Daptonema setihyalocella, Aryuthaka, Chittima & Kito, Kenji, 2012

Aryuthaka, Chittima & Kito, Kenji, 2012, Two new species of the genus Daptonema Cobb, 1920 (Nematoda: Xyalidae) found in the monospecific Halophila ovalis patches within an intertidal mixed-species seagrass bed on the coast of the Andaman Sea, Thailand, Zootaxa 3350, pp. 34-46 : 34-46

Daptonema setihyalocella sp. n.

( Fig. 4 A–H, 5A–F)

Type specimens. Five males and 2 females. Holotype: male ( ZIHU 4081). Allotype: female ( ZIHU 4085). Paratypes: 4 males ( ZIHU 4082-4084; KUMF T0011) and 1 female ( KUMF T0012). Collected on 4th February 2003 by C. Aryuthaka.

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

Measurements. Table 2 .

Males Females Characters: a, b, c—de Man’s ratios; abd—anal/cloacal body diameter; amp abe—distance from amphid to anterior body end; amp cbd—corresponding body diameter; amp d—amphid diameter; cs—length of cephalic setae; gub—length of gubernaculum; 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—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; v abe—distance from vulva to anterior body end; vbd—body diameter at level of vulva; -, absent. * Holotype.

Measurements in µm, except for de Man’s ratios (a, b, c) and V (%).

Holotype: L = 1167 µm, a = 14.4, b = 6.6, c = 6.0.

Males (n = 5):L = 1124–1347 (1213 ± 88.7) µm, a = 14.4–19.2 (16.1 ± 1.9), b = 6.4–6.8 (6.7 ± 0.2), c = 5.9–6.6 (6.1 ± 0.3).

Females (n = 2): L = 1308–1325 (1317) µm, a = 12.4–13.1 (12.8), b = 6.6–7.1 (6.9), c = 6.3 (6.3), V (%) = 61.2–61.5 (61.4).

Description. MALE (Holotype ZIHU 4081; range and/or avg ± sd in parentheses). Body spindle-shaped, about 1.2 (1.1–1.4) mm long; anterior portion gradually tapering to a blunt anterior extremity, middle portion thick, narrowing abruptly in tail region ( Fig. 4 A). Cuticle weakly striated with annulations somewhat obscure on lateral chords; annules 2–3 μm wide over most of body but 3–4 μm in cylindroid portion of tail. Epidermal chords thickened and protruding into body cavity, especially in pharyngeal region; in lateral view, transverse boundaries of each pair of longitudinally adjoining epidermal cells show a peculiar bridge-like appearance as in Daptonema hyalocella sp. n. ( Fig. 4 B, 5A, B). Cervical setae abundant, maximum 13 µm long; short somatic setae sparsely distributed over remaining body, 8µm long.

Head ( Fig. 4 C) blunt, weakly set-off; labial region low, about 4 (4–9) µm in height. Head with 6 tiny papillae and 12 short cephalic setae, 0.4 (0.4–0.5; 0.5 ± 0.04) hd long. Amphids circular, small, about 6 (5.6–7.3; 6.4 ± 0.7) µm in diameter, occupying 15/17 (15–19; 17.0 ± 1.3) % cbd ( Fig. 5 C); anterior margin of amphids 0.6/0.8 (0.6–0.9; 0.8 ± 0.1) hd from anterior body end. Buccal cavity cup-shaped, about 13 (13–15) µm wide, posterior portion surrounded by pharynx. Pharynx ( Fig. 4 B) muscular, short and almost cylindrical, 0.15 (0.15–0.16) body length long; cardia short, 12 (11–15) µm long. Nerve ring 53 (50–55; 52 ± 1.7) % of pharyngeal length from anterior body end. Ventral gland and excretory pore not observed.

Reproductive system monorchic. Testis outstretched, extending to posterior portion of pharynx, left of intestine, 70 (68–72; 70 ± 1.6) % of body length from level of cloaca. Spicules ( Figs 4 E, 5D) well cuticularized, distinctly cephalated at proximally end, strongly curved at middle portion (L-shaped), distal end not furcate, 1.2/1.1 (1.0–1.2; 1.1 ± 0.04) abd long on arc or 1.0/0.9 (0.8–1.0; 0.9 ± 0.04) on chord; 3–4 µm in diameter at middle of proximal and distal halves. Gubernaculum distinct, nearly 0.5 (0.47–0.54: 0.50 ± 0.02) of spicule length on arc, equipped with small, rounded dorsal apophysis and short lateral piece (crura). At least three pairs of ejaculatory glands located between midbody and cloaca on each side of intestine.

Tail ( Fig. 4 D) conico-cylindroid, 4.1 (3.8–4.1; 4.0 ± 0.1) abd long; cylindroid portion about a quarter (0.2–0.3) of tail length; 2 long terminal setae located on each side, 21 (13–21) µm long. Three caudal glands in line and partially overlapping.

FEMALE (Allotype ZIHU 4085; range in parentheses). Similar to males in most features. Body conspicuously spindle-shaped, middle portion relatively thicker than male, 1.3 (1.3–1.4) mm long ( Fig. 4 F). Amphids slightly smaller than male, 13/15 (13–15) % cbd.

Reproductive system monodelphic, prodelphic. Ovary outstretched, extending to posterior portions of pharynx, left of intestine, 47 (47–48) % of body length from level of vulva; with eggs in uterus. Vulva transversely slitlike, located slightly posterior to midbody or 5.1 (5.1–5.5) abd long anterior to anus; postvulval uterine sac absent ( Fig. 4 G, 5E). Small vaginal glands present but number indistinct; small flat gland located between epidermis and muscle layer at each lateral side of vulva ( Fig. 5 F).

Tail ( Fig. 4 H) conico-cylindroid, 3.6 (3.6–3.9) abd long; posterior cylindroid portion about 0.3 tail length. Two long terminal setae on each side, 19 (19–22) µm long.

Etymology. The specific name setihyalocella refers to the abundance of cervical setae that is one of the features diagnosing the species from the sympatric congener Daptonema hyalocella sp. n., which is also characterized by the similar transparent epidermal cells.

Differential diagnosis. Daptonema setihyalocella sp. n. is characterized in the genus by the following features; conspicuous spindle-shaped body with medium length (L = 1.1–1.4 mm, small de Man’s ratio a = 12.4–19.2), well developed epidermal chords consisting of large cells with transparent appearance (bridge-like structures observed in lateral view as if they are in body cavity), abundant short cervical setae (15 µm long), somatic setae short (8 µm long) and sparse except in pharyngeal region, small and anteriorly located circular amphids (13 – 19 % of corresponding body diameter), short pharynx (165–198 µm and de Man’s ratio b = 6.4–7.1), one testis and one ovary, L-shaped spicules with proximal cephalation, gubernaculum with small dorsal apophysis and short lateral piece (crura), and conico-cylindroid tail with 4 long terminal setae.

D. setihyalocella sp. n. resembles D. hyalocella , D. conicum , and D. trabeculosum in having the peculiar appearance of the epidermal chords. However, D. setihyalocella is easily distinguished from all of them by the presence of abundant cervical setae and 4 terminal setae in the tail, compared with no cervical setae and 2 terminal setae in the latter species. Daptonema setihyalocella sp. n. also differs from them in the features of male copulatory apparatus: the L-shaped spicules with proximal cephalation and a gubernaculum with small dorsal apophysis and short lateral piece compare with thin, loose S-shaped spicules with no proximal cephalation and indistinct gubernaculum with no dorsal apophysis in D. hyalocella , curved spicules and gubernaculum lacking both of dorsal apophysis and lateral piece in D. conicum , L-shaped spicules and gubernaculum without dorsal apophysis in D. trabeculosum . Except for the epidermal chords, Daptonema setihyalocella sp. n. is similar to D. normandicum ( De Man, 1890) , D. rectangulatum Pastor de Ward, 1985, D. tortum ( Wieser & Hopper, 1967) and D. vicinum ( Riemann, 1966) in having the L-shaped spicules and a gubernaculum with small dorsal apophysis in the male; cf. De Man (1890), Pastor de Ward (1985), Wieser & Hopper (1967), Riemann (1966). However, it is clearly distinguished from them by the presence of abundant cervical setae and also by a combination of the following features: body length (1.1–1.4 mm); de Man’s ratios (a = 12.4–19.2, b = 6.4–7.1); diameter of amphids (less than 20 % of corresponding body diameter); tail length (3.6–4.1 abd long); and spicule length (41–49µm on chord). This compares with a larger de Man’s a ratio (19–30) and longer tail (more than 5.1 abd long) in D. normandicum , a shorter body (0.5–0.8 mm) and smaller de Man’s b ratio (3.9–5.2) in D. rectangulatum , a shorter body (0.7–0.8 mm) and shorter spicules (less than 40 µm) in D. tortum , and larger amphids (29–60 % of corresponding body diameter) and longer tail (more than 4.5 abd long) in D. vicinum . In the abundance of cervical setae and the shape of spicules and gubernaculum, D. setihyalocella sp. n. resembles D. setosum ( Bütschli, 1874) but differs from it by the following features (cf. Bütschli, 1874; Gerlach, 1951; Hopper, 1969; Warwick et al., 1998): a larger de Man’s b ratio (6.4–7.1 vs. 4–6 in D. setosum ), many shorter cervical setae (15 µm long) located in anterior pharyngeal region (vs. files of long cervical setae remarkable behind amphids, 25 µm long in Hopper’s specimens), shorter somatic setae (8 µm long vs. 30 µm long in Hopper’s specimens), and presence of 4 long tail terminal setae (vs. 2 long setae or 2 long + 2 short setae).

Figures

FIGURE 4. Daptonema setihyalocella sp. n. Male (Holotype ZIHU 4081, left side view): A) Entire body. B) Anterior region. C) Head region. D) Posterior region. E) Spicule and gubernaculum. Female (Allotype ZIHU 4085; left side view): F) Entire body. G) Vulval region. H) Posterior region. Bar scales: A, F, 100 µm; B, D, H, 40 µm; C, E, 20 µm; G, 50 µm.

FIGURE 5. Daptonema setihyalocella sp. n. Male (Holotype ZIHU 4081): A) Epidermal cells showing transparent appearance of the ventral chord in the anterior region. B) Epidermal cells showing transparent appearance of the dorsal chord in the anterior region. C) Amphid and epidermal cells showing transparent appearance of the lateral chord in the head region. D) Spicule and gubernaculum. Female (Allotype ZIHU 4085): E) Eggs and sperm cells in the uterus. F) Flat vulval gland. D, computer-integrated composite of original photomicrographs. A – E, left side view; F, right side view. Bar scales: A, B, 20 µm; C, D, F, 10 µm; E, 50 µm. Abbreviations: asterisk (*) — epidermal cell showing transparent appearance, amp—amphid, da — dorsal apophysis of gubernaculum, e—egg, gub — gubernaculum, lp—lateral piece of gubernaculum, ph—pharynx, s — sperm cell, spic — spicule, u — uterus, v — vulva, vgl — flat vulval gland.

Tables

TABLE 2. Morphometrics of Daptonema setihyalocella sp. n.

Character	ZIHU	ZIHU*	ZIHU	KUMF	ZIHU	ZIHU	KUMF
	4082	4081	4083	T0011	4084	4085	T0012
L	1124	1167	1171	1254	1347	1308	1325
a	15.6	14.4	16.5	14.6	19.2	13.1	12.4
b	6.8	6.6	6.4	6.8	6.8	6.6	7.1
c	5.9	6.0	5.9	6.2	6.6	6.3	6.3
V						61.5	61.2
cs	10.7	11.1	12.7	12.3	13.0	13.1	12.3
hd	25	25	25	27	25	28	27
amp abe	19/21	16/21	18/22	20/18	17/19	21/20	19/21
amp d	6.3/5.7	5.8/6.2	5.6/5.6	7.2/7.0	7.2/7.3	5.1/5.9	4.9/5.1
amp cbd	34/35	38/37	36/36	40/38	41/40	40/40	42/43
nr abe	90	93	97	92	102	104	98
ph	165	176	183	184	197	198	186
ph bd	57	60	58	72	63	73	76
mid bd	72	81	69	86	69	100	107
mbd	72	81	71	86	70	100	107
spic arc (r/l)	52/48	56/55	53/53	54/55	57/57	-	-
spic ch (r/l)	44/41	47/45	41/44	45/45	49/49	-	-
gub	26/26	25/28	25/25	27/29	28/30	-	-
v abe	-	-	-	-	-	804	811
vbd	-	-	-	-	-	89	94
t	190	195	199	201	204	207	212
abd	47	48	49	52	53	58	55