Members of the genus Ophryotrocha are small marine polychaetes -- segmented worms (annelids) with long, bristle-like appendages. The genus has been a subject of scientific scrutiny since the mid-19th century, when it was formally described by Claparède and Mecznikow1 (the same Ilya "Mechnikov" who went on to win the Nobel prize in Physiology or Medicine for his work on phagocytosis and immunity).
Most species of Ophryotrocha are small (less than 5 mm long) and easy to maintain in the laboratory, living in any vessel that will hold seawater, and eating simple food, such as chopped spinach. Among the features that make them attractive experimental subjects are the following:
- Oocytes in these animals develop in polarized 2-cell syncytia or cysts: a single oocyte connected to a single nurse cell. These cysts mature in the coelom, free of surrounding follicular tissue, and thus are an elegantly simple example of asymmetric cell division and divergent cell fate decisions.
Female (top) and male (bottom) O. labronica
- Unlike many marine animals, Ophryotrocha spp. breed year-round, ensuring a dependable supply of various developmental stages for observation. The generation time is roughly 4 weeks, allowing for a reasonably large number of generations in a year.
- In most species, females lay eggs in large cluches, in which individual embryos develop in synchrony, facilitating developmental studies.
- Closely related species within the genus span the full range of sexual mating systems, from separate sexes (e.g,. O. labronica) to both simultaneous (e.g., O. diadema) and sequential hermaphroditism (e.g., O. puerilis). Thus, the group holds promise as a model for studying the evolution of sexual strategies and sex determination.
- As annelids, Ophryotrocha are members of the "lophotrochozoa", a large group of animal phyla that has received little attention relative to the two other major clades of bilaterally symmetrical animals: the ecdysozoa (e.g. insects and nematodes), and the deuterostomes, (e.g. vertebrates and echinoderms). Detailed study of lophotrochozoans is necessary to extend our knowledge of the evolutionary history of animal life.