Paramononchus orientalis Gagarin & Naumova, 2012, sp. n.

Paramononchus orientalis sp. n.

(Fig. 1, Table 1)

Type material. Holotype male, slide reference number 100/44, deposited in the collection of the Institute of Ecology and Evolution, Center for Parasitology, Russian Academy of Sciences (Moscow, Russia).

Paratypes. One male and two females deposited in the collection of the Institute of Ecology and Evolution, Center for Parasitology, Russian Academy of Sciences (Moscow, Russia); nine males and four females deposited in the collection of the Limnological Institute, Siberian Branch of the Russian Academy of Sciences (Irkutsk, Russia).

Measurements. Table 1.

Type locality. Bay Bolshie Koty, opposite Dva Brata (Two Brothers) rock, Lake Baikal, Siberia, Russia, sand, depth 3– 4 m. Collected on 10 June 2008.

Etymology. The specific epithet means “oriental”, “from Orient”.

Description. Male. Body long and thin. Cuticle smooth, 4–5 µm thick at mid-body. Lips well developed, angular. Labial region offset from the adjacent body. Labial and cephalic papillae conical, protruding. Cheilostom small. Buccal cavity large and comparatively narrow. Its length 2.1–2.2 times is more than its width. Stoma walls strongly cuticularized. Stoma 1.5–1.8 times as long as labial region diameter. Large dorsal tooth located in anterior portion of buccal cavity, its apex situated at 87–92% from base of buccal cavity. Opposite dorsal tooth two longitudinal ridges are present, with 2–3 small denticles at the base. A transverse rib extends from ventral wall of cavity to level of dorsal tooth apex. Amphidial fovea located at the level of anterior portion of buccal cavity. Pharynx slender, muscular, comparatively long, slightly swollen proximally. Pharynx-intestinal junction nontuberculate. Reproductive system diorchic, testes opposed. Anterior testis straight, on the right of the intestine; posterior testis reflexed, on the right of the intestine. Spicules long, thin, ventrally curved and 2.8–3.3 times as long as cloacal body width as measured along the curved median line. Gubernaculum stick-shaped and its apical end bifurcated. In front of cloaca are situated 21–24 regularly spaced ventromedian supplements in the form of short tubes. Tail slender, elongate-conical, curved ventrally. One subterminal, 5 pairs of subventral and 4–5 pairs of subdorsal papillae located at tail. Caudal glands and spinneret well developed.

Т ABLE 1. Morphometrics of Paramononchus orientalis sp. n. (all measurements are given in µm unless otherwise stated,

except for the rations a, b, c, c’, V, r.an., st.l.l.r., spic.cl., n.sup.)

Female. General morphology is similar to that of males in structure of cuticle and anterior body end. Cuticle smooth. Buccal cavity large, its length 2.1–2.2 times is more than its width. Large dorsal tooth in anterior body portion. Opposite dorsal tooth two longitudinal ridges are present, with 2–3 small denticles at the base. Amphidial fovea located at the base of labial region, at the level of anterior portion of buccal cavity. Pharynx slender, muscular, comparatively long, slightly swollen proximally. Rectum 0.8–1.1 times as long as anal body diameter. Reproductive system didelphic, amphidelphic. Ovaries reflexed, its tops generally not reaching the uterus-oviduct junction. Anterior ovary on right side and posterior ovary on left side of intestine. Terminal zone of oogonia arranged in one or two rows; growth zone with a single row of gradually enlarging oocytes. Vagina with slightly muscular walls, occupying 40–45% of corresponding body width. Uterus spacious, filled with small rounded spermatozoa and containing 1– 2 eggs measuring 140–155 x 80 –87 µm. Vulva a transverse slit, situated slightly posterior to mid-body. Vulvar lips unsclerotized, not protruding outside the body contour. Tail elongate-conical, slightly curved ventrally. Tail terminus slightly swollen. Caudal papillae absent. Caudal glands and spinneret present.

Diagnosis. Body 3081–3778 µm long in males, 3126–3663 µm long in females. Cuticle smooth. Labial and cephalic sensillae in the shape of papillae. Buccal cavity large, 64–68 µm long and 30–32 µm wide. Dorsal tooth large, its apex situated at 87–92 % from base of buccal cavity. Opposite dorsal tooth two longitudinal ridges are present with 2–3 small denticles at the base. Transversally rib extended from ventral wall of cavity to level of dorsal tooth apex. Stoma 1.5–1.9 times as long as labial region diameter. Pharynx muscular, comparatively long. Pharynx-intestinal junction non-tuberculate. Vulva a transverse slit, situated slightly posterior to mid-body. Uterus spacious, containing one to two eggs measuring 140–155 x 80 –87 µm. Spicules 208–238 µm long, thin, curved ventrally. Gubernaculum stick-shaped and it is apical end bifurcated. Precloacal supplements 21–24 in number, regularly spaced. Tail slender, elongate-conical, curved ventrally.

Differential diagnosis. Paramononchus orientalis sp. n. is similar to P. arcticus Mulvey, 1978, but differs from it in the shorter body (L = 3.08–3.78 mm vs L = 3.5–4.0 mm in P. arcticus), longer buccal cavity (64– 68 x 30–32 µm vs 44– 48 x 19–21 µm in P. a rc t i c u s), larger eggs (140–155 x 80 –87 µm vs 105–110 x 60 –80 µm in P. arcticus), less slender tail in females (c’ = 4.2–5.0 vs c’ = 5.7–6.5), longer spicules (208–238 µm long vs 70 µm long in P. arcticus), and another shape of gubernaculum (Mulvey, 1978; Gagarin & Gusakov, 2008).

A key for the identification of valid species of the genus Paramononchus is given below.