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Paraspathidium apofuscum Long et al 2009 from the coarse sand intertidal benthos of marine estuary Acabonac Harbor at Louse Point launching ramp. Imaged in Nomarski DIC on Olympus BH2 using SPlan 40x objective plus variable phone camera cropping on Samsung Galaxy S9+. This species is quite common in my samples taken from various sites of this estuary. I always just called it "marine spathidiid" since species identification of spathidiidae is very difficult but it seems this is quite distinctive and isn't even a haptorian (see below)!

Fully extended individuals measure from 130 up to 225 um in length but they tend to contract off and on during observation occasionally assuming a markedly contracted "bucket" shape when they stand still. They appear quite dark due to the abundant refractile cytoplasmic inclusions. I show several individuals including one with a more empty cytoplasm showing the punctate pitting of the pellicle and the posterior contractile vacuole with adjacent accessory vacuoles.

At first I thought I was dealing with the congener, P. fuscum which is the type species of the genus (4), but when I found the paper by Long et al 2009 I quickly realized I was dealing with P. apofuscum in view of the smaller size, the absence of collecting canals associated with the contractile vacuole, and the more inconspicuous dorsal brush. Like P. fuscum, L. apofuscum has a variable shape which is usually cylindrical or slightly bursiform and highly reminiscent of slender spathidiids with an anterior mouth-bearing portion distinctly widened and obliquely truncate. Also similar is the presence of innumerable highly refractive globular cytoplasmic inclusions and the punctate pitted cortex as well as two ovoid macronuclei in the center of the cell (4).

Paraspathidium apofuscum: "Diagnosis: Highly contractile Paraspathidiium 130–250 μm long in vivo; single contractile vacuole terminally located, with no distinct collecting canals; 34–43 somatic kineties; dikinetid perioral kinety not forming a closed circle. Type locality: Intertidal zone of a mesotrophic sandy beach near Qingdao (36°08′N; 120°43′E), China. Etymology: Composite of the Greek word apo- (unlike) and the known species name fuscum, meaning a ciliate different from the congener P. fuscum" (1).

"Description (see accompanying figures from (1): Size ca. 200 × 40 μm in vivo, elongate, anterior end shaped like a knife-blade, posterior end rounded (Figures 1A, 2A, D). At rest, cells usually contracted and bucket-shaped. Anterior half of body full of dark granules, giving cell “half black, half transparent” appearance under low magnifications (Figures 1A, 2A, D). Extrusomes thread-like, 8 μm long, thinner in middle portion than at either end, widely distributed in cytoplasm especially around the slit-like, apically located cytostome (Figures 1A, D, G, 2G, H, I). Two ellipsoidal macronuclei, with one micronucleus between them (Figures 1E, F, 2J). One contractile vacuole, terminally located (Figures 1A, 2B, M, N). Somatic cilia ca. 7 μm long in vivo; and oral cilia ca. 12 μm (Figure 1A).

On average, 37 somatic kineties present, each composed of monokinetids plus five to seven dikinetids in anterior portion (Figures 1B, 1H, 1I, 2C, 2E, 2F, 2I). Brush kineties composed of three parts: (1) two short dikinetid kineties; (2) four or five short monokinetid kineties; (3) ca. 20 irregularly distributed kinetosomes (Figures 1B, 1I, 2E). Buccal apparatus located at anterior end of cell. Oral opening apical and irregularly elliptical (Figure 2O). Perioral kinety, consists of ca. 50 pairs of kinetosomes, does not form a closed circle. Numerous fine fibres associated with the buccal margin. Generally inactive, often float in the water, occasionally crawling slowly among sand grains" (1).

"Hitherto, Paraspahidium was a monotypic genus, the only species being P. fuscum (Kahl, 1928) Fjeld, 1955, which was redescribed by Foissner (1997b). Our new species differs clearly from P. fuscum in the following combination of characters: (1) fewer somatic kineties (34–43 vs. 50–60); (2) the absence of conspicuous dorsal brush (vs. the presence of conspicuous, highly differentiated dorsal brush; see Figures 2L, 8D, 8E); (3) perioral kinety open (vs. closed in P. fuscum) (Figures 8D, 8E); (4) contractile vacuole without detectable collecting canals (vs. with several collecting canals extending to mid-body in P. fuscum) (Foissner 1997b)" (1).

"The genus Paraspathidium has a haptorid-like shape and suite of morphological characters (dorsal brush extrusomes, a slit-like, apically located cytostome, dikinetids around buccal field). It has been regarded as a gymnostome haptorid (Litostomatea) by Foissner (4). Nonetheless, recent SSU rRNA gene phylogenies and analysis of the secondary structures of the variable region 2 (V2) and variable region 4 (V4) of this molecule support a relationship with class Plagiopylea rather than with class Litostomatea " (2,3).

Further molecular analyses (2) of three additional genes also "reject a placement of Paraspathidium in the order Haptorida or even in the class Litostomatea. Rather, these two taxa always fall into a well-supported clade X. The predicted secondary structures of V4 regions of the SSU rRNA gene are consistent with this finding. These results, together with the earlier work using SSU rRNA data from Paraspathidium alone indicate strongly that Paraspathidium should be transferred out of the class Litostomatea. It cannot at this stage be placed in any existing order-level taxon or even class. Resolution of its higher taxonomic status should be made once the precise interrelationships between Paraspathidium, plagiopyleans, prostomateans and oligohymenophoreans are resolved, since these varied between our analyses. Improved taxon sampling in this region of the tree for multiple genes would be valuable: (2).

1. Three marine haptorid ciliates from northern China: Paraspathidium apofuscum n. sp., Trachelotractus entzi (Kahl, 1927) Foissner, 1997 and Apotrachelotractus variabialis Long, Song and Warren, 2009 (Protozoa, Ciliophora). Hongan Long, Weibo Song, Khaled A. Al-Rasheid and Jun Gong. Journal of Natural History Vol. 43, Nos. 29–32, August 2009, 1749–1761