PTEROBRANCHIA IN

Jain, Sudhanshi S., Gordon, Dennis P., Huang, Danwei, Kuklinski, Piotr & Liow, Lee Hsiang, 2022, Targeted collections reveal new species and records of Bryozoa and the discovery of Pterobranchia in Singapore, Raffles Bulletin of Zoology 70, pp. 257-274 : 270-271

PTEROBRANCHIA IN SINGAPORE

Inasmuch as our targeted collecting of bryozoans yielded the first record of the hemichordate class Pterobranchia for Singapore, we take the opportunity to report Rhabdopleura sp. observed at Pulau Tekukor (1.2299°N, 103.8376°E; collected as SG2019 No. 119; sequenced as BLEED No. 1688; coll. S.S. Jain & P. Kuklinski, 6 May 2019). Modern species of Rhabdopleuridae are considered to be living graptolites ( Mitchell et al., 2013). The ramifying uniserial colonies, found on coral rubble with bryozoans, are instantly recognisable by their thin creeping tubes in which is a conspicuous black stolon. Erect tubes, each housing the individual zooid that constructs it, arise at intervals from the creeping tubes and are characterised by ringed fusellar ridges ( Fig. 7C–E ). The tube in Rhabdopleura is not a body wall, hence the zooid in this instance (compared to bryozoans) comprises only the soft tentaculated and stalked individual within.

The basal creeping tubes of the colony (tubarium) in the present material are relatively narrow and linear with a slight marginal expansion on either side, or both the tube and expansion can be relatively broad. The central median part of the creeping tube is 144‒248 μm wide (mean 200 μm), with variable subparallel to oblique sutures (each marking the boundary between adjacent fusellar strips) that range from 42 to 99 μm apart (mean 66 μm) ( Fig. 7F, G ). Erect tubes are of variable length, with a diameter of 125‒162 μm (mean 144 μm) and bearing conspicuous irregular fusellar rings 27‒44 μm (mean 34 μm) apart. The edges of these rings project outwards as 6‒13 μm-wide flanges from the tubes.

We are uncertain of the identity of the species, and thus leave it in open nomenclature pending the outcome of molecular sequencing, the results of which can be compared with those published by Beli et al. (2018) and Ramírez-Guerrero et al. (2020).

Hemichordates are already represented in Singapore by two species of class Enteropneusta (acorn worms), found on mud ( Ng et al., 2011: 217).

Figures

Fig. 7. A, Thornelya fuscina Tilbrook, Hayward & Gordon, 2001; white arrows indicate three unbroken latero-oral avicularia; B, Scorpiodinipora costulata (Canu & Bassler, 1929); C‒G, Rhabdopleura sp.; C, D, lateral view of erect tubes with annular fusellar rings; E, part of creeping basal tube in vicinity of three broken bases of erect tubes; here the fusellar sutures are parallel to oblique; F, G, parts of creeping basal tube in which the fusellar sutures (arrowheads) are arranged obliquely. Scale bars = 0.5 mm (A, B); 0.1 mm (C, D); 0.2 mm (E‒G).