Daptonema phuketense, Aryuthaka & Kito, 2018

Aryuthaka, Chittima & Kito, Kenji, 2018, Two new species of the genus Daptonema Cobb, 1920 (Nematoda: Xyalidae) found in an intertidal seagrass bed on the coast of the Andaman Sea, Thailand, with reference to the taxonomic status of the genus Trichotheristus Wieser, 1956, Zootaxa 4394 (1), pp. 77-94 : 82-87

Daptonema phuketense sp. n.

( Fig. 2A–H, 3A–C )

Type specimens. Holotype: male (ICHUM 5330). Allotype: female (ICHUM 5331). Paratypes: 4 males (ICHUM 5332-5334; KUMF, T0015) and 3 females (ICHUM 5335, 5336; KUMF, T0016). Collected on 4th February 2003 by C. Aryuthaka.

Type locality and habitat: in Halophila ovalis patches at Ban Pa Khlok , Phuket Province, Thailand; 8° 01' 20'' N, 98° 24' 40'' E in the Andaman Sea.

Measurements. Table 2.

Holotype: L = 1304 µm, a = 16.9, b = 4.9, c = 5.8.

Males (n = 5): L = 1264–1420 (1327 ± 63.2) µm, a = 15.5–16.9 (16.2 ± 0.7), b = 4.7–5.1 (4.9 ± 0.1), c = 5.8— 6.3 (6.1 ± 0.2).

Females (n = 4): L = 1358–1461 (1415 ± 42.5) µm, a = 14.2–16.2 (14.9 ± 0.9), b = 4.7–4.9 (4.8 ± 0.1), c = 6.2– 6.4 (6.3 ± 0.1), V (%) = 67.7–68.7 (68.2 ± 0.5).

Description. MALE. Body about 1.3 (1.3 –1.4) mm long, diameter almost uniform except for pharyngeal and tail regions, and slightly larger diameter at mid body ( Fig. 2A). Cuticle weakly striated; annules about 2.3 (2.1–2.6) µm apart at pharyngeal end and mid body, 2.6 (2.4–2.8) µm in cloacal region. Epidermal chords obscure but some bridge-like boundaries of longitudinally adjoining cells observed (cf. Aryuthaka & Kito, 2012). Longitudinal somatic musculature conspicuous on whole body. Long cervical setae characteristically located between amphids and just posterior to the nerve ring (0.40–0.45 pharyngeal length from anterior body end), each 36 (33–37; 35.6 ± 1.7) µm or 0.8 (0.7–0.8) cbd long. Somatic setae on remainder of body short and often indistinct, length 15 (12–15) µm or 0.2 (0.1–0.2) cbd.

Head ( Fig. 2C) blunt, weakly set-off; labial region low, about 7 (7–10) µm long. Head with 6 tiny labial papillae, and 12 cephalic setae, 6 longer and 6 shorter, maximum lengths 0.5 (0.5–0.6; 0.53 ± 0.04) and 0.4 (0.3– 0.4; 0.36 ± 0.04) hd respectively; cephalic setae segmented. No subcephalic setae present. Amphids circular, about 7 (6.5–7.7; 6.76 ± 0.39) µm in diameter, diameter about 23 (22–24; 22.5 ± 0.7) % cbd, anterior margin 1.0/1.1 (1.0– 1.1; 1.04 ± 0.05) hd from anterior end of body. Buccal cavity cup-shaped, about 11 (10–11) µm wide, posterior half surrounded by pharynx. Pharynx ( Fig. 2B) almost cylindrical, length 0.20 (0.20–0.21) of total body length. Anterior margin of nerve ring, 40 (37–40; 38.4 ± 1.3) % of pharyngeal length from anterior body end. Cardia short, 10 (9–13) µm in length. Ventral gland and excretory pore not observed.

Reproductive system monorchic. Testis outstretched, on left of intestine, extending to near mid pharynx, length from cloaca, 72 (72–74; 72.8 ± 0.8) % of total body length. Spicules ( Fig. 2E) strongly curved near middle portion (L-shaped), proximally cephalate, length 1.1 (1.1–1.2; 1.12 ± 0.04) abd on arc or 1.0/0.9 (0.9–1.0; 0.96 ± 0.05) on chord; manubrium with rounded end and ventral expansion (6–7 µm wide), distal half gradually narrowing, 2 lateral projections near tip end. Gubernaculum length about 0.4 (0.31–0.43; 0.38 ± 0.04) spicule length on arc, dorso-caudal apophysis 10/9 (8–11) µm long. Ejaculatory glands present but indefinite in number; 2 or 3 glands located on each side of intestine around anterior portion of vas deferens, anterior margin of anteriormost gland about 5.1 (5.1–5.7) abd from cloaca.

Tail ( Fig. 2D) conico-cylindroid, 4.5 (4.2–4.5; 4.30 ± 0.14) abd long, cylindroid portion about one-sixth (0.15– 0.19) of tail length. Three caudal glands in tandem; anterior two transparent, but the posterior one small and distinctly different, containing peculiar fibrous contents inside ( Fig. 3A–C ). A pair of long subventral setae conspicuous, positioned 0.4 (0.4–0.5) tail lengths posterior to cloaca, the length of each about 15 (13–16; 14.4 ± 7.0) µm or 0.4/0.5 (0.4–0.5) cbd. A pair of terminal setae located on each side, dorsal setae longer than ventral setae, 24 (18–27; 22.9 ± 3.0) µm and 13 (13–20; 16.5 ± 8.7) µm long, respectively.

FEMALE. Similar to males in most features. Body about 1.4 (1.4–1.5) mm long, somewhat spindle shaped due to swollen middle portion ( Fig. 2F). Annules about 2.3 (2.2–2.6) µm, 2.5 (2.2–2.7) µm, and 2.7 (2.5–2.9) µm apart at posterior of pharynx, mid body to vulval region, and anal region, respectively. Long cervical setae located from the amphid to posterior to the nerve ring (0.39–0.41 pharyngeal length from anterior body end), length of each about 37 (37–40; 38.8 ± 1.5) µm or about 0.7 cbd; somatic setae on remainder of body each 11 (10–12) µm long or 0.2 (0.1–0.2) cbd long. Amphids smaller than in male, diameter about 5 (5.1–6.3; 5.6 ± 0.43) µm or 16 (15– 19; 16.8 ± 1.3) % cbd, anterior margin 0.8 (0.8–1.0; 0.92 ± 0.07) hd from anterior end of body.

Reproductive system monodelphic and prodelphic. Ovary outstretched, on left of intestine, extending anteriorly to near nerve ring, length from vulva 59 (56–59; 58.0 ± 1.4) % of total body length. Vulva transverse, located at about 0.7 of total body length from anterior end of body, vagina well muscularized; small ventral gland located posterior to vulva ( Fig. 2G). Four (4–6) and 3 (3–7) large coelomocytes arranged longitudinally on ventral and dorsal sides near posterior end of ovary, respectively, each 19–38 µm long and 10–25 µm wide, anterior margin of anteriormost coelomocyte 4.6 (3.9–4.8) vbd anterior to vulva.

Tail ( Fig. 2H) conico-cylindroid, 4.1 (4.1–4.5; 4.23 ± 0.19) abd long, cylindroid portion about 0.2 tail length; with short sparsely-spaced setae. Posteriormost caudal gland filled with fibrous material ( Fig. 3C ). Terminal setae, 26 (26–28; 26.5 ± 1.0) µm long.

Etymology. The specific name phuketense refers to the type locality.

Differential diagnosis. Daptonema phuketense sp. n. is characterized in the genus by the following features: medium body length (1.3–1.4 mm in male and 1.4–1.5 mm in female), de Man’s indices (a = 14.2–16.9, b = 4.7– 5.1, c = 5.8–6.4), 12 cephalic setae (0.5–0.6 hd long), many long cervical setae located between amphids and posterior to the nerve ring (0.7–0.8 cbd long), short somatic setae on the remainder body (0.1–0.2 cbd long), distance of amphids from anterior (0.8–1.1 hd long), amphid diameter (22–24% cbd in male and 15–19% in female), one testis and one ovary, L-shaped spicules with round-shaped manubrium and ventral expansion (1.1–1.2 abd on arc or 0.9–1.0 on chord), gubernaculum with long dorso-caudal apophysis (8–11 µm), posteriorly located vulva (V = 68–69 %), and conico-cylindroid tail (4.1–4.5 abd long) with the peculiar third caudal gland containing fibrous contents and 4 terminal setae (28 µm).

Daptonema phuketense sp. n. is unique in the genus Daptonema in the posterior caudal gland having fibrous contents. This has not been reported in the genus previously. However, the morphology of the caudal glands has not been detailed for many of the known species of Daptonema , except for number, shape and positon, and we have been unable to compare the gland of D. phuketense with all the congeners.

Of the Daptonema species characterized by the long cervical setae in the anterior pharyngeal region, D. phuketense sp. n. is similar to D. chonispiculum sp. n., D. hirsutum ( Vitiello, 1967) , D. platonovae (Gal’tsova, 1976), D. robustum ( Tchesunov, 1980) , in having body length of about 1–2 mm, long cervical setae length about 1 cbd, amphid diameter less than 40% cbd, L-shaped spicules, and a gubernaculum with long dorso-caudal apophysis ( Table 3). Daptonema phuketense sp. n. particularly resembles D. chonispiculum sp. n. in body length, de Man’s b and c indices, and diameter and location of the amphids, but differs from in having a thinner body (de Man’s index a 14.2–16.9 vs. 16.8–26.6 in D. chonispiculum ), shorter cephalic setae (0.5–0.6 hd vs. 0.7–0.9), shorter cervical setae (0.8 cbd vs. 1.1), shorter somatic setae (0.2 cbd vs. 0.5), spicules with rounded manubrium (vs. funnel-shaped in D. chonispiculum ), and shorter tail (4.1–4.5 abd vs. 4.7–6.1), as well as the posterior caudal gland having fibrous contents (vs. fluid contents). D. phuketense sp. n. is distinguished from D. hirsutum , D. platonovae , and D. robustum , by D. hirsutum having a longer body (1.6–2.0 mm), different de Man’s indices (larger a = 22.1–27.1 and smaller b = 3.6–4.1), longer cephalic setae (1.0 hd), longer cervical setae (1.5 cbd), longer somatic setae (0.5 cbd, rarely 1.0), longer spicules (1.4 abd on arc and 1.2–1.5 abd on chord), and longer tail (5.0–6.0 abd) with 4–6 terminal (67 µm); by D. platonovae having a longer body (1.9–2.1 mm), smaller de Man’s index b (3.8–4.0), thick cephalic setae, cervical setae between amphids and anterior to the nerve ring, shorter spicules with weakly cephalate manubrium (0.9 abd on arc and 0.8 abd on chord), and a shorter tail (3.6–4.3 abd) with 2 terminal setae (41 µm); and by D. robustum having a longer body (1.8–2.0 mm in male), different de Man’s indices (larger a = 22.0–28.6, smaller b = 3.3–3.8, larger c = 7.2–8.7), longer cephalic setae (0.9 hd), larger amphids (24–31% cbd), longer cervical setae (1.0 cbd) between the amphids and anterior to the nerve ring, longer spicules (1.5 abd on arc and 1.0–1.2 abd on chord), and gubernaculum with a longer dorso-caudal apophysis (24 µm).

Males Females

Character ICHUM ICHUM ICHUM* KUMF ICHUM ICHUM ICHUM KUMF ICHUM

5332 5333 5330 T0015 5334 5335 5331 T0016 5336

1264 1285 1304 1360 1420 1358 1418 1422 1461

16.9 15.9 16.9 15.5 15.8 14.4 14.2 14.8 16.2

4.8 4.7 4.9 5.1 4.9 4.7 4.7 4.8 4.9

6.1 6.0 5.8 6.1 6.3 6.2 6.4 6.4 6.3

- - - - - 67.7 67.8 68.7 68.4 cs 10.7 10.8 10.8 10.4 12.4 11.9 12.9 12.3 12.1 hd 20 21 21 21 21 25 25 24 25 amp abe 19/20 20/21 21/23 23/23 22/23 23/25 21/21 23/23 23/24 amp d 6.5/6.7 6.7/6.5 6.6/6.5 6.7/6.5 7.7/7.2 5.6/5.3 5.3/5.4 6.2/6.3 5.6/5.1 amp bd 30/30 30/30 28/29 30/30 32/32 33/32 34/34 34/34 34/34 nr abe 98 101 106 104 114 111 109 114 109 ph 264 274 265 268 289 289 301 299 298 ph bd 71 75 67 66 82 82 85 78 85 mid bd 75 81 77 88 90 94 100 96 90 mbd 84 90 80 88 92 94 100 98 97 spic arc (r/l) 57/52 58/58 56/54 58/61 60/59 - - - - spic ch (r/l) 51/44 52/48 48/44 53/51 54/51 - - - - gub 22/19 25/25 22/21 20/19 22/20 - - - - gub apo 11/10 11 / 8 10/9 11/10 10 /9 - - - - abe - - - - - 919 962 977 999 vbd - - - - - 80 91 92 81

208 215 223 223 227 219 220 223 233 abd 49 51 50 51 54 54 54 53 52 s 25 21 24 26 27 28 26 26 26

Characters: a̡ b̡ c—de Man’s indices; abd̡—anal/cloacal body diameter; amp abe (r/l)—distance from right/left amphid to anterior body end; amp bd (r/l)—body diameter level of right/left amphid; amp d (r/l)—right/left amphid diameter; cbd—corresponding body diameter; cs—length of cephalic setae (longest); gub—length of

gubernaculum; gub apo—length of gubernaculum apophysis: hd—head diameter; L—body length; mbd—maximum body diameter; mid bd—diameter at midbody; nr abe—

distance from nerve ring to anterior body end; ph—length of pharynx; ph bd—body diameter at posterior end of pharynx; spic arc (r/l)—length of right/left spicule measured arc; spic ch (r/l)—length of right/left spicule measured on chord; t—tail length; V—position of vulva as a percentage of body length from anterior body end; v abe—

distance from vulva to anterior body end; vbd—body diameter at level of vulva; - ̡ absent. * Holotype. Measurements in µm̡ except for de Man’s indices (a̡ b̡ c) and V (%).

Character: a̡ b̡ c—de Man's indices; amp abe — distance from amphid to anterior body end; amp d— amphid diameter; L—body length; spic arc—length of spicule measured on arc; spic ch—length of spicule measured on chord; t—tail length; V—position of vulva as a percentage of body length from anterior body end. abd—

/cloacal body diameter; cbd—corresponding body diameter; hd—head diameter; nr—nerve ring; *—approximate values calculated from drawing; - data not available. Values for male and female are presented where different separated by a semi-colon (;). Data source: 1 Vitiello (1967) and Boucher & Helléouët (1977); 2 Tchesunov (1990); Tchesunov (1980).

Figures

FIGURE 3. Daptonema phuketense sp. n. Male (Holotype ICHUM 5330, left side view):A) Copulatory apparatus and caudal glands.B) Caudalglands.Female (Paratype KUMF-T0016; leftdorso-lateral view):C) Caudalglands.Bar scales:A, C, 20 µm; B,10 µm. Arrows indicate the third caudal gland.