Micoletzkyia mawatarii, Shimada & Kakui & Kajihara, 2012

Shimada, Daisuke, Kakui, Keiichi & Kajihara, Hiroshi, 2012, A New Species of Deep-sea Nematode, Micoletzkyia mawatarii sp. nov. (Nematoda: Enoplida: Phanodermatidae) from Northern Japan, Species Diversity 17 (2), pp. 221-226 : 222-225

Micoletzkyia mawatarii sp. nov. ( Figs 1–3 )

Material examined. Four males and four females. Holotype. Male ( ZIHU 4073 ), whole mount, collected on 5 August 2009 by K . Kakui. Paratypes. One male ( ZIHU 4074 ) and three females ( ZIHU 4075–4077 ), whole mounts; one male ( ZIHU 4078 ) and one female ( ZIHU 4079 ), Au-coated SEM specimens; same collection data as for holotype . One male ( ZIHU 4080 ), whole mount, collected on 2 August 2009 by K . Kakui.

Type locality and habitat. In muddy sediment, west of Musashi Bank, Sea of Japan (44°41.5′N, 139°48.3′E), depth 528 m .

Other locality and habitat. In muddy sediment, Sea of Okhotsk (44°34.6′N, 144°41.7′E), depth 1,550 m ( ZIHU 4080 ) .

Etymology. The specific name mawatarii , a masculine noun in the genitive singular, honors Professor emeritus Shunsuke F. Mawatari (Hokkaido University) for his great contributions to invertebrate taxonomy in Japan.

Measurements ( Table 1). Holotype: L=11.0 mm, mbd= 196 µm, a=56.2, b=11.0, c=24.0. Males (n =3, including holotype): L=10.5–11.0 mm, mbd= 196–200 µm, a=52.4– 56.2, b=9.8–11.0, c=24.0–27.5. Females (n =3): L= 10.7– 12.7 mm, mbd= 214–227 µm, a=47.2–58.6, b=10.5–11.0, c=24.5–27.7, V=50.2–53.1.

Description. Body long; anterior and posterior regions gradually tapering; anterior part of cervical region ( Figs 1A , 2A ) sharply tapering to anterior body end. Cuticle smooth; somatic setae sparse. Numerous large gland cells ( Figs 1A , 3A ) opening on cuticular surface around intestine, densely present particularly between anterior end of intestine and 30–40% from anterior end of body.

Head ( Figs 1B , 2B, C ) rounded at anterior end, set off by constriction just posterior to cephalic setae. Head diameter at level of cephalic setae 8–9% of mbd. Body diameter at constriction 0.5–1.3 µm smaller than head diameter. Three low lips well developed. Labial and cephalic setae 6+6+4 pattern (observed with SEM, but appearing 6+10 under light microscopy); inner labial setae very short (2–3 µm); outer labial setae 0.8–1.0 times head diameter; cephalic setae slightly shorter than outer labial setae, 0.6–0.9 times head diameter. Cephalic capsule weak. Buccal cavity small, cylindrical, without teeth or denticles. Amphids pocket-like, just posterior to constriction; amphidal foveae deep, cup shaped; apertures oval, width 0.4–0.6 times head diameter.

Esophagus ( Fig. 1A ) gradually tapering to anterior end, length 9.1–10.3% of L. Excretory pore at 17–23% of esophagus from anterior end. Nerve ring at 39–45% of esophagus from anterior end. Cervical setae sparse. Ventral gland ( Figs 1A , 3B ) larger in males than in females; width 0.4–0.5 times corresponding body diameter in males, 0.2–0.3 times in females. Posterior end of ventral gland situated at 1.4–1.5 times esophagus length from anterior end.

Tail ( Figs 1C, D , 2D ) conical in anterior third (27–36%), filiform in posterior two-third; length 4.3–5.3 times abd in males, 4.8–5.8 times in females; 3.6–4.2% of L. Abd 44–47% of mbd in males, 36–40% in females. Width of filiform part of tail 12–14% of abd in males, 14–17% in females. Several short setae in caudal and anal (cloacal) regions, but their arrangement varying among individuals. Tail acute at tip, with spinneret, but without terminal setae. Caudal gland inconspicuous.

Males. Reproductive system ( Fig. 1E ) diorchic. Testes equal, opposed, outstretched; anterior testis beginning at 35–43% of L, posterior testis ending at 49–62% of L from anterior body end. Spicules ( Fig. 1C, F ) paired, equal, proximally expanded, bent ventralwards, distally acute (spicules broken in ZIHU 4080); length 6.9–8.2 times abd, 1.5–1.6 times tail length, 16–17% of L. Gubernaculum ( Fig. 1C, F ) surrounding spicules, conical, strongly tapering to distal end, without apophysis; 9–10% of spicule length. Precloacal supplement ( Fig. 1C, G ) tubular, without accessory structure; length 7–8% of spicule; situated at 2.6–2.8 times abd anterior to cloaca.

Females. Reproductive system ( Fig. 1H ) didelphic. Ovaries equal, opposed, reflexed; anterior ovary beginning at 38–40% of L, posterior ovary ending at 63–65% of L from anterior body end. Eggs (found only in ZIHU 4077) oval, 317–362 µm long, 137–139 µm wide, numbering 2 in uterus. Vulva situated at 50–53% of L from anterior body end; corresponding body diameter 78–81% of mbd.

Diagnosis. Micoletzkyia mawatarii sp. nov. is characterized by its large body size (L=10.5–11.0 mm, mbd= 196–200 µm in males; L= 10.7–12.7 mm, mbd= 214–227 µm in females); particular ranges of De Man’s ratios (a=52.4– 56.2, b=9.8–11.0, c=24.0– 27.5 in males; a=47.2–58.6, b= 10.5–11.0, c=24.5–27.7, V= 50.2–53.1 in females); long out- er labial setae (length 0.8–1.0 times head diameter); short esophagus for the body length (9–10% of L); long spicules (632–708 µm, 6.9–8.2 times as long as abd); conical gubernaculum with no apophysis; simple, tubular precloacal supplement with no accessory appendage; and long tail (381– 458 µm, 4.3–5.3 times as long as abd in males, 387–481 µm, 4.8–5.8 times abd in females).

Micoletzkyia mawatarii resembles M. magna Vitiello, 1970 and M. longispicula Huang and Cheng, 2012 in the shape of the tail (anterior ca. 30% conical, posterior 70% filiform), and the shape of the gubernaculum (conical and tapering to the distal end, without any apophysis), but differs from M. magna in the body diameter (maximally 196– 200 µm, a= 52.4–56.2 in males of M. mawatarii vs 113 µm, a= 71.4 in M. magna ), and the lengths of the outer labial and cephalic setae (10.4–17.5µm, 0.6–1.0 times head diameter vs about 6 µm, less than 0.5 times head diameter) (cf. Vitiello 1970). Micoletzkyia mawatarii also differs from M. longispicula in body size (L=10.5–11.0 mm, mbd= 196–200 µm vs 6.1 mm, 128 µm in M. longispicula ), the proportional length of the tail (4.3–5.3 times as long as abd, c=24.0–27.5 vs 6.5 times abd, c=14.2), the position of the nerve ring (situated 39–42% of way from anterior end of the esophagus vs about mid-way along esophagus), and the simple tubular precloacal supplement (vs tubular with a head-like proximal end in M. longispicula ) (cf. Huang and Cheng 2012). Micoletzkyia mawatarii also resembles M. parelegans Allgén, 1954 in its large body size (L> 10 mm), but differs from the latter in esophagus length (b=9.8–11.0 vs 7.1), shape of the gubernaculum (cylindrical, surrounding the spicules vs tubular or plate-like in M. parelegans ), size and the position of the precloacal supplement (47–49 µm long, 235–240 µm from the cloaca vs 68 µm long, 350 µm from the cloaca), and length of the tail (more than 4 times abd, c=24.0–27.5, vs about 2 times abd, c=45.6) (cf. Allgén 1954b, c).

Remarks. This is the 10th species known in Micoletzkyia , and the deepest record (ZIHU 4080 were collected from 1,550 m deep) for the genus. Although 12 nominal species have been described in the genus, Huang and Cheng (2012) considered M. anomala Wieser, 1953 , M. austrogeorgiae Allgén, 1954 , and M. falklandiae Allgén, 1954 to be invalid because of their incomplete descriptions based on immature female or juvenile specimens. Therefore, the genus Micoletzkyia contains 10 species, viz., M. elegans Ditlevsen, 1926 (type species), M. parelegans , M. nudicapitata Allgén, 1959 , M. magna , M. mucronata Vitiello, 1970 , M. sedata Gagarin, 2009 , M. filicaudata , M. longispicula , M. nanhaiensis Huang and Cheng, 2012 , and M. mawatarii sp. nov.

Referring to the identification key by Huang and Cheng (2012), M. mawatarii can be classified in the same category as M. magna , M. elegans , M. longispicula , and M. sedata (fifth choice in the key) by its having a tail with a long filiform part. The following key distinguishes these five species. Because measurements of M. elegans vary between the original description ( Ditlevsen 1926) and redescriptions ( Stekhoven 1946; Allgén 1954a), we only follow the original description.

1. Longest outer labial or cephalic setae much shorter than head diameter............... M. magna Vitiello

– Longest outer labial or cephalic setae almost equal to or longer than head diameter........................ 2

2. Gubernaculum of peculiar, complex shape......................................... M. elegans Ditlevsen

– Gubernaculum simple........................... 3

3. Spicule shorter than 5 abd, gubernaculum 23 µm ...................................... M. sedata Gagarin

– Spicule longer than 6 abd, gubernaculum 51–63 µm .. 4

4. Nerve ring midway along esophagus, c=14.2, precloacal supplement with head-like proximal end............................ M. longispicula Huang and Cheng

– Nerve ring 39–42% of esophagus length, c=24.0–27.5, precloacal supplement unmodified tubular........................................ M. mawatarii sp. nov.

Figures

Fig. 1. Micoletzkyia mawatarii sp. nov., holotype, ZIHU 4073 (A–C, E–G) and paratypes, ZIHU 4075 (D) and ZIHU 4077 (H). A, anterior region of male body; B, head of male; C, posterior region of male body; D, posterior region of female body; E, reproductive system of male (testes and vas deferens); F, distal end of spicules and gubernaculum at cloacal region of male; G, precloacal supplement of male; H, reproductive system of female (ovaries, uterus, eggs, and vulva). Scale bars: A, E, H, 200µm; B, 10µm; C, D, 100µm; F, 10µm; G, 20µm.

Fig. 2. SEM images of Micoletzkyia mawatarii sp. nov., paratypes, ZIHU 4079 (A–C) and ZIHU 4078 (D). A, lateral view of anterior region of female body; B, anterior view of female head; C, ventrolateral view of female head; D, lateral view of posterior region of male body. Scale bars: A, D, 100µm; B, C, 10µm.

Fig. 3. Light photomicrographs of Micoletzkyia mawatarii sp. nov., holotype, ZIHU 4073. A, gland cells surrounding intestine; B, ventral gland. Scale bars: 100µm.