Parvulastra O’Loughlin, 2004

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 : 27-28

Parvulastra O’Loughlin gen. nov.

Figures 1 (clade V), 2l, 4a–b, 5b, e, 11b, 16a–d

Diagnosis. Rays 5, pentagonal to subpentagonal; noticeable integument; carinal series variably present; abactinal plates broadly notched for papulae, crescentiform more than Ushaped; papulate areas extensive, papulae large or small, a few per space; secondary plates a few per space; abactinal spinelets clustered or spread, not paxilliform; spinelets granuliform or digitiform or thin pointed; lack pedicellariae; superomarginal and inferomarginal plate series predominantly subequal; frequently extensive non-plated actinal area distal to oral plates; actinal interradial plates in oblique series; actinal interradial plates with frequently 2 spines mid-ray to distally, spines digitiform to conical; superambulacral plates present to varying extents, superactinal plates always present.

Type species. Asterias exigua Lamarck, 1816 .

Other species. P. calcarata (Perrier, 1869) ; P. dyscrita (H.L. Clark, 1923) ; P. parvivipara (Keough and Dartnall, 1978) ; P. vivipara (Dartnall, 1969) .

Material examined. P. calcarata . Juan Fernandez I., NMV F96703 (1); F96704 (1); F97445 (1); F97449 (1).

P. dyscrita . South Africa, False Bay , TM H800 (1); H854 (1); Jeffrey’s Bay , NMV F98059 (3).

Patiriella exigua (Lamarck, 1816) . Neotype (by Dartnall, 1971). South Africa, False Bay , TM H508 . Other material. Cape Town, NMV F98062 (4); Durban , F98061 (4); Jeffrey’s Bay , F97450 (5); Saint Helena, F98060 (4); Amsterdam I., F98063 (2); Australia, Victoria, Apollo Bay , F97054 (6); Gabo I., F73079 (9); Port Arthur , F97451 (12) .

P. vivipara . Australia, SE Tasmania, NMV F77984 (3).

P. parvivipara . South Australia, Eyre Peninsula , NMV F97720 (3).

Description with species variations. Rays predominantly 5; interradial margin straight to slightly incurved, form pentagonal to subpentagonal; noticeable integument; flat actinally, low convex abactinally, size small ( dyscrita up to R = 24 mm) to very small ( parvivipara up to R = 3 mm); lacking pedicellariae; 2 smallest viviparous ( parvivipara , vivipar a); none fissiparous; gonopores abactinal ( calcarata , dyscrit a) or actinal ( exigua ).

Abactinal surface appearance granular, upper ray plates with regular carinal series except proximally ( calcarata , dyscrita , exigua ), or irregular ( parvivipara , vivipara ); plates in longitudinal series; plates broadly notched for papulae, crescentiform more than U-shaped; papulate areas extensive, non-papulate interradial areas not extensive, papular spaces large, a few papulae and secondary plates per space; papulae large ( exigua , parvivipara , vivipara ) or small ( calcarata , dyscrita ); disc variably bordered by series of 5 large radial and 5 small interradial plates; abactinal plates with raised spinelet-bearing elevations ( calcarata ) or not; abactinal spinelets in splayed clusters ( calcarata ) or fairly close cover over plates; spinelets both digitiform on primary plates and pointed on secondary and distal interradial plates ( calcarata ), or granuliform globose ( dyscrita ), or short columnar ( exigua , parvivipara , vivipara ); glassy convexities and reticulations variably evident on denuded plates; superomarginal and inferomarginal series of predominantly subequal plates; typically widely projecting inferomarginal plates define margin, with proximal abactinal-type spinelets, distal fringe of thinner and longer spinelets.

Actinal interradial plates in oblique series; actinal proximal areas of non-plated body wall frequently extensive.

Actinal spines per plate: oral 2 tall, 3–5 short sometimes grouped separately with distalmost frequently longest; suboral 1–2, thick; furrow 2 short, thin; subambulacral 1 tall, thick; adradial actinal spines present ( dyscrita ) or few ( vivipara ) or absent ( calcarata , exigua ); actinal interradial frequently 2 midray to distally; actinal interradial spines digitiform ( dyscrita ) or pointed or short conical.

Superambulacral plates present as series (in large dyscrita ), or rare single, or distal only plates; superactinal plates present as single or multiple-plate series (neither seen in the pedomorphic parvivipara ).

Distribution. Southern Pacific Ocean, southern Australia, southern Indian Ocean, southern Africa, SE Atlantic Ocean; 0– 10 m.

Etymology. From the Latin parvulus (very small) and astrum (star), referring to the small to very small species of the genus (feminine).

Remarks. Four species previously included in Patiriella belong to a monophyletic clade V in Waters et al.’s (2004) analysis. They share a consistent morphology characterised by: subpentagonal form; longitudinal series of abactinal plates on rays; oblique series of actinal plates; granuliform and digitiform spinelets; a few papulae per space; and superambulacral and superactinal plates. The clade warrants generic rank. Asterina dyscrita shares these morphological characters and is assigned to the genus on this basis.

Morphologically, Parvulastra is similar to Cryptasterina and Patiriella . Waters et al.’s cladogram suggests that these three genera are not closely related on molecular grounds. Either the similar morphological characters have remained stable while divergence has occurred in characters not considered, or there is strong morphological convergence among the three unrelated genera, or the molecular data are unreliable at levels more basal than inter-species. Nevertheless, the genera can be differentiated by morphological characters. Cryptasterina is differentiated by predominantly single papulae per space, elongate superomarginal plates, narrowly projecting inferomarginal plates, and single mid-actinal spines. The characters which differentiate Patiriella are listed under that genus.

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.