Micoletzkyia nakanoi, Shimada & Kakui, 2019

Shimada, Daisuke & Kakui, Keiichi, 2019, Two new and one known species of Phanodermatidae (Nematoda: Enoplida) from Sagami Bay, Japan, Zootaxa 4608 (3), pp. 484-500 : 489-492

Micoletzkyia nakanoi sp. nov.

Figures 3–4 , Table 1 .

Material examined. Holotype. Adult male, ICHUM 5778 , DESS-fixed, whole mount, off Jogashima , Japan (Station 2: 35°06.832′N, 139°33.496′E to 35°06.587′N, 139°33.408′E, depth 404–465 m), Sagami Bay, North Pacific Ocean, biological dredge, February 15, 2017, by KK . Paratype. Adult female, ICHUM 5779 , same data as for holotype .

Diagnosis. Micoletzkyia nakanoi sp. nov. is characterized by medium body length (approximately 6 mm in both sexes), large body diameter to body length ratio (a = 30 in male and 36 in female), outer labial and cephalic setae shorter than cephalic diameter, absence of a circle of cervical setae, typical tail length for the genus (approximately 4 anal body diameters in male and 5 anal body diameters in female), long spicules (480 μm, 5.8 anal body diameters or 8% of body length), cylindrical gubernaculum without apophysis or any other complex structure, and presence of a precloacal supplement shorter than gubernaculum without proximal head.

Etymology. The specific name nakanoi is a noun in the genitive case, derived from the name Dr. Hiroaki Nakano (Shimoda Marine Research Center, University of Tsukuba), who was one of the organizers of the 12th JAMBIO Coastal Organism Joint Survey.

Description. Body cylindrical, tapering toward both ends. Body cuticle smooth, ca. 10 μm thick. Somatic setae sparse. Numerous large (diameter 40–80 μm) gland cells surrounding overall intestine. Head rounded, width 0.1 maximum body diameters, clearly set off from cervical region by a constriction just posterior to cephalic setae (0.75 cephalic diameters from anterior body end). Type I pharyngo-cephalic complex: pharyngeal capsule poorly developed, without anterior outgrowths; cephalic capsule not observed. Cephalic cuticle 4–5 μm thick. Six inner labial sensilla papilliform. Six outer labial setae (length 12–15 μm or 0.6–0.8 cephalic diameters) and four cephalic setae (length 9–12 μm or 0.5–0.6 cephalic diameters) in separate circles. Amphids pocket-like: aperture transversely elliptical, width 7–9 μm or 0.4–0.5 cephalic diameters, located just posterior to cephalic setae (0.5–0.6 cephalic diameters from anterior body end); fovea 10–12 μm deep from anterior edge. Buccal cavity small cup-shaped, length and width 4–5 μm, without teeth. Excretory pore located at 25% of pharynx length from anterior body end. Nerve ring located at 47% of pharynx length. Ventral gland single, situated at level of posterior end of pharynx, width 0.3 corresponding body diameters in male but inconspicuous in female. Longitudinal rows of cervical setae present. Tail long (4.2 anal body diameters in male and 5.3 anal body diameters in female), conico-cylindrical in shape (conical part 1/3 of tail length), filiform in cylindrical part, acute at tip with small spinneret. Caudal setae sparse. Three small caudal glands situated in cloacal or anal regions.

Male. Reproductive system diorchic. Testes opposed and outstretched, both located on left side of intestine. Anterior testis beginning at 40% of body length from anterior body end; posterior testis ending at 55% of body length. Vas deferens well-developed. Spicules long (5.8 anal body diameters, 1.4 times tail length or 8% of body length), gradually curved, slightly expanded at proximal end, distally waving, acute at distal end. Gubernaculum cylindrical in shape, slightly expanded at distal end, without complex structure or apophysis, 0.65 anal body diameters or 11% of spicule length, situated at dorsal side of spicules. Precloacal supplement tubular, slightly expanded at distal end, located at 2.6 anal body diameters anterior to cloaca.

Female. Reproductive system didelphic. Ovaries opposed and reflexed, both located on left side of intestine. Anterior ovary beginning at 38% of body length from anterior body end; posterior ovary ending at 63% of body length. Uteri 11% of body length. An elongated egg (length 300 μm and width 100 μm) in anterior uterus. Vulva situated just posterior to center of body.

Remarks. The genus Micoletzkyia contains 16 nominal species, of which 12 are valid (see above species list). Micoletzkyia anomala , M. austrogeorgiae , and M. falklandiae should be treated as species inquirendae ( Huang & Cheng 2011), because they were established only based on female ( M. anomala ) or immature ( M. austrogeorgiae and M. falklandiae ) specimens. Although Mawson (1958) redescribed M. austrogeorgiae based on an adult female, it is uncertain whether both individuals really belong to the same species owing to Allgén’s (1954b) brief description. Platycomopsis effilata was transferred to Micoletzkyia by Chen (2015), however, determining whether this species really belongs to Micoletzkyia is not possible because the description by Schuurmans Stekhoven (1946) lacked detail and was based only on a female.

Micoletzkyia nakanoi sp. nov. closely resembles M. parelegans and M. sedata with respect to the simple, cylindrical or plate-like gubernaculum lacking any accessory structures. However, M. nakanoi sp. nov. differs from M. parelegans in the standard tail proportion (4.2 anal body diameters, anterior 1/3 conical and posterior 2/3 cylindrical in M. nakanoi sp. nov. vs 1.8 anal body diameters, mostly conical, with obviously shorter cylindrical part in M. parelegans ). Micoletzkyia nakanoi sp. nov. is also distinguished from M. sedata by the absence of a circle of cervical setae located just behind the cephalic constriction (present in M. sedata ) and larger gubernaculum (length 55 μm and longer than precloacal supplement in M. nakanoi sp. nov. v s length 23 μm and shorter than supplement in M. sedata ). Micoletzkyia nakanoi sp. nov. is much shorter than M. parelegans (body length 5.8 mm in M. nakanoi sp. nov. vs 11.4 mm in M. parelegans ), but body size seems to be highly variable and may not be a good diagnostic character in this genus. According to the redescription of M. longispicula by Ürkmez & Sezgín (2016), a new specimen collected from the Mediterranean Sea in Turkey completely agreed with the holotype from the Yellow Sea in China with respect to the characters of male genital organs, including the proximal head of the precloacal supplement and the shape of the gubernaculum [photographs in Figure 2c in Huang & Cheng (2011) and Figures 2b and 3b in Ürkmez & Sezgín (2016)], despite the differences in their body sizes (12.6 mm in Turkey specimen vs 6.1 mm in holotype). If a single Micoletzkyia species is really distributed from the western Pacific to the Mediterranean Sea, it suggests the possibility of the synonymy of closely related species collected from distant localities, e.g. M. magna from France and M. mawatarii from Japan.

Micoletzkyia nakanoi sp. nov. is also distinguished from two doubtful species only known by females. This species differs from M. anomala , which is characterized by the remarkably forward position of the vulva for this genus (V = 53 in M. nakanoi sp. nov. vs V = 31–33 in M. anomala ), and from M. austrogeorgiae sensu Mawson (1958) by the proportions of the tail (5.3 anal body diameters, conical part shorter than cylindrical part in M. nakanoi sp. nov. vs 2.4 anal body diameters, conical part longer than cylindrical part in M. austrogeorgiae ).

The taxonomic key to males of Micoletzkyia follows.

Figures

FIGURE 2. Phanodermopsis kohtsukai sp. nov. Holotype male:A, head with pharyngo-cephalic complex. B, head with amphid. C, tail. D, spicule. Scale bars: A, B, 10 μm; C, 100 μm; D, 50 μm.

FIGURE 3. Micoletzkyia nakanoi sp. nov. Holotype male: A, body. B, head. C, tail. D, spicule and gubernaculum. E, precloacal supplement. Paratype female: F, body. G, tail. H, vulva. Scale bars: A, F, 1 mm; B, E, 10 μm; C, G, H, 100 μm; D, 50 μm.

FIGURE 4. Micoletzkyia nakanoi sp. nov. Holotype male: A, head with pharyngo-cephalic complex. B, head with amphid. C, tail. D, distal part of spicule and gubernaculum. E, supplement. Paratype female: F, tail. Scale bars: A, B, E, 10 μm; C, F, 100 μm; D, 20 μm.