Cephalopoda is a diverse group of pelagic molluscs that includes squids, cuttlefish, and octopus. Squids, cuttlefish and bobtail squids (Decapodiformes) exemplify the morphological and ecological diversity seen in Cephalopoda: members inhabit a variety of marine environments and possess a number of highly specialized variable features, such as complex light organs, image-forming eyes, and a funnel used for rapid swimming.
Their unique morphology makes decapodiforms interesting to study, but such a high degree of variation also makes it difficult to infer their evolutionary history. Chapter 1 evaluates the conserved nuclear locus 18S rRNA to test the usefulness of variable data for inferring decapodiform relationships. This study demonstrates that length-variable data is locally conserved at the ordinal or family level, indicating that the its phylogenetic utility. Chapter 2 investigates the evolutionary relationships among 87 decapodiforms using five molecular loci, and finds support for several family-level relationships irrespective of alignment parameters or method analysis. Ordinal relationships are less stable due to the lack of a good outgroup to Decapodiformes.
One inherent problem with studying evolutionary relationships of deep-sea organisms is that it is difficult to determine species' boundaries and taxonomy. It is important to have an accurate measure of biodiversity for conservation purposes, but also to infer patterns of speciation and adaptation in the open ocean. Chapter 3 documents diversity and evolution on the firefly squids in the genus Pterygioteuthis (Oegopsida: Pyroteuthidae) in the Eastern Tropical Pacific (ETP). These species exhibit unique morphological features and occur in both the Atlantic and Pacific, making Pterygioteuthis a model group for investigating species boundaries in the open ocean. However, only a single new species P. hoylei is found in (and endemic to) the ETP, a relatively isolated ecosystem bounded by the Central American coast to the east and strong currents and an expansive open ocean to the west, which have likely hindered migration or emigration of pyroteuthids in the ETP.
When evaluated in concert, this research provides unique insight into the evolution of an unusual group of invertebrates, the evolution of complexity, and the evolutionary forces affecting speciation in the open ocean.