Hamacreadium interruptum Nagaty, 1941

Martin, Storm B., Cutmore, Scott C., Ward, Selina & Cribb, Thomas H., 2017, An updated concept and revised composition for Hamacreadium Linton, 1910 (Opecoelidae: Plagioporinae) clarifies a previously obscured pattern of host-specificity among species, Zootaxa 4254 (2), pp. 151-187 : 164

Hamacreadium interruptum Nagaty, 1941

( Figure 3 a)

Synonyms: Hamacreadium interruptus Nagaty, 1941 .

Records. From the pink ear emperor, Lethrinus lentjan (Lacépède) [as “ L. mehsenoides ”], in the Red Sea by Nagaty (1941). From the smalltooth emperor, Lethrinus microdon Valenciennes , and from the Asian swamp eel, Monopterus albus (Zuiew) ( Synbranchiformes : Synbranchidae ) [as Fluta alba (Zuiew) ], from Sabah, Malaysia by Fischthal & Kuntz (1965). From an unidentified marine fish in the Andaman Sea by Hafeezullah & Dutta (1980). Remarks. Nagaty (1941) proposed this species based principally on the consistent and distinct interruption in the vitelline field at the level of the ventral sucker. Additionally, the cirrus-sac is large, cylindrical and curved, the genital pore is extra-caecal, almost lateral, the vitelline follicles become confluent in the forebody and the posterior margin of the body is strongly rounded. These features are consistent in a paratype available for study (SI NMNH IZ #1355315), although the cirrus-sac is not as large as depicted by Nagaty (1941). Nagaty (1941) did not describe the excretory vesicle, but it can be seen in the paratype, terminating midway between the ventral sucker and the intestinal bifurcation. This species is consistent with the concept of the genus and Bray & Cribb (1989) considered it synonymous with H. mutabile . However, here it is recognised as a distinct species, distinguishable from H. mutabile morphologically, biogeographically, and by infection in lethrinids rather than lutjanids.

Six of the 25 specimens collected by Fischthal & Kuntz (1965) from L. microdon (SI NMNH IZ #1355856/1– 6) were available for study. These specimens represent a genuine Hamacreadium species, but probably not H. interruptum ; in none is the posterior strongly rounded, nor do the vitelline follicles become confluent in the forebody, and in only two is the genital pore extra-caecal and the vitelline field interrupted. The eggs are also smaller (54–68 × 32–41 vs 68–77 × 41–50 µm). The record of a single specimen from M. albus by Fischthal & Kuntz (1965) is unconvincing because that fish is a freshwater eel. Although the specimen (SI NMNH IZ #1355857) is superficially consistent with Hamacreadium , the anterior extent of the excretory vesicle cannot be determined and the body is broadly rounded anteriorly and tapers posteriorly; it represents an especially generalised opecoelid of uncertain placement.

Figures

FIGURE 3. Reproduction with modification of type illustrations for (a) Hamacreadium interruptum Nagaty, 1941 and (b) Hamacreadium lethrini Yamaguti, 1934. Abbreviations: C, caecum; Cs, cirrus-sac; Ep, excretory pore; Ev, excretory vesicle; Gp, genital pore; O, ovary; Oes, oesophagus; Os, oral sucker; P, pharynx; T, testis; U, uterus; Vf, vitelline follicles; Vs, ventral sucker. Scale: 1000 µm, 1000 µm.