The lack of data concerning the morphology of male cladocerans greatly impedes our understanding of the systematics of cladocerans. This is because the differentiation of males is of significant importance for distinguishing closely related species. Simocephalus himalayensis himalayensis Chiang & Chen, 1974 (Cladocera, Simocephalus) is an endemic cladoceran species in the Tibetan plateau, China. To date, no information has been available regarding the morphology and biology of its males. In this study, we provide the morphological and biological data of the males that were produced in laboratory populations. The male individuals are about 1.01–1.20 mm long; the margin of antennulae possess two sensory papilla; dorsal valve margin smooth. Two vas deferens are located between the supra-anal angle and the proximal anal teeth. Sperm is round with a diameter of two micrometers. An updated morphological description and reproductive data of the females of this species are also provided.
Discocephalids and pseudoamphisiellids are possibly two of the most confused groups among hypotrichous/euplotid ciliates regarding their systematic position and phylogenetic relationships.The former were often regarded as related to euplotids while the latter,in the absence of molecular data,were mostly assigned to the urostylid-like hypotrichs.In the present work,the small subunit rRNA genes of several rarely observed discocephalid and pseudoamphisiellid genera were analyzed to obtain insights into the phylogenetic relationships of these highly ambiguous Spirotrichea.Four different tree reconstruction algorithms yielded nearly identical topologies,which indicated both groups belong to the same assemblage.This assemblage is clearly isolated as a deep-branching clade and invariably positioned between Euplotida and Hypotricha.The sister group relationship of the Pseudoamphisiellidae and Discocephalidae supports the previous suggestion that they might represent an ordinal taxon,the Discocephalida.Both morphological and morphogenetic features indicate that the pseudoamphisiellids should be placed in the order Discocephalida but as a sister group to other typical discocephalids.Thus we propose establishing a new suborder,Pseudoamphisiellina subord.n.The new taxon is diagnosed by the following characteristics:(i) two distantly separated midventral rows that are morphogenetically formed with an urostylid mode;(ii) absence of the "frontoterminal row",which is formed from the posterior-most frontoventral-transverse cirral anlage in all other typical urostylids;(iii) numerous caudal cirri that derive from each of the dorsal kinety anlagen;(iv) right marginal row that has a unique de novo origin;and (v) inhabiting periphytic communities.The validity of the suborder Pseudoamphisiellina is firmly supported by molecular data.
