COLE, A.G.; HALL, B.K.; Dalhousie University; Dalhousie University: Creating Cartilage: How do Cephalopods do it?

Cartilage has long been thought to be a tissue restricted to vertebrates. However, tissues that are histologically indistinguishable from vertebrate cartilage are found in most Cephalopod species. To determine whether or not these tissues develop in a similar manner to their vertebrate counterparts, we investigated the ontogeny of cartilaginous tissues in the European cuttlefish, Sepia officinalis, using histological techniques. The cuttlefish has many distinct cartilaginous tissues that can be categorized into three different developmental modes: 1) metaplastic development from loose connective tissue, 2) development from a condensation of mesenchymal cells, and 3) development from a cellular condensation that is preceded by the formation of a distinct overlying epithelial layer. In cartilages that form from a cellular condensation, extracellular matrix formation begins with the deposition of polysaccharides followed by collagen. In contrast, a collagenous matrix first surrounds cartilages that develop directly from loose connective tissue, with polysaccharide deposition occurring much later in development. Sepia officinalis develops most of its cartilaginous tissues during embryogenesis, so that many of these structures are present when the juvenile hatches. As part of an ongoing comparative survey, this will be contrasted with the cartilage distribution at hatching in the common squid, Loligo pealeii and the bob-tail squid, Euprymna scolopes. Like the cuttlefish, Euprymna scolopes possesses most, if not all cartilages when it hatches. In contrast, Loligo pealeii hatches with only the scleral and nuchal cartilages present. The functional and evolutionary significance of the distribution of cartilage between species and the development of the different cartilages within Sepia will be discussed.