DACTYLOGYRIDAE Bychowsky, 1933

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 : 1516-1518

DACTYLOGYRIDAE Bychowsky, 1933

Tetrancistrum Goto and Kikuchi, 1917

Synonyms: Pseudohaliotrematoides Yamaguti, 1953 ; Pseudancyrocephalus Yamaguti, 1968 ; Pseudohaliotrematodides of Ktari and Ktari (1974) (lapsus).

Diagnosis. Body foliiform, infrequently fusiform, comprising body proper (cephalic region, trunk, and peduncle) and haptor; haptor a simple extension of peduncle. Tegument smooth. Two terminal and two bilateral subterminal cephalic lobes; three bilateral pairs of head organs; cephalic glands lateral or posterolateral to pharynx. Eyespots usually absent; chromatic granules minute, subovate, scattered throughout cephalic region; randomly distributed accumulations of granules infrequent in cephalic region. Mouth midventral, subterminal at level of head organs, opens into buccal tube; buccal tube extends posteriorly along body midline to pharynx to form buccal cavity; pharynx a muscular, glandular bulb; oesophagus short to moderately elongate; intestinal caeca two, with or without diverticula, apparently terminating blindly posterior to gonads. Common genital pore midventral, posterior to intestinal bifurcation. Gonads intercaecal, tandem; germarium pretesticular, forming a cap over anterior end of testis. Testis subspherical to subovate; vas deferens not observed; seminal vesicle fusiform; two prostatic reservoirs dorsal to copulatory complex, each emptying into base of male copulatory organ (MCO) via single duct. Copulatory complex comprises accessory piece and MCO. Oviduct short; ootype receives ducts of vitellarium and vagina; uterus extends anteriorly along body midline to common genital pore; seminal receptacle not observed. Vaginal aperture dextromarginal in anterior portion of trunk; vagina with distal vestibule and proximal meandering duct. Vitellarium coextensive with gut. Haptor with dorsal and ventral anchor-bar complexes; seven pairs of similar hooks with ancyrocephaline distribution ( Mizelle 1936; Mizelle and Price 1963) present or absent in adults; ventral anchor with large, flat, grooved, subequal basal roots, delicate shaft and short recurved point; dorsal anchor with elongate flat grooved deep root, comparatively short rod-like superficial root, delicate shaft, short recurved point; bars simple. On gills of marine perciform fishes of the Siganidae , Lutjanidae , and Acanthuridae .

Type species. Tetrancistrum sigani Goto and Kikuchi, 1917 from Siganus fuscescens , S. canaliculatus , and Siganus sp. (all Siganidae ).

Other species. Tetrancistrum fusiforme ( Yamaguti, 1953) Young, 1967 from Siganus lineatus and Siganus sp. (both Siganidae ) and Acanthurus xanthopterus (Acanthuridae) ; T. indicum (Paperna, 1972) comb. n. from S. sutor , S. riυulatus, and Siganus sp. (all Siganidae ); T. kala ( Yamaguti, 1968) comb. n. from Naso breυirostris and N. hexacanthus (Bleeker) (both Acanthuridae ); T. lebedeυi Gupta and Sharma, 1982 (species inquirenda) from Lutjanus johnii (Bloch) (Lutjanidae) ; T. longicirrus ( Yamaguti, 1968) comb. n. from N. breυirostris and N. hexacanthus (both Acanthuridae ); T. longispicularis ( Yamaguti, 1968) comb. n. from N. breυirostris ( Acanthuridae ); T. lutiani Tubangui, 1931 from L. lioglossus Bleeker (now L. monostigma [Cuvier]) ( Lutjanidae ); T. makau nom. n. (5 Pseudancyrocephalus nasonis Yamaguti, 1968 ) from N. breυirostris ( Acanthuridae ); T. nasonis Young, 1967 from N. annulatus (Quoy and Gaimard) , N. breυirostris and N. unicornis (Forsskål) (all Acanthuridae ); T. oraminii Young, 1967 from S. canaliculatus (Siganidae) ; T. polymorphum (Paperna, 1972) comb. n. from S. luridus and S. riυulatus (both Siganidae ); T. strophosolenus sp. n. from S. riυulatus ( Siganidae ); T. suezicum (Paperna, 1972) comb. n. from S. riυulatus ( Siganidae ); T. aealtairense nom n. (5 T. indicum Raju and Rao, 1978 ) from S. canaliculatus (Siganidae) ; T. yamagutii sp. n. from Siganus sp. ( Siganidae ).

Remarks. Goto and Kikuchi (1917) did not provide a formal generic diagnosis when they proposed Tetrancistrum and described T. sigani from Japan. In a short paragraph at the end of their paper, these authors stated that the genus was characterized by lacking eyes and ‘‘marginal hooks’’ and by having a lateral vagina and a ‘‘caudal disc’’ bearing two pairs of hooks (anchors) with each pair provided with a connecting ‘‘transverse piece’’ (bar). These authors also noted that the intestinal caeca were united posteriorly and were provided with ‘‘lateral secondary coeca (sic)’’ (diverticula). This characterization was apparently deemed unsatisfactory by Johnston and Tiegs (1922), Price (1937), and Yamaguti (1963), all of whom provided comparatively non-specific diagnoses for the genus. The non-specificity of these diagnoses allowed the assignments of unrelated dactylogyrid species to the genus, which resulted in an apparent unnatural taxon. Young (1967) provided a more detailed diagnosis and recognized that morphological features of the haptoral sclerites as well as internal anatomy were important to define the genus. He limited the taxon to five species parasitizing fishes of the Siganidae , Acanthuridae , and Lutjanidae . The diagnosis provided herein characterizes Tetrancistrum as dactylogyrids having a foliiform (infrequently fusiform) body, tandem gonads with the germarium forming a conical cap over the anterior end of the testis, two prostatic reservoirs, a dextromarginal vaginal aperture, a distal vaginal vestibule, and each ventral anchor with large, grooved, subequal, basal roots and each dorsal anchor with a large, grooved, deep root and a short, rod-like, superficial root. Members of the genus usually lack eyespots and apparently a seminal receptacle, and haptoral hooks are often absent in adult worms.

The morphology of the intestine of Tetrancistrum spp. is problematical. Goto and Kikuchi (1917) described the intestine of T. sigani as running ‘‘backwards on either side of the body and unite directly behind (posterior to) the testis but again separate a little further (sic) backwards and terminate blindly shortly afterwards’’. In their respective descriptions, Young (1967) and Tubangui (1931) showed similar configurations of the intestinal caeca of T. nebulosi (5 T. sigani ), T. oraminii , and T. lutiani , while Young (1967) described a complex of connections between the two caeca posterior to the testis in T. nasonis . Paperna (1972b) and Raju and Rao (1978) reported simple intestinal caeca uniting posterior to the testis in the three subspecies of Pseudohaliotrematoides polymorphus (now T. polymorphum , T. suezicum , and T. indicum ) and T. indicum of Raju and Rao (1978) (now T. aealtairense ), respectively, while Gupta and Sharma (1982) and Yao et al. (1998) did not mention the morphology of the gut in their respective descriptions of T. lutiani and Pseudohaliotrematoides granulosus (now T. sigani ). In the species of Pseudancyrocephalus described from species of Naso by Yamaguti (1968) (all herein transferred to Tetrancistrum ), the gut is described as simple, with each caecum ending blindly in the posterior trunk, including that of P. dupicatus , herein considered a junior synonym of T. nasonis . In none of the specimens available to us, including the types of previously described species, were intestinal caeca seen to have terminal or subterminal connections. Available specimens suggest that the intestinal caeca end blindly in the posterior trunk.

Young (1967) also noted that the intestine of species of Tetrancistum was highly variable and did not consider the presence of lateral diverticula sufficient to differentiate Pseudohaliotrematoides from Tetrancistrum . As a result, he placed Pseudohaliotrematoides in junior subjective synonymy with Tetrancistrum and transferred its type species, P. fusiforme , to the latter genus. We concur with Young’s actions concerning Pseudohaliotrematoides and also consider Pseudancyrocephalus with species from acanthurid fishes a junior subjective synonym of Tetrancistrum .

Machida (1979) proposed Nasoancyrocephalus Machida, 1979 for a dactylogyrid, N. diorchis Machida, 1979 , from the gills of Naso unicornis in Japan. The species was stated to resemble those of Pseudancyrocephalus (5 Tetrancistum) by having longitudinally striated anchor roots, two prostatic reservoirs, and a seminal receptacle. Machida (1979) distinguished Nasoancyrocephalus from Pseudancyrocephalus by its species possessing two testes (testis single in species of Pseudancyrocephalus ), an autapomorphic character that clearly developed secondarily within the Dactylogyridae (see Boeger and Kritsky 1993, 2001). Acceptance of Nasoancyrocephalus may therefore result in Tetrancistrum becoming paraphyletic because a synapomorphy for the latter is not apparent if both genera are recognized. Should it be shown that N. diorchis has a common ancestor with one or more (but not all) species of Tetrancistrum , Machida’s genus should be rejected and placed in synonymy with Tetrancistrum . This synonomy is not proposed at this time, however, pending phylogenetic analyses of species comprising the two genera.