Pseudopecoeloides tenuis Yamaguti, 1940

Aken'Ova, Thelma, Cribb, Thomas & Bray, Rodney, 2009, Seven species of Pseudopecoeloides Yamaguti, 1940 (Digenea, Opecoelidae) from temperate marine fishes of Australia, including five new species, ZooKeys 5 (5), pp. 1-32 : 4-6

Pseudopecoeloides tenuis Yamaguti, 1940

Host: Priacanthus macracanthus Cuvier ( Priacanthidae : Perciformes ), red bigeye.

Localities: Moreton Bay : Off Tangalooma 27°14’S, 153°19’E; off Shorncliffe 27°21’S, 153°07’E.

Site: Pyloric caeca, intestine.

Material studied: 11 adults. Moreton Bay, Queensland: 6 off Tangalooma , February 1993 ; 5 off Shorncliffe , March and April 1995 .

Voucher specimens: QM G 230433 - G 230441 ; BMNH 2008.12.9.44-50 .

Description ( Figures 1-3 ): Based on 8 gravid whole-mounts and 3 sets of serial sections. Measurements are of 8 gravid, unflattened, laterally and dorso-ventrally mount-ed worms.

Body elongate, slender, more or less dorso-ventrally flattened, with 3 distinct constrictions adjacent to gonads; maximum width in region of gonads, 3,600 -5,864 (4,468) × 225-450 (340); width to length ratio 1:10.9-17.7 (14.0). Oral sucker oblong, ventrally subterminal, 225-311 (257) × 135-214 (175). Ventral sucker pedunculate, spherical to subspherical, smaller than oral sucker, 91-113 (102) × 94-117 (104); sucker width ratio 1:0.5-0.8 (0.6). Ventral sucker peduncle moderately long, retractile, 238-454 (353) × 123-156 (137), 5.3-11.1 (8.0) % of body length. Forebody short, 331-425 (379), 6.6-10.4 (8.7) % of body length; peduncle to forebody length ratio 1:0.8-1.6 (1.1). Prepharynx distinct, very short. Pharynx distinct, spherical to subspherical, 75-110 (88) × 84-100 (90). Oesophagus very short, looped. Caeca long, narrow, clearly visible at body constrictions, unite with excretory vesicle close to posterior end of body to form uroproct.

Testes 2, entire, fusiform, tandem, separate, in middle third of body; anterior 250- 428 (319) × 136-214 (166); posterior 275-408 (330) × 143-227 (174). Post-testicular area 1,044 -2,057 (1,582) long, 29-40 (35) % of body length. Cirrus-sac absent. Seminal vesicle long, sinuous anteriorly; expanded posterior portion 227-402 (300) × 65- 130 (93). Pars prostatica distinct, thick-walled, surrounded by gland-cells. Ejaculatory duct short, narrow. Genital atrium indistinct. Genital pore antero-sinistral to intestinal bifurcation, level with or anterior to posterior margin of oral sucker, 207-246 (224) from anterior extremity, 5.8-4.2 (5.0) % of body length.

Ovary oval, entire, directly anterior to anterior testis, 163-220 (192) × 100- 156 (127). Mehlis’ gland, anterior to ovary. Uterine seminal receptacle occupies posterior coils of uterus. Laurer’s canal passes postero-ventrally and opens dorsally at level of anterior margin of ovary. Uterus usually coils intercaecally between anterior margin of ovary and posterior expanded portion of seminal vesicle, then passes to genital aperture with little or no coiling. Metraterm indistinct, thin-walled, with anterior extremity surrounded by gland cells. Eggs relatively small, numerous, oval, operculate, 39-54 (47) × 25-34 (28). Vitelline follicles restricted to area posterior to ventral sucker, extend from 700-925 (801) from anterior extremity, 14.7-25.7 (18) % of body length, to 18-72 (39) from posterior extremity, with bilateral in-terruptions at level of each gonad at points of constriction; follicles in 2 separate fields ventrally in uterine area; fields confluent dorsally in uterine, intergonadal and post-testicular regions, lateral, dorsal and ventral to caeca except in areas adjacent to gonads; anterior limit variously overlaps expanded posterior portion of seminal vesicle.

Excretory pore terminal. Excretory vesicle tubular, I-shaped, passes anteriorly to terminate at point just anterior to posterior margin of ovary.

Comments: Except for a few slight morphological differences, the present material is almost identical to P. tenuis , as originally described. The differences observed between the present material and that of Yamaguti (1940) include: a longer forebody relative to the body length (6.6-10.4 (8.7) versus 5.1%); smaller eggs measuring 39-54 × 25-34 (47 × 28) versus 54-60 × 33-39; and a genital pore which is more posteriorly situated, at 3.8-6.1 (5.1) % compared with 3.1% of the body length from the anterior extremity. Although the difference in egg size is significant, it is not surprising, since Yamaguti measured the eggs from live worms. The other differences are most likely as a result of fixation and may therefore not be taxonomically significant. Moreover, the present material and Yamaguti’s are both from priacanthids.

Pseudopecoeloides tenuis is similar to P. tenuoides in almost every metrical feature and in the bilateral constrictions adjacent to the gonads observed in Yamaguti’s material and the present material. This resemblance was also noted by Martin (1960), but he separated the species on the basis of egg size (smaller in P. tenuoides ), the sizes of the suckers (smaller in P. tenuoides ) and on the occurrence of pads on the ventral sucker in P. tenuoides . The present material is very similar to P. tenuoides and does not exhibit the differences observed by Martin (1960) between his worm and Yamaguti’s P. tenuis . The difference in egg size probably resulted from the fact that Yamaguti measured the eggs of P. tenuis from live material, whereas the egg measurements of P. tenuoides were probably taken from permanent mounts. The only noticeable differences between the present material and P. tenuoides are that the latter has a larger oral sucker relative to the pharynx, reflected by a ratio of 1:2.8 versus 1:1.5-2.4 (1.9) [1.8], and it has pads in its ventral sucker. Yamaguti (1970) also observed the pads described by Martin (1960) in P. tenuoides in the material he examined from the glasseye Heteropriacanthus cruentatus (Lacepède) (Priacanthidae) (the type-host) and the bluelined surgeonfish Acanthurus nigroris Valenciennes (Acanthuridae) off Hawaii (type-locality). No similar pads were observed in the present material, although, if they occurred, it would have been difficult if not impossible to see them, since our worms were mostly mounted laterally. This feature needs to be investigated further before a decision regarding the status of P. tenuoides can be taken.

P. tenuis is widespread in the Indo-Pacific region and is reported in the Great Australian Bight ( Lebedev, 1968), off New Zealand ( Manter, 1954; Korotaeva, 1975) and off New Caledonia ( Bray and Justine, 2008)

Figures

Figs 1-3. Pseudopecoeloides tenuis Yamaguti, 1940 ex Priacanthus macracanthus. 1. Whole-mount lateroventral view. 2. Terminal genitalia. 3. Ventral view of posterior end showing uroproct. Scale bars: 1, 500 µm; 2, 200 µm; 3, 100 µm.