|The Lecanicephalidea (Platyhelminthes: Cestoda) are a morphologically diverse group of elasmobranch (Chondrichthyes: Elasmobranchii) tapeworms. Currently, 95 species in 16 genera are recognized as valid. However, nine genera have previously been considered to be genera inquirenda and these contain nearly 35 species as species inquirendae. The focus of this study was to determine the taxonomic status of some of these genera inquirenda, especially focusing on the enigmatic genus Cephalobothrium Shipley & Hornell, 1906 and its allies, Adelobothrium Shipley, 1900 and Hexacanalis Perrenoud, 1931. The questionable status for these three genera was based on the fact that limited information was presented in the original descriptions of the type species, thus the distinctness of these genera was doubtful. In addition, type material of the type species of these genera was mostly unavailable. The type species of Cephalobothrium, Cephalobothrium aetobatidis Shipley & Hornell, 1906, was originally described for a single specimen collected from an eagle ray in the genus Aetobatus Blainville (Myliobatiformes: Myliobatidae originally identified as Aetobatus narinari [Euphrasen]) from Sri Lanka. The type species of Adelobothrium, Adelobothrium aetiobatidis Shipley, 1900, was originally described for specimens also collected from an eagle ray, Aetobatus ocellatus (Kuhl) (originally identified as A. narinari) from New Caledonia. The type species of Hexacanalis, Hexacanalis abruptus (Southwell, 1911) Perrenoud, 1931, was originally described for specimens collected from a butterfly ray, Gymnura micrura (Bloch & Schneider) (Myliobatiformes: Gymnuridae; as Pteroplatea micrura [Bloch & Schneider]), from Sri Lanka. This dissertation resurrects these three genera, recognizing them as valid and distinct members of the Lecanicephalidea. Their type species are redescribed and generic diagnoses revised. Neotypes are designated for both C. aetobatidis and A. aetiobatidis, while part of the original type series of H. abruptus was available and a lectotype is designated. In addition, species formerly recognized as members of other genera are transferred to Adelobothrium and Hexacanalis; these are Tylocephalum marsupium Linton, 1916 from A. narinari in the Gulf of Mexico transferred to Adelobothrium and Cephalobothrium pteroplateae Zaidi & Khan, 1976 from a species of butterfly ray from Pakistan transferred to Hexacanalis. The new species Hexacanalis folifer n. sp. is described from the zonetail butterfly ray Gymnura zonura (Bleeker) from Borneo. Two new genera are erected, Stoibocephalum n. gen., from the sharkray, Rhina ancylostoma (Rhinopristiformes: Rhinidae) and Floriparicapitus n. gen. from sawfish (Rhinopristiformes: Pristidae) and guitarfish (Rhinopristiformes: Rhinobatidae). Within these two new genera, four new species are described; these are Stoibocephalum arafurense n. sp., Floriparicapitus juliani n. sp., Floriparicapitus euzeti n. sp., and Floriparicapitus chordacistus n. sp. Cephalobothrium variabile Southwell, 1911 and Cephalobothrium rhinobatidis Subhapradha, 1955 are transferred to Floriparicapitus n. gen. The recognition of family-level relationships within the Lecanicephalidea is lagging behind the amount of progress occurring at the alpha-taxonomic level. Familial classification within the Lecanicephalidea has remained at a stand-still since 1994, when four families were recognized in the order. Many genera have not been placed at the family-level because of inconsistencies between family and generic diagnoses. The first molecular phylogeny is generated for representatives of 13 lecanicephalidean genera with taxon sampling focused on the five genera central to this study and representatives of the four families most recently recognized. The results of these phylogenetic analyses show high support for two clades containing the taxa central to this study. One clade unites Cephalobothrium and Adelobothrium, thus the Cephalobothriidae Pintner, 1928 is resurrected and the familial diagnosis is revised. A second clade supports the grouping of Lecanicephalum Linton, 1890, Tylocephalum Linton, 1890, Hexacanalis, Stoibocephalum, and Floriparicapitus. The most suitable family name for this clade is the Lecanicephalidae; the family diagnosis of the Lecanicephalidae is revised to include these five genera. Through the combination of data collected from whole worms, histological sections, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) putative morphological characters were investigated for their potential phylogentic utility. For example, the presence of three pairs of excretory vessels was confirmed for Hexacanalis, and also identified in Stoibocephalum and Floriparicapitus, all members of the Lecanicephalidae. The number of excretory vessels in other members of the Lecanicephalidae, Lecanicephalum and Tylocephalum, needs to be confirmed. Opportunistic collections of a species of Adelobothrium from the Solomon Islands allowed for the investigation of mature spermatozoa for this species. This is the first study which fully characterizes mature spermatozoa for a lecanicephalidean. This study not only investigated spermatozoa with TEM, but also with SEM to describe features. A unique feature, the anterior spiral structure, was identified using both TEM and SEM. This feature has never before been described for cestode spermatozoa. The potential diversity of spermatozoon features within the Lecanicephalidea remains unknown until spermatozoa of other lecanicephalideans are investigated. Future studies on members of the Cephalobothriidae and Lecanicephalidae should focus on a better understanding of species distributions, which are largely contingent on host-specificity and host distribution. Although this study recognizes both the Cephalobothriidae and Lecanicephalidae at the family-level, other lecanicephalidean lineages remain unresolved. A more robust molecular phylogeny, which is expanded to include all lecanicephalidean genera, is needed to resolve the inter-generic relationships in this order. As a result of this study, taxonomic diversity in the Lecanicephalidea has expanded to include 21 valid genera and 107 valid species.