Ascocotyle (Leighia) megalocephala Price, 1932

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 : 1744-1746

Ascocotyle (Leighia) megalocephala Price, 1932

(®gure 5A±D)

Metacercaria

Morphology. Scholz et al. (1995: 179 ±180; ®gure 4) had described a metacercaria designated as Ascocotyle (Ascocotyle) sp. 1 that was later identi®ed as A. (L.) megalocephala by Scholz et al. (1997a). A description of six metacercariae from Poecilia mexicana is provided: cyst widely oval to almost spherical, 432±472 long and 288±368 wide, with thick outer wall, often brownish, and thinner internal wall. Metacercarial body ¯ask-shaped, slightly tapering towards anterior end, 376±700 long and 220±330 wide, densely covered with simple tegumental spines. Spines almost completely covering ventral side of body except for small area around subterminal excretory pore; dorsally, spines reaching only to level of excretory bladder. Remnants of eye-spot granules scattered at pharyngeal level. Preoral lobe feebly developed (®gure 5A) but in some living specimens may be protruded (®gure 5C, D). Oral sucker spherical, 67±97 long and 80±140 wide, with conical posterior appendage, usually not reaching to pharynx, sometimes curved. Oral sucker armed with 74±80 ®ne but well-visible circumoral spines arranged in two complete rows of 36±40 spines each; anterior spines 12±17 long and 3±4 wide; posterior spines 10±16 long and 3±4 wide. Spination pattern 361 38 (n 51); 371 38 (n 51); 381 39 (n 51); 391 39 (n 52); 401 40 (n 51). Prepharynx 80±102 long; pharynx oval to almost pyriform, 40±72 long and 30 ±52 wide; oesophagus very short or indistinct. Intestinal caeca short and wide, often forming a sac, reaching only to anterior margin of ventral sucker. Ventral sucker spherical, postequatorial, 68 ±90 long and 62±80 wide. Sucker ratio 1 5 0.55±0.80. Testes symmetrical, at distance from posterior extremity, 37±80 long and 30±55 wide. Ventrogenital sac feebly developed, with simple, pad-like, transversely oval gonotyl. Primordium of ovary anteromedial to testes. Excretory bladder voluminous, X-shape d to sac-like, in encysted metacercariae occupying more than half of metacercarial body, ®lled with large droplets. Excretory pore subterminal, ventral.

Second intermediate hosts. Poecilia mexicana , P. velifera (Poeciliidae) .

Site of infection. Wall of stomach and intestine, mesenteries.

Distribution. Veracruz (Los TuxtlasÐarroyo Balzapote); YucataÂn (Mitza, Sahkaba).

References from Mexico. Scholz et al. (1995 Ðas Ascocotyle (A.) sp. 1); Scholz et al. (1997a); present study.

Specimens deposited. CHCM-356a, CNHE 3925, IPCAS D-351, USNPC 90189.

Adult

Morphology. No substantial diOEerences were observed between the specimen found in Ardea herodias from CelestuÂn and that described by Scholz et al. (1997a: 176, 178; ®gure 7A, B, D) from the intestine of Casmerodius albus from the same locality. Therefore, only a brief description of newly collected specimen is provided here: body 800 long and 360 wide. Oral sucker 125 long and 197 wide. Sucker armed with simple spines forming two rows, with 38 spines in anterior complete row; posterior row with several spines apparently missing, most probably containing 38 spines as well. Anterior spines 25 long and 6 wide; posterior spines 21±22 long and 5±6 wide. Ventral sucker 56 long and 55 wide. Sucker ratio 1 5 0.34. Testes 107±115 long and 137±160 wide. Ovary 100 long and 140 wide. Seminal receptacle 87 long and 97 wide. Eggs 19±21 long and 9±11 wide.

De W nitive host. Ardea herodias , Casmerodius albus .

Site of infection. Intestine.

Distribution. YucataÂn (CelestuÂn).

References from Mexico. Scholz et al. (1997a); present study.

Specimens deposited. CHCM-356, CNHE 3925, IPCAS D-446.

Comments. Two species of Poecilia from Mexico represent new ®sh hosts of A. (L.) megalocephala . Stein (1968) reported the poeciliid Mollienisia latipinna (5 Poecilia latipinna ) as its natural intermediate host in Florida but he did not provide descriptions or ®gures of the metacercariae.

Ascocotyle (L.) megalocephala was described by Price (1932) from Butorides sp. from Puerto Rico. Up to date, adults have been found only in Puerto Rico (type locality) and Mexico ( Price, 1932; Scholz et al., 1997a). The heron Ardea herodias is a new de®nitive host of this trematode that seems to be a rare parasite of herons.