Microdileptus indica, Ghosh & Bharti & Pathania & Kumar, 2024

Ghosh, Arnab, Bharti, Daizy, Pathania, Prakash Chand & Kumar, Santosh, 2024, Description of two ciliated protists from agricultural soils of India, Records of the Zoological Survey of India 124 (1), pp. 1-10 : 4-5

Microdileptus indica n. sp. ( Figures 2 and 3 )

Diagnosis of Indian population (Data based on two live specimens and four specimens after protargol impregnation): Size 100–147 μm × 5–25 μm in protargol preparations, including 15% shrinkage due to preparation ( Kumar & Foissner, 2016; Kumar et al., 2016). The shape is rod-like, not laterally flattened, and the organism is extremely fragile, with a short proboscis making up approximately one-fifth of the body length. Shedding of the proboscis is frequently observed under coverslip pressure. The oral apparatus is not prominent in the observed specimens, and the tail region is conspicuously, though slightly, flattened. The nuclear apparatus is located near the mid-body, consisting of two spiralized oblong macronuclear nodules. The anterior and posterior nodules measure, on average, 12 μm × 4 μm and 14 μm × 4 μm, respectively. A micronucleus is present between the two macronuclear nodules, measuring about 2 μm in diameter. Four or five contractile vacuoles are located on the dorsal side. Two types of extrusomes are present throughout the body and proboscis. Type 1 extrusomes are thick, short, and slightly dumbbell-shaped, with a more or less flat base and a slightly convex anterior end, each measuring about 2 μm × 1 μm. Type 2 extrusomes are rod-shaped, each measuring 2 -3 μm in length and ≤ 0.5 μm in width. The cytoplasm is colourless, with many colourless cortical granules scattered throughout the body between the cirral rows. Movement is slow and serpentine. There are 6 -7 ciliary rows, with cilia measuring about 4 μm long in protargol-impregnated specimens, and these are comparatively loosely arranged in the posterior third of the trunk. Dorsal brush was not observed due to mediocre quality stained preparations.

Material deposited: The holotype and two paratype slides with protargol-impregnated cells have been deposited at the National Zoological Collections of the Zoological Survey of India, Kolkata, India, with the following accession numbers: Pt. 5276, Pt. 5285 and Pt. 5299 .

Etymology: The species is named after India, the country where it was first discovered.

Occurrence and ecology: The type species was isolated from the soil collected from the pulse field of Ayali Kalan village , Ludhiana, Punjab, India (30°53'35.2"N 75°45'32.4"E). The yellowish-brown-coloured soil was slightly sandy. The species feeds on naked amoebae, algae and other ciliates .

Comparison with the congeners: To date, only three species of the genus Microdileptus have been identified. Microdileptus indica n. sp. is morphologically similar to its congeners: M. breviproboscis ( Foissner, 1981) Vďačný & Foissner, 2012 , M. microstoma ( Vďačný & Foissner, 2008) Vďačný & Foissner, 2012 , and M. semiarmatus ( Vďačný & Foissner, 2008) Vďačný & Foissner, 2012 , with a few but noticeable differences ( Table 3). Microdileptus indica differs from M. breviproboscis in the number of ciliary rows (6 -7 vs. 9 -10) and the shape of Type I extrusomes (slightly dumbbell-shaped vs. oblong). The new species can be distinguished from M. microstoma by the shape of the extrusomes (slightly dumbbell-shaped vs. ampulliform) and the contractile vacuole pattern (a continuous dorsal row vs. a dorsal row without vacuoles in the middle of the trunk). Microdileptus semiarmatus differs from the new species by its conspicuous extrusomes in the proboscis (present only in the posterior half of the proboscis vs. almost throughout its length), the shape of the extrusomes (cuneate vs. slightly dumbbell-shaped), and the number of ciliary rows (8 -13 vs. 6 -7).

Figures

Figure 2. Photomicrographs of live (A-D) and protargol impregnated (E-I) specimens of Microdileptus indica n. sp. A. Specimen showing the body shape. B. Specimen showing the position of contractile vacuole. C. Specimen showing two macronuclear nodules and a single micronucleus. D. Cortical granules. E, F. Right (E) and left (F) side views of specimen depicting the ciliature pattern. G, I. Two types of extrusomes in the proboscis (G) and the trunk (I). H. Macronuclear nodules and micronucleus. CG, cortical granules; CV, contractile vacuoles; E1, type 1 extrusome; E2, type 2 extrusome; FV, food vacuoles; MA, macronuclear nodules; MI, micronucleus; P, proboscis; Scale bars: 50 μm (A, B, E, F), 10 μm (G, H, I).

Figure 3. Microdileptus indica n. sp. From live (A, B, C) and protargol impregnation (D-H). A. Right side view of the specimen. B. Specimen showing the position of the contractile vacuole (arrowheads). C. Surface view showing cortical granulation in the body. D. Two types of extrusomes: dumb bell shaped Type 1 extrusome (left) and rod like type 2 extrusome (right). E. Macronuclear nodules and micronucleus. F, G. Right (F) and left (G) side views of the holotype specimen, showing the extrusomes, nuclear apparatus and ciliary pattern. H. Specimen showing the shape and arrangements of two types of extrusomes in the proboscis and trunk. E1, type 1 extrusome; E2, type 2 extrusome; MA, macronuclear nodules; MI, micronucleus; OO, oral opening; P, proboscis; SK, somatic kinety. Scale bars: 40 μm (A, F, G, H).