Cladaster analogus Fisher 1940

Cladaster analogus Fisher, 1940

(Figures 8 A–D, 9A–D)

Fisher, 1940: 123, fig. D, pl.4, figs. 1–3; Bernasconi, 1963: 14; Clark & Downey, 1992: 239; A.M. Clark, 1993: 251. McKnight, 2006: 95 (as Cladaster latus)

Comments. Larger, more heavily calcified specimens of Cladaster analogus (e.g., USNM 1091176, R= 5.4 cm) (Figures 8 A–D) possessed more well-developed abactinal fasciolar channels and abactinal plates, coarser and more abundant granules, and differentiation between peripheral and central plate granules that most closely resemble the holotype as indicated by Fisher (1940). Smaller specimens (e.g., USNM E38569) (Figures 9 A–D) superficially fall under the general definitions for C. analogus as outlined by Clark and Downey (1992) but, as indicated above for USNM 1091176, morphological differences are substantially pronounced relative to the larger specimen. Smaller specimens also lack abactinal pedicellariae, possess weak differentiation between different granule types, and have much fewer marginal plates per interradius (18 at R= 1.7–3.4 cm vs. R= 26 in the larger specimens, R=5.4). It is unclear if this represents a substantial ontogenetic morphological change, phenotypic variation, or a separate, undescribed species.

Synonymy of Cladaster latus. McKnight (2006) distinguished Cladaster latus from other Cladaster species by the distal, wide carinal plate shape. Other then this character, C. latus shares diagnostic characters with the small “form” of C. analogus, (USNM E38569), including the presence of 22 interbrachial superomarginal plates, the presence of relatively slender, ovate furrow spines, similar body shape, and overall similar granule size, shape, and distribution. Cladaster analogus is described as possessing only two distal superomarginals abutting over the midline, where C. latus possesses three. Specimens of C. latus were not examined, but McKnight (2006: 179, Fig. 82) suggest that while there are two fully abutting superomarginals only a lateral edge from each paired third plate abut in this species. Morphologically, the concept and figures of C. latus as outlined by McKnight 2006 are essentially identical with an identified specimen (USNM E38569) and with the description of C. analogus as described by Fisher 1940. Cladaster latus McKnight 2006 is herein synonymized into C. analogus Fisher, 1940.

Distribution. South Atlantic Ocean: Burwood Bank, Falkland Islands to Tierra Del Fuego. Christabel Seamount, west of the Auckland Islands and from near the Antipodes Islands. 145–1065 m.

Material examined. South Atlantic. USNM E9623. Holotype. South of Falkland Islands, Scotia Sea, South Atlantic. 53°53’30’S, 60°34’30’W. 151 m. Coll. R/V Scoresby, 3 April 1927 (arm fragment only); USNM E38569 South Atlantic Ocean, Scotia Sea. 53˚20’S, 42˚42’W, 417– 514 m. Coll. R/V Siedlecki, USARP 29 Nov. 1986 (1 dry spec. R=3.4, r=2.0); USNM 1082726 Burdwood Bank, Scotia Sea, South Atlantic. 54°43’S, 55°30’W to 54°45’S, 55°37’W, 1647–2044 m. Coll. R/V Eltanin, USARP, 14 March 1966. (1 dry spec. R=1.7, r=1.0); USNM 1091176 (large, thick variant), South Atlantic Ocean, Tierra Del Fuego, Strait of Le Maire. 54˚56’S, 65˚3’W to 54˚59’S, 65˚6’W, 229–265.0 m. Coll. R/V Eltanin. (1 dry spec. R=5.4, r=3.5).

Description—Large, calcified variant. Body stellate, swollen, disk large, arms triangular. R/r =1.54–1.6. Endoskeleton heavily calcified, massive (Fig. 8 A).

Abactinal plates oval to irregularly polygonal in outline (Fig. 8 A, B). Plates higher then wide, forming a low tabulae. Fasciolar grooves well-developed. Plates larger proximally, becoming smaller and more irregularly shaped closer to contact with superomarginal plate series. Papulae, 8–12 surround most plates but are largely absent adjacent on interradial plates adjacent to contact with superomarginal plates. Quadrate to rounded-rectangular granules, 7–40 forming periphery around abactinal plate surface. One to seven, widely and evenly spaced, larger hemispherical granules (about 2x the size of peripheral granules) present on the surface of each plate within the granular periphery of each plate (Fig. 8 B). Granules are deciduous and small, concave pits remain where granules have been removed. Tong-like pedicellariae with spatulate-shaped valves present on abactinal plates but not abundant. Approximately granule-sized. Aside from granules and pedicellariae, abactinal plate surface is bare of other smaller accessories. Madreporite large, with well-developed sulci, bordered by five large abactinal plates.

Marginal plates 26 in each interradius (22 in type) and correspond 1:1 with inferomarginals, wider then long and possess convex surface. Marginal plates widest interradially becoming smaller distally. Smaller granules 20– 100, each rectangular to quadrate, forming distinct periphery around each plate. Large, hemispherical granules, 10– 25 similar to those on abactinal plates present on the surface of each superomarginal plate surface with fewer on dorsal surface, and granules becoming denser laterally. Inferomarginal granules, 15–35 widely spaced but more numerous and densely packed becoming more densely packed on distal armtips. Granules becoming flatter and more polygonal on inferomarginals. Granules on both superomarginals and inferomarginals widely spaced with one exceptionally large tubercule-like granules, that is 2x–3x the size of the typical granules present on each plate. Other than granules, plate surfaces are smooth, bare. Distalmost one to two superomarginals abut with one another at armtip, sometimes separating one or two abactinal plates from remaining plates on disk. Fasciolar grooves welldeveloped. Some superomarginals on USNM 1091176 appear damaged (and regrown) or with growth irregularities.

Actinal intermediate regions moderately large. Approximately five chevron-series in each interbrachium. Series adjacent to the adambulacrals are largest and rounded, becoming smaller and more irregular proximally, next to the inferomarginal series. Plates are quadrate to rounded. Fasciolar grooves present between actinal plates. Actinal plates surrounded by 7–15 peripheral granules, surface granules, 2–9, and pedicellariae identical in arrangement to those on the abactinal plate surface. Pedicellariae, largest, spatulate-valve type present centrally on actinal plates, but most abundant on proximal plates near mouth, especially on actinal plate series adjacent to adambulacrals. Adambulacral armature crowded. Furrow spines, two to three, each compressed-oval in cross-section. Subambulacrals, one or up to three, typically with one very large, thick spine, round in cross-section and a second smaller spine approximately 50% of length of the taller one. Adambulacral plates with angular to pointed peripheral granules, seven to nine, widely spaced from one another. Adambulacral plates separated from other actinal plates with distinct fasciolar groove between adambulacral and actinal plate series.

Description—Smaller variant. Body stellate, arms triangular R/r =1.7. Interbrachial arcs weakly curved.

Abactinal plates round to polygonal, flattened. Fasciolar grooves shallow, weakly expressed. Surface covered by small, deciduous granules, 15–30 with no discrete difference in size or shape differentiating peripheral granules versus those present on the central plate surface. Granules on central surface absent on many plates. Larger more polygonal plates located proximally becoming smaller distally adjacent to contact with superomarginals. Papulae located over radial regions of disk, absent from interradial regions, especially adjacent to contact with superomarginal plates. Pedicellariae not observed.

Marginal plates, weakly swollen, becoming more convex near armtips, 18 from armtip to armtip in each interradial region (at R=1.7 and 3.4). Superomarginal and inferomarginal plate series correspond 1:1. Granules, 15–35, forming periphery of plate. Granules, 20–40 on the dorsolateral surface, widely spaced on on the abactinal surface but becoming denser and more abundant on lateral side. Size and shape distinctions between peripheral and central granules are not evident. One to two distalmost superomarginals abutted on one side at armtip. Papulae present, approximately one to four per plate. Terminal plate smooth, spherical.

Actinal intermediate plates polygonal, arranged in 3–5 chevrons with the series adjacent to the adambulacral plate series becoming more irregular in size and order adjacent to the inferomarginal plate series. Actinal plates covered by round to slightly elongate granules, four to 12 forming periphery with one to four present on actinal plate surface. Granules are deciduous in preserved specimens. At R=1.7 the granules are indistinguishable, becoming more discrete in shape at R=3.4. Granules become more dense on actinal plate surface adjacent to contact with inferomarginal plates. Spatulate-shaped tong-like pedicellariae present on actinal plates adjacent to the adambulacral series. Furrow spines, two, elongate, compressed and ovaloid in cross-section. Subambulacral spines one to two, with one round in cross-section, thick and second approximately 25% of length but similar in thickness. Smaller angular granules, four to eight present around periphery of adambulacral plate.