Ascocotyle (Leighia) mcintoshi Price, 1936

Scholz, T., Aguirre-Macedo, M. L. & Salgado-Maldonado, G., 2001, Trematodes of the family Heterophyidae (Digenea) in Mexico: a review of species and new host and geographical records, Journal of Natural History 35 (12), pp. 1733-1772 : 1740-1744

* Ascocotyle (Leighia) mcintoshi Price, 1936

(®gures 3, 4)

Metacercaria

Morphology. (Morphology based on ®ve ¯attened specimens from Xiphophorus sp. ) Cyst large, oval to almost spherical, 420±432 in diameter, surrounded by thick layer of host tissue and thick (thickness 17±20), mechanically resistant, hyaline internal layer. Body of metacercaria pyriform, 1036±1560 long and 416±556 wide, covered with tegumental spines. Most part of body ®lled with numerous small, transversely oval brownish droplets (lipoid?). Preoral lobe prominent; oral sucker subterminal, 35±70 long and 36±77 wide; posterior appendage conical, often curved or bent, not reaching to pharynx. Oral sucker surrounded with 38±42 circumoral spines forming two complete rows of 19±21 spines each; spination pattern 191 19 (n 51) and 211 21 (n 53). Anterior spines 12±18 long and 4±7 wide; posterior spines 9±12 long and 3±5 wide. Prepharynx 86±278 long; pharynx oval, 52±70 long and 45±80 wide; oesophagus slightly shorter than prepharynx. Caeca long and narrow, surrounding ventral sucker and reaching to ovary, slightly curved medially. Ventral sucker almost spherical, slightly postequatorial, 40±87 long and 55±80 wide. Sucker ratio 1 5 0.95±1.62. Testes symmetrical, close to posterior extremity, 37±170 long and 92±232 wide. Genital sac well-developed, with numerous out-pocketings, anterosinistral to acetabulum, containing very large gonotyl with 8±11 prominent refractile bodies. Mouth of ventrogenital sac slit-like, transversely oval, anterolateral to ventral sucker. Primordium of ovary postacetabular, transversely oval, 50 long and 112 wide. Excretory bladder X-shaped, with short and wide arms, laterally branched in posterior part.

Second intermediate hosts. Poecilia mexicana , Xiphophorus sp. (Poeciliidae) .

Site of infection. Mesenteries, occasionally heart (?) and gills (?).

Distribution. Veracruz (Los TuxtlasÐLa Palma, Laguna Azul, Las MaÂquinas). References from Mexico. Present study.

Specimens deposited. CHCM-354, CNHE 3930, IPCAS D-399.

Adult

Morphology. (Morphology based on ®ve hot-formalin ®xed specimens from experimentally infected chick; 2 days post infection.) Body elongate, tapering towards anterior extremity, 820±980 long and 270±300 wide, entirely covered with scale-like tegumental spines. Preoral lobe prominent, conical, long; oral sucker subterminal, 50±55 long and 47±57 wide; posterior appendage long, often sinuous, not reaching to pharyngeal level. Sucker armed with 38±42 circumoral spines forming two complete rows of 191 19 (n 51); 201 20 (n 52); and 211 21 (n 52) spines each. Anterior spines 14±17 long and 4±6 wide; posterior spines 9±12 long and 3±4 wide. Prepharynx 40±125 long; pharynx muscular, oval to spherical, 55±72 long and 37±45 wide; oesophagus short. Intestinal caeca narrow, long, reaching posteriorly to excretory bladder, slightly curved medially at ovarian level. Ventral sucker spherical to transversely oval, slightly postequatorial, 55±67 long and 57±67 wide. Sucker ratio 1 5 1.09±1.35. Testes symmetrical, close to posterior extremity, 60±102 long and 80±125 wide. Seminal vesicle posterolateral to ventral sucker, C-shaped, 28 long and 36 wide. Ventrogenital sac formed, containing very large, pad-like gonotyl with 10±12 refractile bodies. Mouth of ventrogenital sac large, slit-like. Genital pore anterosinistral to ventral sucker. Ovary dextral, nearly spherical, posterolateral to seminal vesicle, 60±70 long and 70±92 wide. Seminal receptacle voluminous, mediolateral to ovary, 62±87 long and 73±87 wide. Uterus sinuous; uterine loops anteriorly reaching to pharyngeal level, posteriorly crossing testes and reaching to posterior margin of ovary. Vitellarium forming two long lateral bands of vitelline follicles starting at acetabular level anteriorly and passing testes posteriorly. Eggs (n 530) operculate, 21 (19±22) long and 11 (9±13) wide. Excretory bladder voluminous, laterally branched; excretory pore terminal.

De W nitive host. Chick (experimental).

Site of infection. Intestine.

Distribution. Not known.

References from Mexico. Present study.

Specimens deposited. CHCM-354, CNHE 3929, IPCAS D-447, USNPC 90190.

Comments. Metacercariae found in this study did not diOEer from those of A. (L.) mcintoshi as described by Leigh (1974) from Gambusia a nis Baird and Girard and Poecilia latipinna . Both ®sh species from Mexico represent new second intermediate hosts.

Dominant site of infection of metacercariae found in this study were the mesenteries but one specimen (®gure 4A, D) was reported to occur in the gills (? musculature of gill arches) and another one (®gure 4B, C) in the heart (?). Stein (1968) reported metacercariae of this trematode from the liver of G. a nis in Florida but Leigh (1974) found them in various organs such as mesenteries adjacent to the small intestine, attached to the visceral peritoneum, and in the liver, gall bladder and fat bodies.

Experimentally recovered adult trematodes were almost identical with those of A. (L.) mcintoshi as described by Price (1936), Yamaguti (1971) and Leigh (1974). SepuÂlveda et al. (1996, 1999) found this trematode to be a relatively common parasite of the little blue heron ( Egretta caerulea Ðprevalence 29%; mean intensity 84; range 1± 963 specimens) but quite rare (prevalence 6%, mean intensity seven specimens) parasite of the great egret ( Casmerodius albus ) in Florida.

Ostrowski de NuÂnÄez (1992) described Ascocotyle (Leighia) hadra , a sibling species of A. (L.) mcintoshi , from Argentina. Both taxa diOEer one from another in only a few biological and morphological characteristics, most of them being related to cercariae (see Ostrowski de NuÂnÄez, 1992). Metacercariae can be distinguished by the absence of pigmentation in the former species (versus brownish colour of metacercariae of A. (L.) mcintoshi ) and diOEerent spectrum of second intermediate hosts: A. (L.) mcintoshi infects Gambusia a nis whereas A. (L.) hadra only poeciliid ®shes native to Argentina, Cnesterodon decemmaculatus (Jenyns) and Jenynsia lineata (Jenyns) . Adults diOEer in body size (496±798 in A. (L.) hadra versus 680±1200 in A. (L.) mcintoshi and in the number of projections of the gonotyl (10±11 versus 13).

The specimens found in Mexico correspond to A. (L.) mcintoshi in brownish pigmentation of metacercariae, the larger size of adults and the spectrum of ®sh intermediate hosts. Geographical distribution also supports conspeci®city of material from YucataÂn with A. (L.) mcintoshi . The number of digital projections (pockets) of the gonotyl in the present material (8±11 in metacercariae and 10±12 in adults) was more similar to that reported for A. (L.) hadra . However, variability of this character and di culties in counting precise number of projections cast doubts upon reliability of this feature to distinguish taxa that possess numbers of pockets that are not markedly diOEerent. Consequently, the specimens studied by the present authors are identi®ed as A. (L.) mcintoshi .

Ascocotyle (L.) mcintoshi was described from white ibis, Guara alba (5 Eudocimus albus (Linnaeus)) , from Florida by Price (1936) and then reported by Stein (1968), Leigh (1974) and SepuÂlveda et al. (1996, 1999) from the USA. The life cycle of this trematode was elucidated by Leigh (1974) who found the prosobranch snail Littoridinops monroensis to serve as the ®rst intermediate host, in which ophthalmogymnocephalou s cercariae developed. The present ®nding is the ®rst record of A. (L.) mcintoshi from Mexico.