Achaeta brevivasa Graefe, 1980

Chen, Juanjuan, Schmelz, Rüdiger M., Zhang, Zuxu & Xie, Zhicai, 2022, The enchytraeid fauna (Enchytraeidae: Clitellata) of the Fanjing Mountain National Nature Reserve (China) with description of two new species, Journal of Natural History 56, pp. 1957-1996 : 1973-1975

Achaeta brevivasa Graefe, 1980

( Figures 9 , 10 )

Achaeta brevivasa Graefe, 1980 . Wang et al. 1999; Schmelz and Collado 2010.

Material investigated

GZO202007004–GZO202007005, stained and whole-mounted, two mature specimens from site H. CJJ 92– CJJ 94, three mature specimens from site 1, whole worm used for DNA extraction, preserved as total DNA.

Further material investigated

Two mature specimens from site H, two mature specimens from site I, one mature specimen from site A, two mature specimens from site 3, one mature specimen from site 8, one mature specimen from site 11: nine specimens in total, preserved in 75% ethanol.

Description

Small worm, 3.5–3.8 mm long, 0.15–0.18 mm wide at VII and 0.17–0.2 mm wide at clitellum. Number of segments (18) 20–26. Chaeta absent. Head pore on the tip of prostomium ( Figure 9a ). Body wall thin, thickness 8–15 mm, cuticle 1–2 mm (in vivo). No pyriform glands. Six lentiform epidermal gland cells per segment ( Figure 10e ). Clitellum saddled-shaped, hyalocytes in 6 baguette-like longitudinal rows in dorsal, conspicuous and depressed into the coelom, rectangle and closely packed, ca. 30–32 μm long and 9– 14 μm high, granulocytes inserted more or less regularly; granulocytes in dense transverse rows laterally, rectangle, ca. 20 μm long and 11 μm high ( Figures 9a , 10h ).

Brain slightly convex posteriorly, ca. 1.5–2× as long as wide (154 μm long and 91 μm wide, in vivo) ( Figures 9a, b , 10a ). All three pairs of pharyngeal glands untied dorsally in IV/V–VI/VII, with ventral extension in V–VI, one pair of secondary pharyngeal gland lobes in VI ( Figures 9a , 10b, c ). One pair of spongy oesophageal appendages in V, small and inconspicuous (diameter ca. 30 μm, in vivo) ( Figures 9a , 10b ). Dorsal vessel originating from VII, blood colourless. Intestinal diverticula absent. Gut widening gradually in VII ( Figures 9a , 10f ). Chloragocytes yellowish-brown, sparse in IV–VII and dense from VII on. Nephridia two pairs in preclitellar segments, at 6/7 and 7/8 ( Figures 9a , 10d ). Nephridia constricted by septa, anteseptale with funnel and parts of nephridial body, ca. 39 μm long and 26 μm wide (in vivo); postseptale ca. 44 μm long and 27 μm wide (in vivo), with a ventral bump in mid-section, tapering gradually into efferent duct. Coelomocytes abundant and round, pale, ca. 9–13 μm in diameter.

Seminal vesicle absent. Sperm funnel small, barrel-shaped, ca. 35–38 μm long, collar narrower than funnel body, 18–20 μm wide in collar and 21–27 μm wide in funnel body (in vivo) ( Figures 9c , 10i ). Spermatozoa short, 23–26 μm long, heads 10–13 μm long (in vivo) ( Figures 9c , 10i ). Sperm duct in coils, diameter ca. 4–4.5 μm (in vivo). Male copulatory organs small and inconspicuous. Spermathecae small, free, confined to V; ectal pores lateral at 4/5, without ectal glands; ectal ducts short, ca. 40 μm long and 11 μm wide (in vivo), the duct widening into narrow dilations of ampullar, ca. 25 μm long and 17 μm wide (in vivo) ( Figures 9a , 10g ). Only one mature egg ( Figure 10h ) at a time, with yellowishbrown granules, occupying 2–3 segments ( Figure 9a ).

Remarks

The morphological characters of our specimens correspond well with the original description ( Graefe 1980); however, coelomocytes were without attached filaments in the redescription by Wang et al. (1999) based on specimens collected from Hunan Province and Hubei Province. This species has also been found in the Jilin, Gansu and Guizhou Provinces of China ( Wang et al. 1999; J.J. Chen, unpublished data).

Molecular results show that our specimens differ from Achaeta cf. brevivasa collected in Sweden ( Erséus et al. 2010). Clear genetic gaps were observed between the two groups of specimens, with high interspecific distances (up to 18.7%) and low intraspecific distances (0%) based on the K2P distances of COI sequences. Achaeta brevivasa is a widespread morpho-species; it is probably a group of genetic species instead of only one, and the molecular differences are probably caused by weak dispersal capacity and long geographical distance.

Figures

Figure 9. Achaetae brevivasa Graefe, 1980. a) Anterior 13 segments, dorsal view. b) Brain. c) Sperm funnel. Scale bars: 50 µm. Abbreviations: br, brain; ct, clitellum; dp, dorsal pore; ne, nephridium; oa, oesophageal appendage; sf, sperm funnel; st, spermatheca.

Figure 10. Micrographs of Achaetae brevivasa, 1980. a–g and i in vivo; h fixed. Scale bars: 50 µm. a) Brain. b) Pharyngeal glands and oesophageal appendage, dorsal view. c) Pharyngeal glands, lateral view. d) Nephridia at 6/7–7/8. e) Lentiform epidermal glands. f) Gut widening in VII. g) Spermatheca. h) Clitellum, lateral view. i) Sperm funnel. Abbreviations: am, ampulla; dl, dorsal lobes; ed, ectal duct; le, lentiform epidermal gland; ne, nephridia; oa, oesphageal appendage; sl, secondary pharyngeal gland lobe; sf, sperm funnel; ve, ventral extension.