Stegnaster Sladen, 1889

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 : 34-35

Stegnaster Sladen

Figures 1 , 3e , 17a–d

Stegnaster Sladen, 1889 : xxxiv, 375, 376 (key).— Fisher, 1911: 254 (key).— Verrill, 1913: 481 (key).— Verrill, 1915: 65.— Spencer and Wright, 1966: U69.— Clark and Downey, 1992: 194.—A.M. Clark, 1993: 227.—McKnight (in Clark and McKnight), 2001: 161–162.

Diagnosis. Rays 5, subpentagonal, frequently arched, integument cover, rays with median ridge, body very thin interradially; abactinal cover of fine granules only; glassy convexities present; projecting inferomarginal plates lack fringe of spinelets; projecting furrow spines covered by continuous granule-covered integument; actinal interradial plates with thorn-tipped short spines; lacking superambulacral plates, proximal interradius supported by multiple superactinal plate struts, wide thin interradius supported internally by downward projecting abactinal plate extensions meeting actinal plates.

Type species. Pteraster inflatus Hutton, 1872 (original designation).

Other species. S. wesseli ( Perrier, 1875) .

Material examined. S. inflatus . New Zealand, North Island, AM J1856 (1); South Island, NMV F95675 (1); no locality data, AM G2030 (1).

Description with species variations. Rays 5, narrowly elevated median ridge, interradii very thin, form subpentagonal to rounded, body frequently in high domed (arched) shape, body covered by integument; size medium ( inflatus up to R = 53 mm) to small ( wesseli up to R = 20 mm); lacking pedicellariae; not fissiparous; gonopores abactinal ( inflatus ), actinal ( wesseli ).

Abactinal surface even, continuous cover of granuliform spinelets partly obscured by integument, larger globose spinelets on crown of plates ( inflatus ), spinelets slightly enlarged around pores ( wesseli ); cleared plates with prominent glassy convexities; plates of radii in longitudinal series, not to end of ray; carinal series in midray raised, longitudinally oblong, not notched; plates on upper sides of rays slightly notched for papulae; secondary plates rare to absent; papulate areas not extensive, confined to narrow raised radii; papular spaces large ( inflatus ) with up to 6 small papulae per space, to small ( wesseli ) with single papulae in longitudinal series; distinct pentagonal disc bordered by 5 raised radial and 5 small interradial plates; interradial areas extensive, not papulate, small plates in regular series perpendicular to margin; superomarginal and inferomarginal plates subequal, regular series, granule and integument cover; margin formed by inferomarginals, without a fringe of spinelets, continuous with actinal series of plates.

Actinal interradial plates in oblique series.

Actinal spines per plate: oral 3; suboral 0; furrow 2–3, project actinally, continuous integument and granule cover; sub-ambulacral none to rare; adradial series present; actinal 1 proximally, up to 6 distally, partly obscured by granule-covered integument; actinal spines short, thick basally, tapering distally to needle-like glassy point (thorn).

Lacking superambulacral plates; superactinal plates numerous proximally, multiple plate struts between actinal plates and inward projecting extensions of abactinal plates; superactinals absent distally, wide thin interradius supported internally by downward projecting abactinal plate extensions meeting actinal plates.

Distribution. West Indies, Venezuela, New Zealand, Chatham Is; 0– 183 m.

Remarks. This morphological review is based on material examined and description of S. wesseli by Clark and Downey (1992). The phylogenetic trees of Waters et al. (2004) placed S. inflatus on a clade separate from three species placed in Paranepanthia but this distinction received only weak support. Both genera lack superambulacral plates but significant morphological differences reflect the clade separation, such as the dense subpaxilliform tufts of acicular spines and spinelets in Paranepanthia . Distinctive characters of Stegnaster are: noticeable integument and granuliform spinelet cover; furrow spines projecting actinally and covered by continuous granule-covered integument; thorn-tipped spines actinally; lacking superambulacral plates; superactinal plates proximally; wide thin interradii supported internally by downward projecting abactinal plate extensions meeting actinal plates.

Figures

Figure 1. Phylogenetic relationships of asterinid mtDNA sequences (after Waters et al., 2004). Support for particular reconstructions is indicated by bootstrap values (>50%; in bold) and by decay indices (in italics). MtDNA Clades I–VI are identified on the basis of high bootstrap support. Generic assignments made in this paper appear on the right.

Figure 3. Abactinal views of type species of Asterinidae genera (continued; Tremaster mirabilis is figure 17e). a, Patiria miniata (R = 67 mm, NMV F98040). b, Patiriella regularis (R = 31 mm, AM J5594). c, Pseudonepanthia gotoi (R = 74 mm, holotype, USNM 36899). d, Pseudopatiria obtusa (R = 54 mm, holotype, BMNH 1938.6.23.24). e, Stegnaster inflatus (R = 45 mm, NMV F95675). f, Tegulaster emburyi (R = 19 mm, holotype, AM J5605).

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.