The ecology of Magellania venosa, an articulate brachiopod

Abstract

Magellania venosa (Solander) holds a special interest for students of paleoecol- ogy because its size, abundance, and widespread distribution in the Magellanic province are comparable to assemblages in the geologic past. Important factors limiting distribution of this species are nature of the substrate and water current velocities, the largest populations being in areas with a clean shelly or rock bottom where currents are constant and strong but not turbulent. Depth and light do not limit distribution, for the species ranges from subtidal to 1900 m, though it is most common on the shelf. The temperature ranges of 3? to 12? are acceptable to this species, higher temperatures are not. M. venosa is mainly a seasonal breeder though a few sexually mature individuals are present in the populations throughout the year. Sperm is released in a mucous sheet of heavier density than the mucus associated with waste material. Fertilization appears to take place in the nephridia of the female. Terebratella dorsata (Gmelin) is commonly found with M. venosa while other brachiopod species are occasionally present. Where M. venosa is a dominant in a community, the associated dominant filter feeders are never consistently the same from one area to another suggesting that it is much better adapted to the environment than other filter feeders. Two protozoan symbionts have been observed with M. venosa, one being a peritrich of unknown relationship with the brachiopod, while the other is a parasite destructive to the tentacles of the lophophore. Laboratory experiments show that this species is not light sensitive. Experiments also indicate that frequent snapping of the valves appears only during irritation or discomfort of the individual and is not normal behavior.