Homalometron octopapillatum, 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 : 39-42

Homalometron octopapillatum n. sp.

( Figs. 1 A –B, 2 A–B)

Type host. Cichlasoma beani ( Jordan) .

Type locality. San Cristobal Canal, La Tovara, Nayarit State, Northwestern Mexico. 21º 34´20.9´´ N, 105 º 15´20.2´´ W.

Site of infection. Intestine.

Prevalence and abundance. 52% (13 fish infected/ 25 examined), 1.36 worms per examined host (total number of worms, 34).

Specimens deposited. Holotype, CNHE 8231, 11 paratypes, CNHE 8232.

Etymology. This species is named after the 8 papillae arranged in four pairs that are found around the mouth opening, a character that is distinctive of this species.

Description. Based on 12 gravid specimens. Body elongated, 1,53 (1,13–1,98) long, 398 (264–462) wide. Body tegument covered by very tiny spines, hardly visible with light microscopy but evident through SEM study. Oral sucker subterminal, 158 (128–181) long, 150 (123–171) wide, possessing four pairs of papillae around anterior borders of mouth opening. Mouth opening longer than wide, 56 (27–84 long, 35 (16–84) wide. Prepharynx elongated, relatively long 55 (18–99) long; pharynx 99 (51–153) long, 81 (34–129) wide. Esophagus 59 (39–80) long. Ventral sucker 168 (132–202) long, 166 (134–189) wide, 446 (352–542) from anterior end of body. Dispersed eyespots remnants in area between pharynx and oral sucker. Average ratio of oral sucker length to ventral sucker length 1:1.063. Average ratio of oral sucker width to ventral sucker width 1:1.10. Ceca bifurcating approximately half distance between pharynx and ventral sucker, 319 (203–481) from anterior end of body; ceca end blindly, left cecum 201 (161–256) from posterior body end, right cecum 193 (131–237) from posterior body end. Testes subspherical, located in tandem, contiguous; anterior testis 177 (130–254) long, 184 (134–234) wide; posterior testis 213 (157–264) long, 192 (144–250) wide. Postesticular space 337 (251–452), representing approximately 22% of body length. Cirrus sac absent. Seminal vesicle free in parenchyma, submedian, elongate, lying dorsal to ventral sucker, 139 (86–158) long, 94 (72–113) wide, inconspicuous hermaphroditic duct opening through medial genital pore, immediately anterior to ventral sucker, 423 (350–514) from anterior end of body. Ovary subspherical, 91 (76–105) long, 83 (64–99) wide, dextral, located approximately 2/3 distance between ventral sucker and anterior testis. Seminal receptacle spherical, dorsal to ovary, sometimes overlapping. Laurer’s canal muscular not observed. Vitelline follicles in two fields mainly extracecal, 664 (525–826) from anterior end of body, with some follicles confluent at anterior testis level, completely confluent in posttesticular space, with scattered follicles in area terminating 143 (54–98) from posterior end. Vitelline follicles extending from half distance between ovary and ventral sucker to posterior end of body. Uterus pretesticular, intercecal, occupying most of area between ovary and ventral sucker, confluent with ejaculatory duct to form inconspicuous hermaphroditic duct. Eggs 61 (51–70) long, 48 (42–57) wide. Excretory vesicle I-shaped, terminating in postesticular space; excretory pore dorsally subterminal.

Remarks. The new species conforms to the diagnosis of the genus Homalometron given by Cribb & Bray (1999) and Cribb (2005) except in possessing one distinguishing character that is considered rare or unusual within the generic diagnosis. Members of Homalometron posses an oral sucker usually unspecialized, rarely with papillae. Homalometron octopapillatum n. sp. is characterized by having four pairs of papillae around the anterior borders of the mouth opening. This character in combination with the anterior extent of the vitelline follicles (half the distance between ovary and ventral sucker) sets this species apart from all congeners. Four other species of Homalometron have been described possessing oral papillae, H. elongatum , considered to be a widespread parasite of fishes throughout the Caribbean Sea, since it has been found in gerreids in Brazil, Puerto Rico and Florida, U.S.A. (but see Pérez-Ponce de León et al. 2007 who listed this species in gerreids along the Pacific Coast of Mexico, in Baja California Sur and Jalisco states), Homalometron carapevae Amato , also a parasite of gerreids from Brazil, H. papilliferum from a freshwater perch in Argentina, and a recently described species, H. lesliorum from a gerreid in the eastern Pacific Ocean off Central America, particularly in Costa Rica and Nicaragua (see Parker et al. 2010 and references therein). The new species can be readily distinguished from all of them by having four pairs of papillae instead of three. In addition to that, Homalometron octopapillatum n. sp. is described from a cichlid, C. beani , in Northwestern Mexico on the Pacific Ocean slope.

Figures

FIGURE 1. A. Homalometron octopapillatum n. sp. Holotype (gravid specimen). Ventral view. Scale bar = 500 Μm. B. Anterior end showing papillae. Scale bar = 100 Μm.