Epistylis smalli Utz, Santos & Araujo, 2015, n. sp.

Epistylis smalli n. sp. Diagnosis. Freshwater Epistylis with a dichotomously branched colony bearing elongate zooids measuring on average 173 µm in length, and 49 µm in width. A C-shaped macronucleus lies transversally on the oral half of the cell, close to the infundibulum. All infundibular polykinetids are composed of three rows of kinetosomes; Oral polykinetid 1 (OPK 1) has rows of equal lengths, OPK 2 ends at the adstomal curvature of PK 1 and presents rows of different lengths, and PK 3 has all rows of the same length and terminates at the adstomal end of OPK 1. Type locality. Guaíba Lake (30 º 6 ' 38 "S, 51 º 15 ' 38 "W) located in Porto Alegre municipality, Rio Grande do Sul state, Brazil. Etymology. This species name is dedicated to Eugene B. Small for his relevant contributions to ciliate taxonomy. Deposition of Slide. One slide with protargol stained specimens was deposited in the Protist Collection of the Museum of Science and Technology of the Pontificia Universidade Católica do Rio Grande do Sul under the number MCTP 3. Morphology of live specimens. Colonies of E. smalli were dichotomously branched with secondary branches terminating at the same level (Fig 1 A and 2 A). As characteristic of the genus Epistylis the basal or secondary stalks did not present spasmoneme (Fig 1 A and 2 B). The main basal stalk was considerably long (Table 1) and presented smooth longitudinal ridges (Fig 1 H). Live colonies had up to 34 zooids, but generally presented 6-8 zooids that were similar in size and shape. Zooids were elongate and ranged from 145 to 200 µm in length and from 45 to 80 µm in width (Table 1 and Fig 1 B and 2 B). The peristomial lip was thick and wider than the body (Table 1 and Fig 1 B and 2 B). The epistomial disk was elevated (Fig 1 B) and about ½ as wide as the peristomial lip (Table 1). A Cshape macronucleus was located on the first half of the cell close to the infundibulum (Fig 1 C and 2 B). Morphology of stained specimens. The infraciliature and the nuclear apparatus of Epistylis smalli was easily recognized in protargol staining. The size of stained zooid ranged from 92.5 to 117.5 µm in length and from 42.5 to 57.5 µm in width (Table 2). A total of 26 somatic myonemes extend from the scopula to the epistomial disk (Fig 1 D). A C-shaped macronucleus lies on the first half of the cell (Fig 1 D and 2 B). The oral infraciliature was typical of peritrich ciliates with an outer haplokinety and an inner polykinety that performs approximately 1 ½ turns before entering the infundibulum (Fig 1 E and 2 C). Inside the infundibulum the oral polykinetid 1 (OPK 1) is accompanied by the infundibular polikinetids 2 (OPK 2), and 3 (OPK 3). All infundibular polykinetids present three rows of kinetosomes. The middle row of OPK 1 is longer than the other two (Fig 1 E and 2 C). Rows in OPK 2 are of different lengths: the row closer to OPK 1 is shorter than the others (Fig 1 F and 2 C). All three rows of OPK 2 terminate at the adstomal curvature of OPK 1. OPK 3 have three rows of kinetosomes of equal length that terminate above the adstomal end of OPK 1 (Fig 1 G and 2 C). The trochal band in the aboral half of the cell is composed by a single row of staggered kinetosomes (Fig 1 I). Species in the genus Epistylis Ehremberg, 1830 are colonial having contractile zooids on top of non-contractile stalks. Morphologically species of Epistylis are identified by the size and shape of the zooid, overall shape of the colony, and arrangement of the oral polykinetids revealed by protargol impregnation. The species collected from the Guaiba Lake in the present study was identified as Epistylis smalli n. sp. after being compared with several species in the genus Epistylis. These species presented similar zooid and colony shape, and sometimes a similar zooid size, but differed in other relevant morphologhical characters. For example, Epistylis constricta Kellicott, 1855 presents an elevated epistomial disk, and a contractile vacuole below the peristomial border similar to E. smalli, but has a smaller size, presents transversal folds when the zooid is contracted and generally is observed as epibiont (Kahl, 1935; See Table 1 for comparisons). E. rotans Sveç, 1897 has a slender zooid, but differs from E. smalli in the organization of the colony, the ability to swim and in the epibiotic way of life (Kahl, 1935). Epistylis niagarae Kellicott, 1883 has an prominent epistomial disk similar to the studied species, but differs from it in the size of the zooid, in the presence of a strongly projected snout when contracting, and in the epibiotic way of life (Kahl, 1935). Epistylis chrysemydis Bishop & Jahn, 1941 is the described species most similar to E. smalli. The zooids of E. chrysemydis are slender measuring 120 – 220 µm in length and 60 – 110 µm in width, which is in the range found for E. smalli (Table 1). In addition, the macronucleus of E. chrysemydis is C-shaped and surrounds the infundibulum as observed for the species described here (Fig 1 C and 2 B). On the other hand, the arrangement of the oral polykinetids of E. chrysemydis is different from the observed for E. smalli. The oral polykinetid 1 (OPK 1) of E.chrysemydis has three rows of kinetosomes of equal length, while in E. smalli the middle row is longer than the other two (Fig 1 E and 2 C). The rows in OPK 3 of E. chrysemydis terminate at the same level of OPK 1 and OPK 2, while in E. smalli OPK 3 terminates above the adstomal end of OPK 1. OPK 2 is similar in both species. The arrangement of kinetosomal rows in oral polykinetids has been used by several authors to distinguish species in peritrich ciliates (e.g. Esteban & Fernandez-Galiano, 1989; Leitner & Foissner, 1997; Clamp, 2005; Sun et al., 2006; Utz et al., 2014). The relative length of rows and the points they terminate is definitive for species identification (Sun et al., 2006; Gentekaki & Lynn, 2010). Despite the similarities in the size and shape of the live zooid and the overall shape of the colonies observed between E. chrysemydis and E. smalli, differences were pointed out in the pattern of kinetosomal rows in the oral polykinetids. These differences are strong enough to consider a species-level distinction between E. chrysemydis and E. smalli.Published as part of Utz, Laura R. P., Santos, Mariana Silva Dos & Araujo, Gabriella Oliveira De, 2015, Epistylis smalli (Ciliophora: Peritrichia) a new peritrich from Guaiba Lake, Southern Brazil, pp. 483-488 in Zootaxa 4040 (4) on pages 484-487, DOI: 10.11646/zootaxa.4040.4.10, http://zenodo.org/record/24530