Pristina multiseta, Ohtaka, 2022

Ohtaka, Akifumi, 2022, Pristina multiseta sp. nov. (Annelida: Clitellata: Oligochaeta: Naididae: Pristininae) from Paddy Fields in Japan, Species Diversity 27 (1), pp. 95-100 : 95-98

Pristina multiseta sp. nov.

( Figs 1–4 )

Material examined. Holotype. NSMT-An 1876, a sexually mature specimen whole-mounted on slide, 15 July 2007, coll. A. Ohtaka.

Type locality. Paddy field in Nagayama, Shizukuishi Town, Iwate Prefecture, Japan (39.7469°N, 140.9644°E) .

Paratypes. NSMT-An 1877, a whole-mounted mature specimen; NSMT-An 1878, a sagittally-sectioned mature specimen; locality, date and collector the same as for the holotype.

Other material examined. 12 sexually mature and one immature specimens mounted on slides and three mature, sagittally-sectioned specimens; locality, date and collector the same as for the holotype. Three mature and two immature specimens from a paddy field in Hata, Takashima City, Shiga Prefecture, Japan (35.2923°N, 135.9339°E), 24 July 2015, coll . M . J. Grygier.

Etymology. The specific name refers to high number of dorsal chaetae in the present species.

Diagnosis. Body length of single zooid 1.5–3.0 mm in fixed state. Prostomium forming a short proboscis. Dorsal chaetal bundles with 3–5 smooth hairs and 2–5 shortly bifid needles in anterior segments. Ventral chaetae in IV through VII enlarged. No modified genital chaetae. Stomach widening in anterior half of VIII, lined with column-shaped and glandular epithelium embedded in a blood plexus. Male duct with short vas deferens and tubular atrium, opening ventrolaterally in VIII. Blood vessels surrounding ectal half of atrium. Spermatheca with large ampulla and short and conical duct, opening on the chaetal line behind 6/7.

Description. In fixed state, body length 1.5–3.0 mm, width 0.15–0.25 mm at clitellum and 0.13–0.17 mm at middle of body, 25–34 segments. No budding zone observed. No eyes. Prostomium forming a short proboscis ( Fig. 1A–D ): length 24–61 µm, diameter 10–16 µm, shorter than frontal width of segment I. Segments II to VI biannulate ( Fig. 1A ), each with short anterior and long, chaetaebearing posterior annuli. Genital segments longer than nongenital ones. Clitellum conspicuous, from 2/3 VII to end of IX; ventral side of body in VIII–IX indented longitudinally and slightly swollen at male pores laterally in VIII ( Fig. 1A ). Body wall 3–6 µm thick except for clitellum which has up to 10 µm high glandular epidermis. Coelomocytes scattered throughout the segments, spherical, 4–5 µm in diameter. Pharynx in II and III, dorsal wall up to 7 µm thick, slightly thicker than ventral wall ( Fig. 1E ). Pharyngo-esophageal glands developed dorsally in II–IV, each 12–15 µm high ( Fig. 1E ). Esophagus in IV through VII, 15–24µm wide with wall 4–6 µm thick. Esophagus widening and forming stomach in anterior half of VIII. Stomach gradually ( Fig. 1E ) or abruptly widening ( Fig. 4A ), up to 80–96 µm wide and lined with glandular and column-shaped inner epithelium, 20–25µm tall and 3–5 µm wide ( Fig. 1F ). Blood vessels developed on stomach, penetrating epithelium between the individual cells of the stomach. From IX on gut 70–100 µm wide with thin (5–8µm thick) wall. Chloragocytes beginning in V with single cells of less than 8 µm high, covering the alimentary canal. Transverse vessels forming loops in IV–VI ( Fig. 1E ).

Dorsal chaetal bundles ( Fig. 2A ) consisting of hair and needle chaetae, both beginning in II. Hair chaetae smooth under examination with 1000× using oil immersion lens, 3–5 per bundle, 106–200 µm long in preclitellar segments; 1–3 per bundle, 64–170 µm long in postclitellar ones. Dorsal needle chaetae bayonet-shaped, with inconspicuous nodulus, weakly bent at 1/4 from the distal end ( Fig. 2B ), 2–5 per bundle, 35–50 µm long in preclitellar segments; 1–2 per bundle, 30–45 µm long in postclitellar ones. Distal ends of dorsal needle chaetae shortly bifid and slightly divergent; length of teeth almost as long as chaetal width. Upper teeth of dorsal needle chaetae as long as or a little longer and as thick as or a little thinner than weakly bent lower teeth ( Fig. 2C, D ). No intermediate teeth on dorsal needle chaetae. Ventral chaetae all bifid crotchets with slightly distal nodulus ( Fig. 2E–K ). In sexually mature worms, those in II and III smaller than those in the following segments, 3–6 per bundle, 48–56 µm long, upper tooth slightly longer and almost as thick as lower one ( Fig. 2E, F ); those in IV–VII longer and thicker than those in the rest of segments ( Fig. 2G–J ), 2–5 per bundle, 60–70 µm long, 2.0–2.5 µm thick, distal teeth longer and almost as thick as lower ones; ventral chaetae in IV and VII longer and thicker than those in V and VI, with distal teeth 1.5 to 2 times longer than lower teeth; ventral chaeta from VIII on 2–5 per bundle, 48–55 µm long, upper teeth as long as or a little longer and slightly thinner than lower ones ( Fig. 2K ). No modified genital chaetae at genital pores. No chaetophorous or associated glands in any ventral chaetal bundles. In immature worms, ventral chaetae in anterior segments 2–5 per bundle, 40–49 µm long, not especially longer or thicker in IV–VII; upper tooth almost as long as or a little longer and and almost as thick as lower.

Gonads and copulatory organs paired. Testes in VII, ovaries in VIII. Male funnels on anterior face of 7/8, 30–40 µm in diameter ( Figs 3 , 4B ). Vasa deferentia about 45 µm long, 6–8 µm thick, not winding, covered with glandular, 8–10 µm high, prostate cells, connected with atria apically ( Fig. 3 ). Atria tubular, 50–64 µm long, 20–25 µm wide, with thick and glandular inner epithelium and thin muscular cover ( Figs 3 , 4B ). Several thin blood vessels 1.5–2.2 µm in diameter surrounding ectal half of atria ( Figs 3 , 4C ); it is unclear that they are arranged spirally or several circles separate from each other. Ejaculatory ducts not detected and male pores opening on papillae ventrolaterally in anterior part of VIII. Spermathecae in VII ( Fig. 3 ); spermathecal ampullae large and ovoid, 64–128 µm long, 58–96 µm wide, with thin wall; spermathecal ducts well-distinguished from ampullae, short and conical, 16–18 µm long, 14–18 µm wide at junction with ampullae, opening on the chaetal line slightly behind anterior septa ( Fig. 3 ). Loose sperm present in spermathecal ampullae. Sperm sac in VII–VIII. Egg sac in VIII–X.

Variations. Length of proboscis varied from one forth to almost equal to frontal width in segment I ( Fig. 1A–D ). All sexually mature specimens examined (n=15) had enlarged ventral chaetae in IV through VII, and those in IV and VII were invariably larger than those in V and VI. The enlargement of ventral chaetae in V and/or VI varied from slightly larger than in II and III to nearly as large as in IV or VII. All sexually immature specimens examined had ventral chaetae of normal size, not larger than the rest.

Distribution and habitat. The new species was collected from bottom surfaces of two inundated paddy fields in north and central parts of Japan, with water depth of both localities less than 10 cm. At the type locality in Iwate Prefecture, north Japan, three tubificines, Aulodrilus limnobius Bretscher, 1899 , A. pigueti Kowalewski, 1914 , Limnodrilus hoffmeisteri Claparède, 1862 , and two naidines, Nais pardalis Piguet, 1906 and Slavina appendiculata (d’Udekem, 1855) , were found together with the present species.

Figures

Fig. 1. Pristina multiseta sp. nov. from Shizukuishi Town, Iwate Prefecture, Japan. A, Lateral view of anterior segments (holotype); B–D, variation of prostomiums; E, sagittal section of anterior segments; F, longitudinal section of gut in VIII, left side anterior.

Fig. 2. Chaetae of Pristina multiseta sp. nov. from Shizukuishi Town, Iwate Prefecture, Japan. A, Proximal part of a dorsal chaetal bundle in an alimentary segment; B, dorsal chaeta in an anterior segment; C and D, distal ends of dorsal chaetae; E, ventral chaeta in II; F, the same in III; G, the same in IV; H, the same in V; I, the same in VI; J, the same in VII; K, the same in XX. All are based on mature specimens.

Fig. 3. Parasagittal section of genital segments of Pristina multiseta sp. nov. from Shizukuishi Town, Iwate Prefecture, Japan.

Fig. 4. Pristina multiseta sp. nov. from Shizukuishi Town, Iwate Prefecture, Japan. A, Horizontal section in VI–VIII, showing stomach in VIII; B, sagittal section of male duct; C, sagittal section of atrium, showing spiral vessels (arrows) surrounding the ectal part of atrium.