Phyllophorella robusta (Heding & Panning, 1954)

(Figures 2 – 4)

Phyllophorus (Phyllophorella) robusta Heding & Panning, 1954: 155 – 156, pl.68

Phyllophorella robusta — O’Loughlin et al. 2012: 269

Material examined. Holotype. 15 Seemeilen Ostlich Koh Chuen, Siam, Thailand, 10m, 1.ii. 1900, 25 mm length (ZMUC – HOL 249). Holotype Slides MNHN-IE –2005–6362; MNHN –IE-2005–6361.

Redescription. Body curved; tube feet scattered throughout body (Fig. 2a). Color in ethanol, gray. 20 Dendritic tentacles arranged in 2 circles (15 + 5), 15 in outer circle and 5 in inner circle. Anal papillae present. Longitudinal and circular muscles well developed (Fig. 2b). Longitudinal muscles split at anterior end (Fig. 2b). Retractor muscles short, attached to the middle of radial plate (Fig. 2b). Stone canal single, short, attached to globular madreporite (Fig. 2c). Single Polian vesicle (Fig. 2c).

Calcareous ring robust. Radial plates slightly taller, much larger than interradial ones. Interradial plate articulated with both, base of radial plate and first piece of posterior process, such that half of the interradial plate is connected to the posterior process (Fig. 2d). MidIR (IR5), midR (RI) not modified (Figs. 3b, c). Radial plates undivided, rectangular, base convex without projection, two AP, one wider than the other (Fig. 2d, 3a). Posterior processes longer than radial plates, subdivided into about 3–4 large pieces (Figure 3b, e). Interradial plates elongated, base slightly concave, anterior end pointed (Fig. 2d, 3 b, c). Marginal grooves for AB deep (Fig. 3e). TCT rectangular (Fig. 3f).

Body wall tables four-pillared with circular disc (80–100 μm long; Fig.4 a,b); with one large central hole, eight marginal perforations, margin undulated; spire ending in 8–12 spines, borne on a squarish crown. Introvert with rosettes (30–50 μm long; Fig.4c). Tentacles with rods branched and perforated at both ends (40–100 μm long; Fig. 4d, e, respectively). Tube feet with flat perforated plates, irregular margins (100–200 μm long; Fig.4f–h); endplate with numerous small holes, much reduced in diameter medially (endplates up to 500 μm diameter; Fig.4i).

Remarks. In addition to the previously published description of the calcareous ring (Heding & Panning, 1954), new morphological details are provided here by means of microtomography of the aquapharyngeal bulb attachment, longitudinal muscle attachment, and retractor muscle attachment (fig 3d), as well as of the grooves in the radial plate for water vascular canals (fig 3e) and transverse cross-sections at the top region of the calcareous ring (fig 3f). It is worth noting that what was termed calcareous ring posterior projection by Heding & Panning (1954) is referred here as posterior process (see Martins et al. 2021 for definitions). The opportunity of examining the holotype was also taken to provide a photograph of the general aspect of the body (Fig. 2a) and describe for the first time by means of optical microscopy the morphology of the longitudinal retractor and circular muscles (Fig. 2b).