Cephalopod Module

Modern developmental biology has largely focused on models contained within two of the three main groups of animals: the deuterostomes and the ecdysozoans. The third group, known as the Spiralia (or Lophotrochozoa), contains nearly half of all animal phyla and a vast range of adult morphologies. Even among this group, cephalopod molluscs have a highly derived body plan and a suite of innovations with no obvious correlates in other molluscs, including a crown of sucker-lined arms, highly developed eyes, and a complex central nervous system, making them a compelling model to the study of the evolution of novelty. Many cephalopod innovations have been thought to be the result of competition with teleosts (Packard 1972), and therefore also serve as a model for the study of convergence.

Embryogenesis in cephalopods is a complete departure from the otherwise highly conserved lophotrochozoan developmental sequence of holoblastic spiral cleavage followed by larval stages. Instead, cephalopods have superficial cleavage on top of a large yolk followed by direct development. The initial cell divisions produce a blastodisc at the animal pole, which continues to divide, spreading over and eventually enveloping the yolk by epiboly. The profound differences in early cephalopod development relative to other molluscs represents both a true novelty and an additional example of convergence with teleost fish.

Particular traits in different cephalopod species have been leveraged as biological models. For example, the longfin inshore squid Doryteuthis pealeii has long been used as a system to study the neurophysiology of the giant axon, the cuttlefish Sepia officinalis has been a model to understand adaptive coloration, and neuroanatomy and behavior has been studied in Octopus vulgaris. Though cephalopods have been important scientific models, particularly in neurobiology, many modern techniques applied in other animal clades are undeveloped in this group. Recent work at the MBL has focused on developing one or more model cephalopod species, leveraging advances in sequencing, genome editing, and molecular techniques for the study of these remarkable animals. These efforts are focused on the Hawaiian bobtail Euprymna scolopes, the flamboyant cuttlefish Metasepia pfefferii, the stumpy cuttlefish Sepia bandensis, the pyjama squid Sepiolina lineolata, and the California two spot octopus, Octopus bimaculoides. In this module, students will have access to embryos of a variety of cephalopod embryos from those listed above. A number of antibodies and vital stains work well in these species, but students are encouraged to try new techniques to observe these animals, as many have yet to be explored.