Exidmonea sp.

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 : 260

Exidmonea sp.

( Fig. 2A, B )

Only a single colony fragment c. 5 mm long, with several bifurcations, was found in the collection. It lacks basal kenozooids, and so is attributed to the cyclostome genus Exidmonea David, Mongereau & Pouyet, 1972 instead of Idmidronea Canu & Bassler, 1920 . Mean branch width is 353 μm proximally, narrowing to 248 μm in distal parts of the colony fragment. Peristomes are arranged in fascicles of two, curving to right and left along the apex of the branches. The frontal-most peristomes have a mean peristome length of 235 μm, whereas the lower peristomes are very short (<55 μm long). Mean apertural diameter (or length if asymmetrical) of uppermost peristomes is 89 μm whereas that of lower peristomes is 124 μm. At the proximal-most axil of the colony fragment is a swollen densely pseudoporous V-shaped gonozooid. There is no apparent ooeciostome but there is a round ooeciopore. This diminutive species may be new to science. It somewhat resembles material that Harmer (1915) described and illustrated (possibly from the Celebes Sea, but Harmer’s station attribution doesn’t accord with Siboga Expedition data). He ascribed it to “ Tubulipora atlantica var. flexuosa ” but this Atlantic species [= Exidmonea flexuosa ( Smitt, 1873) , illustrated by Winston, 2005] has longer peristomes in fascicles of three and a compact inflated saclike gonozooid. Harmer (1915) included Idmonea tenella Ortmann, 1890 from Japan in the synonymy of E. flexuosa and the two species appear very close. Unfortunately, Ortmann (1890) provided only small line drawings and the species has not been illustrated since (and may no longer exist—see Mawatari, 1997), so comparison is difficult. Canu & Bassler (1929) described two new diminutive species from the Philippines — Idmonea filiformis and Idmonea parvula —that may belong to Exidmonea and which appear similar to our specimen from Singapore. Idmonea filiformis had fascicles of only two peristomes, and a cited peristome diameter of 80 μm, but branch width was larger (500 μm) than in our specimen (353 μm); I. parvula had a cited peristome diameter of 90 μm (matching ours) and a smaller branch width (400 μm) but 2‒3 peristomes per fascicle. More material from Singapore and study of the specimens of Canu & Bassler (1929) are needed for adequate taxonomic characterisation and comparison.

Figures

Fig. 2. A, B, Exidmonea sp., respectively showing dichotomous branching and a gonozooid; the ooeciopore is indicated by an arrow; C, Arbopercula angulata Levinsen, 1909; D, Parellisina albida (Hincks, 1880a), arrows indicate two of the open avicularian mandibles; E, Setosellina constricta Harmer, 1926; F, Canda pecten Thornely, 1907, note the curved avicularium at the bottom of the left-hand branch. Scale bars = 1 mm (A); 0.5 mm (B‒F).