Mediaster mollis

Mah, Christopher L., 2018, New genera, species and occurrence records of Goniasteridae (Asteroidea; Echinodermata) from the Indian Ocean, Zootaxa 4539 (1), pp. 1-116: 54-58

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Mediaster mollis

sp. nov.

Mediaster mollis  sp. nov.

Figure 21View FIGURE 21 A–F

Etymology. The species epithet mollis  is Latin for “soft” alluding to the soft texture of the abactinal body wall.

Diagnosis. This species is distinguished by its strongly stellate body shape (R/r=2.54–3.0), the relatively soft abactinal body wall, low tabulae, abactinal plates with dense, abundant, homogeneous-sized granulation, 15–60 per plate ( Figs 21 B, CView FIGURE 21), numerous pedicellariae on the abactinal ( Fig. 21BView FIGURE 21) and marginal surface, large number of superomarginals, with 10 or 11 furrow spines, adjacent to a subambulacral series of five or six spines ( Fig. 21FView FIGURE 21).

Comments. This species bears a superficial resemblance to Kermitaster pacificus H.E.S. Clark & McKnight 2001  , in that it possesses the granulated surface and overall shape ( Clark & McKnight 2001: Figs. 14View FIGURE 14, 17View FIGURE 17). Clark & McKnight (2001: 62) note the absence of the internal radiating ossicles at the base of each abactinal plate discounting assignment to Kermitaster  .

This species’ generalized appearance also invites comparison with Bathyceramaster careyi  or Bathyceramaster elegans  , but the absence of underlying radial ossicles separates those species from Mediaster mollis  n. sp.

Occurrence. Western Indian Ocean, 452– 833 m.

Description. Body stellate (R/r=2.54–3.0), arms elongate with upturned or attenuated tips. Interradial arcs weakly curved to straight ( Fig. 21A, EView FIGURE 21). Abactinal surface strongly distended.

Abactinal plates short, columnar (i.e. weakly tabulate) with shallow fasciolar grooves throughout most of surface, flattening out with plates becoming more abutted distally on arm tips ( Fig. 21CView FIGURE 21). Abactinal plates extending to arm tip from disk. Plates round to polygonal in outline, plates homogenous in shape, size proximally becoming smaller and more irregular in outline distally, adjacent to the superomarginal contact. Radial and adradial plates distinctly hexagonal in shape, especially proximally. Dissection of abactinal plate shows plates with four distinct bar-shaped ossicles radiating from each plate. These radiating plates with papular pores distributed between them. A bare region present along each radius along the inside of the abactinal plate surface where the two other radiating bars would be present in a comparable position. Abactinal plate surface covered by 15–60 coarse, round granules, approximately 2 to 2.5 granules counted along a 1.0 mm line. Granules form a widely spaced, single series, forming discrete boundary around the surficial edge of each plate, approximately 10–40 (about five to ten per side on most). Central surface granules widely spaced leaving shallow convexities on plate surface when removed. Granules present around edge form discrete cover extending over and obscuring fasciolar groove. Granular cover on abactinal plates present appearance of nearly continuous cover obscuring boundary between plates except where discontinuities or uneven surface integument are present. Granular cover is especially dense interradially adjacent to the superomarginal plate contact. Nearly every plate with one or two alligator-jaw like shaped pedicellariae (about 1.0 mm in length) valves each bearing six to 10 (mostly eight) teeth along the edge of each valve ( Fig. 21BView FIGURE 21). Madreporite relatively flat, flush with abactinal surface, pentagonal to round in shape with five to seven plates surrounding it. Papulae six per plate, present at each edge.

Marginal plates with primarily lateral facing, superomarginals, inferomarginals 62–66 (at R= 7.8 cm) per interradius (arm tip to arm tip), smallest individual with 34 (at R= 2.4 cm) per interradius with R= 3.8 cm showing 38 per interradius. Marginal plates elongate, rectangular in outline, especially interradially ( Fig. 21DView FIGURE 21) becoming more quadrate in dimension distally near arm tip. Superomarginals and inferomarginals similar in size, but inferomarginals with pronounced actinal facing. Superomarginals lateral facing but with collapsed abactinal surface overhanging onto lateral side. Superomarginals and inferomarginals with some offset, forming zigzag contact between them. Marginal plate series transition from lateral facing to more abactinal distally along arm, especially at arm tip. Marginal plates surface with dense granular cover, approximately 100–200 covering each plate surface, granules identical in shape with that on abactinal surface (about 2.0–2.5 along a 1.0 mm lines). Granules show little to poor distinction between peripheral and central series. Each superomarginal and inferomarginal plate with one to three pedicellariae, identical to those present on abactinal surface, alligator-like in shape with six to eight teeth along the edge of each valve. Although pedicellariae are most strongly expressed interradially they do occur more distally along arms as well. Terminal plates triangular, smooth and flush with adjacent superomarginal plates.

Actinal surface large, four to seven full rows in chevron formation ( Fig. 21EView FIGURE 21), individual plates quadrate to round in shape with plates more irregular in size, shape distally adjacent to contact with inferomarginals. Actinal plates form weakly pronounced fasciolar grooves matched up with inferomarginal plate contacts. Actinal surface covered by abundant, but evenly spaced bullet-shaped granules covering the plate surface. Granules similar in shape with those on other surfaces, approximately 2 per 1.0 mm line. As with other surfaces, a small alligatorshaped or in some examples, an elongate tong-like shaped, pedicellaria is present, seated in a flat linear pit, present on the surface of most plates on the actinal intermediate region.

Furrow spines 10–11, mostly 11 in larger specimens, with rounded, blunt tip, slender, compressed, quadrate in cross-section arranged in a weakly convex/palmate to straight formation ( Fig. 21FView FIGURE 21). Adjacent to furrow spines are two distinct rows of subambulacral spines, each set off from the furrow spines with a discrete space ( Fig. 21FView FIGURE 21). The first subambulacral spine row, adjacent to the furrow spines, composed of five spines, each about twice as thick as the furrow spines, quadrate in cross-section, with narrowing, rounded, blunt tips. Third row of subambulacrals composed of five short pointed granules, <25% of the height of the prior subambulacral spines, each widely spaced from one another. Oral plates with 11 or 12 furrow spines, with one spine per plate, similar in shape to the others, triangular in cross-section projecting into the mouth (thus two per interradius). Oral plate with raised mid-line tissue filled sulci flanked on either side by blunt, evenly spaced granules, eight or nine. Surface of oral plate is largely bare save for eight to 10 polygonal shaped granules on distal side of plate adjacent to those with contact to the actinal intermediate plates.

Color in life: bright yellow to orange.

Material Examined. HolotypeGoogleMaps  : IE-2013-17228 Western Indian Ocean   GoogleMaps 12° 43 'S, 45 ° 19' E to 12° 44 'S, 45°

20' E, 664– 617 m. Coll. S. Samadi et al. BIOMAGLO DW 4875 9 Feb. 2017. 1 wet spec. R=5.4 r=2.0. Paratypes: IE-2013-17206 Western Indian Ocean , 12°59’S, 44 ° 56' EGoogleMaps  to 12 ° 59 'S, 44 ° 55' E, 669– 692 m. Coll. S. Samadi et al. BIOMAGLO CP 4858 4.2.17. 1 wet spec. R=5.8 r=1.9. IE-2013-17208 Western Indian Ocean , 12 ° 44 'S, 45 ° 19' EGoogleMaps  to 12° 43 'S, 45° 18' E. 452– 462 m. Coll. S. Samadi et al. BIOMAGLO CP4876, 9.2.2017. 3 wet specs. R=5.6 r=2.2, R=6.6 r=2.3, R=7.8 r=2.9. IE-2013-17209 Western Indian Ocean 12 ° 25 'S, 43 ° 56' EGoogleMaps  to 12 ° 26 'S, 43 ° 56' E, 507– 521 m .. Coll. S. Samadi et al. BIOMAGLO DW 4833. 28.01.17. 2 wet specs. R=7.1 r=2.8, R=7.9 r=3.2. IE-2013-17225 Western Indian Ocean 13 ° 0 'S, 44 ° 55' EGoogleMaps  to 13° 1 'S, 44 ° 54' E. 757– 795 m. Coll. S. Samadi et al. BIOMAGLO CP 4856 4.2.17. 1 wet spec. R=2.4 r=1.1. IE-2013-17227 Western Indian Ocean 13 ° 0 'S, 44 ° 55' EGoogleMaps  to 13 ° 1 'S, 44 ° 53' E, 742– 833 m. Coll. S. Samadi et al. BIOMAGLO CP 4859, Feb. 4. 2017. 1 wet spec. R=3.8 r=1.4. IE-2013-17229 Western Indian Ocean 12 ° 30 'S, 44 ° 55' EGoogleMaps  to 12 ° 30 'S, 44 ° 55' E, 618– 609 m. Coll. S. Samadi et al. BIOMAGLO DW 4862 9?2, 2017. 1 wet spec. R=5.3 r=2.1  .