Tetrancistrum sigani Goto and Kikuchi, 1917

Kritsky, Delane C., Galli, Paolo & Tingbao, Yang, 2007, Dactylogyrids (Monogenoidea) parasitizing the gills of spinefoots (Teleostei, Siganidae): revision of Tetrancistrum Goto and Kikuchi, 1917, with descriptions of two new species from Siganus spp. of the Red Sea and Celebes, Journal of Natural History 41 (25 - 28), pp. 1513-1551 : 1518-1523

Tetrancistrum sigani Goto and Kikuchi, 1917

( Figures 1–7 )

Synonyms: Tetrancistrum nebulosi Young, 1967 ; Pseudohaliotrematoides granulosum Yao, Wang, Xia, and Chen, 1998 ; Pseudohaliotrematoides sp. of Ko and Chan (2002).

Redescription. Based on 15 voucher specimens from S. fuscescens from the Great Barrier Reef. Body foliiform; trunk broad; cephalic region and peduncle narrow, tapered; greatest body width at level of germarium. Cephalic lobes moderately developed; each head organ comprises several groupings of terminations of cephalic-gland ducts; large bilateral groups of cephalic glands posterolateral to pharynx. Eyespots absent; accumulations of minute subovate chromatic granules uncommon; isolated granules scattered throughout cephalic region. Pharynx elongate ovate to pyriform. Testis subspherical; vas deferens not observed; seminal vesicle forming inverted ‘‘J’’ to left of copulatory complex; two small prostatic reservoirs. Copulatory complex comprised of anterior and posterior basal flanges, MCO, and accessory piece. MCO tubular, sigmoid to loosely coiled, appearing J-shaped in slightly to moderately compressed specimens; rod-shaped accessory piece dextroventral to MCO, with flattened proximal end and club-like distal end. Germarium comparatively large; ootype receives vaginal duct and bilateral common vitelline ducts; uterus expanded distally; vaginal pore at level of copulatory complex; vaginal vestibule with posterior bulge near midlength, variable, lightly sclerotized; vaginal duct meandering; vitellarium dense, empties via three bilateral pairs of vitelline ducts, each group of three ducts forming short common vitelline duct just anterior to germarium. Haptoral hooks absent in adult. Ventral and dorsal anchors typical; superficial root of ventral anchor slightly longer than deep root. Ventral and dorsal bars straight, with terminal expansions.

Measurements. Dimensions of specimens from China [in brackets] follow those from Australia. Body 1352 (1107–1576; n 55) [1262 (1031–1576; n 511)] long; greatest width 365 (284–403; n 56) [453 (322–628; n 512)]. Haptor 103 (94–121; n 55) [91 (68–103; n 512)] long, 88 (77–98; n 55) [91 (78–100; n 511)] wide. Pharynx 59 (53–65; n 56) [63 (55–69; n 511)] wide. Copulatory complex 95 (88–104; n 510) [90 (80–103; n 516)] long. Ventral anchor 83 (78–89; n 59) [72 (62–80; n 58)] long; base 42 (38–45; n 59) [38 (35– 40; n 54)] wide. Dorsal anchor 82 (75–94; n 59) 75 (69–83; n 56)] long; base 32 (28–36; n 59) [26 (2–28; n 56)] wide. Ventral bar 28 (25–33; n 55) [26 (24–29; n 53)] long; dorsal bar 35 (34–36; n 54) 31 (29–35; n 53)] long. Germarium 170 (137–206; n 56) [155 (113– 204; n 511)] long, 124 (92–149; n 56) [149 (109–175; n 511)] wide; testis 236 (179–288; n 56) [213 (147–286; n 512)] long, 191 (155–219; n 56) [197 (139–235; n 512)] wide.

Sources of current specimens. Siganus fuscescens : off Heron Island, Great Barrier Reef , Australia (23 ° 279S, 151 ° 559E), 15–22 July 2001 ; Gulf of Tonkin (South China Sea ) near Lingao , Hainan Province, China (20 ° 09N, 109 ° 59E), 11 July 2004, 15 January 2006 .

Type host and locality. Siganus fuscescens : Japan .

Site of infestation. Gills.

Specimens studied. Fifteen voucher specimens from Australia (USNPC 99360, QM G 227592–227594, MPM 18853, BMNH 2007.1.3.53–54); 16 voucher specimens from China (USNPC 99361, 99362, MPM 18852, BMNH 2007.1.3.49–52); holotype, two paratypes of T. nebulosi from S. fuscescens (USNPC 60868, 60869); paratype of T. nebulosi from S. canaliculatus (USNPC 60871); paratype of T. nebulosi from Siganus sp. (USNPC 60870).

Preυious records. Siganus fuscescens : Tokyo ( Japan) to the Philippines by Goto and Kikuchi (1917); Tarumi, Hyôgo Prefecture ( Japan) by Yamaguti (1938); Japan by Ishii and Sawada (1938); Heron Island as Tetrancistrum nebulosi by Lester and Sewell (1989); Aberdeen Market and Blake Pier, Hong Kong as Pseudohaliotrematoides sp. by Ko and Chan (2002); Moreton Bay (Queensland, Australia) as T. nebulosi by Young (1967); small bay west of Xiao Zhizhou Island, South China Sea as T. nebulosi by Yang et al. (2006). S. canaliculatus: Heron Island, Queensland, Australia as T. nebulosi by Young (1967); South China Sea, China as T. nebulosi by Zhang et al. (1999, 2003); Nanao Island, Guangdong, China as P. granulosum by Yao et al. (1998). Siganus sp.: Noumea ( New Caledonia) as T. nebulosi by Young (1967). The record of T. sigani from S. sutor by Geets et al. (1997) is erroneous, and that from Epinephelus chlorostigna (Valenciennes) (Serranidae) by Ishii and Sawada (1938) likely represents an accidental infestation.

Remarks. Tetrancistrum sigani is the type species and is differentiated from congeneric species (sensu nobis) by possessing a club-shaped accessory piece. The MCO is somewhat variable in this species, appearing J-shaped (especially in compressed specimens) ( Figure 2 ) or sigmoid to loosely coiled ( Figure 3 ). Goto and Kikuchi (1917) indicated that T. sigani lacked ‘‘marginal’’ hooks and that absence of hooks was diagnostic for the genus. However, the presence/absence of hooks does not appear to be a consistent character for diagnosis. Although Young (1967) indicated that adult worms of T. nebulosi (5 T. sigani ) possessed 14 (seven pairs) hooks, none was visible in the holotype and four available paratypes. Similarly, Ko and Chan (2002) reported seeing three pairs of haptoral hooks in their specimens from Hong Kong, while Yao et al. (1998) did not mention these structures in the English version of their description of Pseudohaliotrematoides granulosum (5 T. sigani ). In current specimens from S. fuscescens in China and Australia, hooks were not observed, suggesting that occurrence of hooks is variable and may depend on differing age or development of individual specimens of T. sigani .

Although Young (1967) differentiated T. nebulosi from T. sigani by ‘‘constant disparity between the recorded sizes of the penis stylet (MCO), accessory piece and hamuli (anchors), and because of the different shape of the copulation canal (vagina)’’, these characters do not justify specific separation of the two forms. While the respective dimensions reported by Goto and Kikuchi (1917) for the copulatory complex and anchors are greater than those reported by Young (1967), ranges of measurements obtained from specimens collected from Australia and China do not suggest significant differences since considerable overlap exists among them. In addition, the morphology of the vagina and vaginal vestibule is variable among all specimens of T. sigani examined during this study. Thus, T. nebulosi Young, 1967 is considered a junior subjective synonym of T. sigani Goto and Kikuchi, 1917 .

Yao et al. (1998) described Pseudohaliotrematoides granulosum from S. canaliculatus from China. While these authors did not compare their species to T. sigani , their drawing of the copulatory complex and its reported dimensions and those of the anchors are consistent with present specimens. Thus, P. granulosum is placed in synonymy with T. sigani as a junior subjective synonym.

Woodland (1990) and Froese and Pauly (2006) considered S. nebulosus (host to T. nebulosi ) and S. fuscensens (host to T. sigani ) to be synonyms, with S. fuscescens having priority. In addition, Woodland (1990), who considered S. canaliculatus and its sibling S. fuscescens to be distinct, indicated that the two species have frequently been confused during identification or considered to be conspecific by previous workers. Because the latter two fishes are sympatric and morphologically similar, it is uncertain whether or not the reported records of T. sigani on S. canaliculatus are valid. The synonymy of S. nebulosus and S. fuscescens , along with the potential for confusion during identification of S. canaliculatus and S. fuscescens , provides additional support for the proposed synonymies of T. sigani , T. nebulosi , and P. granulosum .

Tetrancistrum fusiforme ( Yamaguti, 1953) Young, 1968

( Figures 8–14 )

Synonyms: Pseudohaliotrema (Pseudohaliotrematoides) fusiforme Yamaguti, 1953 ; Pseudohaliotrematoides fusiforme Yamaguti, 1953 .

Measurements. Body 596 (n 51) long; greatest width 142 (n 51) at body midlength or at level of gonads. Haptor 135 (n 51) long, 108 (n 51) wide. Pharynx 35 (n 51) wide. Copulatory complex 117 (103–141; n 55) long. Ventral anchor 99 (95–102; n 54) long; base 51 (47–57; n 54) wide. Dorsal anchor 100 (93–103; n 54) long; base 30 (24–34; n 54) wide. Ventral bar 32 (27–35; n 53) long; dorsal bar 48 (41–60; n 54) long. Hook 14 (13– 15; n 52) long. Germarium 50 (n 51) long, 69 (n 51) wide; testis 65 (n 51) long, 60 (n 51) wide.

Source of current specimens. Siganus lineatus : off Heron Island, Great Barrier Reef, Australia (23 ° 279S, 151 ° 559E), 16 July 2001.

Type host and locality. Siganus sp.: Macassar, Celebes.

Site of infestation. Gills.

Specimens studied. Five voucher specimens ( USNPC 99363 ; QM G 227590–227591 ); holotype, numerous paratypes ( MPM 22839) ; voucher specimen from Siganus lineatus deposited by Young (1967) ( USNPC 61297 ) ; voucher specimen from Acanthurus xanthopterus deposited by Young (1967) ( USNPC 61296 ) .

Preυious records. Siganus sp.: Macassar, Celebes as Pseudohaliotrema (Pseudohaliotrematoides) fusiforme by Yamaguti (1953). S. lineatus: Green Island, Australia as Tetrancistrum fusiforme by Young (1967); Heron Island, Great Barrier Reef, Australia as T. fusiforme by Young (1967). Acanthurus xanthopterus: Green Island, Australia as T. fusiforme by Young (1967).

Remarks. This species was originally described by Yamaguti (1953) as Pseudohaliotrema (Pseudohaliotrematoides) fusiforme and serves by monotypy as the type species of the subgenus. Yamaguti (1963) subsequently elevated the subgenus to generic rank, but Young (1967) transferred the species to Tetrancistrum based primarily on the comparative morphology of internal body features and haptoral sclerites. Young’s (1967) action resulted in Pseudohaliotrematoides becoming a junior subjective synonym of Tetrancistrum . The species was originally described from an undetermined species of Siganus from Macassar. However, examination of the slide containing the type specimens, and comparing the parasite mix with those found in Australia, suggests that S. lineatus may be its natural host (see Kritsky and Galli 2007).

The original description of this species is adequate for diagnosis. The species is distinguished from all other species of Tetrancistrum by having a copulatory complex comprising a dilated, curved, strongly sclerotized MCO and an accessory piece consisting of two distinct parts, with the sinistral part composed of two portions diagonally articulated to each other ( Figure 9 ). Seven pairs of haptoral hooks with an ancyrocephaline distribution ( Mizelle 1936; Mizelle and Price 1963) appear to occur consistently in adults, although the full complement of hooks is often difficult to observe in fixed and mounted specimens.

Figures

Figures 1–7. Tetrancistrum sigani Goto and Kikuchi, 1917 from the mottled spinefoot, Siganus fuscescens, Great Barrier Reef, Australia. (1) Whole mount (composite, ventral view). (2) Copulatory complex (ventral view, slightly compressed). (3) Copulatory complex (ventral view). (4) Ventral bar. (5) Dorsal bar. (6) Ventral anchor. (7) Dorsal anchor. Scale bar: 400 Mm (1); 30 Mm (2–7).

Figures 8–14. Tetrancistrum fusiforme (Yamaguti, 1953) Young, 1967 from the golden-line spinefoot, Siganus lineatus, Great Barrier Reef, Australia. (8) Whole mount (composite, ventral view). (9) Copulatory complex (ventral view). (10) Dorsal anchor. (11) Ventral bar. (12) Dorsal bar. (13) Ventral anchor. (14) Hook. Scale bar: 150 Mm (8); 30 Mm (9–14).