A revision of Hexacanalis Perrenoud, 1931 (Cestoda: Lecanicephalidea) and description of H. folifer n. sp. from the zonetail butterfly ray Gymnura zonura (Bleeker) (Rajiformes: Gymnuridae)

Ultrastructure of the rhyncheal apparatus and other structures of the scolex of Grillotia (Christianella) carvajalregorum (Cestoda: Trypanorhyncha)

The scolex ultrastructure was studied in Grillotia (Christianella) carvajalregorum (Cestoda: Trypanorhyncha) using histochemistry and transmission electron microscopy. We show for the first time the presence of scolex glands arranged in two longitudinal acini at the pars vaginalis parenchyma. These glands, along with those scattered in bothrial parenchyma, produce potentially adhesive glycoprotein secretions that are discharged via ducts to the bothrial grooves and apex. A particular type of sensory receptor was found around frontal gland pores, with a possible function in regulating their secretion activity. The internal structure of microtriches varies according to their morphotype and distribution on the scolex, this study providing the first description of the ultrastructure of serrate lanceolate spinitriches. The projections that form serrate margins are an extension of the medulla, differing from similar projections of other spinitriches. The large caps observed in serrate lanceolate spinitriches may reflect their specialization in attachment to and abrasion of intestinal mucosa, while the short caps and large bases of acicular filitriches may reflect their involvement in nutrient absorption. We also describe the rhyncheal apparatus ultrastructure, showing a similar basic structure of tentacular walls than that of other trypanorhynchs. Some differences among species in the number of fibrous layers, composition of the apical cytoplasm and presence of microvilli-like projections were discussed. Finally, our study describes in detail the internal ultrastructure of hollow hooks, evidencing the presence of cytoplasm, mitochondria and fibrils. The location of these fibrils may increase the area of contact surface of hooks on tentacles, possibly allowing for a higher tensile strength than that of solid hooks. We consider that gland location and shape, composition of tentacular wall layers, and hook internal structure may serve as useful characters for the taxonomy and phylogeny of Trypanorhyncha. RESEARCH HIGHLIGHTS: This is the first description of scolex internal ultrastructure in Grillotia carvajalregorum, showing the presence of glands arranged in two longitudinal acini at the pars vaginalis parenchyma, with potentially adhesive functions. The internal ultrastructure of serrate lanceolate spinitriches and acicular filitriches may reflect their specialization in attachment to the host intestinal mucosa and their involvement in nutrient absorption, respectively. Internally, hollow hooks have cytoplasm with mitochondria and fibrils, which are more widely distributed than in solid hooks, possibly increasing their tensile strength.

Two new cestode species of Tetragonocephalum Shipley & Hornell, 1905 (Lecanicephalidea, Tetragonocephalidae) from Himantura randalli Last, Manjaji-Matsumoto & Moore (Myliobatiformes, Dasyatidae) from the Gulf of Oman

The original description of the genus Tetragonocephalum was published more than one hundred years ago but its taxonomic status was clarified only recently. To date, approximately 30 nominal species of this genus have been described, mostly from the northern Indian Ocean, but nearly half of them are invalid and only 14 species are recognized as valid. In the present study two new species of Tetragonocephalum are described from the spiral intestine of Himantura randalli from off Jod, on the northern coast of the Gulf of Oman. Tetragonocephalum sabaesp. n. is distinguishable from the valid species of Tetragonocephalum based on number of proglottids (43-53), number of testes (42-50), and size of scolex (401-453×328-455), acetabula (87-109×72-116), mature proglottids (802-1,333×226-336), cirrus sac (92-160×103-154), and eggs (16-19×11-13). Tetragonocephalum salariisp. n. can be distinguished from Tetragonocephalum sabaesp. n. and all other valid species of Tetragonocephalum based on number of proglottids (77-86). Furthermore, it differs from its congeners based on a combination of some characteristics, including the number of mature (3-7) and gravid (18-20) proglottids, the number of testes (30-38), and the size of acetabula (84-111×80-96), mature proglottids (497-833×334-403), gravid proglottids (1,036-1,482×440-575), testes (20-34×31-50), ovary (123-215×210-278), and eggs (24-45×13-21).

When proglottids and scoleces conflict: phylogenetic relationships and a family-level classification of the Lecanicephalidea (Platyhelminthes: Cestoda)

This study presents the first comprehensive phylogenetic analysis of the interrelationships of the morphologically diverse elasmobranch-hosted tapeworm order Lecanicephalidea, based on molecular sequence data. With almost half of current generic diversity having been erected or resurrected within the last decade, an apparent conflict between scolex morphology and proglottid anatomy has hampered the assignment of many of these genera to families. Maximum likelihood and Bayesian analyses of two nuclear markers (D1-D3 of lsrDNA and complete ssrDNA) and two mitochondrial markers (partial rrnL and partial cox1) for 61 lecanicephalidean species representing 22 of the 25 valid genera were conducted; new sequence data were generated for 43 species and 11 genera, including three undescribed genera. The monophyly of the order was confirmed in all but the analyses based on cox1 data alone. Sesquipedalapex placed among species of Anteropora and was thus synonymized with the latter genus. Based on analyses of the concatenated dataset, eight major groups emerged which are herein formally recognised at the familial level. Existing family names (i.e., Lecanicephalidae, Polypocephalidae, Tetragonocephalidae, and Cephalobothriidae) are maintained for four of the eight clades, and new families are proposed for the remaining four groups (Aberrapecidae n. fam., Eniochobothriidae n. fam., Paraberrapecidae n. fam., and Zanobatocestidae n. fam.). The four new families and the Tetragonocephalidae are monogeneric, while the Cephalobothriidae, Lecanicephalidae and Polypocephalidae comprise seven, eight and four genera, respectively. As a result of their unusual morphologies, the three genera not included here (i.e., Corrugatocephalum, Healyum and Quadcuspibothrium) are considered incertae sedis within the order until their familial affinities can be examined in more detail. All eight families are newly circumscribed based on morphological features and a key to the families is provided. Aspects of morphological evolution and host associations are discussed in a phylogenetic context for each family and for the order as a whole. Lecanicephalidean genera lacking apical structures were confirmed as the earliest diverging lineages. Proglottid anatomy was determined to be much more conserved and indicative of phylogenetic affinities than scolex morphology. Collectively, the Lecanicephalidea parasitize three of the four orders of Batoidea-their almost exclusive absence from skates (Order Rajiformes) appears to be real; only a few records from sharks exist. At the family level, the breadth of host associations is correlated with taxonomic diversity of the family. The degree to which factors such as intermediate host use or host specificity at any stage in the life-cycle shape these patterns is currently unknown.

A new genus and two new species of lecanicephalidean tapeworms from the striped panray, Zanobatus schoenleinii (Rhinopristiformes: Zanobatidae), off Senegal

Recognised for their diversity in apical structure morphology, members of the cestode order Lecanicephalidea Wardle et McLeod, 1952 known to date exhibit relatively mundane and uniform acetabular morphology. A new lecanicephalidean genus, Zanobatocestus gen. n., is proposed for two new species found parasitising the spiral intestine of the striped panray, Zanobatus schoenleinii (Müller et Henle), off Senegal that are highly unusual in acetabular morphology. Unlike the members of the 21 recognised lecanicephalidean genera, which possess simple, uniloculate suckers or bothridia, Zanobatocestus minor sp. n. and Z. major sp. n. possess biloculate bothridia. The form of their apical structures and cocoons readily distinguish the two new species from one another. Zanobatocestus minor sp. n. exhibits an apical modification of the scolex proper that is narrow and elongated, an apical organ that is small and internal, and eggs in cocoons forming linear strands, whereas Z. major sp. n. exhibits an apical modification of the scolex proper that is wide and short, an apical organ that is extensive and primarily external, and eggs in cocoons primarily as doublets with bipolar filaments. Given the typically high host specificity of lecanicephalidean cestodes, as parasites of the only genus and species currently considered valid in the family Zanobatidae, Zanobatocestus gen. n. is likely to remain one of the less specious lecanicephalidean genera.

The parasite-host interface in the zonetail butterfly ray, Gymnura zonura (Bleeker), infected with Hexacanalis folifer (Cestoda: Lecanicephalidea)

A wild-caught specimen of the zonetail butterfly ray, Gymnura zonura (Bleeker), harboured numerous specimens of Hexacanalis folifer Cielocha & Jensen, 2011 (Systematic Parasitology, 79, 1-16; Cestoda: Lecanicephalidea) within its spiral intestine. The cestodes were primarily attached in single rows along the base of mucosal folds, each associated with a nodular mucosal thickening. Microscopically, the scolex was embedded within the submucosa and muscularis; the attachment sites were marked by ulceration and necro-proliferative inflammation demarcating the parasite from normal host tissues. Physical attachment of the cestode was restricted to the anterior portion of its scolex where presumed tegumental secretions from the apical organ contributed to a cementing intermediate layer blending with necrotic host cells. The presence of tegumental differentiation between the apical organ and the scolex proper, associated with presumed different roles in attachment, correlated with ultrastructural observations of the surface modifications on the scolex. Despite the locally severe pathological change, insignificant morbidity owing to this particular host-parasite relationship is suggested.