Collotheca algicola (Hudson)

Meksuwan, Phuripong, Pholpunthin, Pornsilp & Segers, Hendrik, 2011, Diversity of sessile rotifers (Gnesiotrocha, Monogononta, Rotifera) in Thale Noi Lake, Thailand, Zootaxa 2997, pp. 1-18 : 6-7

Collotheca algicola (Hudson) ( Figs 2 d–2f) and Collotheca ambigua (Hudson) ( Figs 2 g– 2i)

We tentatively consider these two taxa as separate species, even though the most recent checklist of the group considers C. algicola (Hudson) a synonym of C. ambigua (Hudson) (Segers 2007) . Our material matches well the original description of both species ( Hudson & Gosse 1886). We found three morphological characters that distinguish the two ( Table 3 ):

● the dorso-lateral corona lobes are more prominent in C. algicola than in C. ambigua ● the separation between foot and trunk is more pronounced in C. ambigua than in C. algicola ; ● they differ significantly in size, with C. ambigua being the larger of the two.

Species Characters C. algicola (Hudson) C. ambigua (Hudson) C. campanulata C. trilobata (Collins)

(Dobie)

Corona lobes Five Five Five Three

Separation between foot and Less distinct Distinct Distinct Distinct

trunk

That the relatively small C. algicola is not a young, immature and therefore not fully grown specimen is indicated by the accumulation of excretophores ( Fig. 2 e), a phenomenon which is commonly observed in old specimens of many species of Collotheca , but not in young ones ( Koste 1978). We nevertheless refrain from concluding on the matter as we observed only low numbers of both of the taxa concerned. In particular, we found only a single specimen of what we identify as C. algicola .

Collotheca ambigua could also be confused with C. campanulata (Dobie) ( Figs 3a–3 c) or C. trilobata (Collins) ( Figs 3 d–3f). However, they can be distinguished from C. campanulata by having a deeper and wider sinus separating the ventral corona lobes (compare Fig. 2 i and 3c), and by shape of its relatively narrower dorsal corona (compare Figs 2 h– 2i and 3b–3c). C. ambigua can further be separated from C. trilobata by having small dorso-lateral corona lobes (absent in C. trilobata ) and relatively small ventro-lateral corona lobes when compared to C. trilobata (compare Figs 2 h– 2i and 3e–3f; see also Table 3 ).

Figures

FIGURES 2 A – 2 I. Acyclus sp.; Collotheca spp. 2 a – 2 c: Acyclus sp.; 2 d – 2 f: Collotheca algicola (Hudson, 1886); 2 g – 2 i: Collotheca ambigua (Hudson, 1883). Scale bars: 2 a – 2 c, 2 d, 2 g = 100 µm; 2 e – 2 f, 2 h – 2 i = 50 µm.

FIGURES 3 A – 3 F. Collotheca spp. 3 a – c: Collotheca campanulata (Dobie, 1849); 3 d – 3 f: Collotheca trilobata (Collins, 1872). Scale bars: 3 a – 3 f = 100 µm.

Tables

TABLE 3. Comparison of diagnostic features of four species of Collotheca (after Koste, 1978)

Dorsal corona lobe	Gradually narrow onto Gradually narrow the tip end onto the tip end	Rather parallel with rounded tip	Rather parallel with rounded tip
Dorso-lateral corona lobes	Prominent Small	Rather prominent	Completely lacking
Corona ventral lobe sinus	Rather deep Rather deep	Rather shallow	Very deep