Homeoastiotrema, Karar & Blend & Dronen & Adel, 2023

Karar, Yasser F. M., Blend, Charles K., Dronen, Norman O. & Adel, Asmaa, 2023, Towards resolving the problematic status of the digenean genus Astiotrema Looss 1900: Taxa excluded from Astiotrema (sensu stricto) with special reference to plagiorchioid genera closely related to the restricted concept of Astiotrema, Zootaxa 5284 (3), pp. 445-495 : 450-452

Homeoastiotrema n. gen.

( Fig. 5 )

Type- and only species. Homeoastiotrema turneri ( Bray, Van Oosterhout, Blais & Cable, 2006) n. comb.

(Syn. Astiotrema turneri Bray, Van Oosterhout, Blais & Cable, 2006 )

Etymology. The generic designation is based on the Greek word root “homeo” meaning “similar” and refers to similarities the new genus has with members of Astiotrema (sensu stricto), wherein one species now composing this genus was originally considered.

Diagnosis. Body large, elongate oval, tapers at both ends. Tegument spinous. Forebody approximately 1/3 of total body length. Suckers subglobular, unspecialized. Oral sucker subterminal. Ventral sucker at border between first and second thirds of body, larger than oral sucker. Prepharynx short or apparently absent. Pharynx well developed, smaller than both suckers. Esophagus long, narrow, rectilinear. Intestine bifurcates in posterior forebody. Ceca fairly long, terminate at various levels in post-testicular region. Testes two, intercecal, oblique to virtually symmetrical. Cirrus-pouch claviform, does not reach into hindbody. Internal seminal vesicle large, unipartite; pars prostatica long, slightly sigmoid, tubular; ejaculatory duct tubular, short, indistinct; numerous glandular cells fill space around pars prostatica and upper aspect of seminal vesicle. Genital atrium small. Genital pore post-bifurcal, median to slightly submedian. Ovary spherical, intercecal, larger than testes, pre-equatorial, entire or indented, at base of ventral sucker, contiguous to slightly posterolateral to it. Canalicular seminal receptacle distinct, post-ovarian, variable in size, saccular. Vitellarium follicular; fields extracecal to slightly over ceca, of variable length; anterior extent of vitellarium to pharyngeal, pre-bifurcal or bifurcal levels; posterior extent terminates at posterior testis or just into post-testicular region. Uterus inter and post-cecal, extracecal in fully gravid specimens, fills most of hindbody posterior to ovary, extends to posterior extremity. Metraterm simple. Eggs numerous, unfilamented, tanned, unembryonated in uterus. Excretory vesicle not observed. Excretory pore terminal. In intestine of freshwater fishes ( Cichlidae ); East Africa.

Remarks. From some freshwater localities in Lake Malawi, Bray et al. (2006) described A. turneri for several specimens collected from the intestine of four species of cichlids (Cichliformes: Cichlidae ): the zebra mbuna, Maylandia zebra (Boulenger) (syn. Pseudotropheus zebra [Boulenger]) (type-host); the scrapermouth mbuna, Labeotropheus trewavasae Fryer ; the purple mbuna, Melanochromis vermivorus Trewavas ; and the blue-black zebra, Maylandia emmiltos (Stauffer, Bowers, Kellogg & McKaye) (syn. Pseudotropheus emmiltos [Stauffer, Bowers, Kellogg & McKaye]). Bray et al. (2006) thoroughly compared A. turneri with A. reniferum , A. impletum and Astiotrema lazeri El-Naffar, Saoud & Hassan, 1984 as the most common species of Astiotrema reported form freshwater fish in Africa. Furthermore, Bray et al. (2006) presented a detailed comparative analysis of A. turneri with three species of plagiorchiid-like worms which have been reported from freshwater fishes from Africa: Glossidium pedatum Looss, 1899 , Afromacroderoides lazerae Khalil, 1972 and Alloglossidium fatemi Abdel-Maksoud, 1998 . Due to the considerable confusion as to the status of these forms in Africa, Bray et al. (2006) concluded that: (i) A. reniferum does not commonly occur in African freshwater fishes and it is often confused with G. pedatum ; (ii) Af. lazerae , As. lazeri and G. pedatum are similar morphologically and morphometrically; and (iii) cichlids previously had not been reported as hosts for Astiotrema with the occasional exception of A. reniferum from the Nile tilapia, Oreochromis niloticus (Linnaeus) , and the blue tilapia, Oreochromis aureus (Steindachner) (Cichliformes: Cichlidae ) ( Tawfik et al. 1996; El Garhy 2003), as well as a doubtful record of A. impletum from O. niloticus by Hamada (2002) (see Discussion below).

We find A. turneri to be unique from all taxa of Astiotrema (sensu lato) and particularly distinguished from those recognized in Astiotrema (sensu stricto) and Plesioastiotrema by a combination of five features: (i) the cirrus-pouch in A. turneri does not extend into the hindbody vs extending well into the hindbody to the ovarian level in other taxa of Astiotrema ; (ii) the pars prostatica in A. turneri is fairly long, sigmoid, vesicular proximally and narrower distally vs short and straight with the same width along its length; (iii) A. turneri has numerous and distinct glandular cells filling a large space around the pars prostatica and anterior aspect of the seminal vesicle vs few glandular cells occupying a smaller space around the pars prostatica in other taxa of Astiotrema ; (iv) A. turneri is the only species possessing an ovary larger than the testes; and (v) the ventral sucker in A. turneri is of a slightly larger size than the oral one vs suckers in other Astiotrema spp. either roughly equal in size or the oral sucker is larger than the ventral one. In addition to differential features mentioned earlier, A. turneri differs from species of Plesioastiotrema by possessing a ventral sucker directly posterior to the intestinal bifurcation, a post-bifurcal genital pore and records of freshwater hosts vs a ventral sucker directly ventral to the intestinal bifurcation, a pre-bifurcal genital pore and records of reptilian hosts. Based on the dissimilar morphological features observed in A. turneri as well as its distinct host group ( Cichlidae ), we believe A. turneri belongs in neither Astiotrema (sensu stricto) nor Plesioastiotrema ; therefore, we erect Homeoastiotrema n. gen. and designate A. turneri as its type species, Homeoastiotrema turneri ( Bray, Van Oosterhout, Blais & Cable, 2006) n. comb.

Figures

FIGURES 4 & 5. Plesioastiotrema magniovum (Fischthal & Kuntz, 1965) n. comb. and Homeoastiotrema turneri (Bray, Van Oosterhout, Blais & Cable, 2006) n. gen., n. comb. 4. P. magniovum (syn. Astiotrema magniovum Fischthal & Kuntz, 1965), ventral view, redrawn from Fischthal & Kuntz (1965, fig. 6). 5. H. turneri (syn. Astiotrema turneri Bray, Van Oosterhout, Blais & Cable, 2006), ventral view, redrawn from Bray et al. (2006, fig. 1). Abbreviations: AT, anterior testis; BS, body spines; Ce, cecum; CP, cirrus-pouch; Es, esophagus; GP, genital pore; LT, left testis; OS, oral sucker; Ov, ovary; Ph, pharynx; PP, pars prostatica; PT, posterior testis; RT, right testis; SR, seminal receptacle; SV, seminal vesicle; Ut, uterus; V-D, vas-deferens; VF, vitelline follicle; VS, ventral sucker. Scale bars: Fig. 4 = 1,000 µm; Fig. 5 = 500 µm.