Placotrochides yapensis, Xu, 2017

Xu, Kuidong, 2017, A new species of Placotrochides Alcock, 1902 (Anthozoa: Scleractinia: Flabellidae) from the tropical Western Pacific, including the deepest record of the genus, Zootaxa 4323 (1), pp. 146-150 : 149

Placotrochides yapensis n. sp.

( Figure 2 )

Material examined. Holotype: MBM285987, Y30087 , 20.12.2014, stn. Y3-7 (2). Paratype: MBM285988, Y30087 , same sampling data as holotype.

Description of holotype. Corallum (anthocyathus) subcylindrical, with rather large edge angle, without edge spines or crests ( Fig. 2 ). Holotype 15.2 × 12.5 mm in CD, 9.0 × 7.7 mm in basal scar diameter, 13.3 mm in height, and about 25° of edge angle. Calice and basal scar slightly elliptical and symmetric, the GCD:LCD is 1.22 and the GSD:LSD is 1.17. Calicular edge damaged, scalloped, rising to a low peak corresponding to each septum. Basal scar smaller, V-shaped, indicating septa of the basal anthocyathus ( Fig. 2C, F ). Theca white to brown in ethanol preservation, slightly rough, covered with closely-spaced, horizontal annular chevron-shaped growth lines. Anthocaulus not seen.

Septa 48, hexamerally arranged in four cycles according to the formula: S1–2>S3>S4. S1–2 about 1/3 LCD in width, slightly exsert, vertical edges slightly sinuous, fusing to the columella lower in the fossa. S3 about 1/2–3/4 width of S1–2. S4 small but complete, about 1/5 width of S1–2 (about 1.0 mm wide). All septa relatively thin (S1–2 about 0.5 mm, S3 about 0.25 mm, and S4 about 0.2 mm thick), with adjacent ones spaced 0.4–0.5 mm, and their faces covered with small spines. Fossa of moderate depth and length, elongate, containing an non-discrete trabecular columella that measures about 5.0 × 2.5 mm and is composed of a fusion of trabeculae.

Variability. Paratype slightly larger, 15.7 × 13.9 mm in CD (GCD:LCD = 1.13), 12.2 × 10.3 mm in basal scar diameter (GSD:LSD = 1.18), 17.1 mm in height, and about 20° of edge angle. Other characters of paratype similar to holotype.

Etymology. Named after the seamount adjacent to the Yap Trench, where the species was discovered.

Distribution. Yap-3 seamount adjacent to the Yap Trench in the tropical Western Pacific, 2,700–2,734 m.

Remarks. Placotrochides yapensis n. sp. is the fifth species of the genus Placotrochides . It can be easily distinguished from congeners by having a much larger edge angle in the corallum (20–25° vs. 0–5°) (see table 6 in Cairns 2004 and identification key in Cairns 2016). Placotrochides yapensis n. sp. is most similar to P. scaphula in the corallum size (GCD more than 12 mm) and the arrangement and number of septa (although some S4 of P. scaphula often lacking and having commonly less than 40 septa). However, it differs from this species in having a more rounded corallum (GCD:LCD ratio of 1.1–1.2 vs. 1.4–2.0 and GSD:LSD ratio of 1.17–1.18 vs. 1.54–1.87) and a symmetric calice (vs. often asymmetric). The new species differs distinctly from P. cylindrica , P. minuta and P. frustum by a higher number of septa (48 vs. 32, 32 and 36 respectively); from the former two species also by the larger corallum size (maximum GCD about 15.7 mm vs. 6.56 mm and 4.26 mm, respectively) ( Cairns 1989, 1994, 2004, 2016).

Figures

FIGURE 2. Placotrochides yapensis n. sp. THe HOlOtype (A – C) and paratype (D – F) in lateral, calicular, and base scar view. Scale bar = 5 mm.