Most marine invertebrates, and certainly most brittle stars, spawning gametes (eggs and sperm cells) into the oceans and the embryos are formed and grow externally. But a few species carry live young, with their offspring developing within the parent’s body. How exactly these creatures – which have pretty small central bodies to begin with – accommodate their young around all their vital organs? This is a question that has proven difficult to solve using traditional dissection, as the anatomist will not be able to avoid some level of disruption to the structures within. But stunning images from a micro-CT scan of the brittle star Ophioderma wahlbergii from researchers at Cape Town and Stellenbosch universities in South Africa show thirteen young critters nestled inside the disc of an animal just 3 cm across! One particularly interesting observation was that all the offspring are placed mouths upwards (upside-down if you’re a brittle star), pressing against their embryonic sacs as if being nourished by the parent – a controversial theory that has until now been hypothetical only. The group are working on several other species in order to examine this possibility further and study the variety of live-bearing brittle stars.
Image and video courtesy of Jannes Landschoff and Charles Griffiths