Acutogordius taiwanensis, Chiu, Ming-Chung, Huang, Chin-Gi, Wu, Wen-Jer & Shiao, Shiuh-Feng, 2017

Chiu, Ming-Chung, Huang, Chin-Gi, Wu, Wen-Jer & Shiao, Shiuh-Feng, 2017, A new orthopteran-parasitizing horsehair worm, Acutogordiustaiwanensis sp. n., with a redescription of Chordodesformosanus and novel host records from Taiwan (Nematomorpha, Gordiida), ZooKeys 683, pp. 1-23 : 1-6

Acutogordius taiwanensis sp. n.

Type locality.

Wufengqi Waterfalls (24°49′55.62′′N, 121°44′50.10′′E), Jiaushi Township, Yilan County, Taiwan (holotype and allotype). Paratypes were collected from Sindian, New Taipei City, and the Fushan Botanical Garden, Yilan County. See Table 1 for detailed information.

Type material.

Partial bodies of the holotype and allotype were deposited with their hosts at the National Museum of Natural Science. Paratypes were deposited at the Department of Entomology, National Taiwan University, Taipei; the National Museum of Natural Science, Taichung, Taiwan; and Lake Biwa Museum, Shiga, Japan. See Table 1 for detailed information.

Type hosts.

Eugryllacris sp., Neanias magnus Matsumura and Shiraki, 1908 ( Orthoptera : Gryllacrididae ), Deflorita apicalis (Shiraki, 1930), Elimaea sp., Hexacentrus japonicus Karny, 1907, H. unicolor Serville, 1831, Isopsera sp., Mecopoda elongata (Linnaeus, 1758), Phaulula sp., Pyrgocorypha formosana Matsumura and Shiraki, 1908, Sinochlora longifissa (Matsumura and Shiraki, 1908) ( Orthoptera : Tettigoniidae ). See Table 2 for detailed information.

Etymology.

The specific name refers to the type locality, Taiwan.

Diagnosis.

Acutogordius taiwanensis sp. n. is morphologically similar to A. protectus Schmidt-Rhaesa and Geraci, 2006 with regards to the (1) distribution pattern of tiny bristles on the ventral posterior end, (2) moderately flat areoles (rounded in elevation) covering the tail tips, and (3) cone-shaped spines scattered on the base of the tail lobes of the male samples. However, it is distinct because of the small ornamentations on the mid-body.

Description (Figs 1-7). Male adults (n = 14) (Figs 2, 3). Body length 288.3 ± 90.1 (133-428) mm, width (widest, after dehydration) 623 ± 173 (404-1079) µm. Body light brown, smooth, and slightly mucous covered (liquid on the body surface slightly viscous, light on live worms usually refracted) before fixed in alcohol, alcohol-preserved specimens significantly flat and hard.

Anterior end columnar and slightly narrowed at tip; anterior tip white (white cap) with a dark-brown collar (Fig. 1A); white spots scattered on brown collar (Fig. 1B, C) in some samples (3/14); under SEM, surface of anterior end wrinkled (Fig. 1F) (4/14), smooth (Fig. 1D) (7/14), or smooth but wrinkled on the tip (Fig. 1E) (3/14); short bristles or holes scattered on some samples; no obvious boundary between the white cap and dark-brown collar.

Cuticle in mid-body smooth, slightly wrinkled, or cracked; short or cone-like bristles (Fig. 3D, E) scattered on some samples (6/14).

Posterior end divided into two tail lobes, each 360.25 ± 53.30 (303.70-489.58) µm in length; lobe tips generally tapered, wrinkled, or covered by moderately flat areoles with short spines amongst areoles; inner side of tail lobes smooth; tiny spines scattered around tip; cone-shaped spines or flat areoles scattered on base behind post-cloacal crescent.

Ventral side of posterior end structured with post-cloacal crescent, cloacal opening, and tiny bristles. One post-cloacal crescent not evident as it was covered by larval cuticle, post-cloacal crescent length (extension along longitudinal axis) 275.48 ± 68.84 (195.78-417.03) µm, width (widest) 44.81 ± 16.21 (18.73-83.01) µm, located near base of tail lobes; post-cloacal crescent slightly curved (Fig. 2B, E) (5/13), nearly at right angle (Fig. 2A, D) (5/13, including two samples reared for laying eggs), or semicircular (which were more slender than the curved or angled ones) (Fig. 2C, F) (3/13). Two ends of post-cloacal crescent extending over (Fig. 2 A, C, D, F) (11/13) or anterior to (Fig. 2B, E) (2/13) starting point of tail lobe bifurcation. Cloacal opening circular or slightly oval-shaped, 26.61 ± 7.86 (14.63-43.23) µm in diameter, 55.50 ± 19.71 (32.55-89.90) µm away from anterior margin of post-cloacal crescent, surrounding depressed area in four samples, no circumcloacal spine. Cloacal openings of four specimens not visible as they were covered by the larval cuticle or by mold. Tiny bristles scattered over ventral side of posterior end except in two samples covered by larval skin or mold; tiny bristles scattered over ventral posterior end and concentrated on tail lobes (Fig. 3B) (3/13), anterior post-cloacal crescent (Fig. 3A) (1/13), or randomly scattered on the cuticle (Fig. 3D, E) (9/13).

Female adults (n = 10) (Fig. 4). Body length 271.80 ± 99.14 (73-432) mm, width (widest, after dehydration) 896 ± 171 (578-1120) μm, light brown, slightly mucous covered (liquid on the body surface slightly viscous, light on live worms usually refracted) before fixed in alcohol. Alcohol-preserved specimens flat in egg-laying samples. Anterior end (Fig. 4A) columnar and slightly narrowed at tip; white cap and dark-brown collar present. Under SEM, surface of anterior end smooth or wrinkled; one sample had hole-like structures (Fig. 5J); small spines scattered on surface of three samples; no obvious boundary between the white cap and dark-brown collar. Cuticle in mid-body smooth, wrinkled, or crack-like; most with small spines scattered on cuticle (7/10). Posterior end (Fig. 4B) rounded, smooth, without spines or bristles. Cloacal opening on terminal end circular, 24.70 ± 5.88 (16.80-30.62) μm in diameter, no circum-cloacal spine.

Eggs (Fig. 6G). Egg string (Fig. 6G) length 12.04 ± 3.91 (4.94-19.13) mm, width 0.61 ± 0.11 (0.343-0.708) mm (n = 11), white or light yellow in color, deposited as short pieces not adhering to substrate. Eggs (12 days after being laid, nearly hatching) oval-shaped, length 31.93 ± 3.08 (28.79-34.67) µm, width 25.69 ± 1.25 (24.04-27.71) µm (n = 6).

Larvae (Fig. 6 A–C, E–F, H). Newly hatched larvae near eggs presented as “worm-form” (Fig. 6B, E) or “cyst-form” (Fig. 6A). Both found among crushed egg strings. Under light microscopy, worm form (n = 13) larvae pre-septum length 31.25 ± 2.83 (24.66-34.14) μm, width 13.18 ± 0.44 (12.30-14.13) μm; post-septum length 80.75 ± 3.87 (77.16-89.13) μm, width 11.17 ± 0.70 (9.76-2.60) μm. Proboscis (same as stylet in our previous description in Chiu et al. (2011)) length 11.77 ± 0.87 (10.14-12.46) μm, width 3.29 ± 0.39 (2.79-4.02) μm; pseudo-intestines unequally subdivided, oval with length 48.22 ± 2.86 (44.69-54.32) μm, width 7.99 ± 0.87 (6.57-9.17) μm. Cyst form (n = 15) larvae post-septum folded into an oval shape, length 25.64 ± 1.66 (22.34-27.88) μm, width 17.41 ± 1.40 (14.91-19.38) μm; proboscis the only obvious structure, length 11.19 ± 1.25 (8.22-13.23) μm, width 2.60 ± 0.63 (1.38-3.21) μm.

Under SEM (worm-form larvae), larvae superficially annulated with 13 segments on pre-septum and 35 on post-septum, ectodermal septum not distinguishable (Fig. 6E). Hooks arranged in three rings on anterior pre-septum: outer ring containing seven hooks, including ventral double hooks close to each other; middle and inner rings containing six hooks, and six inner spines, located between each outer hook (Fig. 6F). Proboscis inside the pre-septum covered by sheath, ornamented with two sets of spines: seven larger spines arranged laterally in two lines, except the largest terminal spine; seven smaller spines on dorsal side, no spines on ventral proboscis (Fig. 6H). One single posterior spine located on end of post-septum (Fig. 6E); exterior openings of pseudo-intestine may be present, but not clear (Fig. 6C).

Field-collected cysts (Fig. 6D) Three cysts inside a snail length 23.59-24.35 μm, width 15.33-16.45 μm; proboscis length 11.42-11.91 μm, width 1.67-2.047 μm. Shape of cysts similar to cyst-form larvae, no cyst wall found, likely ruined during sample preparation.

Phylogeny.

Except for one female with insufficient DNA for sequencing, the 23 Acutogordius COI sequences (GenBank numbers KX591922, KX591926-KX591935, KX591937-KX591948) contained eight haplotypes with 442 invariable sites, six singletons, and two parsimoniously informative sites. The genetic distance among them was 0.0025 with a range of 0.0000-0.0112. The phylogenetic tree had a polytomic topology in which some clades were not highly supported because of low bootstrap values and short genetic distances (Fig. 7). The genetic distance between the COI sequences of these 23 Acutogordius individuals and that of G. balticus was 0.27948 compared to 0.25455 and 0.27439 for G. attoni and G. cf. robustus , respectively.

Comments.

The 23 Acutogordius samples from orthopteran hosts were determined to be from a single species based on their low genetic distances, which was similar to the intraspecific pairwise distances found within G. cf. robustus (0.64-2.63%) ( Hanelt et al. 2015) and C. formosanus (0-1.92%) ( Chiu et al. 2011) and lower than the interspecific pairwise distances among species of the genera Gordius (8.0-24.3%) ( Hanelt et al. 2015) and Chordodes (16.84%) ( Chiu et al. 2011).

All three morphological types of post-cloacal crescents identified in A. protectus were apparent in the Acutogordius taiwanensis sp. n. samples. Nevertheless, post-cloacal crescents significantly extending onto the tail lobes were only described in Acutogordius taiwanensis sp. n. and previously in A. acuminatus de Miralles and de Villalobos 1998, A. feae (Camerano, 1897), A. obesus (Camerano, 1895), and A. sulawensis Schmidt-Rhaesa and Geraci, 2006. High intraspecific variation in the post-cloacal crescent makes this structure unsuitable as a diagnostic characteristic at the species level, despite that it is the most obvious structure that can be examined by stereomicroscope.

Short bristles on the mid-body were a newly described character, which were first found in A. finni ( Schmidt-Rhaesa and Schwarz 2016). This character is not likely to be examined by stereomicroscope, but in Acutogordius taiwanensis sp. n., the short bristles were still not consistently present in all individuals examined under SEM. One of the possible reasons is that the bristles were covered by mucus on the cuticle surface. The surface of Acutogordius has been generally described as totally smooth ( de Miralles and de Villalobos 1998, Schmidt-Rhaesa et al. 2006). However, various structures were found on the surface of Acutogordius taiwanensis sp. n., including wrinkled, cracked, or indented structures. A similar structure (fine grooves as described in Schmidt-Rhaesa and Schwarz (2016) have been found in A. finni (Figs 4D, E in Schmidt-Rhaesa and Schwarz (2016)), and some of the bristles look like “sticks” on the cuticle surface. In addition, the areole-like structure on the anterior end of one female, also suggested the possibility that the moderately flat areoles covering male tail tips were caused by mucus. Thus, although the moderately flat areoles and short bristles were applied as the main diagnostic characters for Acutogordius taiwanensis sp. n. and A. protectus , more information may be necessary to confidently distinguish between the two species.