Solaster regularis Sladen, 1889

FIGURE 24A–B, 25A–E

Solaster regularis Sladen, 1889: 454; Fisher 1940: 178; Bernasconi 1973b: 287; Codoceo & Andrade 1978: 157, pl. 3; Clark & Downey 1992: 305; Larrain et al. 1999: 434–436; Stampanato & Jangoux 2004: 13–14; Sellanes et al. 2008: 1107; Mutschke & Mah 2009: 818; Frayasse et al. 2018: 2428–2429 l; Martinez et al. 2018: 24.

Solaster regularis regularis Sladen, 1889: 454 .

Solaster subarcuatus Sladen, 1889: 455; D̂derlein 1927: 296.

Solaster octoradiatus Ludwig, 1903: 25–27, Bell 1908: 11; 1917: 4; Jangoux & Massin 1986: 91.

Solaster regularis subarcuatus Fisher 1940: 179–180; A.M. Clark 1962: 55; McKnight 1976: 28; Jangoux & Massin 1986: 91.

Crossaster canopus H.E.S. Clark, 1963: 55 (syn. by McKnight 1976)

Solaster longoi Stampanato & Jangoux, 1993: 181 .

Diagnosis

Body stellate to strongly stellate, R/r= 2.4–5.2. Arms 7–10, mostly 8 or 9, shape highly variable, ranging from short, thick, arched with sharply tapering tips to arms elongate with gradual taper. Disk large with relatively large actinal intermediate region. Interradial arcs acute (Fig. 24A, D).

Abactinal paxillae widely spaced, short with thick shaft, each bearing 6–10 spinelets with finely spinulose tips (Fig. 24B). Abactinal plates fenestrate in ordered series, variably transverse to more irregular adradially with openings between plates variably quadrate to irregular in shape depending on location, ranging from lateral arm series to disk. Papular pores large.

Superomarginal plates similar or identical to abactinal plate, significantly smaller than inferomarginal plates which are approximately four to five times the size of the superomarginals (Fig. 24C). Inferomarginal plates paxillate with thick, robust shaft, widely spaced, each with wide surface bearing 4–30 short, robust spinelets, each with denticulate tips bearing finely spinose tips. Variably 15–48 inferomarginal paxillae (R=1.3 to R= 7.6 cm) present per arm (30–100 arm tip to arm tip).

Actinal surface forming a V shape with dermis bearing numerous irregular to round plates bearing short spinelets, 4–6 (Fig. 24D). Adambulacral plates each round in shape, transversely oriented to tube foot grove, each plate separated by distinct tissue filled space. Furrow spines blunt, basally webbed, 3–5. Subambulacral spines, 4–5 in transverse series, elongate with blunt tips bearing finely spinose ends, spines arranged in single series along adambulacral plate forming weakly curve array along plate (Fig. 24E). Adambulacral spination sheathed in thin dermis. Mouth plates moderately large, furrow spines 8–10, with two largest spines projecting into mouth, suboral spines, on plate surface, 3–4. Color if life, variably solid orange, yellow or white.

Synonymy of Solaster subarcuatu s (and subspecies) with Solaster regularis

Further data from additional specimens does not provide any further evidence separating Solaster subarcuatus (and thus Solaster regularis subarcuatus) from Solaster regularis .

Sladen’s (1889: 455–456) original description Solaster subarcuatu s (R=3.8, r= 1.2 cm) was characterized by nine arms, widely spaced abactinal paxillae with 5 or 6 spinelets, superomarginal paxillae indistinguishable from the abactinal plates, 26 prominent inferomarginal plates along each arm, each with a broad crown, bearing 8–12 spinelets, 3–4 furrow spines, and 4–5 subambulacral spines. At least one specimen (USNM E38601) corresponded to every character save the number of marginals along each arm.

Fisher (1940: 179–180) observed the overall similarity between the two species reducing S. subarcuatus t o a subspecies of Solaster regularis, stating that the separation would be useful in keeping S. subarcuatus as the “Antarctic representative of S. regularis ”, as S. subarcuatus was described from near Kerguelen and the latter species described from Patagonia in the South Atlantic. These characters have all since been found to overlap or are consistent with those of Solaster regularis (Sladen 1889; Stampanato & Jangoux 1993). A.M. Clark (1962: 55) observed that the two species were practically indistinguishable, using only furrow spine length to diagnose them in her key additionally noting that “The spinelets …provide no reliable guide to the distinction of antarctic and subantarctic forms.” Stampanato & Jangoux (2004: 13) also noted that the two subspecies of Solaster regularis showed “mixed features” and that the subspecies could be “artificial.”

Examination of additional specimens of Solaster arcuatus across its range suggests that it is highly variable, but none of Sladen’s (1889) characters consistently distinguish it from S. regularis . On this basis, I argue that Solaster arcuatus (and thus S. regularis arcuatus) should be placed into the synonymy of Solaster regularis .