A female of the species Gnathophausia zoea with a fully developed brood-chamber (arrow). Photo: Pål Øyvind Aas
Lophogastrida is an order of deep sea Crustaceans inhabiting the mid-Atlantic Ridge. These animals are most commonly found at depths below 1500 meters. They were captured in large numbers on the MAR-ECO expedition in the summer 2004. These animals are related to and quite similar in appearance to shrimp and krill. However, unlike shrimp and krill, the females of this group have a brood-chamber on their ‘belly’ were the eggs are kept, and they are generally known as more primitive in having many characters more similar with ‘older’ fossilized species of crustaceans. Looking at the differences in size, shape and number of spines that cover the bodies of these animals is often very useful for distinguishing between different species. Studying the species compositions at different localities and depths along the MAR provides information about where different species live and how common they are in different areas. This information gives some clues to whether physical structures such as the ridge or the sub polar front create barriers for the distribution of different species.
In addition to knowing which species the animals belong to, it can be useful to determine different population structures such as gender distribution, developmental stage and size of the individuals. This can be used for determining whether male or female, young or old, or individuals of differ sizes are distributed differently at different depths. Additional information on the time and date that the animal’s where captured can reveal whether different individuals migrate vertically between day and night.
A. The two species Eucopia grimaldii (left) and Eucopia unguiculata (right).
B. These two species can easily be distinguished by studying the many spines that cover the telson of each individual. Photos: Pål Øyvind Aas