Hacelia raaraa, Mah, 2021

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 : 423-425

Hacelia raaraa n. sp.

Figures 9A–F

Etymology. The species epithet is taken from the Rapa Nui word ra’ara’a for “rough and rugged” alluding to the very bumpy surface texture of this species.

Diagnosis. A species distinguished by numerous bald, dome-like tubercles present on abactinal and lateral surfaces. Ten irregular papular rows. Papular pores 3 to 35, mostly 10 to 30 per region. Pedicellariae absent. Two furrow spines per plate, alternatively large and small. Subambulacrals twice the width and three times the length of each furrow spine forming a continuous series on either side of the ambulacral furrow. Color in life was light pink with darker red-orange bands on the middle to proximal arm regions and on primary circlet (i.e., central disk). White mottled highlights present throughout disk and arms. Bald dome like tubercles grey to white.

Comments. Placement of this species into Hacelia was complicated by the irregularity of the papular rows, which did not consistently demonstrate ten clear rows. Ultimately, Blake’s (1978) criterion for the identification of marginal plates as tracking to the terminal plate was used to establish full serial papular rows.

This species is most similar to Hacelia tuberculata Liao, 1985 from 100–200 m in the East China Sea with which it shares the distinctive round, bare, dome-like tubercles present on the surface. This species differs in the complete absence of pedicellariae, as described by Liao (1985) and in the irregular distribution of bare, dome-like tubercles along the arm as well as the increased abundance of tubercles on the distal end of the arm. Hacelia raaraa n. sp. displays the furrow and subambulacral spination observed in H. tuberculata and other Hacelia spp.

Hacelia bozanici Hendler, 1996 was is the only other species in this genus known from the East Pacific tropical area. It lacks the numerous tubercles present on H. raaraa n. sp. but shares several other characters with H. raara a n. sp. including a similar number of papulae per papular region, the absence of pedicellariae and a similar furrow and subambulacral spines. The latter tube foot furrow spination is present in several other Hacelia species however.

Occurrence. Isla de Pascua, Rapa Nui, 82 m.

Description. Body stout, strongly stellate (R/r=5.8), small disk, arms elongate, interradial arcs acute. Arms broadly triangular in cross-section.

Ten irregular papular rows present with well-developed rows present proximally becoming increasingly incomplete and irregular halfway along the distance to the end. Papular pores present between plates 3 to 35, mostly 10 to 30 with discrete translucent papulae. Individual plates form cylindrical, pronounced ridges rising above plane of body surface. Individual plates elongate, broadly cruciform in shape forming square quadrate to rectangular papular openings becoming more irregular and poorly defined distally with papular regions becoming smaller in outline with fewer papulae per region. Plates on disk with 3 to 5 cylindrical projections. Body surface covered by fine granule-invested dermal covering present on abactinal, lateral and actinal surface. Granules fine, quadrate to round in outline, approximately 10–15 present along a 1.0 mm line. Bald hemispherical tubercles present on disk primary circlet, central region of most abactinal and marginal plates, occupying a majority of the plate surface. Hemispherical tubercles smooth, bare and dome-like with granule-invested dermal layer present around base. Tubercles present along carinal, adradial, marginal and other plate series. Tubercle abundance increases distally with many more present around the latter half of each arm. Tubercles alternating with a flatter, shorter, granule-invested, dermal layer connecting ossicle present between those plates bearing dome-like tubercles. Madreporite badge-shaped, irregularly polygonal with shallow sulci. No pedicellariae observed.

Marginal series, although present, direct sequence does not clearly track on all arms, with the series becoming more irregular distally. As indicated earlier, both superomarginal and inferomarginal plates with a dome-like tubercle on plates alternating with a flattened, cylindrical plate covered by the fine granular dermis. Distinct papular pores, each bearing 10–30 papulae, present inter-marginally. Superomarginals, inferomarginals approximately 60– 70 per interradius (arm tip to arm tip, 30–35 per side). No pedicellariae observed. Terminal plate, round, smooth.

Actinal surface composed of one complete and one incipient papular row, each containing 5 to 30 papulae. Surface covered by closely articulated granule-covered dermal layer forming transversely oriented, rectangular segments, approximately 65–70 from interradius to arm tip. Inferomarginal series, dome-like tubercles irregularly intergrading with actinal series, with tubercles tracking to terminal plate but dropping out on smaller plates adjacent to terminus. Actinal plate surface adjacent to oral region with one large subambulacral-like spine projecting into each interradius.

Two furrow spines per adambulacral, blunt and thickened, each spine triangular in cross section with round edges, each spine slightly offset on the plate so that they each compliments the other. Subambulacral spine enlarged each approximately twice the width and three times the length of each furrow spine. Subambulacrals blunt, rounded set of from the furrow spines by a discrete space, approximately one or two subambulacrals per actinal segment. Subambulacrals shorter and closer in size to furrow spines distally along arm. No pedicellariae observed. Oral spination crowded, densely packed. Approximately two to three furrow spines on oral plate with one blunt spine projecting into mouth. Two blunt spines, similar to furrow spines present on oral plate surface (determination is difficult due to crowded oral region).

Color in life was light pink with darker red-orange bands on the middle to proximal arm regions and on primary circlet (i.e., central disk). White mottled highlights present throughout disk and arms. Bald dome like tubercles grey to white.

This species was observed on a rocky bottom among hydroids and algae.

Material described. Holotype: CASIZ 22378 . Motu Nui ( Isla de Pascua), Rapa Nui, 82 m. Coll. Bart Shepherd, Tyler Phelps and Luis Rocha, 6 March 2017, CAS Rapa Nui Expedition. 1 wet spec. R =9.9, r=1.7.

Figures

FIGURE 9. Hacelia raaraa n. sp. Holotype. CASIZ 22378 (Rapa Nui): A. Abactinal view. Scale bar equals 2.0 cm. B. In situ observation of holotype. Photo by Dr. Luiz Rocha. C. Actinal view. Scale bar equals 2.0 cm. D. Close-up showing abactinal surface. Scale bar equals 1.0 cm. E. Close-up of actinal surface and furrow spines. Scale bar equals 0.2 cm. F. Interradial, marginal close-up. Scale bar equals 0.5 cm.