Notes on a new marine peritrichous ciliate (Ciliophora: Peritrichida), Zoothamnium xuianum n. sp., with redescription of Z. paraentzii Song, 1991 from northern China

The morphology, infraciliature and silverline system of two marine peritrichous ciliates, Zoothamnium xuianum n. sp. and Z. paraentzii Song, 1991, collected from a shrimp-hatching plant in northern China, were investigated using both in vivo and silver impregnation methods. The new species is recognized by the following characters: colony alternatively branched, zooids in vivo about 45 × 30 μm with single-layered peristomial lip; contractile vacuole apically located; macronucleus band-like and transversely positioned; more than 50 striations from peristomial area to aboral trochal band, about 14 from aboral trochal band to scopula; three equally long kineties in peniculus 3 parallel to each other. Based on both the Qingdao population and the original description, an improved diagnosis for Z. paraentzii is suggested: marine Zoothamnium with irregularly dichotomously branched stalk; zooid 50–80 × 25–45 μm in vivo with single-layered peristomial lip; contractile vacuole apically positioned; macronucleus C-shaped, transversely orientated; number of silverlines between anterior end and aboral trochal band about 75–83, between aboral trochal band and scopula, 28–33; inner row of peniculus 3 displaced from the other two and converges with peniculus 1 at aboral end.