Phyrella trapeza (Clark, 1932)

Figures 1–3; 27 d,e

Phyllophorus trapezus Clark, 1932: 224–226, text-fig. 4–9. Holotype: BMNH 1932.4.28.177; type locality: Low Isles, Queensland, Australia

Phyrella trapeza: Heding & Panning, 1954: 182–183, fig. 87

Material examined: MCZ HOL1488 (2 paratypes), Australia, Queensland, 1/ 4 mile South of Cape Kimberley, 4 fathoms, 2 December 1928, coll. H.L. Clark.

Description based on the paratypes. External morphology. Paratype A with thin, transparent, very relaxed body wall (Fig. 1, bottom); B with thick leathery, contracted body wall (Fig. 1, top). Tube feet dispersed across entire body, denser toward anterior and posterior, less dense than in other Phyrella; generally same color as body wall, except some tube feet darker on venter. Body wall uniformly light brown (paratype A) to dark brown with some lighter areas (paratype B). Body arched, both specimens 35 mm along the dorsum, 45 mm along venter, and 13 mm (B) vs. 15 mm (A) wide. Introvert lighter color than rest of body, 6 mm (A) and 8 mm (B) in length, retracted and partially dissected in both specimens. With 16 tentacles varying in size, 10 on the outer circle and 6 on the inner circle (A) vs. 9 on the outer circle large and 7 on the inner circle (B); larger tentacles ~ 5 mm, shorter tentacles ~ 2 mm long in paratype A (poorly preserved in B). Cloacal area missing in both specimens, probably removed for ossicle preparation by previous workers.

Internal anatomy. Polian vesicle, single, contracted, 6–7 mm long, 1 mm wide, tube-shaped. Stone canal short (<2 mm), with a slight orange coloration, embedded in dorsal mesentery; madreporite small (<1 mm), partially attached to membrane surrounding the calcareous ring (paratype A), missing in paratype B. Gonads in two 8–10 mm long tufts, composed of simple, unbranched, 3–4 mm long tubes. Both specimens eviscerated. Respiratory trees extending almost entire length of animals, bunches more developed in specimens with thick body wall.

Calcareous ring. Calcareous ring 8 mm (A), 10 mm (B) long, 6 (A) 8 (B) mm wide (Fig. 27d, e), embedded in thin and transparent membrane. Radials with 5–8, and inter-radials with 10–12 elements. Anterior margins of radial plates unequally divided by well-formed notches. Anterior margins of inter-radial plates arrow-head shaped. Radials and inter-radials closely associated along most of their lengths. Radials project posteriorly forming tails that curve to point anteriorly.

Ossicle assemblage. Dorsal and ventral body wall with tables only. Tables variable; disc 80-500 µ m in diameter, most with complete rim, with smooth, circular to slightly rectangular outline contoured around marginal perforations, with 8–10 holes in a marginal ring (Fig 2b, f, l, m); irregular tables with 1–3 additional holes peripheral to these (Fig 2d, i, j, k); spire variably developed, often absent in tables from paratype A, but usually developed in B, with four (rarely five) pillars connected by a single cross-beam, giving rise to a relatively narrow, thin, slightly spiny crown; crown usually forming a complete ring, with a 6–15 µ m central opening. Podia with elongate, perforated plates, 140–155 µ m long, 40–80 µ m wide, with holes smaller toward periphery or of relatively constant size throughout (Fig 2g, h, n, o); well-developed end plate. Cloacal region body wall (paratype B) with tables and abundant rosettes (Fig. 12B). Tables variable; disc 80–125 µ m in diameter; regular tables similar to those of dorsal and ventral body wall (Fig 2A); irregular tables with incomplete rims and additional holes (Fig 2w–z), some with spiny lateral projections that connect to the spire (Fig 2x, y). Rosettes abundant, 20–30 µ m long. Podia with few reduced perforated plates, 100–130 µ m long, 60–70 µ m wide (Fig 2B, C). Introvert (paratype B) with tables and rosettes. Table discs 85–105 µ m in diameter, with 11–13 peripheral holes (Fig 2p–r) and smooth margins; crown often incomplete (Fig 2p, r), typically wider and larger than in body wall tables. Rosettes 30–55 µ m long (Fig 3). Podia with few perforated plates (Fig 2s–v). Tentacles (paratype B) with large (80–125 µ m) rods with slightly branching ends, (Fig 2D), and small (15–65 µ m) simple rods with simple ends (Fig 2E).

Remarks. Clark (1932) noted the similarity between P. trapeza and P. fragilis . It can be distinguished from P. fragilis and other Phyrella species by less abundant and smaller podia, relatively large holes in the disc of the tables, perforated plates with barely serrated margins. P. trapeza is the type species of Phyrella .

Ecology and distribution. This species is currently only known from the type material, collected in Queensland, Australia, from Low Isles (holotype) and Cape Kimberley (paratypes). Paratypes were collected by dredging, on a bottom of shells and gravels 4 fathoms (~ 7.5 m) deep.