Placotrochides cylindrica, Cairns, 2004

Cairns, S. D., 2004, The Azooxanthellate Scleractinia (Coelenterata: Anthozoa) of Australia, Records of the Australian Museum 56, pp. 259-329 : 305

Placotrochides cylindrica n.sp.

Figs. 10B–D

Records/Types. Holotype: Cidaris I 30–2, MTQ G55627 . Paratypes: Cidaris I 9–2, 1, MTQ G56394 ; Cidaris I 20–2, 1, MTQ G56396 ; Cidaris I 30–2, 6 (4 in alcohol): 5, MTQ G56402– 56403 and 1, USNM 1008851 . Type Locality: 17°18.96'S 147°11.16'E (off Cairns , Queensland), 1402–1406 m .

Description. Corallum (anthocyathus) almost cylindrical, having rounded thecal faces and edges that are essentially parallel. Most coralla undergo slight periodic retrenchments of growth followed by continued upward growth, which results in slight decreases in the corallum diameter. Largest corallum 6.56× 5.93 mm in CD and 8.40 mm in height, whereas the holotype measures 6.32× 5.46 mm in CD, 5.51× 4.30 mm in basal scar diameter, and 5.42 mm in height. Calice and basal scar only slightly elliptical to circular, and symmetric, the GCD:LCD ranging from 1.07 to 1.16 and the GCD:LSD from 1.00 to 1.28. In wellpreserved coralla, the calicular edge is slightly scalloped, rising to a low peak corresponding to each S1–2. Basal scar flat, such that the corallum will easily sit in an upright position on a level surface; scar reveals septa of the incipient anthocyathus; GSD ranges from 4.21 to 5.51 mm. Theca somewhat rough, covered with small hispid granules as well as displaying closely-spaced, chevron-shaped growth lines that peak at the longitudinal insertion lines corresponding to the S1–2. Theca white. Anthocaulus unknown.

Septa hexamerally arranged in 4 cycles, the fourth cycle never complete, the maximum number of septa observed being 32, although 26 is most common. Twenty-four septa present in a corallum of GCD 4.4 mm, and additional pairs of S4 (up to 4 pairs) are added as pairs to lateral (not end) systems of coralla of larger size. Septa formula: S1>S2>>S3>S4. S1 non-exsert, having smooth, vertical, slightly sinuous axial edges that fuse with the columella low in fossa. S2 similar to S1 but only about 80% the width. S3, if unflanked by S4, quite small, sometimes vestigial, represented only by a series of disconnected spines located considerably beneath the calicular edge. If an S3 is flanked by a pair of S4, it is increased in size to that of an S2. S4 equivalent in size to unflanked S3. Faces of all septa covered with small spines. Fossa quite deep and commodious, the columella being fairly small, restricted to base of fossa just above basal scar.

Remarks. Among the four species in the genus ( Table 6), P. cylindrica is most similar to P. frustum , both species being about the same size. Placotrochides cylindrica differs from P. frustum , as well as the two other species, in having a more rounded corallum (lower GCD:LCD and GSD:LSD), S1 that are larger than the S2, a flat basal scar, a rough theca, and a slightly scalloped thecal margin.

Etymology. From cylindricus, Latin for “in the form of a cylinder”, an allusion to the corallum shape.

Distribution. Known only from off northeastern Queensland, 1117–1402 m.