| Summary: | The Cranchiidae, commonly known as the ‘glass squid’, are a diverse but poorly known family of deep-sea oegopsid squid. Members of the family are found in every ocean, occupying different depths throughout ontogeny, and some members are thought to make up a significant portion of the diets of large marine predators. The systematics of the family has been uncertain since its original establishment in 1817, and historic revisions have seen the creation and subsequent synonymy of numerous taxa. It has been 38 years since the systematics of the family was last revised (Voss, 1980; to genus level) and several genera are believed to contain undescribed species. This thesis describes the cranchiid squids of the Pacific Ocean, a region selected because its cranchiid diversity remains relatively unstudied. Many of the original descriptions for this family were from early research in the Atlantic Ocean, and descriptions of Pacific species have often been a part of smaller biological surveys in specific sub-regions; therefore, a larger familial revision will provide systematic stability in this basin. Ten of the known cranchiid genera are treated: Cranchia, Leachia, Liocranchia, Bathothauma, Galiteuthis, Helicocranchia, Liguriella, Megalocranchia, Sandalops, and Taonius. Of the remaining three, Teuthowenia was recently treated by a previous study (Evans, 2013), Mesonychoteuthis occurs solely in the Antarctic, and Egea is presently known only from the Atlantic. Herein, 26 species are included: 20 previously known species and six species new to science, plus four additional forms that will likely prove to represent additional novel taxa (but will require additional material before full descriptions and names can be given). Diversity of the genus Taonius, in particular, is expanded by these results, with four new species being recognised and described herein. Species delineations were made using both traditional morphological and molecular characters (which identified 34 unique BINs, likely representing species, from both the ...
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