Fridericia callosa ( Eisen, 1878 )

Chen, Juanjuan, Zhang, Junqian & Xie, Zhicai, 2025, List of species records of enchytraeids (Enchytraeidae, Clitellata, Annelida) in China, Zootaxa 5566 (1), pp. 61-96 : 69-70

Fridericia callosa ( Eisen, 1878) (T)

Neoenchytraeus callosus Eisen, 1878 .

Enchytraeus subgen. Neoenchytraeus callosus Eisen, 1879 .

Enchytraeus callosus Vejdovský 1884 .

Fridericia callosa Michaelsen 1889 ; Christensen & Dózsa-Farkas 1999; Schmelz 2003; Chen 2009.

For further synonymies see Schmelz (2003).

[non] Fridericia callosa Nielsen & Christensen 1959 ; Liang & Xie 1992.

Distribution and habitat. Russian Far East ( Degtyarev et al. 2020); Widely distributed in the Siberian Boreal and Palaearctic ( Schmelz 2003). Humus-rich soil.

Distribution in China. Zhejiang Province (?) ( Liang & Xie 1992); Liaoning and Jilin Province (Chen 2009; Lian et al. 2011).

Remarks. Schmelz (2003) revised and redescribed Fridericia callosa ( Eisen, 1878) based on the reinvestigation of syntypes and a comparison with the original description. He excluded a number of specimens from the type series and showed that F. callosa sensu Nielsen & Christensen is a different species, named F. parathalassia Schmelz, 2002 , a marine coastal species. Almost all records of F. callosa after the publication of Nielsen & Christensen (1959) used this influential monograph for the identification of their specimens, and the same can be assumed for the record of Liang & Xie (1992) from China. The brief description of their specimens (in Chinese) can be summarized as follows: Length 13–14 mm. Segment number 66. Chaetae 4 per bundle. Dorsal pore beginning at VII. Clitellum at XIII. Oesophageal appendages with few branches. Spermathecal ampulla onion-shaped, large, diameter over 100 μm; ectal duct short, a small gland at the opening. The account is too short to ascertain the identity of these specimens. The spermatheca agrees with F. parathalassia but segment number is too high (66 vs. 42–49) ( Schmelz 2003). Furthermore, according to the revised diagnosis in Schmelz (2003), F. callosa has much branched oesophageal appendages, a very long spermathecal ectal duct, and no ectal glands, which disagrees with the account in Liang & Xie (1992). Unfortunately, reference material is lost (Xie, unpublished data).

Chen (2009) redescribed F. callosa based on specimens collected from Shenyang and Jilin Province, and the information is summarized as follows: Slender worms, slow-moving. Length 9–12 mm. Dorsal pore beginning at VII. Chaetal formula 2–4 – 2: 2–4 - 2–4. Epidermal gland cells scarce. Clitellum in XII–1/2XIII, slightly thickened, cells arrangement irregular, gland cells absent ventrally. Brain ca. 125–160 μm long, ca. 50–100 μm wide; posteriorly rounded, anteriorly slightly convex, sides slightly converging. A pair of oesophageal appendages, unbranched or with 2–3 branches, branches elongate to V. Origin of dorsal blood vessel in XIII–XV, blood colourless. Five pairs of preclitellar nephridia from 6/7–10/11, medial origin of efferent duct. Chloragocytes yellowish-brown, from V.

Coelomocytes. Mucocytes with refractile vesicles, the outline of like wave, ca. 40 μm long; lenticytes small, ca. 5 μm long. Chylus cells from XI–XIII, occupying 2 segments. Seminal vesicle well-developed, extending 2 segments (XI–XII). Sperm funnel cylindrical, twice as long as wide; collar as wide as funnel body. Spermatozoa long, head ca. 200 μm long. Vas deferens long and irregular coiled in XII. Bursal slit longitudinal. Spermatheca. Ectal duct thin and long, ca. 20 μm wide; ampulla onion-shaped, ca. 120 μm in diameter; ental ducts ca. 25 μm wide, joint opening into oesophagus.

To conclude, F. callosa exists in China, and at the same time, there is an undetermined species similar to F. callosa . F. callosa is distributed in northeast China (Liaoning and Jilin Province); records from other provinces require verification.