; both sides approximately equal in pinnular 3; inner side much larger than outer in pinnular 4 and beyond. Pinnular 3 also asymmetrical (with larger inner side) in distal pinnules. Muscular synarthry between pinnular 1 and pinnular 2; rudimentary synarthrial characters remaining visible in other pinnulars. Proximal pinnules usually with pores (?genital pores): one pore in central area of pinnulars 3–7. Overgrowth of soft tissue of Ps containing numerous perforated plate-like ossicles and irregular perforated or imperforate rod-like ossicles of differing size and form ( Figure 3 A). Ossicles not regularly arranged. Cover and side plates absent, although some plates embedded in soft tissue resemble cover plates. Ambulacral feet contain x-shaped perforated plates ( Figure 3 B). Ambulacral grooves of Ps are bordered by two high longitudinal folds (plicae) of soft tissue. Ambulacral feet coalescent with soft-tissue walls in their basal part. Ambulacral grooves in proximal arms bordered by series of distinctive soft-tissue structures resembling ambulacral lappets.

Remaining proximal stalk attached to aboral cup of 11 complete and 2 incomplete columnals ( Figure 2 ). Stalk diameter decreasing from proximalmost (3.5 mm) to 11th columnal (3.1 mm); columnal height respectively increasing from 0.4 mm to 0.7 mm.

Other material ( Figures 1 B–D, 4A, D–E, 5A, E, F, 6A, D, E, F). Each paratype composed of aboral cup, bases of arms and short part of proxistele, except for paratype 4 consisting of RR and bases of arms. Main quantitative characters of the paratypes given in Table 1 . Morphological variation is low and seems to be independent of growth stage. One primibrachitaxis and two free arms removed from paratype 6 to examine the top of the tegmen and inner face of knobby processes in IBrs 1–2 ( Figure 1 B–C). Tegmen tapering (conical) from IIBr1 to IIBr3, then cylindrical (tube-shaped) up to IIBr5 ( Figure 1 B). All paratypes with well developed inner knobby processes on IBrs 1–2, looking similar to knobby soles of shoes ( Figures 1 B–D, 6). Knobby processes extended along 2/3 of IBr1 and throughout IBr2 length. Most frequent proximal free arm pattern 1+2 3 4+5 6 7+ 8 9 10 (27 of 33 cases). Most frequent position of first pinnules on Br11 (8 of 16 cases) ( Table 1 ). Best preserved pinnule comprises 17 pinnulars; distal region lacking. Pinnulars 3–7 of proximal pinnules have usually a deep pit or pore (?genital pore) in central area ( Figure 4 A, 5E).

Characters Holotype Paratypes *Other variants of proximal free 1+2 5+6 1+2 5+6 - - - 1+2+3 1+2 4+5

arm pattern 8+9 (1), 8+9 11 (1), 4+5 7 (1), 7+8 9+10 1+2 4+5 11 (2) 1+2 4+5 1+2 4+5 7+8 9+10 6+7 8+9 (2), 9+10 (1), (1) 1+2 4+5+6 1+2 4+5 7+8 (1) 7+8 9+10 (1)

*IIBr bearing first pinnule 12 (2), 13 11 (1), 13 11 (5) 12 - - 11 (2) 12 10 (1) 13 (1), 14 (3) (1), 14 (1) (1) (1) (1) 14 (2) Proximal stalk preserved in paratype 1 with 16 columnals. Stalk diameter decreasing from columnal 1 (2.7 mm) to 16 (2.0 mm); columnal height respectively increasing from 0.36 mm to 0.88 mm. Columnals 1–12 with flat circular synostoses. Articulation facets of columnals 13–16 with small depressions, and two opposing areas show in-plane distortion and more compact stereom ( Figure 5 F). These features typical of proxistele of Bathycrinidae , where semicircular fossae often begin as a group of small depressions, and rudimentary fulcral ridge shows opposing areas with more compact stereom and very low irregular relief ( Mironov, 2000, Fig. 3 ). Pentagonal lumen occupies 22% of facet diameter. Best preserved proxistele (paratype 2) 9.3 mm long, with 19 columnals; Ratio height/diameter of 19th columnal 0.49. Mesistele and dististele are lacking.

Remarks. Discolocrinus iselini n. sp. mainly differs from D. thieli in being of much larger size, with a different pattern of proximal arm articulations, pinnules not flattened, and smooth proximal columnals. The morphology of these two species is compared in Table 2 . According to Mironov (2008), only IBrs 2 possess inner knobby processes in D. thieli . However, the single known specimen of this species was not dissociated, and the supposed absence of knobby processes on the IBrs 1 requires confirmation.

Discolocrinus differs from other bathycrinids in having more elongated primibrachials (much longer than aboral cup height), and in lacking covering plates in ambulacral grooves. The conspicuous differences in D. thieli from other bathycrinids include circular (not oval) articulations in dististele, and anchoring by the expanded terminal columnal with two very short radicles. These differences may seem to be of taxonomic importance at the family level, but knowledge of the morphology and variability of both species of Discolocrinus is incomplete and, until a richer material becomes available, they should remain in the family Bathycrinidae .

Distribution. The species is known off the Bahamas, western tropical Atlantic Ocean, from depths of 4,243 to 4,558 meters ( Fig. 7 ).

Figures

FIGURE 1. Discolocrinus iselini n. sp. Holotype, USNM E 00048150 (A), paratype 6, USNM E 00048151 (B – C) and paratype 2, USNM 1229429 (D). A: General view consisting of calyx, proximal arms and proxistele. B – C: RR with proximal arms, A primibrachitaxis and two free arms removed to show the inner knobby processes on IBrs 1 – 2 (B – C) and the top of the tegmen (B). D: Aboral cup with proximal arms, sides of tegmen torn, inner knobby processes visible. Scale: 10 mm.

FIGURE 2. Discolocrinus iselini n. sp. Holotype, USNM E 00048150. Aboral cup with proximal arms and proxistele.

FIGURE 3. Discolocrinus iselini n. sp.. Holotype, USNM E 00048150. A: Plates and other ossicles from Brs and pinnules. B: X-shaped tube feet plates. C: Plates and rod-like ossicles from the tegmen.

FIGURE 4. Discolocrinus iselini n. sp. Paratype, fragment of the arm USNM 1229429 (A, D – E) and holotype, USNM E 00048150 (B, C). A: Fragment of the arm with pinnule 1, pores (? genital pores) visible on pinnules 3 – 6. B: Proximal part of arm with pinnule 1 on Br 14. C: Pn 2 from Br 20; two thick plates (marked by black). D – F: pinnules 1 – 2 viewed from lateral (D), external (E) and inner (F) sides.

FIGURE 5. Discolocrinus iselini n. sp. Holotype, USNM E 00048150 (B – D), paratype 1, USNM 1229429 (F), paratype 6, USNM E 00048151 (A); arm fragment, USNM 1229429 (E). A: Distal articular facet of IIBr 1, non-muscular joint with rudimentary aborsal areola pit (transverse synarthry). B: Proximal articular facet of IIBr 9, muscular synarthry. C: Distal articular facet of IIBr 10, non-muscular joint (synostosis). D: Proximal articular facet of IIBr 10, muscular synarthry with disruption in middle fulcral ridge. E: Pinnule 5 with genital (?) pore, lateral / external oblique view. F: facet of columnal 15 (proxistele) with rudimental fulcral ridge. Scale: 1 mm.

FIGURE 6. Discolocrinus iselini n. sp. Paratype 6, USNM E 00048151, primibrachitaxis. A: First primibrachial viewed from

FIGURE 7. Distribution of the genus Discolocrinus. Circles: D. iselini n. sp. Square: D. thieli.

Tables

TABLE 1. Quantitative characters of Discolocrinus iselini n. sp., RV Columbus Iselin, St. 0 56, USNM E 00048150 (holotype) and USNM 1229429 (paratypes 1 – 4), and St. 0 57, USNM E 00048151 (paratypes 5 and 6). * Proximal brachial formula and position of the first pinnule in the regenerated arms was not taken into account. ** proximal arm pattern restricted to brachial pairs before Br 11. () number of arms observed for arm pattern and brachial bearing the first pinnule.

	1	2	3	4	5	6
Maximum diameter of upper radial 10.4 ring (mm)	7.4	8.37	8.23	9.02	7.7	9.9
Aboral cup height (mm) 7.1	5.5	5.29	5.59	-	5.4	5.8
Proximalmost stalk diameter (mm) 3.5	2.7	2.64	2.72	-	2.8	3.1
Ratio height/diameter of aboral cup 0.68	0.74	0.61	0.68	-	0.70	0.60
Ratio BB/RR height 0.39	0.31	0.29	0.38	-	0.36	0.29
Ratio upper/lower diameter of 0.34 aboral cup	0.36	0.36	0.33	-	0.36	0.31
Ratio IBr1/RR height 1.79	1.76	1.86	1.93	1.79	1.66	2.05
Ratio IBr1/IBr2 height 1.06	1.04	1.04	1.11	1.00	1.06	1.0
Ratio height/width of IBr1 1.55	1.76	1.57	1.73	1.67	1.55	1.68
Ratio height/width of IBr2 1.50	1.69	1.59	1.52	1.53	1.60	1.66
Most frequent proximal free arm 1+2 4+5 pattern ** 7+8 10 (5)	1+2 4+5 7+8 10 (4)	1+2 4+5 7+8 10 (7)	1+2 4+5 7+8 10 (6)	-	1+2 4+5 7+8 10 (6)	1+2 4+5 7+8 10 (4)

TABLE 2. Differences between Discolocrinus thieli and Discolocrinus iselini n. sp.

Characters	Discolocrinus thieli	Discolocrinus iselini n. sp.
Maximum upper diameter of aboral cup (mm)	5.2	10.4
Pinnules in cross-section	V-shaped, strongly flattened	From V-shaped to crescent-shaped
Structure of ambulacral groove on the pinnules	Not known with certainty (groove is reduced to narrow space;?single series of tube feet)	Groove is bordered by two high longitudinal folds of overgrowth soft tissue containing numerous plates and rod-like ossicles of various size and form; two series of tube feet
Most frequent proximal free arm pattern	1+2 3+4 5+6 7	1+2 3 4+5 6 7+8 9 10
Sutures between BB	indistinct	distinct
Shape of IBr1	Proximal ends of IBr1 conspicuously expanded	Proximal ends of IBr1 slightly expanded
Pn articulations	Non-muscular synostosis	Characters of rudimentary synarthry remaining visible
Thorns on proximal columnals	Present	Lacking