Bratislavia gusevi, Gusakov, 2021

Gusakov, Vladimir A., 2021, A new naidid oligochaete species (Annelida, Clitellata, Naididae) from Vietnam with asexual reproduction by fragmentation, Zootaxa 5082 (4), pp. 357-372 : 359-364

publication ID	https://doi.org/ 10.11646/zootaxa.5082.4.4
publication LSID	lsid:zoobank.org:pub:01853ABA-E033-4968-AC32-6BC0DE592D6A
DOI	https://doi.org/10.5281/zenodo.5794005
persistent identifier	https://treatment.plazi.org/id/03ABD617-1E53-2023-FF46-FAC093145084
treatment provided by	Plazi
scientific name	Bratislavia gusevi
status	sp. nov.

Treatment

Bratislavia gusevi sp. n.

( Figures 2–4 View FIGURE 2 View FIGURE 3 View FIGURE 4 ; Table 1 View TABLE 1 ; Appendix)

Pristina sp. No 2. Gusakov et al. 2014: 170, 176; Figs 3.2.1а, б.

Holotype. Complete specimen, sexually immature; deposited in the collection of the Zoological Institute of the Russian Academy of Sciences , St. Petersburg, slide inventory number 1/48237.

Paratypes. Two complete immature individuals and nine fragments; deposited in the Laboratory of Ecology of Aquatic Invertebrates of the Papanin Institute for Biology of Inland Waters Russian Academy of Sciences (Borok, Yaroslavl Province), in the collection of representatives of meiobenthos from water bodies of Vietnam: slides No. 121, 413 .

Type locality. Vietnam, Đồng Nai Province , Cát Tiên National Park, forest stream Bển Cự. Holotype collected on September 8, 2010 (leg. V. A. Gusakov), paratype specimens collected on September 8, 2010, and on June 26, 2019 (leg. V. A. Gusakov and E.S. Gusev).

Etymology. The species is named after our friend, colleague and a regular workmate of our expeditions in Vietnam, well-known algologist, Evgeniy S. Gusev, who collected material with the new oligochaete species described here in the Bển Cự stream in 2019.

Species diagnosis. Small naidid oligochaetes, body length of fixed specimens 1.6–2.2 mm. Body wall without outer papilla-like or branchial formations. Segment number 23–39 or more. Asexual reproduction by architomy. No eyes, no proboscis, no intestinal dilatation. Coelomocytes present. Dorsal bundles of chaetae from II, with one, rarely two, hair and one, rarely two, simple-pointed or bifid, or trifid needle chaetae. Bifid and trifid needles mostly in anterior segments, simple-pointed chaetae mostly in posterior segments; in IV always peculiar, enlarged simplepointed needle chaetae. Ventral chaetae from II, commonly 3–5 per bundle, bifid. Anterior and subsequent ventral chaetae are similar in shape and size, with upper teeth somewhat longer than the lower in the first 4–7 segments, the teeth approximately equal in length in the 3–5 following segments, and the upper teeth a little shorter than the lower afterwards.

Description of the material. Body. Small worms with a weakly transparent body in fixed state. All individuals without sexual organs or budding zones. Complete specimens with 23–34 segments and have a body length 1.6– 2.2 mm and maximum diameter 186–257 μm (mostly in IX–XII) ( Fig. 2A View FIGURE 2 ; Table 1 View TABLE 1 ; Appendix). One posteriorly incomplete specimen with 39 segments. Integument slightly wrinkled, with shallow transverse grooves, without papillae-like and/or branchial formations. No eyes. Prostomium conical-rounded, proboscis absent. Body ends with a short pygidium ( Fig. 2A, E View FIGURE 2 ). No intestinal dilatation. Coelomocytes present, most numerous in the mid-body ( Fig. 2C View FIGURE 2 ). Body surface of one worm with randomly attached grains of sand and detritus, in the rest of specimens, the integument is practically clean. No indications of tubes created from secreted mucus and foreign matter detected.

Incomplete individuals. All incomplete body ends (anteriorly and/or posteriorly) intact and complete. Segment number 12–39, body length 0.8–3.2 mm, diameter 135–262 μm ( Fig. 2F View FIGURE 2 ; Fig. 3A View FIGURE 3 ; Table 1 View TABLE 1 ;). Three types of incomplete individuals were detected: (1) head complete, posterior end incomplete, (2) head incomplete, posterior end complete, (3) both head and posterior end incomplete (see Appendix); in the following referred to as "anterior", "posterior", and "mid-body" fragments, respectively. One anterior fragment with inchoate pygidium, while in four others, the body abruptly ends on one of the segments ( Fig. 2F View FIGURE 2 ; Appendix). Two posterior fragments with an abruptly terminating anterior end, head segments plus prostomium missing, and with a complete posterior end, including pygidium. One of the latter with a constriction at the end of the first third of the body (between VIII and IX counting from the anterior-most segment), probably an incipient fission zone. Another posterior fragment with partially broken body between XIII and XIV, apparently in the process of fission ( Fig. 3A, C, D View FIGURE 3 ; Appendix). Both mid-body fragments with incipient pygidium and partially regenerated anterior body ends: prostomium and mouth distinguishable ( Fig. 3B View FIGURE 3 ; Appendix).

Dorsal chaetae. Dorsal bundles from II ( Fig. 2D View FIGURE 2 ; Appendix) with five types of the chaetae: hairs, regular simple-pointed needles, enlarged simple-pointed needles, bifid needles, and trifid needles ( Figs. 3A, B View FIGURE 3 , 4A–E View FIGURE 4 ). Bifid and trifid needles mostly in anterior segments, being gradually replaced by single-pointed needles in posterior segments, with variations among specimens (see Appendix and further description for more details).

Hair chaetae mostly finely pilose (predominantly in the proximal half) (DIC-contrast, x900–1500 magnification), some apparently smooth. One hair per bundle; in anterior segments sometimes two. Hairs often absent especially in one to three posterior segments. In bundles with two hairs, one clearly shorter and thinner than the other, most likely a growing replacement hair. At times, only a short hair present in a bundle (see Appendix). Length and diameter (proximally) of long hairs 103–291 μm and 1.1–2.5 μm, respectively, short hairs 51–88 μm long and 0.5–1.2 μm wide ( Table 1 View TABLE 1 ). The longest hair chaetae usually in IV–X, except for some regenerating specimens with incomplete heads, here longest hairs in the most anterior segments.

The regular simple-pointed needles without nodulus, slightly sickle-like curved in the dorsal third to half, with a pointed tip, distinctly rounded at the end ( Fig. 4A, C View FIGURE 4 ); 47–72 μm long and 1.6–2.7 μm wide ( Table 1 View TABLE 1 ). Longest regular needles usually in mid-body segments, more anteriorly in some specimens with incomplete head. Generally, one regular needle per bundle, very rarely together with a bifid needle (2 specimens, see Appendix). Two specimens with segments that have a regular needle on one side and a bifid needle on the other. Regular simple-pointed needles usually from VII–XIII, in some fragments as early as from III. Within the first 7–17 segments (rarely also in the posterior half of the body), the regular needle chaetae usually alternating with bifid or trifid ones, for variations from this pattern see Appendix.

Enlarged needle chaetae similar in shape to regular needles, but about 1.1–1.3 times as long (62–75 μm) and 1.5–2.0 times as thick (3.1–4.4 μm) ( Table 1 View TABLE 1 ; Fig. 4A, B View FIGURE 4 ). In individuals with a complete head, enlarged needles normally present in segment IV, one, rarely two per bundle (see Appendix; Fig. 2D View FIGURE 2 ). One posterior fragment has enlarged needles in the very first segment; one mid-body fragment has them in the second segment ( Fig. 3A, B View FIGURE 3 ). Enlarged needles absent in three further incomplete specimens (see Appendix).

Bifid and trifid needle chaetae of same size and shape, except for the intermediate tooth in the latter, slightly curved in the distal 1/4 to 1/3, without nodulus, 29–52 μm long, 1.3–2.1 μm wide; the smallest in segments II–III. Teeth short, slightly diverging, upper tooth usually somewhat longer (0.90–1.86 μm) than the lower (0.85–1.72 μm), occasionally teeth equal in length ( Fig. 4A, D, E View FIGURE 4 ; Table 1 View TABLE 1 ). Usually one bifid or trifid needle per bundle, for variations see Appendix. Bifid and trifid needle chaetae mainly in the anterior part of the body, within the first 7–17 segments, excluding IV, which normally bears enlarged simple-pointed needles. In single cases bifid needles in more posterior bundles. Trifid needles less common than bifid needles, absent in anterior segments. As previously noted, bifid and trifid needles may alternate with the regular simple-pointed needles in different segments. In some individuals bifid and/or trifid needles absent. In individuals with incomplete head, any type of needle chaetae may be absent in the first one to three segments (see Appendix).

Ventral chaetae. Ventral chaetae from II, in the recently detached fragments without a head part, sometimes directly in I. As a rule, 3–5 per bundle, 4–5 in anterior body half, 3–4 in the posterior half. Some posterior segments with only 1–2 chaetae per bundle, rarely 1–2 chaetae per bundle also in other body regions (see Appendix). Anterior and subsequent ventral chaetae alike, bifid, moderately s-shaped, more curved towards the posterior end of the body, 47–72 μm in length and 1.8–3.1 μm in width, with a feebly marked, slightly distal (anteriorly) or slightly proximal (posteriorly) nodulus ( Fig. 4F–H View FIGURE 4 ; Table 1 View TABLE 1 ). In complete specimens, longest chaetae usually in IV–IX and further, excluding the hindmost segments. Upper teeth always slightly thinner than lower, longer than lower in the first 4–7 segments, as long as lower in 3–5 subsequent segments, slightly shorter than lower following segments (see Fig. 4F–H View FIGURE 4 ). In some individuals with incomplete front part of the body, chaetae with equal teeth present from the very first segments.

Distribution. To date the species has not been found outside of the type locality.