Daptonema chonispiculum, 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 : 78-82

Daptonema chonispiculum sp. n.

( Fig. 1A–H )

Type specimens. Holotype: male (ICHUM 5323). Allotype: female (ICHUM 5324). Paratypes: 4 males (ICHUM 5325-5327 KUMF, T0013) and 3 females (ICHUM 5328, 5329; KUMF, T0014). Collected on 4th February 2003 by C. Aryuthaka.

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

TABLE 1. Morphometrics of Daptonema chonispiculum sp. n.

Males Females

Character ICHUM ICHUM ICHUM * KUMF ICHUM ICHUM ICHUM KUMF ICHUM 5325 5326 5323 T0013 5327 5328 5329 T0014 5324 1154 1223 1265 1327 1453 1475 1509 1511 1569 26.2 26.6 20.4 25.0 22.7 16.8 17.5 20.7 23.1 4.4 4.7 4.3 4.5 4.6 4.6 4.2 4.3 4.5 6.3 5.9 5.8 6.2 6.1 5.9 6.2 5.9 6.1 - - - - - 68.2 67.9 68.4 69.5

cs 16.4 17.4 15.8 15.2 15.9 18.8 19.4 18.6 20.4

hd 20 20 22 22 24 28 28 26 28

amp abe 18/17 18/18 20/20 20/19 21/20 22/22 23/23 23/22 22/21

amp d 7.5/7.7 7.6/8.1 9.9/9.6 8.4/9.7 9.6/9.4 8.6/8.0 7.7/6.7 7.0/7.2 7.7/7.9

amp bd 23/23 23/24 29/29 27/27 29/29 36/36 35/34 35/34 32/32

nr abe 94 100 114 113 117 120 121 128 128

ph 263 260 297 294 313 321 360 354 349

ph bd 42 44 58 44 55 78 78 69 65

mid bd 43 43 62 45 61 88 86 72 67

mbd 44 46 62 53 64 88 86 73 68

spic arc (r/l) 48/49 50/47 49/47 52/52 52/53 - - -

spic ch (r/l) 41/42 43/40 45/40 45/46 45/46 - - - -

gub 17/16 16/16 16/15 17/13 20/18 - - - -

gub apo 8/ 8 10/10 11/12 10 / 9 11/10 - - - -

abe - - - - - 1006 1025 1034 1090

vbd - - - - - 80 77 64 68 182 207 217 213 240 251 244 254 257

abd 39 38 43 38 44 50 47 44 42 33 39 43 31 broken 36 40 44 35

Characters: a̡ b̡ c—de Man’s indices; abd—anal/cloacal body diameter; amp abe (r/l)—distance from right/left amphid to anterior body end; amp bd (r/l)—body diameter at 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;

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 on arc; spic ch 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

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 (%).

Measurements. Table 1.

Holotype: L = 1265 µm, a = 20.4, b = 4.3, c = 5.8.

Males (n = 5, including holotype): L = 1154–1453 (1284 ± 113.3) µm, a = 20.4–26.6 (24.2 ± 2.60), b = 4.3–4.7 (4.5 ± 0.16), c = 5.8–6.3 (6.1 ± 0.21).

Females (n = 4): L = 1475–1569 (1516 ± 39.0) µm, a = 16.8–23.1 (19.5 ± 2.93), b = 4.2–4.6 (4.4 ± 0.18), c = 5.9–6.2 (6.0 ± 0.15), V (%) = 67.9–69.5 (68.5 ± 0.70).

Description. MALE. Body about 1.3 (1.2–1.5) mm long, almost uniform diameter except for pharyngeal and tail regions ( Fig. 1A ). Cuticle weakly striated, annules about 1.6 (1.5–1.8) µm apart at posterior end of pharynx, 1.8 (1.7–2.2) µm apart at mid body, 2.1 (1.7–2.5) µm at cloacal region; lateral alae distinct, 11 (7–11) µm wide or about 0.2 cbd at mid body. Epidermal cells indistinct. Longitudinal somatic musculature distinct. Somatic setae densely distributed throughout body. Cervical setae between amphids and just posterior to nerve ring (0.43–0.47 pharyngeal length from anterior body end) distinctly long, 41 (33–41) µm in length or 0.9 (0.8–1.1) cbd. Somatic setae on remainder of body shorter than cervical setae, 27 (16–32; 22.2 ± 7.1) µm in length or 0.5 (0.4–0.5) cbd.

Head ( Fig. 1C ) blunt, weakly set-off; labial region low, about 9 (9–10) µm in length. Head with 6 labial papillae, each about 2 µm long, and 12 cephalic setae, 6 longer and 6 shorter, maximum length 0.7 (0.7–0.9) and 0.5 (0.4–0.6) hd respectively; cephalic setae appearing segmented anteriorly. No subcephalic setae. Amphids circular, about 10 (7.5–9.9; 8.75 ± 1.00) µm in diameter, occupying about 33 (31–36; 33.3 ± 1.3) % cbd; anterior margin of amphids 0.9 (0.8–0.9; 0.89 ± 0.03) hd from anterior body end. Buccal cavity cup-shaped, about 12 (10– 13) µm wide, posterior half surrounded by pharynx. Pharynx ( Fig. 1B ) muscular, almost cylindrical, length 0.23 (0.21–0.23) of total body length. Cardia short, 9 (9–10) µm long. Anterior margin of nerve ring, 38 (36–39; 37.6 ± 1.1) % of pharyngeal length from anterior body end. Ventral gland and excretory pore not observed.

Reproductive system monorchic. Testis outstretched, on left of intestine, extending to near mid pharynx, length from cloaca 69 (69–75; 71.0 ± 2.4) % of total body length. Spicules ( Fig. 1E ) strongly curved near middle portion (L-shaped), proximally cephalate, 1.1 (1.1–1.4; 1.24 ± 0.11) abd long on arc or 1.0/0.9 (0.9–1.2; 1.07 ± 0.09) on chord; manubrium with funnel-shaped end and ventral expansion (6–7 µm wide), distal half gradually narrowing, tip end with a projection extending laterodorsally. Gubernaculum about 0.3 (0.3–0.4) spicule length, with 11/12 (8– 12) µm long dorso-caudal apophysis. Ejaculatory glands present but indistinct; number indefinite, appearing as 3 or 4 glands located on each side of intestine around anterior portion of vas deferens, anterior margin of anteriormost gland about 6.5 (6.5–7.7) abd long from cloaca.

Tail ( Fig. 1D ) conico-cylindroid, 5.0 (4.7–5.6; 5.24 ± 0.38) abd long; posterior cylindroid portion about onefifth (0.18–0.23) of total tail length. Longest subventral setae, 26 (23–27; 25.4 ± 1.52) µm long, conspicuous on each side at about 0.4 (0.37–0.43) tail length from level of cloaca. A pair of terminal setae located on each side, dorsal setae much longer than ventral setae, 42/41 (28–42; 35.6 ± 5.2) µm and 10/12 (7–12; 9.6 ± 2.1) µm long respectively. Three transparent caudal glands, arranged in tandem.

FEMALE. Similar to males in most features. Body longer than male, about 1.6 (1.4–1.6) mm long ( Fig. 1F ). Annules about 2.3 (2.1-2.5) µm apart, spacing differing little from end of pharynx to anal region. Cervical setae length 54 (51–54; 53.0 ± 1.4) µm or 1.0 (0.8–1.0) cbd; somatic setae on remainder of body of length 26 (26–33; 29.8 ± 0.4) µm or 0.4 (0.3–0.4) cbd. Amphids smaller than in male, about 8 (6.7–8.6; 7.60 ± 0.61) µm in diameter, occupying 24 (20–24; 22.3 ± 1.8) % cbd.

Reproductive system monodelphic, prodelphic. Ovary outstretched, on left of intestine, extending near to mid length of pharynx, 57 (54–57; 55.5 ± 1.7) % of total body length from vulva. Vagina surrounded by thick musculature. Vulva transverse, located at about 0.7 body length from anterior body end, 5.3 (4.4–5.3; 4.98 ± 0.39) abd anterior to anus; a small postvulval gland distinct ( Fig. 1G ). About 3 (3–5) ventral and 2 (2–4) dorsal coelomocytes located slightly posterior to the junction of the ovary and uterus, each about 19-38 µm long and 10- 25 µm wide, the anterior margin of anteriormost coelomocyte about 4.6 (3.9–4.8) vbd from the vulva.

Tail ( Fig. 1H ) conico-cylindroid, conical portion narrowing more than in male, 6.1 (5.0–6.1; 5.53 ± 0.51) abd long; posterior fifth almost cylindroid (18–24% of tail length). Longest caudal setae 13 (13–19) µm long, no peculiar subventral setae; terminal setae, 35 (35–44; 37.7 ± 13.7) µm long.

Etymology. The specific name chonispiculum refers to the spicules with funnel-shaped manubrium, from Greek.

Differential diagnosis. Daptonema chonispiculum sp. n. is characterized within the genus by the following features: body length (1.2–1.5 mm in male and 1.5–1.6 mm in female), de Man’s indices (a = 16.8–26.6, b = 4.2– 4.7, c = 5.8–6.3), cephalic setae 0.7–0.9 hd in length, cervical setae located between the level of the amphids and just posterior to the nerve ring long (0.8–1.1 cbd in length), somatic setae on the remainder of the body short (0.3– 0.5 cbd in length), amphids 0.8–0.9 hd from anterior body end, amphid diameter 31–36 % cbd in male and 20-24 % cbd in female, one testis and one ovary, L-shaped spicules with funnel-shaped manubrium and ventral expansion (1.1–1.4 abd long on arc or 0.9-1.2 abd on chord), gubernaculum with long dorso-caudal apophysis (8–12 µm), posteriorly located vulva (V = 68–70 %), and conico-cylindroid tail (4.7–6.1 abd long) with 4 terminal setae (the longest dorsal and 44 µm in length).

Of the Daptonema species characterized by long cervical setae in the anterior pharyngeal region, D. chonispiculum sp. n. most resembles D. hirsutum ( Vitiello, 1967) , D. platonovae (Gal’tsova, 1976), D. robustum ( Tchesunov, 1980) and the new species described below. All have body length about 1–2 mm, cervical setae around 1 cbd long, amphids with diameters less than 40% cbd, L-shaped spicules, and gubernaculum with long dorsocaudal apophysis ( Table 3). However, D. chonispiculum sp. n. differs from them all in the shape of the manubrium of spicules which is funnel-shaped in D. chonispiculum but round in D. hirsutum , D. robustum and the new species described below, and weakly cephalate in D. platonovae . Daptonema chonispiculum sp. n. is rather similar to the new species described below in body length, de Man’s indices b and c, and in the diameter and location of the amphids, but is distinguished from it by the following features besides the shape of spicules: larger de Man’s index a (16.8–26.6 vs. 14.2–16.9 in the new species below), longer cephalic setae (0.7–0.9 hd vs. 0.5–0.6), longer cervical setae (0.8–1.1 cbd vs. 0.7–0.8), longer somatic setae (0.3–0.5 cbd vs. 0.1–0.2), and longer tail (4.7–6.1 abd long vs. 4.1–4.5), and with different caudal glands (the posterior gland with fluid contents vs. with peculiar fibrous contents). Daptonema chonispiculum sp. n. is also distinguished from D. hirsutum , D. platonovae , and D. robustum by a combination of the following: a smaller de Man’s index b (3.6–4.1), longer cephalic setae (1.0 hd), more posteriorly located amphids (1.0–1.3 hd abe), and longer spicules (1.2–1.5 abd on chord) in D. hirsutum ; a longer body (1.9–2.1 mm), smaller de Man's index b (3.8–4.0), shorter cephalic setae (thick, 0.5 hd), more posteriorly located amphids (1.1 hd), long cervical setae located between amphids and anterior to the nerve ring, shorter spicules (0.9 abd on arc or 0.8 on chord) and shorter tail (3.6–4.3 abd) with 2 long terminal setae (41 µm) in D. platonovae (cf. Tchesunov, 1990); and de Man's indices (smaller b = 3.3–3.8 and larger c = 7.2–8.7), long cervical setae located between amphids and anterior to the nerve ring, longer spicules (1.5 abd on arc), gubernaculum with longer dorso-caudal apophysis (24 µm), more posteriorly located vulva (V = 78%) and tail with 2 shorter terminal setae (18 µm) in D. robustum .

Daptonema chonispiculum sp. n. somewhat resembles D. sanctimarteni ( Timm, 1957) , known from the coast of Bengal Bay in Bangladesh, which is quite near the type locality of D. chonispiculum , in features such as the body length, long cervical setae located between amphids and posterior to the nerve ring, spicules with funnelshaped manubrium and gubernaculum with long dorso-caudal apophysis. However, D. chonispiculum sp. n. differs from D. sanctimarteni by the labial papillae (vs. labial setae in the latter), shorter cephalic setae (0.9 hd vs. 1.2), shorter cervical setae (1.1 cbd vs. 1.5), and L-shaped spicules (vs. arcuate spicules).

Figures

FIGURE 1. Daptonema chonispiculum sp. n. Male (Holotype ICHUM 5323; left side view): A) Entire body. B) Anterior region.C) Head region.D) Posterior region.E) Spiculesand gubernaculum.Female (Allotype ICHUM 5324; leftside view):F) Entire body. G) Vulvalregion. H) Posteriorregion. Barscales:A, F, 100 µm; B,D, H, 40 µm; C, E, 10µm; G, 40 µm.