Revue suisse de Zoologie 111 (1): 11-20; mars 2004 Redescription ofMonticellia magna (Rego, dos Santos & Silva, 1974) (Eucestoda: Monticelliidae) parasite ofPimelodus spp. (Pisces: Siluriformes) from Argentina, and morphological study of microtriches AliciaA. GILde PERTIERRA Laboratorio de Helmintologia. Dpto. Biodiversidady BiologìaExperimental. Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Ciudad Universitaria, Pab. n, 4°Piso. CP: C1428EHA-BuenosAires,Argentina. E-mail: [email protected] Redescription of Monticellia magna (Rego, dos Santos & Silva, 1974) (Eucestoda: Monticelliidae) parasite ofPimelodus spp. (Pisces: Siluri- formes) from Argentina, and morphological study of microtriches. - Monticellia magna (Rego, dos Santos & Silva, 1974) is redescribed and the microtriches and theirdistribution are studied forthe firsttime. This species is characterised by the following combination of characters: (1) vagina anterior to cirrus pouch; (2) muscular asymmetrical sphincter present; (3) testes in one layerandintwo fields connectedanteriorly andposteriorly; (4) vitelline follicles distributed cortical, paramuscular and a few follicles medullary; (5) internal longitudinal musculature strongly developed; and (6) scolexwith filiformmicrotriches in apicalregion, filiformand spiniform microtriches in central cavity, marginal ring and nonadherent surface of suckers, and spiniformmicrotriches inneckandimmatureproglottides. The species parasitised fishes of Pimelodus spp. Strict specificity of South American proteocephalids for their hosts is placed into consideration since recently new hostrecords have been reported, especially forhosts commer- cially exploited. Key-words: microtriches - Proteocephalidea - Monticellia magna - Pimelodidae - host specificity - Argentina. INTRODUCTION Monticellia magna (Rego, dos Santos & Silva, 1974) was originally described from Pimelodus clarias (Bloch, 1782) (junior synonym) (= P. blochii Valenciennes, 1840, original combination) as Nomimoscolex magna. However, de Chambrier & Vaucher (1997) studied the type material and found it composed by specimens that belong to two different genera, Proteocephalus and Monticellia; and transferred N. magna to Monticellia. Manuscriptaccepted21.07.2003 12 A.A. GILDEPERTŒRRA Latter, Rego & Pavanelli (1992) describedMonticellia loyolai fromPimelodus maculatusLacépède, 1803. DeChambrier&Vaucher(1999) synonymizedthis species with M. magna based on the study ofthe type material and new material collected in Paraguay. Eventhough, theseauthorsexposedremarkableanddistinctivecharactersfor M. magna, and did notpresent drawings ofthis species. During asurvey ofproteocephalideancestodes fromfreshwaterteleostfishes in Argentina, specimens of M. magna were collected from Pimelodus albicans (Valen- ciennes, 1840), P. argenteus Perugia, 1891, and P. maculatus. M. magna is described indetailforthefirsttimeinthispaper, basedontypeandthenewmaterial.The surface ofthe tegument ofthe scolex and portions ofthe strobila were studiedusing scanning electron microscopy (SEM). MATERIALAND METHODS Eighty specimensoff. albicans, 6ofP. argenteusand212ofP. maculatusfrom Colastiné, La Plata, and Parana rivers were examined for helminths. Worms found in theintestine wereisolatedandfixedinhot4% v/vformaldehyde solution and storedin 75% v/v ethanol. Entire tapeworms were stained with Langeron's alcoholic chlorhy- dric carmine (Langeron, 1949), differentiated in acid ethanol, dehydrated through a gradualethanol series, cleared in beechwood creosote andmountedin Canadabalsam. Thicktransversehand-cutting serialsections ofproglottideswere stainedfollowingthe same procedure. Eggs were mounted in distilled water, after fixation for drawing. Three specimens were prepared for SEM as follows: post-fixed in 1% osmium tetroxide, dried with tetrametylsilane (Analyticals', Carlo Erba), mounted on stubs with adhesive tape, sputter coated with gold in a Thermo VG Scientific Polaron SC 7630 and examined with a Philips XL 30 scanning electron microscope. Microthrix density values (D) were obtained by counting microtriches from randomly selected areas of 1 urn . Voucher specimens of M. magna from Argentina were deposited at Colección Parasitológica del Museo Argentino de Ciencias Naturales "Bernardino Rivadavia",BuenosAires,Argentina(MACN-Pa), andattheNaturalHistoryMuseum, Geneva, Switzerland (MHNG). Syntypes of M. magna (Rego, dos Santos & Silva, 1974) andM. loyolai (Pavanelli & Machado dos Santos, 1992) fromHelminthological Collection ofthe Instituto Oswaldo Cruz (CHIOC) were also studied. The information on taxonomic classification of fishes was obtained from FishBase Online (www.fish- base.org). All measurements are given in micrometers, unless otherwise stated, with the range followed by the mean, the standard deviation and the number of measure- ments (n) in parentheses. Measurements ofmicrotriches were determined fromphoto- micrographs. Illustrations were made with the aid ofa camera lucida using Nomarski interference contrast in a Zeiss Axioscope microscope. RESULTS Monticellia magna (Rego, dos Santos & Silva, 1974) Figs 1-14 Nomimoscolexmagna Rego, dos Santos & Silva, 1974 Monticellia loyolaiPavanelli & Machado dos Santos, 1992 Typehost:Pimelodusclarias(Bloch, 1782) (juniorsynonym)(=P. blochiiValenciennes, 1840, original combination). REDESCRIPTION OFMONTICELL1A MAGNA 13 Figs 1-2 Monticellia magna (Rego, dos Santos & Silva, 1974). 1. Scolex, apicalregion showingunicel- lularglandcells. 2. Gravidproglottis, ventral view. Scale-bars: 1 = 250 um; 2 = 500 um. Additionalhosts: Pimelodus albicans (Valenciennes, 1840), vernacularname: moncho- lo,bagrebianco;PimelodusargenteusPerugia, 1891,vernacularname:bagrebianco;Pimelodus maculatusLacépède, 1803, vernacularname: bagreamarillo (Siluriformes: Pimelodidae). Materialstudied:Argentina: 1)BuenosAiresProvince,BuenosAiresPort,LaPlatariv- er (34°37'S, 58°22'W), MACN-Pa 419/1-3, collected from P. albicans on 23/10/1989, and MACN-Pa 423/1-2 collected from P. maculatus on 10/09/1994. 2) Santa Fé Province, Santo Tome City, Colastiné river (tributary ofParana river) (31°40'S, 60°46'W), MACN-Pa 423/3-4 MNHG and 34660 INVE, collected from P. maculatus on 15/02/2002 and 31/07/2001 respec- tively, and MACN-Pa 424/1-2 and MNHG 34661 INVE collected from P. argenteus on 13/12/2002. Type specimens from Brazil: 1) Mato Grosso State, Esperanza Port, syntypes M. magna (Rego, dos Santos & Silva, 1974) CHIOC 31049 a-c, 2 contracted specimens; CHIOC 33137 (=4476), fragment ofstrobila; CHIOC 33139 (= 4480), fragment ofstrobila. 2) Parana State, Parana river, M. loyolai (Pavanelli & Machado dos Santos, 1992), CHIOC 32715 (holo- type); CHIOC 32716 c-dand32717 a-b transverse sections ofproglottides (paratypes). Prevalence: 40% (80P. albicansexamined), 33% (6P. argenteusexamined), 70% (212 P. maculatusexamined). 14 A. A. GILDEPERTIERRA 4 Figs 3-5 Monticellia magna (Rego, dos Santos & Silva, 1974). 3. Mature proglottis, dorsal view. 4-5. Transverse sections ofproglottides showing internal longitudinal musculature, and topography ofthe genitalia. 4. Transverse section anteriorto ovary. 5. Transverse section at level ofovary. Scale-bars: 3-5 =500 um. REDESCRIPTION OFMONTICELLIAMAGNA 15 Figs 6-7 Monticelliamagna(Rego,dosSantos&Silva, 1974).6.Detailofcirruspouchandvaginashow- ing the asymmetrical sphincter. 7. Eggs drawn in distilled water, after fixation. Scale-bars: 6 = 200 urn; 7 = 100 urn. Intensityofinfection: 2-20wormsperfish. Siteofinfection: anteriorandmiddlepartofintestine. Description (based on 15 specimens and measurements on 9 specimens from Argentina): Proteocephalidea, Monticelliidae, Monticelliinae. Testes, ovary anduterus cortical. Vitelline follicles partly in the cortex and partly in the medulla. Medium size worms, 23-125 mm, flatteneddorsoventrally. Strobilaacraspedote, anapolytic, consist- ing of53-125 (n = 9) proglottides: 20-60 immature, 8-22 mature, and 12-60 gravid. Scolexwiderthanproliferationzone(Figs 1, 8),480-830(582±58,n=9)wide. Apical organ absent, numerous spherical-shaped glandular cells with granular inclu- sions, distributedin apicalregion.Apicalregionofscolexpropercoveredwithdensely packed filiformmicrotriches 1.1-1.3 (n=4) long, 0.1 wide, D = 21-25 (n =4) (Fig. 9). Suckers sphericalto oval, unilobate, uniloculate, strongly muscular, 220-300 (246, n= 18) long, 160-300 (217) wide. Central cavity surface ofsuckers covered with filiform microtriches 0.8-1.2 (n = 5) long, 0.1 wide, interspersed with spiniform microtriches 0.9-1.1 (n = 6) long, 0.2-0.3 wide, D = 23 filiform : 1-2 spiniform (n = 4) (Fig. 11). Marginal ring surface of suckers covered with filiform microtriches 0.9-1.2 (n = 5) long, 0.1 wide, interspersed with spiniform microtriches 1.0-1.3 (n = 6) long, 0.2-0.3 wide, D = 14-20 filiform : 1-2 spiniform (n = 4) (Fig. 10). Nonadherent surface of suckers covered with filiform 1.0-1.2 (n = 5) long, 0.1 wide, interspersed with spini- form microtriches, 1.1-1.3 (n = 4) long, 0.2 wide, D = 8-14 filiform : 2-3 spiniform (n = 4) (Fig. 12). Proliferation zone (neck), 800-3000 (1422, n = 9) long, surface coveredwith spiniformmicrotriches, 0.6-0.8 (n=4) long, 0.2 wide, D = 31-35 (n=4) (Fig. 13). 16 A.A. GILDEPERTIERRA Figs 8-14.Monticelliamagna (Rego, dos Santos & Silva, 1974) SEMmicrographs. 8. Scolexin dorsoventral view, and positions of high magnification views for Figs 9-13. 9. Apical region surface, filiform microtriches. 10-12. Suckers: marginal ring, central cavity, and nonadherent surface, respectively, filiform microtriches interspersed with spiniform microtriches. 13. Proli- feration zone surface, spiniform microtriches. 14. Immature proglottis surface, spiniform microtriches. Scale-bars: 8 = 100 um; 9-12, 14 = 1 um; 13 = 2 um. Full arrows show filiform microtriches, empty arrows show spiniformmicrotriches. REDESCRIPTION OFMONTICELLIA MAGNA 17 Immature proglottides wider than long, 120-590 (338, n = 12) long, 430-800 (598)wide. Immatureproglottides surfacecoveredwith spiniformmicrotriches 0.6-0.7 (n = 5) long, 0.2 wide, D = 38-43 (n = 4) (Fig. 14). The surface ofproliferation zone and the immature proglottis is covered with spiniform microtriches, and they are the regions with higher densities (D = 31-35 and 38-43 respectively). Mature proglottides wider than long or longer than wide, 400-1010 (674 ± 154, n = 37) long, 880-2620 (1340 ± 547) wide (Fig. 3). Gravid proglottides wider than long or longer than wide, 500-2200 (1150 ± 373, n = 34) long, 870-2740 (1602 ± 621) wide (Fig. 2). Internal longitudinal musculature strongly developed, forming thick fibre bun- dles, delimiting areducedmedulla. Osmoregulatory canals situatedbetweentestes and vittelline follicles. Ventral canal, 12-20 in diameter, with secondary osmoregulatory canals ending on ventral surface lateral to ovarian lobes. Dorsal canal, 5-10 in diame- ter (Figs 4, 5). Testes cortical, total number 85-146 (106, n = 22) in mature proglottides, 40- 100 (70, n = 18) in diameter; in one layer, in two fields connected anteriorly and pos- teriorly (Fig. 3). Occasionally, 1-3 testes overlapping vas deferens and distal part of cirrus pouch. Cirrus pouch pyriform with thin muscular wall, 210-320 (260 ± 36, n = 31) long, 40-85 (66 ± 13) wide; occupying 21-29% (24% ± 2, n = 31) of proglottis width in mature proglottides. Cirrus occupying about 30-62% ofcirrus pouch length. Vas deferens coiled, 20-25 in diameter, usually not surpassing mid-line of body in matureproglottides. Genitalporesirregularly alternating, situatedanteriorly at20-42% (28% ± 4, n = 31) ofproglottis width. Vaginaanterior(99%)tocirruspouch, 13-20indiameter, stronglyasymmetrical and muscularsphincterpresent (Fig. 6). Ovary cortical, with 2 lobulate lobes; occupy- ing 56-74% (67% ±4, n = 31) ofproglottis width in mature proglottides. Vitelline follicles cortical andparamuscular, with 1-2 follicles lyingin medulla. Forming 2 lateral bands concentrated in mid-lateral region ofproglottis, interrupted at cirrus pouch and vagina level on ventral side, reaching 98-100% of total proglottis length (Figs 3, 4, 5). Uterine primordium stem and uterine branches cortical. Uterine branches occupyingupto70% ofgravidproglottis width; 19-29 (22,n= 14)lateralbranches op- posite to cirrus pouch side, and 18-28 (20) on cirrus pouch side. Cortical uterine diverticula nearly completely overlap the ovary. Mature eggs released by a ventral longitudinal slit (Fig. 2). Eggs with thickhyaline outerenvelope, 160-275 (228, n = 7) in diameter; embryophore 35-48 (41, n = 7) in diameter; oncosphere 18-20 (n = 7) in , diameter; hooks 10-12 long (Fig. 7). DISCUSSION The genus Monticellia La Rue, 1911 includes 11 species, all distributed in the Neotropical region: M. amazonica de Chambrier & Vaucher, 1997, M. belavistensis Pavanelli, Machado, Takemoto & dos Santos, 1994, M. coryphicephala (Monticelli, 1891), M. dlouhyi de Chambrier & Vaucher, 1999, M. lenha Woodland, 1933, M. magna, M. mandi (Pavanelli & Takemoto, 1996), M. megacephala Woodland, 1934, M. ophisterni Scholz, de Chambrier & Salgado-Maldonado, 2001, M. spinulifera, Woodland, 1935, and M. ventrei de Chambrier & Vaucher, 1999. M. diesingii 18 A. A. GILDEPERTIERRA (Monticelli, 1891) and M. macrocotylea (Monticelli, 1892) are considered species inquirendae (Rego etal, 1999). Amongthemorpho-anatomicalfeatures studiedinthisredescriptionthefollow- ing combination ofcharacters are important to characterise M. magna: (1) vagina an- terior to cirrus pouch; (2) muscular asymmetrical sphincter present; (3) testes in one layer and in two fields connected anteriorly and posteriorly; (4) vitelline follicles distributed cortical, paramuscular and a few follicles medullary; (5) internal longitu- dinal musculature strongly developed; and (6) scolex with filiform microtriches in apical region, filiform and spiniform microtriches in central cavity, marginal ring and nonadherent surface of suckers, and spiniform microtriches in proliferation zone and immature proglottides. The syntypes ofM. magna were studied and the conspecificity with the speci- mens fromArgentina was confirmed. Transverse sections were not available from the material examined. The holotype and the paratypes of Monticellia loyolai (= M. magna) were also studied. The asymmetrical vaginal sphincter and uterine branches nearly completely overlapping the ovary were clearly observedintype specimens.The vitelline follicles are situated cortical, paramuscular, and medullary (Figs 15, 16). The same topography was observed in the specimens collected from P. albicans, P. urgen- tem andP. maculatus fromArgentina, thus the conspecificity withM. magna was also confirmed. In the genus Monticellia, only M. spinulifera has been partially examined with SEM (Rego, 1999). Even when this author studied the sucker at very low magni- fication, and the giant spiniform microtriches on the marginal ring ofthe suckercould be easily observed. However, from the photomicrograph it is not known ifthe spini- form microtriches are the only kind ofmicrotriches on the marginal ring surface or if they are interspersed with other types of microtriches. Therefore, it is necessary to study in detail all the regions ofthe scolex proper to confirm the microthrix distribu- tion ofM. spinulifera. To date, in the Neotropical proteocephalids onlyNomimoscolex semenasae Gil de Pertierra, 2002 (Monticelliidae, Zygobothriinae), and M. magna in this paper were completely analysed forthe microthrix distribution with SEM. Host-specificity varies widely among different taxa of fish helminths. Highly host-specific parasites are restricted to one host species and specificity declines as the number ofsuitable host species increases (Poulin, 1998). The SouthAmerican proteo- cephalideans have beenconsideredtobe specific to one fishhost species. Infact, afew examples ofspecies having more than one final host were registered: (1)Amazotaenia yvettae de Chambrier, 2001 from Brachyplatystomafilamentosum Lichtenstein, 1819, and B. vaillantii Valenciennes, 1840; (2) Choanoscolex abscissus (Riggenbach, 1896) fromZungaro zungaro (Humboldt, 1821) [(=Paulicea luetkeni (Steindachner, 1876)], Pseudoplaty'stoma corruscans (Agassiz, 1829), P. fasciatimi Linnaeus, 1766, and Raphiodon vulpinus Spix &Agassiz, 1829 (see Regoetal, 1999); (3) Harriscolexka- parari(Woodland, 1934)from/5, corruscans, andP. tigrinum (Valenciennes, 1840); (4) Monticellia magna from Pimelodus albicans (new record), P. argenteus (new record), P. clarias, and P. maculatus; (5) M. ventrei de Chambrier & Vaucher, 1999 from Luciopimelodus pati (Valenciennes, 1836) (new record), and Pinirampus pirinampu (Spix &Agassiz, 1829); (6)Nomimoscolexmicroacetabula GildePertierra, 1995 from REDESCRIPTION OFMONT1CELLIAMAGNA 19 Figs 15-16 Monticellia magna (Rego, dos Santos & Silva, 1974), transverse sections ofproglottides drawn from holotype CHIOC 32715a, showing internal longitudinal musculature, and topography of the genitalia. 15. Transverse section anterior to ovary. 16. Transverse section at level ofovary. Scale-bar: 15, 16 = 500 urn. P. albicans, and P. maculatus; (7) N. suspectus Zehnder, de Chambrier, Vaucher & Mariaux, 2000 from B. filamentosum, B. vaillantii, and Z. zungaro [(= B. flavicans (Castelnau, 1885)]; (8) Nupelia tornasi de Chambrier & Vaucher, 1999 from Trachelyopterus galeatus (-Parauchenipterus galeatus) (Linnaeus, 1766), and T. cf. striatulus (= P. striatulus) (Steindachner, 1877); (9) Peltidocotyle rugosa Diesing, 1850 (see Zehnder & de Chambrier, 2000) from P. corruscans, P. fasciatimi, and P. & tigrinum; (10) Peltidocotyle lenha (Woodland, 1933) (see Zehnder de Chambrier, & 2000) from Z. Zungaro, and Sorubimichthys planiceps (Spix Agassiz, 1829); and & (11) Proteocephalus microscopicus Woodland, 1935 from Cichla monoculus Spix & Agassiz, 1831, and Cichla ocellaris Bloch Schneider, 1801. Poulin (1992, 1997) stated that high host-specificity can be an artefact of inadequate sampling, and among species of parasites of freshwater fishes sampling effort explains much of the variability in host-specificity. The number of South American proteocephalid species known parasitising more than one fish host might be correlated with a larger sampling effort. Among the fishes mentioned previously 81% are commercially exploited (Cichla, 2 species; Brachyplatystoma, 2 species; Luciopi- 20 A. A. GBLDE PERTffiRRA melodus pati; Pimelodus, 3 species; Pinirampus pirinampu; Pseudoplatystoma, 3 species; Z. zungaro) M. magna is widespread within Pimelodus spp., these host species are very frequent, and is common food among people living nearby theArgentinian rivers. In this study accurate drawings of the scolex, mature and gravid proglottides, transverse sections ofthe proglottides at different levels, detail ofthe vaginal sphinc- ter, eggs are revisited for the first, and the types ofmicrotriches and their distribution arepresentedforthe firsttime, theranges ofmeasurements and the mean are in agree- ment with the values given by de Chambrier & Vaucher (1999), differences were registered only forthe number ofuterine branches (18-36 vs 37-57 in this paper), and cirrus length/cirrus pouch length (30% vs 30-62% in this paper). ACKNOWLEDGEMENTS TheauthorthanksDrV. Ivanov, atUniversidaddeBuenosAires,forfruitfuldis- cussions during the preparation ofthis manuscript and its critical revision; the review- er for constructive critisism; and Dr Dely Noronha, at Instituto Oswaldo Cruz, forthe loan ofspecimens. The research was supported by SEPCYT Grant BID 1201 OC-AR PICTN° 1-6604. REFERENCES de Chambrier, A. & Vaucher, C. 1997. 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