Fridericia korobushkini Degtyarev, 2025

Fridericia korobushkini Degtyarev , sp. nov.

( Figures 2 View FIGURE 2 , 3 View FIGURE 3 )

Holotype. ZMMU 1266 View Materials , adult specimen, fixed in 100% ethanol. Ulmus forest (39.80037°N, 67.34411°E; 720 m a.s.l.), Baxmal District , Jizzakh Region, Uzbekistan. Site 10 ( Fig. 1 View FIGURE 1 , Table 1 View TABLE 1 ). 01 November 2022, D.I. Korobushkin leg. GoogleMaps

Paratypes. Two adult specimens ( ZMMU 1267 View Materials ) from the type locality, fixed in 100% ethanol, same date and collector GoogleMaps . Three specimens (personal collection of M. Degtyarev) from grove patch surrounded by vineyards (39.40397°N, 67.02527°E; 936 m a.s.l.), Urgut District , Samarqand Region, Uzbekistan. Site 11 ( Fig. 1 View FIGURE 1 , Table 1 View TABLE 1 ); 31.10.2022, D.I. Korobushkin leg. GoogleMaps

Further material. Ten specimens from the two above-mentioned localities, investigated in vivo, not preserved.

Etymology. The species is named after the prominent soil zoologist Daniil I. Korobushkin, who collected the soil samples in which the species was found.

Distribution and habitat. Central Uzbekistan, forests and groves.

Diagnosis. The new species can be recognized by the following combination of characters: (1) max. 5 chaetae per bundle; (2) subneural gland in XIV; (3) 5 pairs of preclitellar nephridia; (4) chylus cells postclitellar; (5) spermathecae with 2–4 diverticula of irregular shape, spermathecal ectal glands absent.

Description. Medium-sized Fridericia species, body length 11–15 mm (here and further: in vivo), width 300– 430 µm at VIII and 340–480 µm at clitellum. Small soil particles usually attached to the body surface ( Fig. 2 View FIGURE 2 ). Segment number (33) 43–53. Chaetal formula (1,2,3),4 – 4,3,2: 3,4,5 – 4,3,2. Chaetae within almost all bundles arranged in pairs: larger outer chaetae (length 45–55 µm; diameter 3.5–4.5 µm) and smaller inner chaetae (length 35–45 µm, diameter c. 2.5 µm). In few caudal segments only 2 chaetae per bundle, ventral caudal chaetae slightly enlarged (c. 60 µm). Head pore at 0/1. Dorsal pores from VII. Epidermal gland cells pale, arranged in 2–3 rows per segment. One small subneural gland in XIV ( Fig. 2 View FIGURE 2 ).

Body wall c. 25 µm thick, cuticle c. 1 µm thick. Brain slightly concave anteriorly, truncate or slightly rounded posteriorly, c. 150 µm long, 80–100 µm wide. Oesophageal appendages long but not coiled, prolonged to V–VI or even VII, with few small terminal branches. Pharyngeal glands in IV–VI, all pairs with broad dorsal connection, in all pairs both dorsal and ventral lobes present. Chylus cells in XIII–XIV or XIV–XV, occupying two segments. Chloragocytes from V, brownish in transparent light. Midgut pars tumida not seen. Nephridia 5 pairs in preclitellar segments, from 6/7 to 10/11, length ratio anteseptale: postseptale 1: 1.5–2. Origin of the efferent duct medial ( Schmelz 2003). Dorsal blood vessel from XVII. Blood colorless. Two types of coelomocytes: coelomo-mucocytes ellipsoid, hyaline, without refractile vesicles, “ type a” ( Möller 1971), 30–42 µm long and 20–30 µm wide; coelomolenticytes small, 6–12 µm long and 2.5–4 µm wide ( Fig. 3 View FIGURE 3 ).

Clitellum in XII–1/2XIII, saddle-shaped; cells in c. 30 irregular rows, not much elevated ( Fig. 2 View FIGURE 2 ). Testes and sperm funnels in XI. Mature spermatozoa about 100 µm long, aligned on top of sperm funnel. Sperm funnels barrelshaped, yielding, 150–230 µm long and 100–150 µm wide; collar narrower than funnel body, c. 30 µm long and 50 µm wide ( Fig. 3 View FIGURE 3 ). Vasa deferentia confined to XII in a dense coil, c. 13 µm wide. Seminal vesicle in X–XI, occupying two segments. Male glandular bulbs large, compact, c. 200 µm long and c. 150 µm wide. Bursal slit mostly stapleshaped, with few additional protrusions at tips ( Fig. 2 View FIGURE 2 ). Spermathecal ectal glands absent. Spermathecal ectal ducts 330–370 µm long, (15)–20–25 µm wide, proximally projecting into ampulla, canal 5–8 µm wide, slightly widening proximally. Ampulla 100–130 µm long, c. 50 µm wide ( Fig. 3 View FIGURE 3 ). Spermathecae with 2–4 (usually 2) diverticula each. Diverticula of irregular shape, usually ear-shaped, sometimes longer than wide and variously bent, some bifurcating. Small diverticula-like protrusions often present. Diverticula not subdivided into different chambers. Max. length of diverticula c. 140 µm, max. width c. 45 µm. Lumen of all diverticula and distal part of ampulla forming a common sperm-containing chamber. Ampullae open separately into oesophagus in V. 1 to 3 mature eggs at time.

Remarks. Since the number of spermathecal diverticula varies in this species, and it has more than 2 but not more than 5 chaetae in ventral preclitellar bundles, it belongs either to the group “E” or to the group “G” as established by Schmelz (2003). Among these groups, many species possess subneural glands, but the majority combines this character with the presence of spermathecal ectal glands. Only two species without any spermathecal glands are F. hegemon ( Vejdovský, 1878) (partim., see: Rota 2001) and F. baskini Černosvitov, 1937 . F. hegemon is an exceptionally large (c. 35 mm long) Fridericia species, with 20–50 spermathecal diverticula and 5–6 subneural glands. Mysterious F. baskini , which is known only from the original description from Kharkiv, Ukraine [ Baskin, 1929, as F.connata , for further details see Schmelz (2003)], is probably morphologically most close to F.korobushkini sp. nov. However, it clearly differs from F. korobushkini sp. nov. by the fusion of the spermathecal ampullae and chylus cells in the preclitellar regions.

The analysis of the mitochondrial COI gene and the nuclear H3 gene reveals that F. korobushkini sp. nov. is genetically distinct from other species included in the analysis. The monophyletic nature of the clade formed by F. korobushkini sp. nov. specimens is demonstrated in gene trees constructed based on COI sequences and H3 sequences ( Fig. 4a, b View FIGURE 4 ). At the same time, node support connecting F. korobushkini sp. nov. with other species is extremely low. Additionally, a significant K2P P-distance separating F. korobushkini sp. nov. from other Fridericia species ( Table 2 View TABLE 2 ), corresponding to the species-level differentiation in Enchytraeidae , which, according to previously published data, ranges from 3 to 23.2 % for the cytochrome oxidase COI gene and from 0 to 3.5 % for the histone H3 gene in closely related species of Enhytraeidae ( Erséus et al. 2019; Martinsson & Erséus 2018; Vivien et al. 2017). Branch support expressed in bootstrap indices does not allow us to identify the closest relatives of F. korobushkini sp. nov. based on its position in the gene trees, but considering the P-distances separating species of Enchytraeidae ( Table 2 View TABLE 2 ), Fridericia loretensis Schmelz, 2023 and F. bargaglii Rota, 2015 appear to be closest, based on COI and H3 gene analysis, respectively. Both of them are easily distinguished from F. korobushkini sp. nov.: F. loretensis lacks spermathecal diverticulae and subneural glands, F. bargaglii is a large species with maximum of 7 chaetae per bundle, which also possesses extra lobes of pharyngeal glands ventrally in VII and spermathecal diverticulae with ciliated subchamber.

F. korobushkini sp. nov. was previously listed in ( Degtyarev et al. 2024) as “ Fridericia sp. 1 ”.