Trachelolophos binucleatus Yan & Xu & Al-Farraj & Al-Rasheid & Song 2016, SP. NOV

TRACHELOLOPHOS BINUCLEATUS SP. NOV. (FIGS 4, 5; TABLE 1) Diagnosis: Body size in vivo 500–1000 × 25–35 μm; 9–19 and 17–26 somatic kineties on head and trunk, respectively; single nuclear group composed of two or three macronuclei and one micronucleus; narrow glabrous stripe, corresponding to area occupied by two somatic kineties; cortical granules colourless and about 0.5 μm in diameter. Type locality: The intertidal zone of a bathing beach in Qingdao, China (35°55′45″N, 120°12′59″E), where the water temperature was 16 °C and salinity about 33‰ (Fig. 1A). Type specimens: A protargol-impregnated slide containing the holotype specimen marked with an ink circle is deposited in the Laboratory of Protozoology, Ocean University of China, China (No. YY2013052403). One paratype slide is deposited in the Natural History Museum, London, UK, with registration number NHMUK 2015.9.15.2. Etymology: The species-group name binucleatus reflects the fact that this organism usually has two macronuclei. Description: Fully extended cells about 700 × 30 μm in vivo; body flexible and flattened ribbon-like with claviform head and pointed tail (Figs 4A–C, 5A–C). Body colour dark at low magnification with neck and tail portion transparent due to packed inclusions (Figs 4A, D, 5A, D). Single nuclear group located in centre of trunk, containing two or three macronuclei, 7–10 μm in diameter, and one micronucleus, 3–6 μm in diameter (Figs 4A, D, I, 5D, G, H). Colourless cortical granules, c. 0.5 μm in diameter, arranged in line between ciliary rows and scattered in glabrous stripe (Figs 4F, 5E, F). Locomotion by gliding between sand grains and organic debris. Cell surface densely ciliated with unciliated zone, glabrous stripe, about as wide as two somatic kineties (Figs 4F, H, 5J, M). Entire infraciliature consisting of dikinetids with cilia c. 10 μm long (Figs 4H, I, 5G). About 14 and 19 somatic kineties on head and trunk, respectively. Anterior and posterior secant system formed on left side of glabrous stripe where some kineties abut to bristle kinety (Figs 4F, H, 5J, M). Oral infraciliature consisting of uninterrupted circumoral kinety and conspicuous ciliary tuft located in centre of oral cavity (Figs 4F, G, 3I, L). Comparison: Similar to Trachelolophos quadrinucleatus sp. nov., the current new species should be compared with its known congeners. All measurements in μm. Abbreviations: CV, coefficient of variation (%); Ma, macronuclei; Mi, micronuclei; NG, nuclear groups; SD, standard deviation; SK, somatic kineties; N, number of specimens. Trachelolophos filum can be separated from the new species by having more somatic kineties on the trunk (26–35 vs. 17–26) and more macronuclei (6–30 forming a strand vs. two or three forming a nuclear group) (Foissner & Dragesco, 1996b). Trachelolophos gigas differs from T. binucleatus sp. nov. in possessing a longer body length (2000 μm vs. 500–1000 μm), more somatic kineties on the trunk (52– 71 vs. 17–26) and more macronuclei (17–33 macronuclei forming a strand vs. two or three forming a nuclear group) (Foissner & Dragesco, 1996b). Trachelolophos binucleatus sp. nov. differs from T. quadrinucleatus sp. nov. (above) in having far fewer somatic kineties on the trunk (17–26 vs. 26– 40) and fewer macronuclei (two or three vs. three or four).