Haber subnivalis, Ohtaka, 2024

Ohtaka, Akifumi, 2024, Three new tubificine species (Annelida: Clitellata: Naididae) from Japan, Zootaxa 5529 (1), pp. 186-200 : 190-193

Haber subnivalis sp. nov.

( Figures 4–7 )

Holotype. NSMT-An 1926 , a whole-mounted mature specimen, 3 April 2005, coll. A. Ohtaka. Posterior segments missing .

Type locality. Fallow field in Sakamoto , Hirosaki City, Aomori Prefecture, Japan (40.5464°N, 140.4375°E), from bottom layer of watery snow.

Paratypes. NSMT-An 1927 , a whole-mounted intact mature specimen and NSMT-An 1928 , a sagittally sectioned mature specimen; locality, date and collector the same as for the holotype .

Other material examined. One whole-mounted mature and four immature specimens; locality, date and collector the same as for the holotype . One whole-mounted immature specimen from the type locality, 16 April 2005, coll. A. Ohtaka . All specimens incomplete posteriorly.

Etymology. The specific name refers to the habitat, under the snow from which specimens were collected at the type locality.

Diagnosis. Body slender, 21 mm long in preserved state. Body surface smooth. Dorsal chaetal bundles with long and hispid hairs and pectinate chaetae. Ventral somatic chaetae bifid with upper teeth longer than lower. Spermathecal chaetae in X and penial chaetae in XI; both single per bundle, with two elongate teeth forming a hollow end distally. Vasa deferentia long and uniform in width, winding in XI and XII. Atria tubular with stalked solid prostate glands medially. Penes conical, set in deep penial chambers and opening ventrally in XI. No strong basal membranes around penes.

Description. Live worms reddish anteriorly ( Fig. 4C ), pinkish posteriorly. In preserved state of an intact worm with 126 segments, body length 21.0 mm, width 0.20–0.32 mm in anterior segments, 0.15 mm in mid-segments. Body surface smooth. Body slender ( Fig. 4A ), segments stretched from XI on, longer than wide. Segments II to V biannulate, each with short anterior and long, chaetae-bearing posterior annuli; annulation becoming inconspicuous from VI on, here each segment with several narrow transverse fullows. Prostomium rounded conical, almost as long as basal diameter.

Epidermis 8–15 µm thick in anterior segments, 5–8 µm in middle and posterior segments, 10–20 µm thick in clitellum. Pharynx in II and III, dorsal wall up to 60 µm thick, thicker than ventral wall (40 µm thick) ( Fig. 4B ). Pharyngeal glands developed dorsally in II–V ( Fig. 4B, C ), each pear-shaped and 32–45 µm in height. Wall of gut 13–28 μm thick, without stomachal dilatation. Chloragogen cells 15–30 µm high covering gut from beginning of VI backwards. Transverse vessels forming complicated loops in prostomium to V ( Fig. 4 C , tv). Nephridia from VII on. Coelomocytes sparsely present throughout the segments, spherical, 10–20 µm in diameter.

Dorsal chaetal bundles consisting of hair and pectinate chaetae throughout the segments from II ( Fig. 5A ). Hair chaetae distinctly hispid ( Fig. 5B ). In preclitellar segments 2–3 long and 0–2 short hair chaetae per bundle, long hairs up to 1,200 µm long, 1.9–2.5 µm wide proximally; hair chaetae in postclitellar segments 0–2 per bundle, up to 600 µm long. Dorsal pectinate chaetae sigmoid in shape, with nodulus at 1/4 from the distal end ( Fig. 5C ), 1–3 per bundle, 80–92 µm long in preclitellar segments; 0–1 per bundle, 70–83 µm long in postclitellar ones. Upper teeth of dorsal pectinate chaetae slightly longer and slightly thicker than lower teeth, and 2–4 distinct intermediate teeth present between upper and lower tooth ( Fig. 5D ). Ventral somatic chaetae bifid crotchets with nodulus at 1/3–1/4 from the distal end ( Fig. 5E, F ); 1–4 per bundle, 80–96 µm long in preclitellar segments, and 1–2 per bundle, 64–90 µm long in postclitellar segments. Upper teeth of ventral chaetae 1.5–2.0 times longer and slightly thinner than lower teeth. In mature worms, ventral chaetae in X modified into single, 90–100 μm long spermathecal chaeta with two elongate teeth forming a hollow end distally ( Fig. 5G ); those in XI modified into 90–100 μm long penial chaeta ( Fig. 5H ), resembling spermathecal chaeta.

Clitellum from X to XII, inconspicuous, slightly thickened and glandular. Gonads and copulatory organs paired ( Fig. 6 ). Testes in X, ovaries in XI. Male funnels on 10/11, large, 140 μm in diameter. Vasa deferentia at least 2,500 μm long, winding in XI and XII; width not different between ental and ectal parts ( Fig. 7A, B ), 20–25 μm wide and the wall 8–10 μm thick. Vasa deferentia connected with atria apically. Atria tubular, about 100 μm long, 30–40 μm thick, inner epithelium 10–15 μm high and glandular. Prostate glands solid, 100 μm wide, connected at middle part of atria through short stalks. Ejaculatory ducts short. Penes conical, 40 μm long, set in deep penial chambers opening in ventral chaetal line posteriorly in XI ( Fig. 7C ). No thick basal membrane around the penis, no penial sheath. Penial chaetophore located at posterior side of penial chamber, consisting of a layer of glandular cells surrounding single penial chaeta and thin muscular covering, opening in posterior wall of the penial chamber ( Fig. 7C , cp). Accessory glands formed by a mass of glandular cap cells attached to the chaetophore near the apex. Spermathecae in X ( Fig. 6 ). Spermathecal ampullae pear shaped, 175 μm long, 120 μm wide. Spermathecal ducts not well-marked off from ampullae,180 μm long, 50 μm wide entally and 20 μm wide ectally, opening on the chaetal line at middle part of X. Specimens without sperm in the spermathecal ampullae. Single spermathecal chaeta located in front of spermathecal pore ( Fig. 6 , stc; 7D, arrow), enclosed by chaetophore with glandular cap cells. Sperm sac in X–XIV. Eggs observed only in the ovarian segment.

Distribution and habitat. Specimens of the present species were collected in northern Japan as a part of intranivean and subnivean fauna in the snowmelt season ( Ohtaka et al. 2008; Ohtaka 2012), and they correspond to “ Tubificinae sp.” of Ohtaka (2012). Specimens were found in the bottom layer of the snow, which contained large amounts of water. On 3 Apr. 2005 when the majority of the specimens examined here were collected, snow depth at the locality was 95 cm, temperature of the habitat, the inundated bottom layer of the snow was 0.1–0.3°C, and the pH of the water was 6.2–6.5 ( Ohtaka 2012). Other oligochaetes, Nais communis Piguet, 1906 and Rhyacodrilus coccineus (Vejdovský, 1876) were collected in the habitat.

Remarks. The smooth body wall, modified spermathecal and penial chaetae of similar shape, and the long vasa deferentia entering the tubular atria apically fit the definition of the genus Haber as given by Holmquist (1978) and later, emended, by Milligan (1986). The genus Haber is holarctic, and 10 valid species have been known worldwide to date ( Martin et al. 2016; Dumnicka & Wojtal 2021). Among the congeners, Haber subnivalis sp. nov. resembles Haber vetus ( Semernoy, 1982) from Lake Baikal in having long and hispid hairs, dorsal pectinate chaetae with slightly longer upper tooth and 2–4 distinct intermediate teeth in anterior bundles ( Semernoy 1982 under the name of Tubifex specious vetus Semernoy, 1982 ). However, in H. subnivalis sp. nov., hair and pectinate chaetae are present also in posterior segments, while postclitellar dorsal bundles of H. vetus each consist of a single bifid chaeta only ( Semernoy 1982; Timm & Martin 2019). Although Haber subnivalis sp. nov. is devoid of a spermathecal ental process as described in Haber vetus , this may be due to the unmated condition of the specimens. Hispid hairs are also encountered in Holarctic H. speciosus (Hrabě, 1931) and H. hubsugulensis (Semernoy in Semernoy & Tomilov, 1972) from Lake Hubsugul and Lake Baikal ( Semernoy 2004). However hair chaetae of these two species are distinctly shorter than those in H. subnivalis sp. nov. In addition, armored body surface with transverse rows of glandular epidermis, encrusted with foreign particles in H. speciosus ( Timm & Martin 2019) is absent in H. subnivalis sp. nov., upper teeth are shorter than lower in anterior ventral chaetae in H. hubsugulensis , while upper teeth of ventral chaetae are 1.5–2.0 times longer than lower in H. subnivalis sp. nov..

Hraber species generally have a thickened basal membrane resembling a penis sheath lining the internal canal of the penis ( Holmquist 1978; Milligan 1986). However, no such structure was found in any specimen of H. subnivalis sp. nov. In this respect, H. subnivalis sp. nov. could be unique in the genus, but it is also probable that a thickened basal membrane had not yet developed, because all available specimens were unmated and with slightly thickened and less glandular clitellum, suggesting incomplete maturity. Further examination on mated specimens are needed to determine the detailed structure of penial apparatus.

Figures

FIGURE 4. Haber subnivalis sp. nov. from Hirosaki, Aomori Prefecture, Japan. A. Whole body of an immature specimen. B. Parasagittal section of anterior segments. C. Dorso-lateral view of a living specimen, showing vascular and digestive systems.

FIGURE 5. Chaetae of Haber subnivalis sp. nov. from Hirosaki, Aomori Prefecture, Japan. A. Dorsal chaetal bundle in an anterior segment. B. Part of a dorsal hair chaeta in an anterior segment. C. Dorsal pectinate chaeta in IV. D. The same, distal end E. Ventral chaeta in VI. F. Ventral chaeta in a posterior segment. G. Spermathecal chaeta in X. H. Penial chaeta in XI.

FIGURE 6. Arrangement of reproductive organs in Haber subnivalis sp. nov. from Hirosaki, Aomori Prefecture, Japan.

FIGURE 7. Sections of several reproductive organs in Haber subnivalis sp. nov. from Hirosaki, Aomori Prefecture, Japan. A. Ental part of vas deferens. B. Ectal part of vas deferens. C. Sagittal section of penial chamber in XI, showing penis and chaetophore. D. Sagittal section of spermatheca in X, showing opening of chaetophore with arrow.