Zoroaster marambioensis, Palópolo & Brezina & Casadio & Griffin & Santillana, 2021

Palópolo, Evangelina E., Brezina, Soledad S., Casadio, Silvio, Griffin, Miguel & Santillana, Sergio, 2021, A new zoroasterid asteroid from the Eocene of Seymour Island, Antarctica, Acta Palaeontologica Polonica 66 (2), pp. 301-318 : 305-313

publication ID	https://doi.org/ 10.4202/app.00714.2019
publication LSID	lsid:zoobank.org:pub:38AF70B7-F4FE-4166-9DE5-3EC8D68A30E6
persistent identifier	https://treatment.plazi.org/id/A9C9FB9D-A846-48CD-A6A3-FB3B8B65A00E
taxon LSID	lsid:zoobank.org:act:A9C9FB9D-A846-48CD-A6A3-FB3B8B65A00E
treatment provided by	Felipe
scientific name	Zoroaster marambioensis
status	sp. nov.

Treatment

Zoroaster marambioensis View in CoL sp. nov.

Figs. 4–9 View Fig View Fig View Fig View Fig View Fig View Fig , SOM.

Zoobank LSID: urn:lsid:zoobank.org:act:A9C9FB9D-A846-48CD-A6A3-FB3B8B65A00E

1979 Zoroaster View in CoL aff. Z. fulgens Thomson, 1873 View in CoL ; Blake and Zinsmeister 1979: 1151–1152, pl. 2: 1–11.

1988 Zoroaster View in CoL aff. Z. fulgens Thomson, 1873 View in CoL ; Blake and Zinsmeister, 1988: 495, figs. 3: 7–10, 4: 1–4.

1998 Zoroaster View in CoL aff. Z. fulgens Thomson, 1873 View in CoL ; Blake and Aronson, 1998: 345.

Etymology: After the place of discovery, i.e., Marambio (Seymour) Island, Antarctic Peninsula.

Type material: Holotype: IAA-P-373-A, incomplete specimen comprising five fragments. Paratypes: IAA-P-373-B to K, ten incomplete specimens comprising four specimens with incomplete disc and arms, three specimens with complete disc and partially preserved arms, and three almost complete arm fragments without disc structures.

Type locality: GPS POI 64°14’24” S, 56°40’02” W, Seymour Island , Antarctica GoogleMaps .

Type horizon: Cucullaea I Allomember, La Meseta Formation, Eocene.

Material.— Type material and twenty (including IAA-Pi- 373-L–N, Q1, R) additional arm and disc fragments. All from the same locality and layer .

Diagnosis.—Central disc plate enlarged, lobate, flattened or slightly depressed. Primary circlet with enlarged, lobate, tumid radials that abut small, polygonal and flattened inter-radials ( Figs. 5A View Fig 2 View Fig , 7A View Fig , 9A View Fig 3 View Fig , B 1 View Fig , C 2 View Fig ). Small abactinal disc plates between radials and central plate, and between primary circlet and marginals ( Figs. 4A, B View Fig 2, F 2 View Fig , 5A View Fig 2 View Fig , D). Primary spines on disc only present on radials. Marginals hexagonal, proximally with one spine every two marginals, distally lacking spines ( Fig. 4A View Fig ). Four or five rows of actinolaterals proximally, the upper row polygonal, without primary spines, extending distally until the area between the last two marginals at the arm tip ( Figs. 5C View Fig 3 View Fig , 6A View Fig 2 View Fig , B 1 View Fig , B 2 View Fig , 8A View Fig 1 View Fig , A 2 View Fig ). Oral armature well developed ( Fig. 8B View Fig 1 View Fig , one to three spines for each prominent adambulacral and one or two secondary spines). One or two big pedicellariae and 2–3 small pedicellariae associated to each prominent adambulacral plate ( Fig. 6H View Fig 1 View Fig , H 2 View Fig ). Each ambulacral plate with a long and well-developed furrow on actinal view ( Figs. 4B View Fig 1 View Fig , H 2 View Fig , 6E View Fig ). Terminals enlarged, crescent-shaped, wider than long, with a prominent notch ( Fig. 8A View Fig 1 View Fig , A 2 View Fig ). Primary spines short and blunt (on carinals) and long and slender (on actinolaterals). Secondary spines blunt on abactinal surface, sharp on actinal surface (see Table 1 for a succinct summary of the characters which distinguish this species from other zoroasterids).

Description.—Rays five. Major radius (R): 103–150 mm. Minor radius (r): 15–18 mm. R/r: 6.87–8.33. Breadth of the ray at its base: 13 mm. Eighteen marginals to first 10 carinals ( Figs. 4F View Fig 2 View Fig , G 1, H 1 View Fig , 9B View Fig 1 View Fig ). Arms long, narrow, tapering distally ( Fig. 4A, C View Fig 1 View Fig ). Cross section of arms subcylindrical ( Figs. 6B View Fig 2 View Fig , 7B, C View Fig ). Entire body surface covered mainly by secondary spines ( Fig. 4 View Fig ).

Disc small, tumid, interbrachial angles acute. Abactinal surface of the disc formed by a central ossicle, surrounded by a ring of five radials and five interradials, a madreporic plate, slightly modified marginals and a variable number of small abactinal disc ossicles ( Figs. 5B View Fig 1 View Fig , 7A View Fig , 9B View Fig 1 View Fig ). Centrale ossicle, when preserved, flattened or slightly depressed (the last character maybe as a taphonomic feature). Radials enlarged, tumid, weakly lobate, bearing a central primary spine, intercalated with smaller, flattened, polygonal interradials, covered by secondary spines ( Figs. 5B View Fig 1 View Fig , 7A View Fig ). Radials abut interradial ossicles ( Fig. 9A View Fig 3 View Fig , C 2 View Fig ). Madreporic plate relatively small (half the size of interradials), circular, slightly elevated, with multiple channels and pores radiating from the center ( Figs. 4B View Fig 2 View Fig , 5 E View Fig 1 View Fig , E 2 View Fig ), not fused to the adjacent interradial ossicle ( Fig. 7A View Fig ), surrounded by secondary spines and pedicellariae, cup-shaped basal plates. Marginal plates on interbrachial angles enlarged, raised, subtriangular in shape, separated from the radials by small irregular inset adradial ossicles ( Figs. 4A, B View Fig 2, F 2 View Fig , 5A View Fig 2 View Fig , D). Disc ossicles articulated, leaving relatively large spaces for papulae.

Almost complete or fragmented arms articulated with the disc in most cases.

Arm plates articulated by proximal and distal lobes, relatively large spaces for papulae between plates at proximal part of the arms ( Fig. 5C View Fig 1 View Fig , C 4 View Fig ), becoming smaller distally. Ossicles arranged in well-defined longitudinal and transverse rows along arms ( Figs. 5C View Fig 1 View Fig , C 2 View Fig , 9 View Fig ).

Carinals large, subcircular to hexagonal, weakly lobate ( Fig. 5C View Fig 4 View Fig ), transversely elongated proximally, equidimensional or slightly longitudinally elongated distally. Each carinal overlaps adjacent adradials and proximal carinal ( Figs. 5C View Fig 1 View Fig , 9A View Fig 3 View Fig , C 2 View Fig ). One big, short and blunt spine to each carinal, in a central knob of the ossicle ( Figs. 4A View Fig , 6D View Fig , 7C View Fig ).

Well-developed adradials in a single series along both sides of carinals, slightly depressed, covered by small secondary spines. Adradial ossicles hexagonal, almost equidimensional, sometimes transversely elongated ( Figs. 5C View Fig 1 View Fig , 7B–D View Fig , 9A View Fig 3 View Fig , B 1 View Fig , C 2 View Fig ), overlapped by carinals and marginals.

Marginals in a single series ( Figs. 4 View Fig , 9 View Fig ), hexagonal, twice as wide as long, proximally bearing one primary spine every two marginals, distally without spines ( Fig. 4A View Fig ). Marginal series abutting adradials, but not actinolaterals ( Figs. 5C View Fig 2 View Fig , 7B–D View Fig , 9A View Fig 3 View Fig , B 1 View Fig , C 2 View Fig ).

Actinolaterals polygonal to subtriangular, arranged in 4–5 rows proximally, reduced to three on the distal half of the arm and becoming a single row near the arm tip Figs. 5C View Fig 2 View Fig , C 3 View Fig , 7B–D View Fig , 9A View Fig 1 View Fig , A 2 View Fig ). Upper row of actinolaterals smaller than marginals, equidimensional, alternated with marginals, without spines ( Figs. 5C View Fig 2 View Fig , C 3 View Fig , 9A View Fig 3 View Fig ). This series does not articulate with the terminal ossicle, although the last actinolateral ossicle is located near the last distal marginal ( Fig. 8A View Fig 2 View Fig ). The three lower abactinal series bearing slender, elongated, usually flattened spines, directed upward and towards proximal part of arm, articulating with a central knob on each plate ( Fig. 5C View Fig 2 View Fig , C 3 View Fig ).

Adambulacral plates alternating long carinate and short non-carinate ones ( Figs. 4B View Fig 1 View Fig , D 2 View Fig , 6E View Fig , G, 9C View Fig 3 View Fig ). Carinate adambulacrals bearing transverse series of stout cylindrical spines ( Fig. 9A View Fig 2, B 2 View Fig ). Non-carinate adambulacrals at one side of the furrow is opposite to a carinate adambulacrals on the other side ( Fig. 9A View Fig 1 View Fig , B 2 View Fig ). One to three spines for each prominent adambulacral, preserved in (or near) life position. One or two big pedicellariae (or cup-shaped basal piece), two or three small pedicellariae, and one or two secondary spines ( Figs. 6H View Fig 1 View Fig , H 2 View Fig , 9B View Fig 2 View Fig ) associated to each prominent adambulacral.

Ambulacrals compressed, high, squarish-blocky in shape, directed towards the center of the ambulacral groove, with a long and well-developed furrow on actinal view ( Figs. 4B View Fig 1 View Fig , H 2 View Fig , 6E View Fig , H 1 View Fig ). Four rows of podial pores on actinal surface in the proximal part of the arm, becoming reduced to two series at the arm tip. Superambulacrals not observed, apparently reduced or absent.

Terminals, when preserved, highly enlarged, crescent-shaped, wider than long (terminal length = 2/3 terminal width; Figs. 6B View Fig 1 View Fig , B 2 View Fig , 8A View Fig 1 View Fig , A 2 View Fig ). Two lobes on abactinal surface of terminals articulated with last marginals, last carinal on prominent notch of terminals ( Fig. 8A View Fig 1 View Fig ). On actinal view, terminals have an oval depression, where the last pair of distal ambulacral and adambulacral ossicles are articulated Fig. 8A View Fig 2 View Fig ). Stereom of terminal plate well preserved on actinal side (with smooth and regular calcitic trabeculae), altered and pitted on abactinal side ( Fig. 8A View Fig 3 View Fig , A 4 View Fig ).

Primary and secondary spines attached in life position in adambulacrals, actinolaterals, marginals, and carinal ossicles, with massive spine bases. Secondary spines arranged in groups around the carinal spine bases, closely spaced in other plates of actinal and abactinal surface. When not preserved, secondary spine position is inferred by circular marks on the ossicles ( Figs. 4D View Fig 1 View Fig , F 2 View Fig , G 1, H 1 View Fig , 5C View Fig 1 View Fig , C 2 View Fig ). There are two types of secondary spines; those on the actinal surface are slender and longer than those on the abactinal surface ( Figs. 4F View Fig 2 View Fig , G 1 View Fig , 6G, H View Fig 1 View Fig , H 2 View Fig ). Pedicellariae straight, 200–600 μm long, formed by two blades and a cup-shaped basal piece. Pedicellariae significantly more abundant on actinal surface than in abactinal surface, inferred by the presence of complete pedicellariae and basal pieces without attached blades on both actinal and abactinal surfaces.

Actinal surface of disc preserved in detail. Actinostome deeply sunken, in a central depression ( Figs. 5B View Fig 2 View Fig , 9B View Fig 2 View Fig ). Oral area delimited by one pair of adambulacrals from each arm, articulated with small orals ( Figs. 5A, B View Fig 2 View Fig , 9B View Fig 2 View Fig ). Each oral ossicle bearing oral spines ( Fig. 9A View Fig 4 View Fig ).

Remarks.—Studied specimens are assigned to Zoroaster because of disc characters (i.e., weakly lobate disc plates, disc and arm plates continuous, see Figs. 4A View Fig , 5A View Fig 2 View Fig , 7A View Fig , 8B View Fig 2 View Fig ), imbricate ossicle arrangement ( Figs. 4 View Fig , 9 View Fig ), the presence of plates aligned in transverse and longitudinal series ( Figs. 5C View Fig , 9A View Fig 1 –A View Fig 3 View Fig ), consistently sized marginals ( Figs. 4A View Fig , 7D View Fig , 9B View Fig 1 View Fig ), secondary spines widely spaced in actinal and abactinal surface ( Figs. 5 View Fig , 6H View Fig ), carinate adambulacral plates alternating with non-carinate plates ( Fig. 6E View Fig ) and podial pores quadriserial proximally, becoming biserial distally. Within the imbricate Zoroasteridae, Bythiolopus Fisher, 1916 , Doraster Downey, 1970 , and Cnemidaster Sladen, 1889 , have internal buttress and a ring of oral pedicellariae, while these structures are absent in Zoroaster and Pholidaster Sladen, 1889 . Also, Bythiolopus and Pholidaster have alternated big and small marginal plates, while in Zoroaster marginals are consistently sized. Cnemidaster has enlarged, rounded and swollen disc plates, and discontinuous disc and arm plates. Doraster has a similar disc plate arrangement, but differs from Cnemidaster in having highly stellated disc plates. Zoroaster has weakly lobated disc plates, similar in size with the arm plates. The body wall in Cnemidaster is covered by membranous skin, while in Zoroaster is covered by secondary spines, that are frequently absent in Doraster and Pholidaster . Straight pedicellariae are absent in Pholidaster but present in Zoroaster .

Zoroaster marambioensis View in CoL sp. nov. has the same number of actinolateral rows as Zoroaster microporus Fisher, 1916 View in CoL , but the former has spines only in the three or four actinolateral lower rows while the latter has primary spines in all actinolaterals. Also, Z. microporus View in CoL lacks primary spines on carinals and marginals, while Z. marambioensis View in CoL sp. nov. has primary spines on each carinal, and on some proximal marginals. The carinal plates of Z. marambioensis View in CoL sp. nov are weakly lobate, as in all the other species of the genus, except Z. microporus View in CoL , which has quadrate carinals. Zoroaster marambioensis View in CoL sp. nov. has quadriserial arrangement of podial pores proximally, while Z. microporus View in CoL and Zoroaster ophiactis Fisher, 1916 View in CoL , have a biserial tube feet arrangement.

Zoroaster carinatus Alcock, 1893 View in CoL , differs from Antarctic species by showing a centrally domed disc, disc plates without secondary spines, lack of carinal and marginal spines along arms, and quadriserial tube feet along almost all of the rays.

Zoroaster marambioensis View in CoL sp. nov. is similar to Zoroaster variacanthus McKnight, 2006 View in CoL , in having four or five rows of actinolaterals at arm base reduced to three or two at proximal half of the arm (the lower three with a large and usually flattened spine), plates densely covered by secondary spines partially obscuring ossicle outlines, and rare pedicellariae in abactinal surface. Nevertheless, Z. variacanthus View in CoL has longer than wide carinal plates, inconspicuous madreporite, more than one spine on disc plates, and spines in each marginal plate.

Zoroaster marambioensis View in CoL sp. nov. differs from Zoroaster fulgens Thomson, 1873 View in CoL , in having a flattened or slightly depressed central disc plate ( Fig. 9B View Fig 1 View Fig , C 2 View Fig ); weakly lobate radials overlapping polygonal interradials on the disc circlet ( Figs. 4B View Fig 2 View Fig , 5A View Fig 2 View Fig , 9A View Fig 3 View Fig , B 1 View Fig , C 2 View Fig ); marginal plates hexagonal or polygonal in shape lacking spines distally ( Figs. 4A, D View Fig 1, G 1 View Fig , 5C View Fig ; 7B–C View Fig , 9B View Fig 1 View Fig ); but with spines present on all carinals and radials ( Figs. 4B View Fig 2 View Fig , H 1 View Fig , 6A View Fig 2 View Fig , D, 7C View Fig ; note that in Z. fulgens View in CoL primary carinal spines are absent and radials and interradial plates of disc have the same shape). Z. marambioensis View in CoL sp. nov. has wider than long terminal ossicle, with a prominent notch ( Figs. 6B View Fig 1 View Fig , B 2 View Fig , 8A View Fig 1 View Fig , A 2 View Fig ), while terminal plates on Z. fulgens View in CoL are longer than wide and have reduced notch. Also, their primary and secondary spine arrangement on the actinal surface is different ( Z. fulgens View in CoL has two primary spines and three secondary spines by each carinate adambulacral, while Z. marambioensis View in CoL sp. nov. has one to three primary spines and one or two secondary spines by each adambulacral; see Figs. 6G, H View Fig 1 View Fig , H 2 View Fig , 8B View Fig 1 View Fig , B 2 View Fig ). In Z. marambioensis View in CoL sp. nov. the adradials and the last row of actinolaterals extends until most distal part of the arm, near the terminal ossicle, separated from it only for the last marginal plate ( Figs. 6A View Fig 1 –C View Fig 2 View Fig , 8A View Fig 1 View Fig , A 2 View Fig ), while in Z. fulgens View in CoL the last adradial and actinolateral plates are aligned with the fourth or fifth marginal plate (counting from the arm tip). This actinolateral row arrangement is closer to those described by Ludwig (1905) for Zoroaster magnificus View in CoL than the observed in Z. fulgens View in CoL specimens.

As described by Howell et al. (2004), Recent Z. fulgens from the Atlantic Ocean appears as three morphotypes that could show reproductive isolation: the robust morphotype, the slender form and the long-armed one, which inhabit at depths of 975–1750 m, 1300–2200 m, and 3300–4020 m, respectively. This suggests that cryptic species are present across the bathymetric range of this species. Zoroaster marambioensis sp. nov. shows many similarities with the robust morphotype of Z. fulgens in characters typically associated with shallower environments (i.e., solid skeletons, short arms and strong oral armature), although the former were found in beds deposited at 10–20 m depth and the latter inhabits (at least) at 200 m depth.

In addition to Zoroaster marambioensis , described herein from Seymour Island, only one other Eocene fossil Zoroaster species is known, i.e., Zoroaster whangareiensis Eagle, 2006 , from New Zealand. Despite the poor preservation of Z. whangareiensis , several differences with Z. marambioensis sp.nov. are recognizable. Z. whangareiensis has carinal spines placed proximally after the 4th or 5th carinal, and distally every second carinal; enlarged, central, single, conical spines every second marginal and 5–6 small spinules for each marginal. Z. marambioensis sp. nov. is larger than Z. whangareiensis and has a more robust armature. Madreporite, terminal ossicles, pedicellariae, secondary spines, ambulacral armature, spine number, size and arrangement on oral surface are unknown characters in Z. whangareiensis .

Stratigraphic and geographic range.— Type locality and horizon only.