Abstract
The mature spermatozoa of Stephanostomum murielae and Stephanostomoides tenuis are described by transmission electron microscopy. They present several ultrastructural features previously reported in other digeneans. Their spermatozoa possess two axonemes of different length showing the 9 + ‘1’ trepaxonematan pattern, four attachment zones, two mitochondria (with an anterior moniliform one in S. murielae), a nucleus, two bundles of parallel cortical microtubules, external ornamentation of the plasma membrane, spine-like bodies and granules of glycogen. The main differences between the mature spermatozoon of S. murielae and S. tenuis are the maximum number of cortical microtubules, the morphology of the anterior spermatozoon extremity and the anterior mitochondrion. This study is the first concerning members of the family Acanthocolpidae. The main ultrastructural characteristics discussed are the morphology of the anterior and posterior spermatozoon extremities, antero-lateral electron dense material, external ornamentations, spine-like bodies and number and morphology of mitochondria. In addition, the phylogenetic significance of all these ultrastructural features is discussed and compared to molecular results in order to highlight the complex relationships in the Digenea.
Highlights
The Platyhelminthes are invertebrate organisms characterized by the absence of fossils
Live adult specimens of Stephanostomum murielae (Bray & Justine, 2011) and Stephanostomoides tenuis (Manter, 1963) were collected respectively from Carangoides hedlandensis (Whitley, 1934) and Chirocentrus dorab (Forsskal, 1775) both fish caught off Noumea, New Caledonia; specimens of both digenean species are kept in the collections of the Museum National d’Histoire Naturelle, Paris, and Natural History Museum, London (Bray & Justine, 2011; Bray & Justine, 2012)
Spermatozoa showing two axonemes in their anterior extremities have been reported in Deropristis inflata (Foata, Quilichini & Marchand, 2007) and Neoapocreadium chabaudi (Kacem et al, 2010)
Summary
The Platyhelminthes are invertebrate organisms characterized by the absence of fossils. Members of the Acanthocolpidae Luhe, 1906 (Digenea, Platyhelminthes) are parasites of marine teleost fishes and occasionally of sea snakes They are mainly characterized by a spinous tegument, the lack of an external seminal vesicle and the presence of an uterine seminal receptacle (Bray, 2005a). Bray (2005b) in Jones, Bray & Gibson (2005) morphological key to the Trematoda, included ten families in the superfamily Lepocreadioidea Odhner, 1905 Those are the Acanthocolpidae Luhe 1906; Apocreadiidae Skrjabin, 1942; Brachycladiidae Odhner, 1905; Deropristidae Cable and Hunninen, 1942; Enenteridae Yamaguti, 1958; Gorgocephalidae Manter, 1966; Gyliauchenidae Fukui, 1929; Lepocreadiidae Odhner, 1905; Liliatrematidae Gubanov, 1953 and Megaperidae Manter, 1934. The remaining families, including two new families Aephnidiogenidae and Lepidapedidae previously considered as subfamilies (Bray, 2005c), form a monophyletic group known under the name Lepocreadioidea
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