Odontophora odontophoroides Shimada, 2021

Shimada, Daisuke, Suzuki, Atsushi C., Tsujimoto, Megumu, Imura, Satoshi & Kakui, Keiichi, 2021, Two New Species of Free-living Marine Nematodes (Nematoda: Axonolaimidae and Tripyloididae) from the Coast of Antarctica, Species Diversity 26 (1), pp. 49-63 : 51-56

Odontophora odontophoroides Shimada , sp. nov. ( Figs 1–3 )

Axonolaimidae gen. sp. in Shimada et al. (2017): table 1.

Material examined. Holotype. Male ( ICHUM 5373 ), formalin fixed, whole mount in glycerin, upper subtidal sandy sediment, Langhovde (69°14′24.3″S, 39°42′55.8″E), Lützow- Holm Bay, Dronning Maud Land, Antarctica . Paratypes. Five males ( ICHUM 5484–5488 ) and five females ( ICHUM 5374 , 5489–5492 ), formalin fixed, whole mount in glycerin, same collection data as for holotype . Other material. One male, formalin fixed, dissected for observation from ventral side. Two males and one female, Au-coated for SEM, same collection data as for holotype .

Etymology. The specific name odontophoroides is a noun in apposition (in the nominative case), referring to the bicuspidate odontia similar to those in the genus Odontophoroides Boucher and Helléouët, 1977.

Diagnosis. Six bicuspidate odontia; amphids with longitudinally elongate aperture at level of pharyngostoma; cephalic sensilla shorter than cephalic body diameter; no subcephalic sensilla; conical tail with slightly expanded tip, without long subterminal setae; arcuate spicules with capitulum at proximal end and two spine-like structures at distal end; gubernacula with dorso-caudal apophysis; precloacal pore and supplements present.

Measurements. See Table 1.

Description of males. Body ( Fig. 1A ) cylindrical, gradu- ally tapering toward both ends. Cuticle colorless, 3–6 µm thick, with very fine, indistinct transverse striations. Somatic sensilla absent except in cervical, cloacal, and caudal regions. Head ( Figs 1B, C , 2A–C ) truncate at anterior end. Six lips low, inconspicuous under light microscope. Inner labial sensilla not observed. Six papilliform outer labial sensilla, located at anterior body end. Four setiform cephalic sensilla, 0.5–0.7 cephalic diameters long, located 0.4–0.6 cephalic diameters from anterior body end. Subcephalic sensilla absent. Amphids ( Figs 1C , 2B, D ) loop-shaped with longitudinally elongate aperture, dorsal and ventral branches equal in length, 1.0–1.2 cephalic diameters long, 0.25–0.35 cephalic diameters wide (length/width=3.0–4.3), located at level of pharyngostoma, beginning just posterior to cephalic sensilla and ending at level of posterior end of buccal cavity. Buccal cavity ( Figs 1C , 2A ) funnel-shaped or conical, with well-developed cuticular walls, 1.4–1.7 cephalic diameters long, divided into two sections: cheilostoma 5–7 µm long, movable by linkage with lips, equipped with six bicuspidate odontia (5–6µm long, 4–5 µm wide) ( Figs 1C , 2B, C ) similar in shape to odontia in Odontophoroides; pharyngostoma immovable, 19–23 µm or 1.1–1.4 cephalic diameters long, at most 7–10 µm or 0.2–0.4 cephalic diameters wide. Other solid structures in buccal cavity, e.g., “accessory buccal structures” reported in O. atrox by Leduc and Zhao (2016), absent. Pharynx ( Fig. 1B, C ) surrounding posterior 20–40% of buccal cavity, nearly cylindrical, slightly enlarged at posterior end but not forming distinct bulb. Nerve ring located at 60–70% of pharyngeal length. Secretory-excretory system well developed; pore 1.4–2.1 buccal cavity lengths from anterior body end; renette cell 1.3–1.5 pharyngeal lengths from anterior end, 0.4–0.6 corresponding body diameters wide, accompanied by two smaller ventrolateral cells. Cervical sensilla setiform, shorter than cephalic sensilla, 0.4–0.6 cephalic diameters long, arranged in four longitudinal rows, dense in anterior half of cervical region and sparser posteriorly, anteriormost setae located at level of amphids. Cardia short, surrounded by intestine. Tail ( Fig. 1D ) conical, slightly expanded at tip, 3.3–4.3 cloacal body diameters long, with three terminal setae (4–9 µm long). Long subterminal setae absent. Rows of ventrolateral setae (5–12 µm long) and sparser dorsolateral setae (4–7 µm long) present on each side in cloacal and caudal regions. Number and position of setae differ among specimens. Three caudal glands located postcloacally. Spinneret present. Spicules ( Figs 1D–G , 2E ) paired, belonging to arcuate type in Leduc and Zhao’s (2016) classification, as long as 1.1–1.4 cloacal body diameters or 0.3–0.4 tail lengths, with capitulum at proximal end and two spine-like structures at distal end. Gubernacula ( Figs 1D–G , 2F, G ) also paired, as long as 0.4–0.6 cloacal body diameters or 0.3–0.4 spicule lengths, located between spicules, with twisted dorso-caudal apophysis. Precloacal pore ( Figs 1D, E , 2H ) present with gland cell 8–14 µm anterior to cloaca. Precloacal supplements ( Figs 1D, E , 2I ) papilliform, 16–23 in number, each with gland cell; anteriormost supplement 377–492 µm or 6.2–8.8 cloacal body diameters from cloaca. Reproductive system ( Figs 1A , 2J, K ) diorchic with opposed, outstretched testes: anterior testis beginning at 18–27% of body length from anterior body end, as long as 11–20% of body length, located on right side of intestine in four specimens including holotype but on left side in two other specimens (ICHUM 5486 and 5488); posterior testis ending 63–75% of body length from anterior body end, as long as 16–20% of body length, located on left side of intestine in three specimens including holotype but on right side in three other specimens (two testes located on opposite sides of intestine in five specimens including holotype, but both on right side in ICHUM 5487). In total length, reproductive system (from anterior end of anterior testis to posterior end of posterior testis) 44–55% of body length. Seminal vesicle well developed, located between two testes, beginning at 34–43% of body length and ending at 47–58%, filled with globular sperm (10–20 µm in diameter). Vas deferens ( Fig. 1A, D ) distinct, strongly muscular in posterior part, with 10 or more large (20–40 µm in diameter) ejaculatory gland cells on both sides.

Description of females. Body ( Fig. 3A ) similar to males, with following differences. Cephalic and cervical sensilla ( Fig. 3B ) slightly shorter than in males: cephalic sensilla 0.3–0.6 cephalic diameters long; cervical sensilla 0.25–0.5 cephalic diameters long. Buccal cavity slightly larger than in males, 1.5–1.8 cephalic diameters long and 0.4–0.5 cephalic diameters wide. Somatic sensilla absent in preanal region. Tail ( Fig. 3C ) not sexually dimorphic. Arrangement of caudal sensilla as in males, but ventrolateral sensilla as short as dorsolateral setae (4–7 µm long) and sparser, often not observed in anterior half of tail. Reproductive system ( Fig. 3A, D ) didelphic, with opposed, outstretched ovaries: anterior ovary beginning at 20–26% of body length from anterior body end and ending at 43–48%, as long as 20–25% of body length, located on right side of intestine in four specimens but on left side in another specimen (ICHUM 5489); posterior ovary beginning at 60–66% of body length and ending at 83–86%; as long as 17–25% of body length, located on opposite side of intestine from anterior ovary. In total length, reproductive system 60–65% of body length. Mature eggs 75–95 µm long, 50–60 µm wide. One egg present in each uterus in two specimens (ICHUM 5489 and 5490); one egg present only in anterior uterus in ICHUM 5374; and no egg present in two specimens. Vulva slit-like, located at 54–55% of body length. Vagina sclerotized, 30–37 µm long, with well-developed vaginal glands. Sperm not observed in ovi- ducts or uteri.

Remarks. Odontophora odontophoroides sp. nov. differs from congeners in having anteriorly bicuspidate odontia. Most species in Odontophora have a single anterior cusp on each odontium, but nine species have odontia with three or more cusps: O. brevispicula , O. fatisca , O. furcata , O. paravilloti , and O. villoti have three cusps ( Luc and De Coninck 1959; Gerlach 1962; Vitiello 1971; Blome 1982; Keppner 1988); O. articulata , O. bermudensis , and O. carrolli , five cusps ( Jensen and Gerlach 1976; Keppner 1988); and O. serrata , seven cusps ( Hourston and Warwick 2010). Species in Odontophoroides and Synodontium Cobb, 1920 , also have bicuspidate odontia, but differ from O. odontophoroides sp. nov. in having only a posterior ovary, rather than two ovaries (cf. Bütschli 1874; Cobb 1920; Wieser 1956; Boucher and Helléouët 1977; Tarjan and Nguyen 1988; Fonseca and Bezerra 2014).

Following is a taxonomic key to males of Odontophora species , modified from Leduc and Zhao (2016). Although Leduc and Zhao (2016) used presence or absence of the subcephalic sensilla located just posterior to the cephalic sensilla (group C) as a diagnostic character, we did not use this character, as presence/absence was difficult to distinguish in several species (cf. Cobb 1914; Ditlevsen 1918; Filipjev 1918; Allgén 1928, 1929, 1935; De Coninck and Schuurmans Stekhoven 1933; Timm 1952; Wieser 1956, 1959; Gerlach 1957; Luc and De Coninck 1959; Wieser and Hopper 1967; Lorenzen 1971; Vitiello 1971; Ott 1972; Boucher 1973; Warwick and Platt 1973; Galtsova 1976; Jensen and Gerlach 1976; Boucher and Helléouët 1977; Nichols and Musselman 1979; Blome 1982; Pastor de Ward 1984; Keppner 1988; Turpeenniemi et al. 2001; Hourston and Warwick 2010; Leduc and Zhao 2016; Pinto and Neres 2020): 1. Single lateral subcephalic sensillum present just poste-

rior to each amphid.............................. 2 — Lateral subcephalic sensillum absent just posterior to

each amphid.................................... 5 2. Pair of long subterminal setae present on tail.........

........................................ O. wieseri — Long subterminal setae absent..................... 3 3. Tail conico-cylindrical.............. O. tenuicaudata — Tail conical..................................... 4 4. Gubernaculum with dorso-caudal apophysis.........

....................................... O. octoseta — Gubernaculum without dorso-caudal apophysis......

................................... O. sinapophysis

5. Pair of sublateral subcephalic sensilla at mid-level of each amphid.................................... 6

— Pair of sublateral subcephalic sensilla absent....... 10

6. Pair of long subterminal setae on tail............... 7

— Long subterminal setae absent..................... 9

7. Cuticularized lateral spines in cloacal region.... O. atrox

— Cuticularized lateral spines absent................. 8

8. Each odontium with three cusps............. O. villoti

— Each odontium with single cusp.......... O. variabilis

9. Precloacal supplements large, with cuticular elevations..................................... O. articulata

— Precloacal supplements minute............. O. setosa

10. Each odontium with two or more cusps........... 11

— Each odontium with single cusp.................. 18

11. Each odontium with two cusps............................................. O. odontophoroides sp. nov.

— Each odontium with three or more cusps.......... 12

12. Each odontium with three cusps.................. 13

— Each odontium with five or more cusps............ 16

13. Pair of long subterminal setae on tail.............. 14

— Long subterminal setae absent.............. O. fatisca

14. Distal end of spicule unequally bicuspid................................................ O. brevispicula

— Distal end of spicule not bicuspid................. 15

15. Spicules without capitulum............. O. paravilloti

— Spicules with capitulum.................. O. furcata

16. Each odontium with seven cusps........... O. serrata

— Each odontium with five cusps................... 17

17. Precloacal supplements large, with cuticular elevations....................................... O. carrolli

— Precloacal supplements minute........ O. bermudensis

18. Pair of long subterminal setae on tail.............. 19

— Long subterminal setae absent.................... 29

19. Distal end of spicules hook-shaped...... O. mercurialis

— Distal end of spicules not hook-shaped............ 20

20. Spicules without capitulum...................... 21

— Spicules with capitulum......................... 22

21. Amphidial aperture longitudinally elongate... O. ornata

— Amphidial aperture circular............ O. mucronata

22. Capitulum of spicules pointed dorsally... O. peritricha

— Capitulum of spicules not pointed dorsally......... 23

23. Spicules L-shaped (sharply bent in middle)............................................... O. rectangula

— Spicules gradually bent.......................... 24

24. Amphidial aperture longitudinally elongate................................................ O. exharena

— Amphidial aperture circular...................... 25

25. Precloacal supplements present................... 26

— Precloacal supplements absent................... 27

26. Subterminal setae on tail much longer than cloacal body diameter........................ O. phalarata

— Subterminal setae on tail shorter than cloacal body diameter............................ O. longisetosa

27. Cephalic sensilla shorter than cephalic body diameter.................................. O. angustilaima

— Cephalic sensilla much longer than cephalic body diameter...................................... 28

28. Longest cervical sensilla as long as cephalic sensilla.......................................... O. falcifera

— Longest cervical sensilla much shorter than cephalic sensilla................................ O. urothrix

29. Spicules with capitulum......................... 30

— Spicules without capitulum...................... 33

30. Amphids at level of pharyngostoma..... O. deconincki

— Amphids at level of cheilostoma.................. 31

31. Cephalic sensilla longer than 1.5 cephalic body diameters............................. O. polynesiae

— Cephalic sensilla shorter than cephalic body diameter .............................................. 32

32. Spicules as long as cloacal body diameter... O. armata

— Spicules longer than 1.5 cloacal body diameters............................................ O. setosoides

33. Spicules L-shaped........................ O. polaris

— Spicules gradually bent.......................... 34

34. Amphidial aperture longitudinally elongate............................................ O. hawksbiensis

— Amphidial aperture circular...................... 35

35. Cervical sensilla equal to or longer than cephalic body diameter................................ O. regalia

— Cervical sensilla much shorter than cephalic body diameter...................................... 36

36. Cephalic sensilla as long as cephalic body diameter..................................... O. spiculodentata

— Cephalic sensilla twice as long as cephalic body diameter............................... O. lituifera

Figures

Fig. 1. Odontophora odontophoroides sp. nov. A, male body (holotype); B, male anterior region (holotype); C, male head with closed mouth (holotype); D, male posterior region (holotype); E, male genital apparatus (holotype); F, G, spicule and gubernaculum (ICHUM 5486 and 5488, respectively). Abbreviations: a.t., anterior testis; e.g., ejaculatory glands; p.p., precloacal pore; p.s., precloacal supplement; p.t., posterior testis; s.v., seminal vesicle; v.d., vas deferens. Scale bars: A, 500µm; B, D, 100µm; C, 20µm; E–G, 10µm.

Fig. 2. Odontophora odontophoroides sp. nov. A, B, E–J, differential interference contrast photomicrographs; C, D, SEM images. A, inner view of head (holotype); B, amphid and odontia (holotype); C, mouth opening with odontia (non-type male); D, amphidial aperture (nontype male); E, distal end of spicule with spine-like structures (holotype); F, ventral view of left spicule (white arrowheads) and gubernacula (black arrowheads) (dissected non-type); G, gubernaculum (holotype); H, precloacal pore (holotype); I, precloacal supplement (black arrowhead) (holotype); J, contents of testis (holotype); K, sperms in seminal vesicle (holotype). Scale bars:A–G, J, K, 10µm; H, I, 5µm.

Fig. 3. Odontophora odontophoroides sp. nov. A, female body (ICHUM 5490); B, female head with open mouth (ICHUM 5490); C, female posterior region (ICHUM 5490); D, vaginal region (ICHUM 5490). Scale bars: A, 500µm; B, 20µm; C, D, 100µm.