Two new genera, shape Provitellus and shape Ovipusillus, and four new species of Monorchiidae (Digenea) from carangid fishes of Queensland, Australia

Systematic Parasitology 40: 21–33, 1998. © 1998 Kluwer Academic Publishers. Printed in the Netherlands.

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Two new genera, Provitellus and Ovipusillus, and four new species of Monorchiidae (Digenea) from carangid fishes of Queensland, Australia Alistair D.M. Dove & Thomas H. Cribb Department of Parasitology, The University of Queensland, Brisbane, Queensland 4072, Australia Accepted for publication 25th September, 1997

Abstract Two new genera and four new species of monorchiid digeneans are described from the Great Barrier Reef and Moreton Bay, Queensland. Provitellus turrum n. g., n. sp. from Pseudocaranx dentex and Trachinotus coppingeri is characterised by the presence of vitelline follicles in the forebody, a single testis, a unipartite terminal organ and filamented eggs. Ovipusillus mayu n. g., n. sp. from Gnathanodon speciosus is characterised by the presence of two testes, vitelline follicles overlapping the ventral sucker and a large, complex cirrus-sac that contains a coiled eversible ejaculatory duct joined by the pars prostatica halfway along its length. Paramonorcheides pseudocaranxi n. sp. from Pseudocaranx dentex differs from other species described in this genus in the longer flatter forebody, entire ovary and the well-developed cirrus-sac. Chrisomon gaigai n. sp. from Trachinotus coppingeri and T. botla is characterised by the unflattened forebody and transversely oval pharynx. Chrisomon is redefined to include species of Lasiotocus with a vitellarium composed of clusters of tubular acini, creating the following new combinations: C. albulae n. comb. for L. albulae Overstreet, 1969, C. ulua n. comb. for L. ulua Yamaguti, 1970 and C. weke n. comb. for L. weke Yamaguti, 1970. The diagnosis of Lasiotocus is amended accordingly and the new combinations, L. polynemi n. comb. and L. sunderbanensis n. comb., are created for C. polynemi Dutta, Hafeezullah & Manna, 1994 and C. sunderbanensis Dutta, Hafeezullah & Manna, 1994, respectively. Extrapolation of our collection data suggests that there may be as many as 80 species of monorchiids infecting carangid fishes in Australia and 180 species infecting carangids in all oceans of the world. The latter figure greatly exceeds the number of monorchiids described from all host families to date. Introduction The Monorchiidae Odhner, 1911 is a large family of small digenean trematodes living in the intestine of teleosts. They are characterised by the possession of complex terminal genitalia covered with recurved spines, a spiny tegument and restricted fields of vitelline follicles (Schell, 1985). Approximately 50 genera have been proposed (Bray & Gaevskaya, 1993) and there are more than 120 described species. Monorchiids have been recorded from at least 28 families of marine fishes. Fish become infected by eating benthic invertebrates, in which metacercariae occur (De Martini & Pratt, 1964; Prévot, 1967; Stunkard, 1981a,b). The species described here are from a survey of carangid fishes from Queensland, Australia. The Carangidae is a large family of medium-sized to large

perciform fishes; 63 species are present in Australian waters, 8 of which are endemic (Gunn, 1990). The world carangid fauna includes four well-defined subfamilies and 140 species, many of which are of considerable economic importance to fisheries industries (Kailola, Williams, Stewart, Reichelt, McNee & Grieve, 1993).

Materials and methods Fish were collected at Heron Island and Moreton Bay, Queensland, by trawling, seining and line fishing. Fish were identified using the keys in Gunn (1990) wherever possible. If not, identification was made using Randall, Allen & Steene (1990), Grant (1987), Hutchins & Swainston (1986), Kuiter (1993) and Gomon, Glover & Kuiter (1994). Whenever possible,

22 fish were kept alive until dissection; fish which died prior to this time were stored in an ice slurry until dissection. Living fish were killed using an overdose of benzocaine anaesthetic, pithing through the brain, or by a blow to the head. Worms were dissected from the gut of each fish under a dissecting microscope and the opened gut was then shaken vigorously in a jar of saline to dislodge further worms and remove mucus. Worms were fixed unflattened in hot 5–10% formalin or hot saline before storage in 70% ethanol or 5–10% formalin. Specimens were stained in Mayer’s haematoxylin, dehydrated through a graded series of ethanol solutions, cleared in methyl salicylate and mounted in Canada balsam. Specimens for sectioning were double vacuum embedded in paraffin wax and sectioned at 7 µm on a rotary microtome. Sections were rehydrated, stained in Mayer’s haematoxylin and eosin, dehydrated, cleared in toluene and mounted in Depex mounting medium. Measurements of specimens were made using a calibrated eye-piece micrometer and figures were made using a drawing tube. Measurements are in micrometres unless indicated otherwise and are given as min.–max. (mean). The Material examined sections of each description below are structured as follows unless indicated otherwise: Host species THC autopsy number (number of specimens examined from that autopsy) locality. The following locality abbreviations are used: HI = Heron Island, Queensland, Australia 23◦ 270 S, 151◦ 550 E; MB = Moreton Bay, Queensland, Australia 27◦ 250 S, 153◦ 200 E.

Results Fourteen putative species of Monorchiidae were recovered from 25 species of carangid fishes examined in this study. Four are described here.

Family Monorchiidae Odhner, 1911 Provitellus n. g. Diagnosis Monorchiidae. Body small, elongate oval. Tegument spinose. Oral sucker small, globular. Prepharynx present. Pharynx globular to transverse oval. Caeca short, terminate at level of ventral sucker. Ventral sucker small, in middle third of body. Excretory vesicle saccular. Testis single, oval, in mid-hindbody.

Ovary entire, slightly pre-testicular. Cirrus-sac encloses spherical seminal vesicle, short pars prostatica and spiny eversible ejaculatory duct. Terminal organ unipartite, spinose; uterus enters at proximal end. Vitellarium composed of two lateral fields in forebody. Eggs filamented at anopercular end. Provitellus turrum n. sp. (Figure 1a,b) Type-host: Carangidae, Caranginae: Pseudocaranx dentex. Other hosts: Carangidae, Trachinotinae: Trachinotus coppingeri. Type locality: Heron Island, Queensland, Australia. Material examined: P. dentex 1440 (3) HI, 1855 (19 + 4 sectioned) HI, 1877 (1) HI, 3000 (10) HI, 3018 (7) HI, 3437 (7) HI, 4545 (10) HI, 5652 (20) HI; T. coppingeri PA201/101 (4) HI. Type-material: QMG 213892 (Holotype), QMG 213893-213901 (Paratypes). Description Measurements are of 17 wholemounts from P. dentex unless indicated otherwise. Body elongate oval, dorsoventrally flattened anteriorly, 488–603 (532) × 106–151 (124). Tegument strongly spined anteriorly; spination becoming more sparse posteriorly. Mouth sub-terminal. Oral sucker rounded, 32–48 (38) × 35– 45 (39). Ventral sucker oval, weakly developed, in middle third of body, 29–39 (34) × 34–45 (39). Forebody 218–273 (244) long. Oral sucker width to ventral sucker width ratio 1 : 1. Prepharynx present, 6–29 (17) long. Pharynx oval, 19–35 (26) × 26–42 (34). Oesophagus 44–84 (62) long, bifurcates in middle of forebody. Caeca terminate at level of ventral sucker, 64–192 (124) long. Excretory pore terminal; excretory vesicle saccular, not measurable in wholemounts or sectioned specimens. Testis single, in mid-hindbody, oblong to oval, often indistinct, 83–122 (105) × 51–87 (64) (n = 14). Cirrus-sac small, dextral to midline, dorsal to ventral sucker, 82–124 (97) × 26-42 (35) (n = 16), encloses round internal seminal vesicle, short pars prostatica surrounded by prostate cells, and denselyspined eversible ejaculatory duct. Genital atrium narrow, unspined, reflexing ventrally and posteriorly before reaching ventral surface. Genital pore opening medially just anterior to ventral sucker. Ovary entire, dextral to mid-line, anterior to testis, sometimes adpressed to it, 45–74 (64) × 39–51 (45)

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Figure 1. Provitellus turrum n. g., n. sp. a. Holotype in ventral view. b. Sagittal section. Abbreviations: ca, caecum; e, egg; ed, eversible ejaculatory duct; ep, excretory pore; ph, pharynx; ov, ovary; oes, oesophagus; os, oral sucker; s, tegumental spines; t, testis; to, terminal organ; v, median vitelline reservoir; vf, vitelline follicles; vs, ventral sucker. Scale-bars: 100 µm.

24 (n = 12). Uterus fills most of hindbody, spirals around testis, joins terminal organ at latter’s proximal end. Terminal organ unipartite, less densely-spined than eversible ejaculatory duct but spines more robust; more densely spined at distal end, 56–86 (69) × 24–42 (29). Uterine seminal receptacle present. Laurer’s canal absent. Vitellarium in two lateral, largely extra-caecal bunches of follicles bordered anteriorly by gut-bifurcation, posteriorly by anterior margin of ventral sucker. Vitelline reservoir triangular, medial, dorsal, near anterior margin of testis, receives common vitelline ducts laterally. Eggs unembryonated, operculate, oval, with single filament at anopercular end; eggs 29–35 (32) × 14–18 (16) (n = 16). Etymology: The generic name derives from the Latin, pro = in front of, vitellus = yolk, and refers to the presence of vitelline follicles in the forebody. The specific name is a word of uncertain origin but is probably Australian aboriginal and refers to any of several species of trevally. Systematic position This species has characteristics typical of two subfamilies of monorchiids. The saccular excretory vesicle and filamented eggs suggest affinity with the Lasiotocinae. In contrast, the distribution of the vitelline follicles entirely anterior to the ventral sucker is typical of the Monorchiinae. Indeed, the two genera most similar to this material, Diplohurleytrema Nahhas & Cable, 1964 and Monorchis Monticelli, 1893, are representatives of these two different subfamilies. This species matches the diagnosis of Monorchis given in Yamaguti (1971), except that the intestinal caeca do not reach the posterior extremity, the excretory vesicle is saccular (not V- or Y-shaped) and the eggs are filamented. It matches the description of Diplohurleytrema, except that there is only one testis, the vitelline follicles are entirely anterior to the ventral sucker, a terminal organ is present, and that the internal seminal vesicle of the cirrus-sac is unipartite (not bipartite). Another genus with which Provitellus shares some similarity, Parahurleytrema Nahhas & Powell, 1965, differs in the possession of a funnelshaped oral sucker, spined genital atrium, bipartite seminal vesicle and vitelline follicles in the hindbody. A comprehensive revision of the subfamilial structure of the Monorchiidae is clearly needed but beyond the scope of the present study. The conflict created by this species suggests that these subfamilies, as

presently understood, are untenable. To avoid confusing the taxonomy of the group further, it is therefore necessary to leave the subfamilial position of this species unresolved. Despite this uncertainty, this material does appear to represent a new genus, characterised by vitellarium in the forebody only, filamented eggs, a unipartite terminal organ, a saccular excretory vesicle and a single testis.

Ovipusillus n. g. Diagnosis Monorchiidae. Body oval. Tegument spinose. Oral sucker small, globular. Prepharynx present. Pharynx globular. Caeca short, terminate in ovarian zone. Ventral sucker small, in middle third of body. Excretory vesicle V- or Y-shaped. Testes two, symmetrical or oblique, lateral, largely anterior to ovary, may overlap ventral sucker zone. Ovary deeply lobed, medial in hindbody. Cirrus-sac very large, encloses round seminal vesicle, pars prostatica and long, coiled spiny eversible ejaculatory duct. Pars prostatica joins eversible ejaculatory duct roughly half way along. Terminal organ unipartite, evenly spined, receives uterus at its proximal end. Vitellarium in two largely lateral fields in posterior forebody, may overlap ventral sucker zone. Eggs very small, operculate.

Ovipusillus mayu n. sp. (Figure 2a–c) Type-host: Carangidae, Caranginae: Gnathanodon speciosus. Other hosts: Nil. Type-locality: Moreton Bay, Queensland, Australia. Material examined: 33 wholemounts, 3 sagittallysectioned, one transversely-sectioned and one horizontally-sectioned specimens from a single host. Type-material: QMG 213925 (Holotype), QMG 213926-213935 (Paratypes) Description Measurements are of 21 wholemounted specimens unless indicated otherwise. Body oval, tapers at extremities, flattened anteriorly, 822–1021 (897) × 292– 385 (338). Forebody 289–456 (366) long. Tegument spinose; spination becoming more sparse posteriorly. Mouth sub-terminal. Oral sucker globular, 59–80 (69) × 62–76 (70). Prepharynx present, 16–30 (21) long.

25 Pharynx globular 41–57 (49) × 43–56 (51). Oesophagus reaches mid-forebody before bifurcating, 73–159 (107) long. Caeca short, terminate slightly posterior to ventral sucker, 222–353 (265) long. Ventral sucker round, weak, pre-equatorial, 60–87 (69) × 60–90 (70). Excretory pore terminal; excretory vesicle Y-shaped, often obscured by eggs; arms extend to mid-hindbody. Testes 2, in anterior hindbody, irregular, indistinct, may overlap ventral sucker zone, oblique with sinistral testis more anterior. Sinistral testis 154–234 (191) × 77–135 (103); dextral testis 109–260 (192) × 64– 128 (98). Cirrus-sac very large, dextral to midline, oval, 161–273 (216) × 116–167 (148), encloses round seminal vesicle, pars prostatica and very long, coiled, spiny eversible ejaculatory duct; remainder of cirrussac filled with weak parenchyma except for basophilic gland-cells anteriorly. Eversible ejaculatory duct coils once sinistrally, pars prostatica enters partway along, at most posterior extent of coil; unspined bulbous section present at proximal end in most specimens. Distinct diagonal muscle fibres encircle eversible ejaculatory duct for much of its length. Genital atrium unspined, genital pore medial, slightly anterior to ventral sucker. Ovary deeply lobed, large, medial, lies between testes, in anterior hindbody, overlaps cirrus-sac zone, 151–196 (178) × 92-147 (121). Terminal organ sinistral to mid-line, unipartite, evenly spined, 119–234 (158) × 55–96 (69). Uterus extensive, winds in diagonal coils posteriorly in sinistral half of hindbody, then anteriorly in dextral half. Uterus enters proximal end of terminal organ. Uterine seminal receptacle present. Laurer’s canal absent. Vitellarium in 2 largely lateral fields of follicles reaching from zone of ventral sucker anteriorly no further than gut-bifurcation. Vitelline ducts run posteriorly, unite to form common vitelline reservoir in ovarian zone. Eggs very small, oval, unfilamented, operculate, becoming more tanned towards distal end of uterus, 10–13 (11) × 7–10 (8). Etymology: The generic name derives from the Latin, ovus = an egg, pusillus = insignificant, and refers to the extremely small eggs. The specific name is from a Torres Strait Island language, Meryam mir, and means golden trevally – the common name of the host. Systematic position This species is clearly a member of the subfamily Monorchiinae as defined by Yamaguti (1971) because it has a Y-shaped excretory vesicle and a flask-shaped

body. Its generic identity is, however, less clear cut. The large cirrus-sac and unipartite terminal organ suggest that it belongs with Monorchis. However, two testes are present and the vitelline follicles overlap the ventral sucker zone, character states found in Monorcheides. It differs from both genera in the shorter gut caeca and in the long coiled eversible ejaculatory duct receiving the pars prostatica halfway along. It also differs from Bathymonorchis Bray & Gaevskaya, 1993 in the shorter gut-caeca, the presence of two testes, the proximal junction of the uterus with the terminal organ (rather than halfway along), and in the location of the ovary medially in the hindbody (rather than laterally in the forebody). Two main characteristics of this species justify the erection of a new genus in the Monorchiinae. Firstly, the enormous size of the cirrus-sac and the junction of the pars prostatica partway along the coiled eversible ejaculatory duct are characters not found in any described monorchiid genus. Also, the testes are lateral to the ovary and in some cases largely anterior to it, to the extent of overlapping the ventral sucker zone. These characters, in combination with the simultaneous presence of a unipartite terminal organ, the extremely small eggs (the smallest digenean eggs we are familiar with) and two testes serve to separate this species from existing genera. Paramonorcheides pseudocaranxi n. sp. (Figure 3a,b) Type-host: Carangidae, Caranginae: Pseudocaranx dentex. Other hosts: Haemulidae: Diagramma labiosum. Type-locality: Heron Island, Queensland, Australia. Material examined: 3000 (3 + 2 sectioned) HI, 3018 (18) HI, 4545 (6) HI, 5652 (2) HI Type-material: QMG 213902 (Holotype), QMG 213903-213912 (Paratypes). Description Measurements are of 20 wholemounts unless indicated otherwise. Body elongate, dorsoventrally flattened anteriorly, 632–911 (699) × 141–225 (172). Tegument spinose; spines weaken posteriorly. Eye-spot pigment present in forebody. Forebody 249–390 (314) long. Hindbody often slightly hourglass-shaped. Mouth subterminal. Oral sucker globular, 37–54 (43) × 42–64 (49) wide. Prepharynx present, 10–38 (25) long. Pharynx oval, 23–34 (29) × 17–32 (27). Oesophagus

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Figure 2. Ovipusillus mayu n.g., n. sp. a. Holotype in ventral view. b. Terminal genitalia, semi-diagrammatic drawing from set of horizontal sections. c. Terminal genitalia, semi-diagrammatic drawing from a set of sagittal sections. Abbreviations: e, egg; ed, eversible ejaculatory duct; ga, common genital atrium; gc, gland cells; gp, genital pore; isv, internal seminal vesicle; ph, pharynx, pp, pars prostatica; ov, ovary; oes, oesophagus; os, oral sucker; t, testis; to, terminal organ; ut, uterus; vf, vitelline follicles. Scale-bars: a, 200 µm; b, c, 100 µm.

27 long, narrow, bifurcates in posterior third of forebody, 93–184 (115) long. Caeca terminate blindly in ovarian zone, 183–262 (228) long. Ventral sucker round, larger than oral sucker, weakly developed, equatorial or slightly pre-equatorial, 45–70 (55) × 49–72 (57). Excretory vesicle very small, saccular, 32–75 (51) × 18–49 (34) (n = 19). Testes 2, in hindbody, elongate, oval, often wider anteriorly than posteriorly, symmetrical or more often oblique, indistinct. Sinistral testis 116–200 (149) × 30–64 (46) (n = 15); dextral testis 113–200 (154) × 32–70 (46) (n = 18). Cirrus-sac well developed, dextral to mid-line, club-shaped, curved, extends from genital atrium well past ventral sucker into midhindbody, 146–227 (168) long (n = 17), 33–76 (44) wide, encloses large spherical internal seminal vesicle, narrow pars prostatica surrounded by well-developed prostatic cells, and large, very heavily spined eversible ejaculatory duct. Cirrus spines long, with longest at proximal end of inverted cirrus, slightly curved, apparently hollow, arranged in alternating longitudinal rows. Common genital atrium unspined; common genital pore slightly anterior to ventral sucker, medial. Ovary entire, anterior to dextral testis, 68–111 (85) × 33–64 (42). Terminal organ sinistral, bipartite, 67–103 (86) × 33–76 (44), spined distally, with few spines or none proximally; spines narrower than those of eversible ejaculatory duct, not curved. Proximal terminal organ often irregular in shape. Uterus fills most of hindbody, joins terminal organ from dorsal aspect at junction of distal and proximal portions. Uterine seminal receptacle present. Vitelline follicles in region of ventral sucker, extend anteriorly slightly past genital pore, in 2 largely lateral bunches. Vitelline ducts lead posteriorly, unite in mid-hindbody to form common vitelline reservoir. Eggs oval to pyriform, unfilamented, operculate at narrower end, 18–24 (20) long (n = 42), 10–14 (12) wide (n = 42). Systematic position Overall, this species resembles members of the subfamily Monorchiinae. However, the excretory vesicle is small and saccular, which is atypical of monorchiines and more commonly associated with the Anamonorchiinae, Lasiotocinae, Opisthomonorchiinae, Opisthomonorcheidinae, Pseudoproctotrematinae and Telolecithinae (the Hurleytrematinae have a Y-shaped excretory vesicle). Therefore, like Provitellus turrum, this species suggests that the present subfamilial

arrangement of the Monorchiidae is unnatural and unsatisfactory. This material matches the diagnosis of Paramonorcheides Yamaguti, 1938, which is presently included in the subfamily Lasiotocinae. It differs from the type-species, P. awatati Yamaguti, 1938, in having a longer forebody and an unlobed ovary, from P. spicularis Yamaguti, 1970 in lacking the few extremely long spines at the base of the eversible ejaculatory duct, from P. sirembonis Yamaguti, 1938 in the long forebody and the unlobed ovary and from P. brotulidorum Toman, 1973 in the unlobed ovary distinctly anterior to the testes, the longer forebody and the longer oesophagus.

Chrisomon gaigai n. sp. (Figure 4a,b) Type-host: Carangidae, Trachinotinae: Trachinotus coppingeri. Other hosts: Carangidae, Trachinotinae: T. botla. Type-locality: Heron Island, Queensland, Australia. Material examined: T. coppingeri PA201/101 (10) HI; T. botla 4155 (8 + 2 sectioned) HI. Type-material: QMG 213914 (Holotype), QMG213915-213918 (Paratypes), QMG 213920-213924 (Paratypes). Description Measurements are of 16 wholemounts unless indicated otherwise. Body elongate; forebody narrow, cylindrical, hindbody more robust, especially in gravid specimens, body 1,136–1,600 (1,373) × 185–305 (233). Tegument spinose; spination becoming more sparse posteriorly. Eye-spot pigment present at oesophagus level. Mouth subterminal. Oral sucker globular, 68– 84 (73) × 73–89 (81). Oral sucker to ventral sucker width ratio 1 : 1. Prepharynx present, 30–59 (47) long. Pharynx transversely oval, 35–58 (45) × 57–78 (65). Oesophagus long, narrow, bifurcates close to posterior extremity of forebody, 244–421 (325) long. Caeca long, terminate blindly close to posterior extremity. Ventral sucker weakly developed, round, slightly pre-equatorial, 73–98 (85) × 78–94 (87). Excretory pore terminal; excretory vesicle very small, saccular, 67–108 (83) × 16–37 (27). Testis single, large, elongate oval, in posterior half of hindbody, 202–334 (246) × 96–164 (127). Cirrussac well developed, dorsal to ventral sucker, elongate, extends into mid-hindbody, 295–488 (407) × 71–103

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Figure 3. Paramonorcheides pseudocaranxi n. sp. a. Holotype in ventral view. b. Terminal genitalia in ventral view. Abbreviations: c, caecum; dto, distal terminal organ; ed, eversible ejaculatory duct; ga, common genital atrium; gp, genital pore; isv, internal seminal vesicle; ph, pharynx; pto, proximal terminal organ; ov, ovary; oes, oesophagus; os, oral sucker; t, testis; to, terminal organ; ut, uterus; vf, vitelline follicles; vs, ventral sucker. Scale-bars: 100 µm.

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Figure 4. Chrisomon gaigai n. sp. a. Holotype in ventral view. For clarity the cirrus-sac is not shown and only the uterine loops ventral to the testis are shown. b. Paratype in right lateral view. Abbreviations: c, caecum; cs, cirrus sac; dto, distal terminal organ; ed, eversible ejaculatory duct; ep, excretory pore; ev, excretory vesicle; isv, internal seminal vesicle; oes, oesophagus; os, oral sucker; p-ph, prepharynx; ph, pharynx; pp, pars prostatica; pto, proximal terminal organ; s, tegumental spines; t, testis; vf, vitelline follicles. Scale-bars: 200 µm.

30 (85), encloses saccular seminal vesicle, long, narrow pars prostatica surrounded by well-developed prostatic cells (brown in live specimens), and long, densely spined eversible ejaculatory duct. Common genital atrium unspined, narrow; genital pore medial, slightly anterior to ventral sucker. Ovary deeply lobed, gives appearance of 3–5 separate globular ovaries, anterior or antero-dextral to testis, 112–196 (140) × 74–225 (120). Terminal organ ventral to cirrus-sac, bipartite, spined distally, unspined proximally, 193–308 (251) × 55–128 (84); proximal portion contains large, eosinophilic, fibrous mass in most specimens. Uterus winds towards posterior end, then anteriorly, joins terminal organ close to distal end of distal, spined portion. Uterine seminal receptacle present. Vitellarium composed of 2 lateral, extra-caecal star-shaped clusters of tubular acini, which extend from testicular zone or slightly posterior to it, anteriorly to zone of proximal terminal organ. Vitelline reservoir in ovarian zone or just anterior to it. Laurer’s canal present, runs postero-dorsally, opens on dorsal surface in testicular zone. Eggs oval, unfilamented, operculate, 19–24 (21) (n = 32), 10–13 (12) (n = 32). Etymology: The specific name is from the Torres Strait Creole language and refers to any trevally.

and, therefore, sperm may be discharged into a blind sac. Histological sections stained with haematoxylin and eosin, however, revealed that it is eosinophilic, whereas sperm are typically basophilic. The prostatic cells of the cirrus-sac are similarly eosinophilic. The fibrous mass appears to be the remnants of prostatic secretions associated with mating or spermatophores as sperm in this species is also basophilic (as observed in the seminal receptacle). The production of spermatophores has not yet been recorded in the Monorchiidae. If the fibrous mass is ignored, Chrisomon is separated from Lasiotocus, as defined by Yamaguti (1971), only in that there is no distinct sphincter at the distal end of the distal portion of the terminal organ. We consider this character of dubious value at the generic level as we have observed it in another, undescribed, species of monorchiid which has other characters precluding its inclusion in Lasiotocus. In addition, it has not been mentioned in the descriptions of species of Lasiotocus by many authors, including a redescription of the type-species, L. mulli (Stossich, 1883) by Bartoli & Prévot (1966). In our view, Chrisomon and Lasiotocus can be separated more easily by the configuration of the vitelline follicles. Transferring members of Lasiotocus with star-shaped clusters of tubular acini to Chrisomon and members of Chrisomon with a follicular vitellarium to Lasiotocus represents a more convincing systematic arrangement.

Systematic position This species fits well into the genus Chrisomon Manter & Pritchard, 1961. Prior to this paper, six species have been placed in this genus: C. tropicus (Manter, 1940) Manter & Pritchard, 1961; C. decapteri Nahhas & Cable, 1964; C. brotulidorum Toman, 1973; C. israelensis Fischthal, 1980; C. polynemi Dutta, Hafeezullah & Manna, 1994; and C. sunderbanensis Dutta, Hafeezullah & Manna, 1994. C. gaigai differs from the first four in the shape of the body, which is not flattened anteriorly, the length of the testis and the shape of the pharynx, which is not elongate. We consider the latter two to be members of the genus Lasiotocus, as discussed below. The fibrous mass in the proximal portion of the terminal organ, described by Manter (1940) and figured by Nahhas & Cable (1964), was clearly evident in the present material. It was used by Yamaguti (1971) in defining the genus. In wholemounts it appeared to be sperm, which makes sense given that the uterus joins the terminal organ close to the genital atrium

Chrisomon Manter & Pritchard, 1961 Amended diagnosis Body elongate; tegument spinose. Oral sucker subterminal. Prepharynx present; pharynx elongate to transversely oval. Ventral sucker in middle third of body, slightly larger than oral sucker. Excretory vesicle Y-shaped or saccular, very small. Testis single, large, elongate, in hindbody. Cirrus-sac clavate to elongate, dextral to mid-line, encloses saccular seminal vesicle, narrow pars prostatica surrounded by prostate cells and spined eversible ejaculatory duct. Genital atrium short, unspined. Genital pore anterior to ventral sucker, medial. Ovary lobed or not, anterior to testis. Uterine seminal receptacle present. Vitellarium composed of two extra-caecal star-shaped clusters of tubular acini extending from level of caecal ends anteriorly to ovarian zone. Terminal organ bipartite; proximal portion with few or no spines; distal por-

31 tion spined, receives uterus towards distal end of distal portion. Type-species: C. tropicus (Manter, 1940) Manter & Pritchard, 1961. Other species: C. albulae (Overstreet, 1969) n. comb. (syn. Lasiotocus albulae Overstreet, 1969); C. delicatus (Manter & Pritchard, 1961) n. comb. (syn. L. delicatus Manter & Pritchard, 1961); C. ulua (Yamaguti, 1970) n. comb. (syn. L. ulua Yamaguti, 1970); C. weke (Yamaguti, 1970) n. comb. (syn. L. weke Yamaguti, 1970); C. decapteri Nahhas & Cable, 1964; C. israelensis Fischthal 1980; C. brotulidorum Toman, 1973.

Lasiotocus Looss 1907 Amended diagnosis Body plump to elongate; tegument spinose. Oral sucker subterminal; prepharynx present; pharynx small. Ventral sucker in middle third of body, small. Excretory vesicle saccular to tubular. Testis single, in posterior half of body. Cirrus-sac encloses saccular seminal vesicle, pars prostatica surrounded by prostatic cells and spiny eversible ejaculatory duct. Ovary anterior to testis. Uterine seminal receptacle present; Laurer’s canal present. Vitellarium composed of two lateral bunches of follicles in region between ventral sucker and testis. Terminal organ bipartite; proximal portion with few or no spines, distal portion spined and receiving uterus part-way along its length. Genital atrium unspined; genital pore anterior to ventral sucker, medial. Type-species: Lasiotocus mulli (Stossich, 1883) Looss, 1907. Other species: Lasiotocus now includes all the species listed in Yamaguti (1971) except the four transferred above to Chrisomon. In addition, new combinations are created for two species previously assigned to Chrisomon, and several new species have been added since the summary provided by Yamaguti (1971): L. polynemi (Dutta, Hafeezullah & Manna, 1994) n. comb. (syn. C. polynemi); L. sunderbanensis (Dutta, Hafeezullah & Manna, 1994) n. comb. (syn. C. sunderbanensis); L. assymetricus Fischthal, 1977; L. bengalensis Ahmad & Gupta, 1986; L. chichibu Iwashita, Hirose & Deguchi, 1995; L. engraulisi Gupta & Gupta, 1976; L. glebulentis Overstreet, 1971; L. guptai Ahmad & Dhar, 1987; L. hastai Madhavi, 1974; L. jagannathi Ahmad & Gupta, 1986; L. maculatus Mad-

havi, 1974; L. niloticus Ebaid, 1994; L. overstreeti Gupta & Gupta, 1990; L. puriensis Ahmad & Gupta, 1986; L. rainai Gupta & Jain, 1992; L. rohitai Bilqees & Khan, 1990; L. sparisomae Fischthal & Nasir, 1974; L. trachinoti Overstreet & Brown, 1970.

Discussion The morphology of Provitellus turrum n. g., n. sp. has major implications for the taxonomy of the Monorchiidae. In resembling members of two subfamilies, it throws doubt on the characters used to delineate groups at that systematic level. The presence of the vitellarium entirely anterior to the ventral sucker, in particular, is a character which had, until the present study, been well established as a character of the Monorchiinae. In fact, all the steps in the subfamilial key to the Monorchiidae provided by Yamaguti (1971) involve description of the configuration of the vitellarium. The use of the fibrous mass in the terminal organ of Chrisomon spp. as a taxonomic character must be questioned. We found specimens of C. gaigai n. sp., both mature and immature, in which the mass was not present. Furthermore, if it proves to be a product of two individuals mating (prostatic secretion), it is not really an anatomical feature at all. It does, however, represent the product of a real biological process subject to the effects of natural selection in the same way anatomical features are. It may then prove to be taxonomically useful, but a large number of specimens in a range of states of maturity should be examined. The use of the shape of the excretory vesicle in the generic and subfamilial systematics of monorchiids is also under question. Although saccular vesicles occur in most subfamilies and V or Y-shaped vesicles occur in the Hurleytrematinae and Monorchiinae, both conditions can be seen in the same subfamily, indeed the same genus. Such is the case in the lasiotocine genus Chrisomon. Manter (1940) described the type-species, C. tropicum (as Telolecithus tropicus), as having a short Y-shaped vesicle. Nahhas & Cable (1964) described another member of the genus, C. decapteri, in which the excretory vesicle is saccular, and commented that Manter may have misinterpreted the inflated proximal parts of the two main excretory ducts in C. tropicum. The figure in Manter (1940) may be interpreted either way. Similarly, the genus Paramonorcheides is essentially monorchiine in its characteristics, including the presence of vitelline

32 follicles mostly anterior to the ventral sucker, yet is included in the Lasiotocinae because it has a saccular excretory vesicle. Manter (1942) discussed the excretory vesicle shape of Genolopa ampullacea Linton, 1910 (Lasiotocinae) and questioned its taxonomic significance. The vesicle in that species (the type of its genus) is intermediate between Y- and I-shaped because it possesses a rudimentary right fork, a character clearly seen in Manter’s figure. Perhaps the best characters for use in the generic and subfamilial systematics of the Monorchiidae are the configurations of the terminal genitalia, particularly the terminal organ, and the number of testes. These characters have an advantage over the distribution of vitelline follicles and shape of the excretory vesicle because they are unequivocal. The terminal organ may be unipartite or bipartite and may receive the uterus proximally, either partway along or distally. Alternatively, the uterus may join the genital atrium directly. The atrium itself may be spined or not. The cirrus-sac may be characterised by an internal or external seminal vesicle which may be tubular, bipartite or saccular. These characters may provide a more manageable and realistic basis for systematics in the Monorchiidae. The 25 species of carangid fishes examined in this study amount to only slightly more than one third of the Australian and one sixth of the global fauna of carangids. The number of monorchiid species recovered in the present study may therefore be extrapolated to predict the number of monorchiid species which may be present in the entire Australian and World carangid faunas. Cribb, Bray, Barker, Adlard & Anderson (1994) used the following equation to predict the number of species of digenean trematodes harboured by fishes of the Great Barrier Reef: Number of fish species present × Average number of digenean species per host species Average number of host species per digenean species These authors suggested that nine specimens of each host was sufficient for conservatively estimating the diversity of parasites harboured by a given host. In the present study, more than nine individuals were dissected from each of the following species: Alepes sp., Caranx sexfasciatus, Pseudocaranx dentex, P. wrighti, Scomberoides lysan, Selaroides leptolepis, Trachinotus blochii, T. coppingeri and Trachurus novaezealandiae. From these species, the average number of monorchiid species per host species was 1.67

and the average number of host species per monorchiid species was 1.3. The number of carangid fish species present is 63 for Australia (Gunn, 1990) and 140 for the world (Nelson, 1994). Using the equation of Cribb et al. (1994) and including only these nine host species, results of the present study predict conservatively that there are 81 species of monorchiids infecting the carangids of Australia and 180 species infecting carangids of the world. The latter figure exceeds the total number of monorchiids described at present, from all host families combined, by 70 species.

Acknowledgements We thank Trudy Wright for assistance catching fish and in the laboratory and Rod Bray for his creative input. This work was supported by an Australian Biological Resources Study grant to THC.

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