Megaperidae Manter, 1934

Blend, Charles K., Karar, Yasser F. M. & Dronen, Norman O., 2017, Revision of the Megaperidae Manter, 1934 n. comb. (Syn. Apocreadiidae Skrjabin, 1942) including a reorganization of the Schistorchiinae Yamaguti, 1942, Zootaxa 4358 (1), pp. 1-44 : 5-6

Family Megaperidae Manter, 1934 n. comb.

(Syns. Apocreadiidae Skrjabin, 1942 ; Euryperidae Manter, 1933 ; Homalometridae Cable & Hunninen, 1942 ; Schistorchiidae Yamaguti, 1942 ; Sphincterostomatidae Yamaguti, 1937 ; Trematobrienidae Dollfus, 1950 )

Diagnosis. (Based on Bray 2005b; Cribb 2005; Pulis et al. 2014) Body rounded, oval or elongate-oval. Tegument spinous or unarmed. Eye-spot pigment present or rarely absent, usually dispersed near pharynx. Oral sucker subterminal or terminal, either unspecialized or with reduced musculature and highly glandular, papillae present or absent. Ventral sucker rounded, equatorial to pre-equatorial, unspecialized, sometimes with lamellar lips or flaps. Prepharynx present, usually very short, rarely longer than pharynx. Pharynx unspecialized, rarely massive and larger than ventral sucker, with or without lamellar flaps on anterior margin. Esophagus absent or short or long. Intestinal bifurcation in forebody, sometimes just posterior to ventral sucker. Caeca with our without extensions anterior to intestinal bifurcation, extend to near posterior end of body, end blindly or open to exterior through separate ani or form cyclocoel or uroproct. Testes two to multiple (five or more) in number, tandem, oblique or opposite, can occur in one or more rows, smooth to deeply lobed, pre-ovarian or post-ovarian, in forebody or hindbody. Cirrus pouch absent. Seminal vesicle naked, usually dorsal or just posterior to ventral sucker. Pars prostatica distinct with prostatic cells free in parenchyma, unites with uterus to form long or short hermaphroditic duct which opens at common median genital pore located immediately anterior to or overlapped by anterior margin of ventral sucker (some distance anterior in Pancreadium Manter, 1954 ; immediately posterior in Postporus Manter, 1949 ). Ovary smooth, weakly lobed or distinctly trilobed, at level of or posterior to ventral sucker, median or submedian, pre- or post-testicular. Canalicular seminal receptacle and Mehlis’ gland present. Laurer’s canal present or absent. Vitellarium follicular; follicles extensive, either restricted to hindbody or enter forebody, extend to posterior extremity. Uterus winds between ovary or anterior testis/testes and ventral sucker, unites with ejaculatory duct to form hermaphroditic duct. Eggs tanned, operculate, medium to large. Excretory vesicle Ishaped, very short or extends anteriorly to posterior testis/testes or to ovary or to pharynx level; primary excretory ducts distinct; excretory pore terminal or dorsally or ventrally subterminal. Lymphatic vessels present or absent. Eggs unembryonated when laid, embryonate to produce miracidia which infect freshwater and marine amnicolid, hydrobiid, calyptraeid, cochliopid, viviparid, planorbid and littorinid snails, undergo polyembryony to produce redia that develop cercariae that are shed, and encyst out in open environment or in same snail host, in freshwater sphaeriid and unionid or marine venerid clams, or in small polychaete annelids, and form metacercariae infective to definitive host. Adults in intestine of marine, freshwater and brackish-water teleosts; cosmopolitan.

Type genus. Homalometron Stafford, 1904 (Syn. Apocreadium Manter, 1937 —see Cribb 2005).

Remarks. As mentioned earlier, Pulis et al. (2014) considered the Megaperidae to be a subfamily ( Megaperinae ) within the Apocreadiidae ; however, the present work recognizes that based on the senior family group name, the family under consideration should be recognized as the Megaperidae n. comb. (Syn. Apocreadiidae ) (see ICZN 1999). Furthermore, the earlier key to the three subfamilies of the Apocreadiidae by Cribb (2005) is updated to include the four subfamilies of the Megaperidae n. comb.

Key to subfamilies of Megaperidae Manter, 1934 n. comb. (based on Bray 2005b; Cribb 2005; Pulis et al. 2014)

1a. Genital pore immediately posterior to ventral sucker.................................. Postporinae Yamaguti, 1958 . 1b. Genital pore anterior to ventral sucker.................................................................... 2. 2a. Oral sucker with partial U-shaped sphincter half encircling oral aperture posteroventrally... Schistorchiinae Yamaguti, 1942 . 2b. Oral sucker without partial muscular sphincter at aperture..................................................... 3. 3a. Caeca end blindly or form cyclocoel............................................... Apocreadiinae Skrjabin, 1942 . 3b. Caeca open via ani................................................................ Megaperinae Manter, 1934 .