Trididemnum cyclops Michaelsen, 1921

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

Trididemnum cyclops Michaelsen, 1921

Specimens: NMNS-8141-025 (Shimen).

The colonies were oval or elongated cushions and aggregated on a side wall of a tide pool ( Fig. 3M ). They were green due to Prochloron in the common cloacal cavities, while the colony peripheries and substratum side were white due to tunic spicules with burred surfaces ( Fig. 3N ). In an enlarged image of the colonies, there was a black spot in each zooid ( Fig. 3O ). This is a black (or dark brown) pigmentation at the apical end of the endostyle referred to as pigment cap ( Fig. 3P ), which is unique to the T. cyclops and Trididemnum paracyclops ( Kott, 1980) . Although T. paracyclops is distinguished from T. cyclops by several characters such as larger colony size, colony shape, larger zooids, and the number of coils in the vas deferens ( Kott 1980 2001), Monniot and Monniot (1987) made no distinction between the two species. Although the size of the tunic spicules differed significantly between T. cyclops and T. paracyclops , the molecular phylogeny inferred from the partial COI sequences did not recognize two species ( Hirose et al. 2010b). Based on the colony size and shape, the present specimens were identified as T. cyclops .

Figures

Fig. 3. Lissoclinum and Trididemnum species. (A, B), Lissoclinum bistratum at Gonzibi (A, colony; B, tunic spicules). (C–E), Lissoclinum midui at Gonzibi (C, colony; D, thorax; E, tunic spicules). (F–H), Lissoclinum punctatum at Gonzibi (F, colony; G tunic phycocyte; H, tunic spicules). (I–L), Trididemnum clinides at Shimen (I, colony; J, tunic spicules; K, unicellular cyanobacteria in the tunic; L, filamentous, multicellular cyanobacteria in the tunic). (M–P), Trididemnum cyclops at Shimen (M, colony; N, tunic spicules; O, enlargement of colony surface showing a zooid; P, thorax). Arrows in O and P indicate pigmentation at the top of endostyle (pigment cap). an, anus; fp, fecal pellet; g, greenish cyanobacteria; n, nucleus of tunic phycocyte; r, reddish cyanobacterium; un, unknown organ. Scale bars: B, E, G, H, J–L, N, and O = 20 µm; D and P = 0.1 mm; O = 0.2 mm.