Deep Sea Cherry Blossom Starfish

Astrosarkus idipi is a species of sea stars in the family Oreasteridae. It is the sole species in the genus Astrosarkus. It is sometimes referred to as a "Pumpkin sea star".

External Morphology. Size of adult specimens: mean R of three specimens = 14.1 cm, r = 10.0 cm, R/r = 1.4. Mean thickness at arm = 6.3 cm, mean thickness interradially = 3.1 cm. Arms short, bell-shaped. Disk large, thick, confluent with arms (Fig. 1A). Interradii rounded with obtuse angles. Arm tips curve abactinally, abruptly terminate in nipple-like extremity (Fig. 1A,B). Actinal surface concave. Endoskeleton highly-reduced. Modified, almost completely engulfed by thick tissue. Marginal, abactinal, actinal plates not visible externally. Large spines, tubercles, prominent ornamentation absent. Body surface of preserved specimens firm to the touch. Abactinal, lateral surfaces with fleshy, rounded triangular to oval-shaped, low relief, mounds each bearing 100–150 papulae. Mounds separated by granular densities of 16 mm-2. Granules < 1.0 mm in length, round at base, with mace-shaped tips. Tiny, sessile tong-shaped valvate pedicellariae (typically about 0.5 mm width) present in densities of 16–18 cm-2 interspersed throughout the granular and papular regions (Fig. 2C). Madreporite subquadrate with curving, sinusoidal grooves projecting from central furrow. Mean madreporite length = 9.0 mm, mean madreporite width = 3.3 mm. Madreporite surrounded by granules, papulae. Madreporite approximately 23 mm from anus. Anus central on abactinal surface, covered with large, slender, rounded, rod-shaped granules (approximately 0.8–1.0 mm in diameter). Polygonal granules peripheral to rodshaped granules, these large, coarse (0.8–0.6 mm in diameter), becoming progressively smaller, finer, away from anus until size-normalized with other abactinal granules. Actinal surface concave, depressed toward mouth (Fig. 1B,2A). Actinal surface uniformly granular. Granules round, subquadrate, coarser than those of abactinal surface (approximately 0.5 mm in diameter) (Fig. 2B,C). Dense concentrations of slightly larger valvate pedicellariae (approximately 1.0 mm in width) near mouth (Fig. 2B,C). Smaller (approximately 0.4–0.5 mm) pedicellariae, widely scattered farther from mouth, extending to edge of actinal surface. Papulae present only on abactinal, lateral surface of body. Absent from actinal surface. Adambulacral spines 11 per plate to 24th or 25th plate, reducing to nine by 40th, one at distalmost adambulacral plate. Adambulacral spines slender, blunt, of varied size. Centrally located spines longest, progressively shorter laterally. Shortest spines blunt, subtriangular. Three to five prismatic to quadrate subambulacral spines (Fig. 2C) per plate. Five subambulacral spines present at 24–25th adambulacral plate from mouth, decreasing to four at 42nd, then to three and finally two near arm terminus. Adambulacral and subambulacral spines progressively smaller toward arm tip. Two to five shorter, but thicker quadrate to prismatic granules irregularly flank subambulacral spines. Occasional gaps present between subambulacral spines and granules (Fig. 2B,C). Adambulacral plates, subadambulacral spines flanked by two tong-like, or duck-bill shaped pedicellariae. Pedicellariae present between successive adambulacral plates, some recessed into ambulacral groove. Proximal-most adambulacral (= mouth angle) spines approximately twice as wide as other adambulacral spines, with 13–15 (= 26–30 per MAO) forming distinct stellate perimeter around mouth (Fig. 2B). Spines prismatic, subquadrate, decreasing in size distally. First 6–8 adambulacral (= mouth angle or oral) spines thickest. Two, closely abutting, irregular rows of relatively large (2–3¥ of surface granules), prismatic, quadrate subambulacral granules present abradial to mouth angle spines. Internal Morphology, Body wall tissue firm, dense. When taken in cross section after mesenteries and peritoneum have been removed, body wall tissue is smooth and soft. (Fig. 3). Extremely dense and structureless at macroscopic levels (i.e., very fine grains lacking). Body wall envelops actinal, abactinal, marginal plates. In the dried specimen, the shriveled body wall substantially decreases in cross sectional thickness from 3.0–4.0 to 1.0 cm. A complex series of interconnecting channels present throughout body wall (see Fig. 3C). Channels open from dorsal and ventral coelomic surfaces (Fig. 3B). Peritoneum inundated with openings corresponding to those on coelomic surface (Fig. 3A,C). Coelomic openings for channels vary in diameter from 3.0–10 mm. Channels from central coelomic body cavity extend widely through body wall to surface. Channel diameter broadest in central coelom, narrowing distally (diameter < 1.0 mm). Many channels confluent with papulae, which extend from surface 1.0–2.0 mm of body wall. Several channels reticulate and fork into numerous, smaller channels near surface. Each arm with at least four sets of parallel channels that are paired at different elevations within body wall (Fig. 3C). Ampullae striate, elongated, located in two series along ambulacral plate series, one along upper half and one along lower half. Tube feet striate, disks distinct. Spicules in tube feet delicate, fine (Fig. 6B), openly perforate. Tube foot spicules of Astrosarkus are apparently smaller (fragment length ~ 60 mm) and more delicate relative to those sampled from Choriaster (fragment length ~ 100 mm). This is consistent with the overall trend demonstrating reduced endoskeletal body characters. However, spicules could only be obtained from relatively fresh material and were absent from the dried specimen. Preservation history of the dried specimen is unknown, but if the specimen were preserved in formalin for an extended period of time, dissolution of the tube foot spicules may have resulted. Gonads granulate, multi-branched, rooted at single points of internal side of body wall in each interradius. Pyloric caeca highly branched, numerous, hanging from a flattened mesentery extending along dorsal surface of the coelom of each arm (Fig. 3B). Pyloric caecal lobe with basal bulb, several plumose branches. Polian vesicles relatively large (bulb ~ 9.0 mm length), elongate, sacculate (Fig. 3A) in interradii projecting from the oral region. Tiedemann’s bodies elongate with narrow base, thicker distal trunk terminating in a blunt, frond-like tip. Endoskeleton. Only terminal plates, adambulacral, and mouth angle spines visible externally. Abactinal, actinal, and marginal plates reduced, deeply embedded within the fleshy body wall. Comparisons between cross-sections through the abactinal body wall of wet and dry specimens suggest that plates comprise at most about 1/5 (20%) of the total body wall volume. Abactinal plates extremely reduced compared to actinal plates, 1/2–1/3 times the actinal plate diameter. Abactinal plates arranged into reticulated arrays that correspond with coelomic openings along internal surface of the dorsal and lateral body wall. Precise articulation points with marginal, actinal plates unclear. Plates absent from uppermost dorsal tissue of body wall (i.e., approximately top 1/2). Actinals arranged in transverse series of irregular, rod-like plates; most transverse series separated, but some merge toward the body margin, or are linked by additional small plates (Fig. 4A). Many short, pointed processes are distributed from actinal plate series, projecting undetermined distances into body wall. Dissection suggests that many of these extend into the body wall at oblique angles. Rod-like actinal plates articulate obliquely with adambulacral plates (Fig. 5C). Actinal plates terminate (or seem to terminate) in proximity to concave, crescentic plates along edge of the body within body wall. The position of these plates suggests that they are the marginal plate series. Marginal plates vary in size, shape with respect to location. In the dried specimen, the actinal plate series are distended through the body wall from the actinal surface of the body wall. Interradially, they are thicker and more tooth-shaped in outline. Distally, they become slender, and nearly crescentic. Marginal plates found along the entire lateral edge extending to terminal plate in direct contact with actinal plates. Enveloping, fleshy body wall and extent of modified endoskeleton prevent definitive recognition of the supero- and inferomarginal series. Exact limits of marginal plates are unclear, since plates adjoining the marginals may either be a marginal series, or modified actinals. In cross-section, ambulacral and adambulacral plates form diamond-shaped chamber extending into arm coelom (Fig. 5C). Prominent, fixed spine-like process present on narrow ridge of ambulacral plate between ampullar bulbs (Fig. 5A,B). Adambulacral plates large, high, nearly identical in height to ambulacral plate, forming lower half of diamondshaped tube-foot chamber (Fig. 5A,C). Ambulacral and adambulacral series, including terminal plate, turn upward toward abactinal surface near terminus (Figs. 3B,6A). Terminal plate is externally visible. Subquadrate with l ¥ w = approximately 2.0 ¥ 2.0 mm. Single, smaller accessory plate sits on abactinal side of terminal. Granules absent from terminal plate. Color in Life Based on images of three observed, living specimens, A. idipi is dark orange with cream to beige colored spots and patchy mottling on the abactinal surface (L. Bell, CRRF, pers. comm.). The actinal surface is colored with a large, poorly defined, cream to beige patch around the mouth; patch branching, outward from the mouth, flanking the tube foot grooves (Fig. 1A,B). Another larger specimen was observed with a more yellowish color (R. Pyle, Bernice P. Bishop Museum, 2000 pers. comm.). No information on color was available for the individual collected from Reunion Island. Specimens in ethanol turn a pale, creamy tan. Body wall tissue is a light orange to creamy tan. The single dry specimen is brown.