Homalometron mesoamericanum, León, Pérez-Ponce De & García-Magaña, Leticia, 2012

León, Pérez-Ponce De & García-Magaña, Leticia, 2012, Morphological and molecular evidences for the existence of two new species of Homalometron (Digenea: Apocreadiidae), parasites of cichlids (Osteichthyes: Cichlidae), Zootaxa 3407, pp. 37-48 : 42-44

Homalometron mesoamericanum n. sp.

( Figs. 3 A , B, C)

Type host. Vieja synspila (Hubbs) .

Other hosts. Cichlasoma urophthalmus (Günther) .

Type locality. Laguna Santa Anita, Tabasco 18°22’05’’ N, 92°52’00’’ W.

Other localities. El Espino, Tabasco 18°14’49’’ N, 95°50’00’’ W. Lago Macanche, Guatemala 16º 58´21.0´´ N, 89 º 38´24´´ W.

Site of infection. Intestine.

Prevalence and abundance (Lago Macanche): 16.6% (2 fish infected/ 12 examined), 1.5 worms per analyzed host (total number of worms, 3).

Specimens deposited. Holotype, CNHE (8233), 3 paratypes (8234-8236); 7 paratypes CPSMUJAT ( Tr 002- 0 5,0 6,0 7, Tr 002/331002, originally labelled as H. pallidum ).

Etymology. The species is named after the region where it is currently distributed. The term "Mesoamerica" refers to a geographical and cultural area which extends from central Mexico down through Central America, including Guatemala, Belize, Honduras and El Salvador.

Description. Based on 11 gravid specimens. Body elongated, 2,14 (1,30–3,19) long, 599 (400–890) wide. Spines on body tegument hardly visible on mounted specimens. Oral sucker subterminal, 209 (134–275) long, 216 (152–287) wide, lacking papillae around mouth opening. Mouth opening longer than wide, 71 (51–98 long, 70 (47–90) wide. Prepharynx elongated, relatively short 36 (7–66) long; pharynx 122 (80–193) long, 100 (60–160) wide. Esophagus 70 (26–129) long. Ventral sucker 227 (148–304) long, 243 (150–318) wide, 653 (451–938) from anterior end of body. Two compact eyespots on each side of anterior border of pharynx. Average ratio of oral sucker length to ventral sucker length 1:1.08. Average ratio of oral sucker width to ventral sucker width 1:1.12. Ceca bifurcating approximately half distance between pharynx and ventral sucker, 493 (292–717) from anterior end of body; ceca end blindly, left cecum 275 (149–297) from posterior body end, right cecum 257 (198–287) from posterior body end. Testes subspherical, located in tandem, contiguous; anterior testis 195 (133–283) long, 199 (133–299) wide; posterior testis 210 (127–310) long, 213 (140–308) wide. Postesticular space 561 (299–878), representing approximately 26% of body length. Cirrus sac absent. Seminal vesicle free in parenchyma, submedian, elongate, lying dorsal to ventral sucker, 121 (51–208) long, 123 (60–275) wide, inconspicuous hermaphroditic duct opening through medial genital pore, immediately anterior to ventral sucker, 618 (415–911) from anterior end of body. Ovary subspherical, 133 (60–190) long, 129 (66–183) wide, dextral, located approximately half distance between ventral sucker and the anterior border of anterior testis. Seminal receptacle spherical, dorsal to ovary, sometimes overlapping. Laurer’s canal muscular, inconspicuous, only observed in one individual. Vitelline follicles in two fields mainly extracecal, 1033 (664–1478) from anterior end of body, with scattered follicles confluent at pretesticular area, and completely confluent in the postesticular space, terminating 62 (41–100) from posterior end. Vitelline follicles extending from level of anterior border of ovary to almost reach posterior end of body. Uterus pretesticular, inter and extracecal, occupying most of area between ovary and ventral sucker, confluent with ejaculatory duct to form inconspicuous hermaphroditic duct. Eggs 85 (73–93) long, 48 (45–56) wide. Excretory vesicle I-shaped, ending in posttesticular space; excretory pore dorsally subterminal.

Remarks. Homalometron mesoamericanum n. sp. also conforms to the diagnosis of the genus Homalometron given by Cribb & Bray (1999) and Cribb (2005) excepting by possessing, consistently, two compact eyespots on each side of the anterior border of pharynx instead of dispersed eyespots. The vitelline follicles in this new species hardly reach the anterior border of the ovary. The new species resembles morphologically a group of species that are found in either brackish or freshwater fishes in the Americas, particularly the type-species, H. pallidum , a parasite mainly found in fundulids in North America (and apparently other hosts, see Yamaguti 1971, Hoffman 1999), H. armatum , found in Aplodinotus grunniens and Lepomis spp. in Texas, U.S.A. and H. pseudopallidum from the cichlid Gymnogeophagus australis in Argentina. However, it is distinguished from all of them by the constant presence of two compact eyespots rather than diffuse eyespots around the pharynx. In addition to that, the new species differs from H. pallidum and H. armatum by having smaller eggs (85 long by 48 wide vs 92–110 long by 42–70 wide in H. pallidum , and 110 long by 70 wide in H. armatum (see Miller 1959; Stunkard 1964; Yamaguti 1971). Homalometron mesoamericanum n. sp. differs from H. pseudopallidum , a species described by Martorelli (1986) from Gymnogeophagus australis by having an elongate rather than an oval-shaped body, and by the anterior extent of vitellaria since in H. pseudopallidum vitelline follicles extend up to the posterior border of ventral sucker meanwhile, in the new species, they hardly reach the anterior border of ovary.

Figures

FIGURE 3. A. Homalometron masoamericanum n. sp. Holotype (gravid specimen). Ventral view. Scale bar = 500 Μm. B. Anterior end showing compact eye-spots. Scale bar = 75 Μm. C) Detail of the female genitalia. Scale bar = 100 Μm.