Phyrella thyonoides

Phyrella thyonoides (Clark, 1938)

Figures 17–22; 27 f,g

Phyllophorus thyonoides, Clark, 1938:492–494. fig. 48. Holotype, MCZ HOL1654; type locality: Western Australia, Cottesloe Beach (Perth)

Phyrella thyonoides: Heding & Panning, 1954:183–184, fig. 88

Material examined. MCZ HOL1654, (Holotype), Western Australia, Cottesloe Beach, from beach drift, July 1926, coll. L. Glauert. Phyrella cf. thyonoides: UF 9414, UF 9598, UF 9601, Western Australia, Ningaloo Reef, Ningaloo station, -22.6753 113.684, 1– 3 m, under rocks on sand, May 2009. coll. François Michonneau.

Description of holotype. Specimen in poor condition; 33 mm along dorsum, about 45 mm along venter, 13 mm wide at mid-body (Fig. 17). Body wall dried out, very stiff, leathery. Body wall and most organs uniformly dark brown. Introvert retracted; only a small piece remains; 12 mm long. With 16 tentacles of varying sizes, longest about 13 mm, shortest about 1 mm; arrangement difficult to discern because of the state of contraction and preservation of specimen. Cloacal region dissected out, missing. Calcareous ring 17 mm long, 8 mm wide, embedded in a fairly thin and transparent membrane (Fig. 27f). Anterior margins of radials divided slightly unequally by deep notch. Anterior margins of the inter-radials arrow-head shaped. Inter-radials each composed of 11–13 elements. Radials each composed of 14–18 elements, forming long posterior tails. Radials and inter-radials closely associated along most of their lengths. Single Polian vesicle, 4 mm long, brown and pear-shaped. Stone canal and madreporite embedded in membrane surrounding the calcareous ring. Stone canal 2 mm long, madreporite about 1 mm in diameter, spherical with convolutions. After multiple attempts in different parts of specimen, no ossicles were found in the body wall or in the tentacles, likely because of corrosion. Clark illustrated and described body wall tables and tentacle supporting rods.

Description of Phyrella cf. thyonoides from Ningaloo. External morphology. Body wall slightly firmer and more leathery than in other Phyrella. Living animal dark brown, densely covered with tube feet with yellow base color overlain with dark brown transverse lines and with red ring around sucker margin (Fig. 18). Preserved specimens relatively straight 30–35 mm (excluding introvert and tentacles when extended) and 13 mm wide. Introvert short (4 mm). Introvert and tentacles white, peppered with small, dark brown flecks; base of tentacles also have small light brown blotches. With 15 tentacles in outer circle (about 3 mm) and 5 tentacles in inner circle (<1 mm), latter aligned with ambulacra (UF 9414 and UF 9601). Oral disc with light brown line around mouth. Cloacal membrane white, with 5 lightly calcified anal teeth, each associated with a few tube feet with minute brown spots.

Internal anatomy (based on UF 9601). Polian vesicle single, light brown with very sparse minute dark spots, 5 mm long. Madreporite and stone canal inconspicuous, embedded in the membrane surrounding the calcareous ring. Stone canal short (<2 mm) and narrow (<1 mm) embedded in the membrane surrounding the pharyngeal complex. Gonads with two well-developed tufts of unbranched, semi-transparent tubes, with small dark purple spots, up to 5 mm long. Respiratory trees light gray with minute dark purple spots, both extending almost entire length of animal. Specimen eviscerated, but retaining pharyngeal complex, gonads, respiratory trees and proximal end of esophagus.

Calcareous ring (based on UF 9601). Calcareous ring embedded in a relatively thin membrane (Fig. 27g). Anterior margins of radials divided unequally by a well-formed notch. Anterior margins of inter-radials arrow-head shaped. Radial and inter-radial elements are closely associated along most of their respective lengths. Inter-radials each composed of 5–8 elements. Radials each composed of 14–18 elements. Radials project posteriorly forming long tails that curve anteriorly at their tips.

Ossicles. Dorsal and ventral body wall lacking ossicles except in podia. Podia with perforated plates (120– 220 µ m long, 20–65 µ m wide), more elongated and with typically larger holes, in particular towards the ends of the plates than in the other species (Fig. 19a–i; Fig. 20a–e). Cloacal body wall with tables and rosettes (20–40 µ m long, Fig. 22B). Tables variables; disc 90–115 µ m in diameter, with either a single circle of 8–11 holes (Fig. 19u,v), sometimes with a few extra holes at the periphery (Fig. 19t), or with very numerous holes that are not arranged in any particular order (Fig. 20i), with a highly serrated rim; spire (sometimes wanting, Fig. 19x) formed by four (rarely five) pillars united by a single cross-beam, surmounted with a crown; crown often incomplete (Fig. 19r), when complete sometimes with spines (Fig. 19w), which in some tables that have numerous holes in their disc, extend and connect to the disc margin (Fig. 20i). Podia with perforated plates; less abundant and generally smaller than in mid body wall, 110–165 µ m long, 40–60 µ m wide (Fig. 20j). Podia that flank anal teeth with rosettes and perforated plates (Fig. 20l, Fig. 21a–c), some of the latter with unusual lateral extensions (Fig. 20k), many plates incomplete with no or few large perforations and only a few small perforations at the extremities (Fig. 21d). Introvert body wall with variable tables, disc 60–80 µ m in diameter, with smooth rim margins, complete and regular with 10–12 holes in the rim, to irregular either with incomplete rim or with additional scattered holes; spire poorly developed or missing for most (Fig. 19l). Podia with abundant rosettes, 30–50 µ m long (Fig. 22A); perforated plates that range from typical to small, more or less circular (60–80 µ m in diameter), with a few large holes in the center and smaller holes toward the periphery (Fig. 19m –q). Tentacles with two sizes of rods. Large rods (110–270 µ m) with one or a few holes at the ends. Small rods (50–100 µ m) generally with no holes at the ends (Fig. 19z). No ossicles observed in cloacal, longitudinal and retractor muscles; cloacal wall; gonads; or respiratory tree.

Remarks. In the original description of Phyrella thyonoides, Clark only illustrates one table from the body wall and three rods from the tentacles. Overall, the description he provides and the holotype fit reasonably well with our new material from Ningaloo, but there are some differences. Thus, in Clark's description, the ends of the large rods in the tentacles have numerous perforations and are spiny; in our specimens, the large rods have only a few holes at their ends and are not spiny. In our specimens, we did not observe any tables in the mid-dorsal or midventral body wall, whereas Clark noted that the tables were “rather scattered, but by no means rare” but did not indicate in which part of the animal he observed them. The table he illustrates is relatively similar to the ones we observed in the anal region of our specimens. Unfortunately, the poor condition of the holotype and the complete corrosion of the ossicles do not allow for an adequate comparison with the Ningaloo material. A full evaluation of P. thyonoides and its relation to the Ningaloo population must await collection of new topotypical material. Surprisingly, none of the specimens loaned to us by the Western Australian Museum identified as P. thyonoides, turned out to belong to this species or to Phyrella. P. thyonoides can be distinguished from other Phyrella by its thick, leathery, dark brown body wall; the elongated perforated plates with large perforations, and the circular perforated plates in the introvert.

Recently, O'Loughlin et al. (2012) proposed to transfer Phyrella thyonoides to Phyllophorella based on the number of tentacles and the shape of the calcareous ring for the specimens they examined, however most of the specimens they report upon do not appear to pertain to P. thyonoides, but to an undescribed species of Phyllophorella. The tables illustrated (O'Loughlin et al., 2012: Fig. 10) with marginal teeth are unlike those found in any Phyrella. The general appearance of the animal and shape of the calcareous ring illustrated (O'Loughlin et al., 2012: Fig. 9) also do not match Phyrella. O’Loughlin et al. (2012) note that there are single posterior extensions on the calcareous ring in this species (and other Phyllophorella) arising either from radial or jointly from radial and inter-radial elements; this contrasts with the clearly separate series of plates that arise from the fragmentation of both inter-radial and radial elements of all Phyrella species. One of the specimens examined by the authors (WAM Z31837) was sequenced and matches a Phyllophorus species we collected along with P. thyonoides, in Ningaloo, Western Australia (Phyllophorus sp. 1 in Fig. 28).

Ecology & distribution. In Ningaloo, animals were adhering to dead shells or rocks that were buried in sand and on which algae was growing, close to shore at 1–3 m depth. They co-occurred with Holothuria michaelseni. The types were cast up on the beach, suggesting shallow habits. Known from Perth and Ningaloo, Western Australia.