Strobilidium pelagicum Fauré-Fremiet, 1924

Song, Wen, Li, Jiamei, Huang, Yaoyao, Al-Rasheid, Khaled A. S., Liu, Weiwei, Hu, Xiaozhong & Miao, Miao, 2018, Morphology of Three Aloricate Choreotrich ciliates, Including Description of a New Species Parastrombidinopsis costalis sp. n. (Ciliophora, Choreotrichia), and phylogeny of the genus Parastrombidinopsis, Acta Protozoologica 57 (3), pp. 153-167 : 159-160

Synonyms: Strobilidium pelagicum Fauré-Fremiet, 1924

Strombidinopsis pelagicum ( Fauré-Fremiet, 1924) Jankowski, 2007

This species was simply described by Fauré-Fremiet (1924), here we present an improved diagnosis based on the original description and the present population.

Improved diagnosis: Cell size 100–170 × 40–60 μm in vivo, 95–135 × 40–66 μm after protargol staining. Body broadly elongated obconical with posterior portion pointed. About 31–36 collar membranelles with proximal end located below the distal end, no elongated membranelles and buccal membranelle. About 13–15 somatic kineties equally spaced around the body, with 52–79 dikinetids each. Three globular micronuclei, located between two ellipsoidal macronuclear nodules. Marine habitat.

Locality: Coastal waters off Zhanjiang (21°14´N, 110°35´E), China. Salinity about 25.0 ‰.

Voucher slide: A protargol slide containing voucher specimens is deposited in the Laboratory of Protozoology, OUC, China (registration number: SW2013110202).

Description: Cell size 100–130 × 40–60 μm in vivo, 95–135 × 40–66 μm after protargol staining. Although body shapes vary from slimly to broadly elongated obconical, in essence, anterior two-thirds of cell cylindrical and posterior one-third of cell pointed; length: width ratio about 2.5: 1 in vivo. Anterior end of body transversely truncated ( Figs 4A, B, D , 5A–D ).

Cytoplasm colourless, with some lipid droplets about 2 μm across and food vacuoles ~ 8 μm across containing some yellow algae ( Figs 5C, L ). Cell surface smooth, without mineral envelope. Extrusomes and contractile vacuole not observed. Two macronuclear nodules arranged obliquely up and down and located in the anterior half of cell, 10–17 × 8–12 μm in size after protargol staining, ellipsoidal, with several nucleoli ~ 2–3 μm across. Three globular micronuclei about 2 μm across, located between two macronuclear nodules ( Figs 4G , 5F ). Locomotion by swimming forward while rotating about the main cell axis, or by touching the substrate with collar membranelles ( Fig. 4C ).

Oral apparatus in vivo about 45 μm across, but only 30–38 μm across after protargol impregnation; oral cavity extending posteriad to about one-tenth of cell length ( Figs 5E, G ). About 31–36 collar membranelles formed a slightly spiralled membranellar zone, with a conspicuous gap at the ventral side, and cilia about 25 μm long. Bases of the collar membranelles extend obliquely across the peristomial rim, about 10 μm long; no elongate bases recognized ( Figs 4E, I , 5K ). Buccal membranelle not observed, nor the endoral membrane, which may be due to poor staining.

Somatic ciliature arranged in 13–15 kineties and evenly distributed around body. The somatic kineties generally commence below membranellar zone and extend to posterior end of cell, without forming a subterminal or subcaudal suture ( Figs 4H , 5I, J ). Each somatic kinety consists of 52–79 dikinetids; in each dikinetid, both basal bodies bear cilia, with anterior cilium about 4 μm long and the posterior cilium about 2 μm long ( Fig. 5H ). One early divider was observed; its oral primordium was located anteriorly at the left of the body ( Fig. 5K ).

Figures

Fig. 4. Parastrombidinopsis pelagica (Fauré-Fremiet, 1924) comb. n. from life (A–D, F) and after protargol staining (E, G–I). (A, B) Ventral views of two individuals. (C) Swimming pattern. (D) Different individuals to show the variations in body shape. (E) Detail of oral mem- branelles. (F) From Fauré-Fremiet (1924). (G, H) Ventral and dorsal views of the same specimen showing the ciliature. (I) Lateral view of a specimen. CM, collar membranelles; Ma, macronucleus; Mi, micronucleus; SK, somatic kinety. Scale bars: 50 μm.

Fig. 5. Photomicrographs of Parastrombidinopsis pelagica (Fauré-Fremiet, 1924) comb. n. from life (A–D, G, H, L) and after protargol staining (E, F, I–K). (A–D) Four individuals, showing the cell shape. (E) Ventral view, showing ciliature. (F) Detail of macronuclei, arrowheads mark micronuclei. (G) Ventral view of oral membranelles. (H) Arrows mark somatic cilia. (I, J) Showing somatic kineties. (K) An early divider; arrow marks oral primordium. (L) Cytoplasm. CM, collar membranelles; Ma, macronucleus; SK, somatic kinety. Scale bars: 20 μm (A–E); 10 μm (H).