Gymnanthenea difficilis ( Liao & Clark 1995 )

Yiu, Sam King Fung & Mah, Christopher L., 2024, New Ecological Observations and Occurrence for Asteroidea and Echinoidea in Hong Kong, Zootaxa 5526 (1), pp. 1-69 : 56-58

Gymnanthenea difficilis ( Liao & Clark 1995)

FIGURE 41A–C

Comments

This species was identified based on the well-expressed carinal and adradial spination, large single pedicellariae on the inferomarginal plates, the numerous actinal pedicellariae and body shape as outlined by Liao & Clark (1995).

Distinctions for this species based on the number of “adambulacral spine rows”, as established by Liao & Clark (1995) are more difficult to establish when compared with similar species such as Anthenea chinensis . Liao & Clark (1995) outline the distinction between A. difficilis from A. chinensis and others based on two versus three adambulacral spine series respectively. However, most specimens of A. difficilis listed by Liao & Clark were relatively small, with most showing R=~ 45 mm but ranging from 20 to 56 mm whereas those observed herein are approximately twice the size. Liao & Clark also mention that the subambulacral rows are oblique and the addition of one or two additional spines would from two rows of subambulacrals. Larger sized individuals observed herein would presumably show an additional row of subambulacral spines. Fujita & Marsh (2002) accounted for the two rows of ambulacral spination and accordingly moved this species into Gymnanthenea .

In situ o bservations of this species showed a wide range of color variation, which agrees with colors as described by Liao & Clark (1995). This includes orange and red banding and coloration on arms and disk with some individuals showing mottled orange patches all along the abactinal surface contrasted by gray, olive, green and dark colors. Furthermore, there was one six-armed specimen collected from Steep Island.

Occurrence/Distribution

Hong Kong, 5–20 m.

Outside Hong Kong. Southern China, Guangdong and Fujian Province. “shallow water” Observed on rocky wall, 3–20 m.

Description

Body stellate (R/r=2.38), arms triangular, wide at base, interradial arcs curved. Disk and arms thickened. Body surface covered by thick dermis. Armtips upturned, overall shape curved, terminating at a fine point.

Abactinal surface covered by dermis with widely spaced coarse granules, continuous with dermis on superomarginal plates. Skeleton reticulate. Granules larger, most widely spaced on distalmost arm surface but most coarse surrounding papular pore regions along arms. Papular pores, 6 to 30, mostly 12 to 20, present on disk and arms, but absent interradially. Papulae separated by mesh-like network, present especially on disk and along radial arm regions to armtip. Large granules interspersed between papulae on each papular pore. Prominent blunt spines present primarily along radial region along arms. Carinal series composed of one or two conical spines per plate, 11 to 16 along each arm at R=6.2, with largest spines present proximally, tapering out at approximately 80% of distance along the arm before the tip. Although most are full grown, some spines appear to be regrown and are only 25% of the size of the others. Two full adradial series of smaller, blunt spines in single series on either side of the carinal series with other shorter series of blunt spines along adradial arm regions on disk. Interradial regions devoid of spines or papulae, forming a “fold” which corresponds to contact between interradial superomarginal plates. Large bivalve pedicellariae, approximately 1–2 mm in length, each flanked by 4 to 6 blunt spines. Approximately 1 to 3 pedicellariae present primarily on proximal arms regions or on disk. Madreporite large, approximately 5.0 mm in diameter, flanked by approximately 7 to 8 papular regions.

Marginal plates, approximately 28–30 per interradius (15 along each arm), call covered by thick dermis. Superomarginals approximately 30 per interradius, inferomarginals 28 (14 along each arm) oriented vertically interradially, but forming more of a peripheral edge distally along the arms. Superomarginals and inferomarginals show 1:1 correspondence, separated by discrete groove between them. Interradial disk “fold” shows direct association with contact between interradial superomarginal plates. Superomarginals with large, round tubercles, 1 to 4 with 6 to 40 smaller tubercles (approximately 20% of the size of larger tubercles) present on the plate surface. Tubercles/ granules on superomarginal plates more homogeneous in size distally along arm distance. No pedicellariae observed on superomarginals. Inferomarginal plates covered by large, round tubercles, up to 40 on plate surface. One large bivalve pedicellariae bisecting plate at an oblique angle flanked by tubercles.

Actinal surface composed of quadrate to polygonal plates in chevron-like formation in 3 to 4 incomplete series. Surface covered by coarse conical, weakly pointed granules, 6 to 15, close-set, irregularly arranged. Large bivalve pedicellariae, 6 to 8 present on intermediate plates, each approximately 2 mm in length. Actinal plate series adjacent to adambulacral plates each with a large bivalve pedicellariae, approximately 3 mm in length oriented at oblique to transverse angles relative to the adambulacral plates.

Furrow spines 5 to 6, webbed, subambulacral spines in 2 irregularly arranged rows. Subambulacral spines adjacent to but spaced from furrow spines, each thick and enlarged, each approximately 2 to 3 times the thickness of the furrow spines with a third row of subambulacral spines similarly thick and enlarged. Furrow spines on oral plates, 9 to 10, webbed similar in size, shape to those along arms. Oral plate surface covered by 7 to 8 thick, blunt spines, all oral plates covered by dermis.

Material Examined

USNM 3036 Hong Kong, China. Coll. W. Stimpson. 3 wet specs. R=5.8 r=2.6 R= 6.1 r=2.8 R=5.1 r=2.4. CASIZ 308834 , on rock. Breaker reef in Mirs Bay NE of Hong Kong Island, Hong Kong, China, 22º27.78’N, 114º25.11’E. 3 m. Coll. Coral Reef Research Foundation, 4 Oct. 1994 1 wet spec. R=6.2 r=2.6 .

Figures

FIGURE 41. Gymnanthenea difficilis. Color variation. A. In situ, red color variant. B. In situ, mottled color variant. C. In situ, orange-white color variant. Photographer: Sam King Fung Yiu.