Calliaster chaos, Mah, 2018

Mah, Christopher L., 2018, New genera, species and occurrence records of Goniasteridae (Asteroidea; Echinodermata) from the Indian Ocean, Zootaxa 4539 (1), pp. 1-116 : 18-19

Calliaster chaos n. sp.

Figure 5 A–F

Etymology. The species epithet “ chaos ” alludes to the irregular spination pattern present on the disk as well as the abactinal plate pattern on the disk and arms.

Diagnosis. A species distinguished by stellate body (R/r=2.7–3.0 at R>9.5), triangular arms, curved interradii, the absence of spination on the abactinal arm plates (Individuals studied with R> 9.5 cm), wide superomarginal spines forming an abactinal-facing border ( Fig. 5A ). Numerous conical, sharp abactinal spines present irregularly distributed on disk ( Fig. 5A, B ). Three to five superomarginal plates abutted at arm tip. Furrow spines nine or ten. Actinal surface covered by coarse granules and or one large pedicellaria per plate.

Comments. This species shows close morphological affinities with Calliaster (formerly Milteliphaster ) wanganellensis ( Clark & McKnight 2001) nov. comb. Both species display similar body shape with wide superomarginals forming a distinct abactinal periphery, and possess numerous large, conical spines projecting from the abactinal and superomarginal plates. Calliaster chaos n. sp. is distinguished by the absence of spines from the abactinal arm plates (present in Calliaster wanganellensis nov. comb.), the presence of three to five abutted superomarginal plates on the distal region of the arm (none in Calliaster wanganellensis ), and nine or ten furrow spines (five to seven in Calliaster wanganellensis ).

In the Indian Ocean, this species differs from Calliaster (formerly Mabahissaster ) zengi ( Macan 1938) nov. comb. primarily in that the abactinal plates on this species extend along about 75–80% of the arm distance with three to five abutted superomarginals in contact only at the arm tips whereas C. zengi possesses abutted superomarginals along the entire arm distance with no abactinal plates extending along the arm. Calliaster zengi displays seven to nine furrow spines with only a single subambulacral spine whereas C. chaos n. sp. displays nine or 10 furrow spines with consistently two subambulacral spines. Several similarities in terms of spine type and distribution as well as superomarginal plate types are similar between the two species, including a similar shared carinal plate type which is wide and irregularly quadrate in shape.

Occurrence: Mascarene Islands, 350 m.

Description. Body stout, stellate (R/r=2.79–3.02) arms elongate, interradial arcs broadly curved (Fig. A). Disk is weakly arched ( Fig. 5B ). Interradial regions on the paratype appear sunken, suggesting that the coelom and abactinal surface might be inflated when alive. Arms upturned, trapezoid in cross-section.

Abactinal surface composed of flattened, polygonal to irregularly shaped plates. Plates largest, most homogeneous proximally on disk becoming smaller and more heterogeneous distally. Carinal series wider than long flanked by smaller quadrate to irregularly shaped plates about 50% of the size of those in the carinal series. Disk plates round to polygonal, about two to four times the size of small plates on the arm. Arm plates extend along arms, ending where superomarginals abut over arm mid-line. Disk plates each with a large, single, exceptionally two, conical pointed spines (~1.0 cm in length at R> 9.5 cm) ( Fig. 5A, B ). Spines extend along carinal plates to arm base, but do not extend beyond the base of the arm ( Fig. 5B ). Each spine occupies nearly the entire center of its corresponding disk plate. Although spines are present on most disk plates, smaller, intermediate plates present between those with a spine especially those interradially lacking spines. Other than spines, other accessories include small round, low tubercles present on plate center. Paddle-shaped pedicellariae, about 1.0 mm at widest, which occur individually on plates as well shared on plate surface with the large spines. Spines completely absent from arm plates on specimens examined. Where spines are absent, plates are smooth and bare with no surficial accessories (i.e. no granules, spinelets on surface). Individual plates surrounded by peripheral granules, evenly spaced, seven to 60, mostly 10 to 50, quadrate to polygonal in shape with some disk granules displaying fluted tips. Madreporite large, similar in width to other abactinal disk plates, strongly convex forming distinct prominence on abactinal surface.

Marginal plates ~34 (at R= 9.5 cm) to ~42 (at R= 10.9 cm), superomarginal and inferomarginal series offset forming a jagged contact between them. Superomarginal plates wide, each quadrate-rectangular in shape forming a prominent dorsal-facing border around body ( Fig. 5B ), approximately 14–20% (0.5/3.4 to 0.7/3.6) of the full “r” distance on disk with superomarginals occupying increasingly high % of surface on arms, especially distally ( Fig. 5A ). Counting from the terminus, approximately three to five superomarginals abutted on abactinal surface with contacts between them variably straight, if 1:1 correspondence, or offset forming jagged contact between them along midline. Superomarginals and inferomarginals range from very wide interradially becoming more quadrate and wider distally. Interradial marginals much more flat relative to those distally. Large prominent spines, one or two present on the surface of superomarginal and inferomarginal plates ( Fig. 5B, D ). Spines identical to those on abactinal surface, conical, pointed, approximately 0.6 to 0.8 cm in length sitting above the surface of the plate. Central five to eight superomarginal plates with two spines directed in different directions, one directed dorsally on upper edge forming part of the bristling spine formation on the disk ( Fig 5B ). The second superomarginal spine series present as a linear, lateral series with each plate bearing a single, large primary spine with one or two smaller, secondary spines emerging on a minority of plates from the plate center. Inferomarginals with multiple spines ( Fig. 5D, E ). Central ten to 12 interradial (i.e. disk) inferomarginals with two to eight short spines decreasing to two then one along arm. Spines along arm becoming larger distally. Terminal plate triangular with smooth surface, approximately twice the size of adjacent small-sized superomarginals.

Actinal plate surface composed of three complete series of quadrate plates in chevron formation with one or two incomplete series adjacent to the inferomarginal contact ( Fig. 5C ). Actinal plates limited to disk, not extending to arms. Surface of each plate covered by four to 20 closely oriented, evenly spaced, irregularly sized, angular granules. Some granules present only on plate center with wide spaces showing bare surface around actinal plate periphery. Most actinal plates with paddle-shaped pedicellariae, each with wide valves displaying variable edges. Plates with pedicellariae display either a discrete concavity or a smooth, mound-like plate bearing the pedicellariae within a discrete channel or pocket. The paratype shows valves with smooth edges versus the holotype which shows six to 13 teeth along each valve edge. Approximately 25% of actinal plates with a large (3–5 mm long), conical pointed spine rising well above the actinal surface ( Fig. 5D ). Some plates with both spine and pedicellariae at spine base. Pedicellariae occur on every plate in series adjacent to adambulacral plate series, but present on most other actinal plates in each interradius.

Furrow spines, slender, variably cylindrical to rounded quadrate, in cross-section, nine or ten in palmate series ( Fig. 5F ). Adambulacral plates rectangular with one to three (mostly two or three) large, elongate blunt spines in transverse series ( Fig. 5F ). Each spine with rough, etched tips, each spine round in cross-section, two to three times the length and thickness of an individual furrow spine. Subambulacral spines number three proximally decreasing to only two then one distally. Some distalmost plates lacking subambulacral spines completely. Adambulacral plates otherwise only with three to six other angular granules. Adambulacral plates with approximately 30–40 peripheral granules, angular to irregular in shape, in single evenly spaced series. Peripheral granules 10 per longside, the contact with the actinal surface with two to three enlarged granules, five total per side. Oral plates with nine to 12 furrow spines, laterally compressed, round in cross-section. One spine projecting into mouth, triangular in cross-section. Two prominent spines, similar to other actinal spines, enlarged, about 2.0 to 4.0 mm in length, one per side of the paired oral plates. Oral plate surface with angular granules, eight per side of the oral plate sulcus in irregular series.

Material Examined. Mascarene Islands. Holotype: IE-2013-6998 . Mascarene Islands 22°27.3’S, 43°7’E, 350 m, Coll. R / V Cleva, Mascarene Islands III expedition. 1 dry spec. R=9.5, r=3.4. Paratype: IE-2013-6999 . Mascarene Islands (no other data). Coll. R / V Cleva, Mascarene Islands III expedition. 1 dry spec. R=10.9, r=3.6 .

Figures

FIGURE 5. Calliaster chaos n. sp. Holotype IE-2013-6998. R=9.5, r=3.4 cm. Scale bar=1.0 cm. throughout. A. Abactinal surface. B. Closeup showing spines, superomarginal side. C. Actinal surface. D. Closeup of actinal surface and inferomarginals. E. Inferomarginal plates. F. Furrow and adambulacral spines.