Comparison with similar genera
Amphisiellidae were divided into three groups by Berger (2008). Group I comprises marine taxa (Amphisiella, Caudiamphisiella, Maregastrostyla and Spiroamphisiella).. All of these possess a buccal cirrus and a very prominent ACR, commencing at about the level of the distal end of the adoral zone of membranelles, and terminating beyond the midbody. Hence the new genus, Parasincirra n. g., can be distinguished from others in group I.
The group II genera (Lamtostyla and Uroleptoides) exhibit a continuous adoral zone of membranelles and possess a buccal cirrus whereas Parasincirra n. g. has a bipartite adoral zone of membranelles and lacks a buccal cirrus. Parasincirra n. g. can therefore be easily distinguished by these morphological characteristics.
Group III comprises two genera, i.e. Lamtostylides and Paramphisiella. These possess a buccal cirrus and have only one cirrus (cirrus III/2) left of the ACR. In Parasincirra n. g., however, there is no buccal cirrus and one frontoventral cirri left of the ACR. So, the new genus also differs from species of this group.
Up to now, six genera, that is, Afroamphisiella, Cossothigma, Hemisincirra, Mucotrichidium, Terricirra and Tetrastyla, are incertae sedis in Amphisiellidae. Of these, Hemisincirra is the most similar to Parasincirra n. g., however, the type species of Hemisincirra has a buccal cirrus (vs. absent in Parasincirra n. g.). Afroamphisiella can be distinguished from Parasincirra n. g. since it possesses a buccal cirrus (vs. absent) and lacks transverse cirri (vs. present). Cossothigma can be separated from the new genus through its trachelostylid body shape and oral apparatus (vs. elliptical to elongate elliptical in shape and oral apparatus in Oxytricha-pattern), and the probable presence of caudal cirri (vs. absent in the new genus). Mucotrichidium differs from the new genus in having a continuous adoral zone of membranelles (vs. bipartite), and in possessing a buccal cirrus, postperistomial cirrus and caudal cirri (vs. absent in Parasincirra n. g.). Terricirra and Tetrastyla can also be separated from Parasincirra n. g.; Terricirra possesses a buccal cirrus (vs. absent in Parasincirra n. g.) while Tetrastyla has a continuous adoral zone of membranelles (vs. bipartite in Parasincirra n. g.).
Comparison of Parasincirra sinica n. sp. with similar species
Species assigned to Hemisincirra have an infraciliature which is very similar to that of our new species; namely, three frontal cirri, a short amphisiellid median cirral row, fewer transverse cirri and a lack of caudal cirri.
According to the ventral infraciliature, our new species resembles Hemisincirra interrupta and H. vermicularismost in that these species also have a bipartite adoral zone of membranelles and lack a buccal cirrus. Differences between Parasincirra sinica n. sp. and H. interrupta, however, are that the latter has fewer dorsal kineties (one vs. three), and more macronuclear nodules (about 30 vs. two to six) as well as more cirri in amphisiellid median cirral row (six to eight vs. invariably four). Hemisincirra vermicularis can be distinguished Parasincirra sinica n. sp. in having more macronuclear nodules (about ten vs. two to six) and contractile vacuoles (four vs. one), and fewer dorsal kineties (one vs. three) .
Further, the infraciliature of Lamtostyla decorata, L. perisincirra, L. islandica, Uroleptoides magnigranulosus and U. longiseries closely resembles Parasincirra sinican. sp. and thus should be compared.
Parasincirra sinica n. sp. differs from Lamtostyla decorata in: (i) smaller body size (90–140 × 20–40 μm vs. 100–220 × 20–35 μm) in vivo; (ii) buccal cirrus and pretransverse cirri absent (vs. present); (iii) lower number of transverse cirri (two to four vs. five to nine); and (iv) adoral zone of membranelles bipartite (vs. continuous) .
Parasincirra sinica n. sp. can be separated fromLamtostyla perisincirra due to (i) larger body size (90–140 × 20–40 μm vs. 50–80 × 20–30 μm); (ii) cell outline fusiform (vs. parallel body margins with both ends broadly rounded); (iii) buccal cirrus absent (vs. present); (iv) larger number of cirri in ACR (four vs. six to eight); (v) cortical granules present (vs. absent); and (vi) adoral zone of membranelles bipartite (vs. continuous) .
Parasincirra sinica n. sp. is closely related to Lamtostyla islandica, butthe former can be recognised by: (i) larger body size (90–140 × 20–40 μm vs. 60–80 × 20–25 μm) in vivo; (ii) cell outline fusiform (vs. parallel body margins with both ends broadly rounded); (iii) buccal cirrus absent (vs. present); (iv) adoral zone of membranelles interrupted (vs. continuous); (v) cortical granules present (vs. absent); and (vi) arrangement of endoral and paroral (at about same level vs. overlapping only by about half of their length) .
Uroleptoides magnigranulosus has a close relationship to Parasincirra sinica n. sp.in the SSU rDNA tree of our present work. Parasincirra sinica n. sp., however, can be recognised by: (i) buccal cirrus absent (vs. present); (ii) lower number of cirri in ACR (four vs. 12–19) and transverse cirri (two to four vs. constantly five); and (iii) adoral zone of membranelles interrupted (vs. continuous) .
Parasincirra sinica n. sp. can be distinguished from Uroleptoides longiseries by buccal cirrus absent (vs. present), fewer cirri in ACR (four vs. 24–54), and adoral zone of membranelles interrupted (vs. continuous) .
One of the most remarkable morphogenetic features in Parasincirra sinica n. sp. is that the rightmost frontoventral row is formed by two anlage, which is a specific character for amphisiellids and called the amphisiellid median cirral row. Hitherto, accounts of morphogenesis are available for only several taxa in Amphisiellidae with the main morphogenesis comprising a diversity of processes:
- the parental adoral zone of membranelles is completely retained in some genera/species, e.g. Amphisiella, Lamtostyla, Lamtostylides, Paramphisiella and Hemisincirra inquieta, while it is partly renewed in other taxa, e.g. Parasincirra n. g.;
- ventral cirri develop from five (e.g. Lamtostylides and Paramphisiella), six (e.g. Amphisiella, Parasincirra n. g., Spiroamphisiella, Hemisincirra inquieta, Terricirra, Mucotrichidium and most Lamtostyla species) or seven (e.g. Lamtostyla salina) FVT-anlagen;
- FVT-anlage II generates the buccal cirrus (in Amphisiella, Spiroamphisiella, Lamtostyla, Lamtostylides, Paramphisiella, Afroamphisiella, Hemisincirra inquieta, Terricirra and Mucotrichidium) or not (in Parasincirra n. g.);
- the amphisiellid median cirral row is formed by two (in Amphisiella, Hemisincirra inquieta, Parasincirra n. g., Lamtostyla, Lamtostylides, Mucotrichidium and Paramphisiella) or three (in Terricirra and Spiroamphisiella) anlagen;
- caudal cirri are formed in some taxa, i.e. Spiroamphisiella, Paramphisiella and Mucotrichidium, while not formed in other genera, i.e. Amphisiella, Parasincirra n. g., Lamtostyla, Lamtostylides, Afroamphisiella, Hemisincirra inquieta and Terricirra;
- no transverse cirri are formed in Afroamphisiella and Paramphisiella while transverse cirri are formed in Amphisiella, Parasincirra n. g., Lamtostyla, Lamtostylides, Terricirra, Mucotrichidium, Hemisincirra inquieta and Spiroamphisiella [28, 30–32].
Molecular phylogenetic analyses cannot resolve the relationship of the four polytomies represented by Parasincirra, Uroleptoides and Parabistichella genera (Fig. 6, 7). Whether or not the assignments of the latter two genera to the family Amphisiellidae need further clarification [25, 28, 29, 31, 33–37], the new genus Parasincirra has the critical character of the family Amphisiellidae of an ACR that originates from two separate anlagen, and apparently it should be assigned in this family [27, 28]. Furthermore, the genera within this clade share the same three enlarged frontal cirri and one marginal cirral row on each side pattern. The main difference between Parabistichella and Parasincirra is the number and origin of the frontoventral rows; that is, the most remarkable morphogenetic features in Parasincirraisthe long frontoventral row ( = amphisiellid cirral row) formed by two anlage while it is formed by just a single anlage in Parabistichella. The main difference between the species of the genera Uroleptoides andParasincirra, meanwhile,is whether or not the buccal cirrus appears [28, 33–35]. The reason why these obvious differences in morphological characters are not reflected in the phylogeny might simply be that there is currently insufficient data to figure out how those lineages are related . By contrast, the phylogenetic relationship between P. sinica and the most morphologically similar genus, Lamtostyla,shows a high intra-node scattering, which might indicate that the critical character of the family Amphisiellidae (the ACR originating from two separate anlagen) is a plesiomorphic trait within the amphisiellid hypotrichs evolving independently under different conditions.
Moreover, other amphisiellid species, even for the type genus Amphisiella, are also not resolved well in our phylogenetic analyses, as has also been the case in previous studies (Fig. 7) [31, 33, 36]. Given the species being sampled and the deficient data on the morphogenesis and SSU rDNA sequences, there is insufficient evidence to unravel a robust phylogeny for this complex group [29, 31, 33–36, 39]. Future studies therefore need to gather more data on other gene markers and morphogenetic studies from a wider range of taxa in order to begin to develop a more accurate classification and evolution of Parasincirra and its relationship with other amphisiellid species.