Acyclus sp.

(Figs 2a–2 c)

Although only a single specimen of this taxon was observed, we believe that it may represent an undescribed species. Morphologically, the animal is characterized by a prominent bifid anterior margin of dorsal corona lobe (Fig. 2 c) which is reminiscent of Atrochus tentaculatus Wierzejski, 1893, the sister taxon of Acyclus . The single known species of Acyclus, A. inquietus Leidy, also occurs in Thale Noi Lake but is easily distinguished by a rounded anterior margin of dorsal corona lobe. Moreover, the specimen of Acyclus sp. was observed predating on a colony of Lacinularia flosculosa (Müller), whereas all of the specimens of Acyclus inquietus we observed were found in association with colonies of Sinantherina socialis (Linnaeus) . Acyclus inquietus feeds on eggs and larvae of S. socialis whereas Acyclus sp. was seen to predate on adult specimens of L. flosculosa; the Acyclus sp. takes up a Lacinularia in its vestibulum, sucks out its content of its victim and finally releases the remains, an empty trunk and foot.