Limnasterias oinops, Setiadi, 2019

Setiadi, Anargha, 2019, A new genus and two new species of sea stars (Family Asterinidae) from Indonesian marine lakes, with notes on habitat and feeding ecology, Zootaxa 4712 (3), pp. 392-402 : 394-397

Limnasterias oinops sp. nov.

( Fig.1 ; Fig. 2A, B ; Fig. 4A, D ).

Type locality. Haji Buang Lake , Maratua Island, Derawan Archipelago, 0-1 m, on mud, sponges and green algae .

Material examined. Holotype. MZB. Astr. 00040, D. Kusuma, 20 February 2019, in ethanol, 0-1 m; 4 Paratypes, MZB. Astr. 00041 (Type locality), A. Setiadi, 15 December 2017, in ethanol; 3 Paratypes, MZB. Astr. 00042 (Type locality), A. Setiadi, 30 October 2018, in ethanol; 4 Paratypes, MZB. Astr. 00043 (Type locality), D. Kusuma, 20 February 2019, in ethanol.

Diagnosis. Non-fissiparous, medium-sized asterinid with R up to 27.4 mm. Form five-rayed stellate, rays long, basally narrow with acute tips, R:r 2.6–3.3; body and rays high, semicircular in cross-section; integument thick, obscuring plates; abactinal plates thin, flat; single papulae large, protruding, numerous; spinelets sacciform, glassy and readily lost; up to 4 spinelets per proximal plate but predominantly 1-2 spinelets; superomarginal plates circular; each inferomarginal plate armed with predominantly one large, conical spinelet surrounded by up to 5 smaller spinelets at the base; oral spines straight, occasionally with spatulate tips ( Fig. 1C ); subambulacral spines predominantly singular and up to two spines, taller than furrow spines. Color in life dark indigo to black abactinally, which may appear navy to cobalt blue underwater or in photographs; prominent papulae translucent white, with yellowish spinelets; grayish beige to olive green actinally.

Taxonomic comments. In general, L. oinops sp. nov. possesses fewer and finer abactinal armature, thinner plates, greater maximum body size and higher R: r ratio compared to L. estradivariae sp. nov. ( Table 2 ). Abactinal spinelets are sacciform with slender, tapering tips in L. oinops sp. nov., predominantly in singlets or couplets ( Fig. 1E ), and thick conical to digitiform in L. estradivariae sp. nov., frequently four to six near disc or ray median ( Fig. 3F ). Inferomarginal spinelets of L. oinops sp. nov. are often composed of one tall, thicker spinelet surrounded by smaller, shorter spinelets, less than half to three-quarters the length of the large spinelet ( Fig. 1F ). In comparison, frequently two or three inferomarginal spinelets of L. estradivariae sp. nov. are equal or subequal in length, robust conical in form ( Fig. 3B, C ).

Description. Non-fissiparous, five-rayed asterinid, R up to 27.4 mm, R:r 1.8–3.3. Disc border variable, occasionally with pentagonal outline but also ovoid, irregular or incomplete. Single madreporite. Abactinal surface covered in thick integument. Imbricating abactinal plates thin, flat, slightly thicker proximally; shape triangular to crescentiform or quadrangular with strong crescentiform notches. Plates at proximal and midradial regions irregularly arranged, bordered dorsoventrally by regular series of crescentiform plates. Papulate areas extensive with up to five rows of papulae at the proximal sides of rays, in addition to irregular papular array at the ray median; papulate plates directly bordering superomarginals for much of ray length in larger individuals ( Fig. 1D ) or separated from superomarginal plates by one to two non-papulate plates in smaller individuals; papulae large, pore diameters on average three-fourth the width of adjacent plates, predominantly single. Secondary plates present in some papular pores at midradial regions. Non-papulate area at the interradii present as opposing triangular fields adjacent to disc borders, and at distal interradial margins ( Fig. 1B ).

Abactinal spinelets glassy, short to long sacciform with tapered points, fragile ( Fig. 1E ); spinelets shorter proximal-dorsally, longer toward distal-marginal regions; up to 4 spinelets proximally but predominantly 1–2 spinelets on rays. Glassy convexities present on plates. Pedicellariae absent. Superomarginal plates circular with single sacciform spinelets. Inferomarginal plates longitudinally elongate with distal protrusion, boot-shaped ( Fig. 1D ); the apex is armed primarily with a single large, conical spinelet, surrounded by up to five smaller subsacciform to conical spinelets at the base ( Fig. 1F ); clusters in triplets or couplets with at least one large spinelet are also common.

Thin actinal plates oblique in arrangement, with up to two sacciform spines per plate, predominantly one; aspinous plates variably present in some individuals. Spines sheathed by translucent tissue in intact specimens. Furrow spines up to four, tall sacciform, webbed in intact specimens. Subambulacral spines up to two, subsacciform and taller than furrow spines; proximal subambulacral spines occasionally with spatulate tips. Adradial plates spinous, not dissimilar from adjacent actinal plates. Oral plates with five straight spines; tips may be spatulate in some large specimens; one to two suboral spines.

Superambulacral plates absent, internal plate projections are also absent ( Fig. 2A ); superactinal plates are reduced, short and appressed to the intersection between abactinal and actinal walls, and are occasionally fused to the abactinal wall in larger specimens ( Fig. 2B ); interradial pillars present. Interior with smooth plate surface and resinous lining, appearing empty in larger individuals; gonads attached to abactinal wall of the interradii, indicating abactinal gonopores.

Color in life ( Fig. 4A, D ) abactinal surface dark grayish indigo or black, often appearing navy to cobalt blue underwater and in photographs; madreporite and spinelets yellowish, cream or otherwise pale color; actinal surface grayish beige to olive green.

Distribution. Haji Buang Lake on Maratua Island, at depths of 0– 2m.

Habitat. Mud, macroalgae, sponges, rocks, submerged branches and mangrove roots in very shallow water.

Etymology. The specific name (Gk. oinops = “wine-faced”) refers to the ambiguous dark color in live animals, which are often visibly blue underwater and appearing black when brought to surface. The term was quoted from the chromatically enigmatic phrase “wine-faced sea” ( oinops pontos) in the writings of Homer.

In situ observations. Remnants of smaller conspecifics are occasionally discovered under feeding individuals. Sampled fragments show recognizable furrow spines ( Fig. 4B ) and bluish tissue prior to preservation. This suggests that intraspecific cannibalism may occur at times; it is unknown whether the prey were healthy, moribund or dead animals. Smaller L. oinops sp. nov. are also frequently observed attached to the thalli of green macroalgae ( Fig. 4D ) or on submerged, decaying branches and leaves.

Figures

FIGURE 1. Limnasterias oinops sp. nov., A-C Holotype, MZB.Astr.00040: A. Abactinal surface of disc (R = 22.6). B. Abactinal interradial region showing interradial non-papulate regions (arrows) and five rows of papulate plates at ray base. C. Actinal surface. D. Paratype, MZB.Astr.00041, cleared lateral ray, with boot-shaped inferomarginal plates (arrow) and circular superomarginal plates. E-F Paratype, MZB.Astr.00043: E. Sacciform abactinal spinelets. F. Marginal interradius and inferomarginal spinelets. Note that residual fibers from packaging are present in Figs. 1B, C, and F.

FIGURE 2. Internal structures of Limnasterias gen. nov., A–B Limnasterias oinops holotype, MZB.Astr.00040: A. Ray and abactinal surface removed to show absence of superambulacral plates (arrow) B. Appressed superactinal plate at distal edge of interradius (arrow) C. Limnasterias estradivariae paratype, MZB.Astr.00047, abactinal surface and ray removed, showing interradial pillar (arrow) and absence of superambulacral plates D. L. estradivariae paratype, MZB.Astr.00048, superactinal plate (arrow). Note that residual fibers from packaging are present in Fig. 2C.

FIGURE 3. Limnasterias estradivariae sp. nov., A–E Holotype, MZB.Astr.00046: A. Abactinal surface (R = 12.05). B. Abactinal interradius, with upper and lower non-papulate regions (arrows). C. Lower lateral ray with boot-shaped inferomarginal plates (arrow) D. Oral plates. E. Actinal surface. F. Conical abactinal spinelets. Note that residual fibers from packaging are present in Figs. 3B and D.

FIGURE 4. Live and in situ observations of Limnasterias gen. nov. A. Limnasterias oinops, paratype, MZB.Astr.00042, live animal. B. Regurgitated remains of cannibalized L. oinops with visible furrow spines (arrow). C. Limnasterias estradivariae, paratype, MZB.Astr.00047, live animal. D. L. oinops on macroalgae. E. L. estradivariae on macroalgae.

Tables

TABLE 2. Distinguishing characters between Limnasterias oinops sp. nov. and Limnasterias estradivariae sp. nov.

Morphological characters	Limnasterias oinops	Limnasterias estradivariae
Maximum R length	27.4 mm	12.35 mm
R: r ratio	2.6–3.3	2.1–2.6
Abactinal plates	Thin, flat	Thicker with blunt or rounded keel
Abactinal spinelet shape	Glassy sacciform, fragile	Digitiform to conical, robust
Abactinal spinelets per plate	Up to 4 proximally; primarily 1–2	Up to 7; 4–6 spinelets near disc region, 3–2 distally
Superomarginal spinelets per plate	1	Up to 2 spinelets proximally
Inferomarginal spinelets	Frequently with one large conical spinelet surrounded by smaller spinelets; smaller spinelets up to 5	Frequently with 2 or 3 subequal, large spinelets, may be adjacent to smaller spinelets