Ophidiaster agassizi Perrier, 1881

Mah, Christopher L., 2021, The East Pacific / South Pacific Boundary: New taxa and occurrences from Rapa Nui (Easter Island), New Caledonia and adjacent regions, Zootaxa 4980 (3), pp. 401-450 : 434-436

Ophidiaster agassizi Perrier, 1881

Figure 14 A–D

Perrier 1881: 10; H.L. Clark 1921: 83; Deichmann et al. 1924: 387; Codoceo 1976: 94 (as Ophidiaster agassizi ). Ziesenhenne 1963: 461 (as Ophidiaster easterensis ).

Comments. The first occurrence records of this species were made from relatively deep-water [40–73 m (22–40 fathoms)] with subsequent records showing a much wider and shallower range up to intertidal or shoreline depths. New specimens also show occurrence from the nearby Juan Fernandez Islands. Mecho et al. (2019) has presented in situ observations of O. easterensis from between 160–180 m on rocky bottoms. These individuals were orange in color.

Synonymy of Ophidiaster easterensis Ziesenhenne, 1963 . Numerous characters strongly support Ophidiaster easterensis Ziesenhenne 1963 as a synonym of Ophidiaster agassizi Perrier 1881 . Specimens of the latter (USNM E4662) were compared with specimens of the former. Both specimens displayed pedicellariae valves with identical pointed tips as well as identical subambulacral morphology and positions of the furrow spination. Ziesenhenne (1963) compared the two species claiming they were distinct based on body shape, pedicellariae, alternation of large oval actinal spines, interlocking arrangement of the furrow spines and tubercles on the terminal plate.

The interlocking arrangement of furrow spines is a post-mortem artefact which likely occurred as the animal was assuming a defensive position and was frozen as such during preservation. Pedicellariae morphology, contrary to Ziesenhenne’s statements were identical. The “actinal spines” described by Ziesenhenne (1963: 463) occur on the adambulacral plates and are correctly identified as subambulacral spines. They are similar if not outright identical to those figured by Ziesenhenne as well as in other compared specimens from Rapa Nui. The body shape differences were observed but this appeared to be variable with area and with size with larger individuals showing more rounded arm tips. Finally, the tubercles present on the terminal plate were observed on O. easterensis are absent on specimens identified as O. agassizi but these could represent phenotypic variation.

The type locality of Ophidiaster agassizi was listed without a specific locality in Perrier (1881) a monograph that primarily documents species from the Gulf of Mexico and the tropical Atlantic. A note accompanying the type in the MNHN identifies the locality as “ Chili ” (= Chile) making the specimen consistent with modern published accounts [e.g., H.L. Clark (1921)] indicating that the species was found only in the Juan Fernandez Islands.

This species shares the identical type of curved, pointed pedicellariae observed in the New Zealand species Ophidiaster macknighti and, with one or two character differences, is very similar to O. macknighti .

Occurrence. Juan Fernandez Islands, Rapa Nui (La Perouse Bay, Anakena, Motu Tautara, Isla de Pascua), 0–73.1 m.

Small sized specimen description. Body stellate (R/r=5.0), interradial arcs acute.

Carinal, superomarginal and inferomarginal plate series present. Carinal series composed of eight quadrate abutted plates extending from disk to arm terminus. Elongate, diamond-shaped adradials, approximately seven or eight present along arm series. Primary circlet on disk evident. Surface covered by coarse granules, six to eight along a 1.0 mm line. Anal region on disk with slightly coarser granules, unevenly arranged. Body showing two fully developed, two partially developed intermarginal papular rows. The former extending from the interradius to the arm terminus, the latter with only one or two papular pores present along the serial rows along the arm.

Superomarginals, approximately 10 per arm, 20 per interradius (arm tip to arm tip), plates quadrate. Superomarginals large with upper lateral plate forming a prominent edge visible on the abactinal side, covered by large numbers of coarse granules with larger bullet shaped ones present centrally on the plate. Inferomarginals also with identical numbers of plates, covered by large, coarse granules with larger bullet-shaped granules present centrally. Inferomarginals abut directly with adambulacrals.

Actinal plates in approximately two series, coarse granules similar to those elsewhere present covering the surface. Furrow spines two, pointed conical in shape. Single subambulacral spine per adambulacral plate, 20 along the arm, each spine paddle-shaped with jagged knife-like tip. Subambulacral spines approximately one or two granule series away from the furrow spines. A further short, pointed spine similar to those on the furrow present between the subambulacral and the furrow spines. Granules, one to six present around the surface of the adambulacral plate around base of the subambulacral spine. Oral region sunken, two furrow spines on the oral plate with one pointing into the mouth along with two spines present on the oral plate surface. Oral plates otherwise bare.

Material described. Rapa Nui: CASIZ 220291 . Anakena , Rapa Nui ( Isla de Pascua), 27.07ºS, 109.32ºW, 0–14.6 m. Coll. T.M. Gosliner, 6 March 2017, 1 wet spec. R =1.2, r=0.2. CASIZ 221594 . Frente de Hotel dive site, Rapa Nui ( Isla de Pascua), 27.15ºS, 109.44ºW, 20 m, 5 March 2017. 1 wet spec. R =2.3, r=0.3. USNM E33994. Motu Tautara , Rapa Nui, 30 m. Coll. Feb. 1984, 5 dry specs. R =2.6, r=0.3; R =2.1, r=0.3; R =1.1, r=0.2; R =1.4, r=0.3; R =0.7, r=0.1 (6 arms); R =0.3, r=0.5. CASIZ 224117 . Anakena , Rapa Nui ( Isla de Pascua). 27.07ºS, 109.32ºW, 0–14.6 m. Coll. T.M. Gosliner, 6 March 2017, 1 wet spec. R =0.5, r=0.1.

Juan Fernandez Islands: USNM E46260 . Robinson Crusoe Island , Juan Fernandez Islands, South Pacific, Chile, 33º38′20″S, 78º48′50″W, 6– 11 m. Coll. R / V Anton Bruun , Cru. 12, 11 Dec. 1965. 1 dry spec. R =8.6, r=1.0. USNM E46261 . Juan Fernandez Islands , South Pacific, Chile., 28 m, Coll. R / V Anton Bruun , 16 Dec. 1965, 2 dry specs. R =5.2, r=0.6; R =8.6, r=1.2.

Figures

FIGURE 14. Ophidiaster agassizi USNM E46260 (Juan Fernandez Islands, Chile): A. Abactinal view. Scale bar equals 1.5 cm. B. Abactinal surface close-up. Scale bar equals 0.4 cm. C. Actinal surface. Scale bar equals 1.5 cm. Inset scale bar equals 1.0 mm. D. Actinal surface showing furrow spination. Scale bar equals 0.4 cm.