Didemnum molle (Herdman, 1886)

Hirose, Euichi & Nozawa, Yoko, 2020, Fig. 6 in Bruggmanniella sanlianensis Lin, Yang & Tokuda, 2020, sp. nov., Zoological Studies 59 (19), pp. 1-11 : 2

Didemnum molle (Herdman, 1886)

Specimens: NMNS-8141-015 (Shimen), -016 (Wushibi).

Dome- or irregularly-shaped colonies of about 5 mm or larger were attached to hydrozoan colonies ( Fig. 2A ). Each colony had one or a few cloacal apertures (white arrows in Fig. 2A ). Colonies were entirely white with brown patches. Globular spicules in the tunic reflected light, resulting in the white color of the colony ( Fig. 2B ). Several morphotypes are genetically defined in D. molle ( Hirose et al. 2009c 2010a). Based on the colony size and coloration, all colonies in the present survey were “small type ”, which was also recorded from Tiao-shi and Wanlitung in Kenting, while “large type ” was recorded from Lyudao ( Hirose and Nozawa 2010).

The expansion of D. molle was reported on the Great Barrier Reef (GBR); the colony density increased significantly following a mass coral bleaching ( Tebbett et al. 2019). The D. molle colonies do not smother the live corals, but they may reduce the number of settlement sites suitable for coral recruits. Based on the photographs in Tebbett et al. (2019), the morphotype of the expanding colonies appears to be the “brown type ” that was recorded in the Ryukyus but not in Taiwan.

Figures

Fig. 2. Didemnum and Diplosoma species. (A, B), Didemnum molle at Shimen (A, colonies; B, tunic spicules). (C, D), Diplosoma gumavirens at Xiaoyeliu (C, colonies; D, thorax with 5-5-5-4 pattern of stigmata). (E, F), Diplosoma ooru at Gonzibi (E, colonies; D, thorax with 5-6-5-4 pattern of stigmata). (G, H), Diplosoma simile at Maobitou (G, colonies; H, thorax with 6-6-6-5 pattern of stigmata). (I, J), Diplosoma virens at Gonzibi (I, colonies; J, thorax with 6-6-6-5 pattern of stigmata). (K, L), Diplosoma watanabei at He-mei (K, colonies; L, thorax with 6-7-6-5 pattern of stigmata). White arrows in A indicate some cloacal aperture. an, anus; es, esophagus; rm, retractor muscle. Scale bars: B = 20 µm; D, F, H, J, L = 0.1 mm.