A Systematic Review of the Squid Family Cranchiidae (Cephalopoda: Oegopsida) in the Pacific Ocean
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 Pacific and Atlantic Ocean). Data were collected primarily from preserved material in museum collections around the Pacific Ocean, illustrating important physical characters, with fresh material sampled when available. Although this research focussed primarily on external morphology, when internal features (e.g. beaks) were readily available or already extracted, these were included in the description.
Using COI, a preliminary phylogeny of the family is presented, which includes over half of the family’s estimated 60+ species, including 18 sequenced herein for the first time. Genetic results support monophyly of each of the twelve genera included (no Egea tissue or sequences were available), supporting the morphology-based genera hypothesised by Voss (1980).
As a result of this thesis, 26+ cranchiid species are now known to occur in the Pacific Ocean. The descriptions, illustrations, and sequences presented herein should facilitate both morphological re-identification of these taxa, and the positive identification via barcoding of damaged specimens and tissues of these taxa collected (e.g., from predator gut contents) in future studies. The characters used herein to help delineate taxa can be helpful in future research that assesses the diversity of the family.
Comparative studies of Atlantic and Indian Ocean material are still badly needed, and global revisions of several genera (Helicocranchia and Megalocranchia) would greatly benefit the stability of this family.