Tremaster Verrill, 1880

O’Loughlin, P. Mark & Waters, Jonathan M., 2004, A molecular and morphological revision of genera of Asterinidae (Echinodermata: Asteroidea), Memoirs of Museum Victoria 61 (1), pp. 1-40 : 36-37

Tremaster Verrill

Figures 17e–f

Tremaster Verrill, 1879: 201 .— Sladen, 1889: xxxiv, 375, 394.— Spencer and Wright, 1966: U69.— Jangoux, 1982: 155–158, 161–162.— Leeling, 1984: 263–274.— Clark and Downey, 1992: 195–196.—A.M. Clark, 1993: 228.—McKnight (in Clark and McKnight), 2001: 163.

Diagnosis. Rays 5, subpentagonal, frequently strongly arched; 5 plated ducts between proximal abactinal and proximal actinal conspicuous interradial openings; abactinal plates with integument cover and large conical (proximal) and small granuliform (overall) spinelets; lacking series of superomarginal plates; 4 rows of tube feet in each ambulacrum; furrow spines in vertical series on adambulacral plates; actinal spines single, tall, slender, spatulate, in oblique series; lacking superambulacral and superactinal plates, wide thin interradial body supported by interior distal keels on actinal plates meeting abactinal plates.

Type species. Tremaster mirabilis Verrill, 1879 (original designation) (junior synonym: Tremaster novaecaledoniae Jangoux, 1982 proposed by Leeling, 1984 and confirmed in this work).

Material examined. T. mirabilis . Southern Ocean , Heard I., 226–252 m., NMV F67741 (6) , F87362 (1), F67363 (1).

Description. Rays 5; interradial margin straight or slightly convex or concave; body frequently strongly arched; conspicuous proximal abactinal interradial openings to plate-lined ducts and chambers, opening actinally distal to oral plates; wide very thin body distally; size large (up to R = 85 mm); 4 rows of tube feet in each ambulacrum; lacking pedicellariae; ducts act as brood chambers.

Appearance dominated by domed form of body, 5 proximal duct openings, regular fish-scale plates, large conical spinelets on free edge of proximal plates, small granuliform spinelets on plates; abactinal proximal plates large, rhombic, thin, irregular on upper rays, singly notched for papula on upper sides of rays, distal plates small, covered by integument and weakly attached small granuliform spinelets; papular spaces small, predominantly single papula, secondary plates absent; 3–4 longitudinal series of small papulae along each upper side of rays; proximal abactinal plates with series of conical spinelets on proximal edge over papular space; cleared plates lacking conspicuous glassy convexities; abactinal interradial plates in longitudinal series, irregular distally, not in series perpendicular to margin; lacking series of superomarginal plates; acute margin formed by projecting series of inferomarginal plates; margin fragile, frequently broken off.

Actinal plates in oblique series, each plate with prominent proximal spine-bearing dome, series separated by decalcified body wall.

Actinal spines per plate: oral 1 tall proximally, adjacent pair, few upper small conical; suboral 0; furrow vertical series of 4–5, short to tall actinally; subambulacral 1 tall; adradial actinal series present; actinal 1 (rarely 2); actinal spines tall, slender, spatulate, subsacciform.

Lacking superambulacral plates; wide thin interradial margin supported by interior distal keels on actinal plates meeting abactinal plates; lacking superactinal plates.

Distribution. Atlantic, Pacific and Southern Oceans; 150–1060 m.

Remarks. No molecular data have been obtained for T. mirabilis , and this review is based on morphology. Leeling (1984) questioned the specific status of T. novaecaledoniae as its characters fell within the variation seen in T. mirabilis . We agree with her proposed synonymy. The significantly different characters of Tremaster from other asterinid genera are: abactinal and actinal duct openings, and internal plated brood chambers; absence of superomarginal series of plates; four rows of tube feet in each ambulacrum; furrow spines in vertical series on adambulacral plates; and extensive thin interradial margin supported by internal keels on actinal plates.

Figures

Figure 17. a–d, Stegnaster inflatus (cleared, R = 45 mm, NMV F95675): a, abactinal globose spinelets and granules; b, internal adradial interradius, showing absence of superambulacral plates (left) and presence of superactinal plates (right); c, actinal furrow spines, and granule-covered integument; d, actinal glassy thorn-tipped spines. e–f, Tremaster mirabilis (R = 60 mm, NMV F67741): e, arched body, with abactinal brood chamber pore (arrow); f, ambulacrum showing vertical series of furrow spines.