is an opossum shrimp; these are small, shrimp-like creatures with pinnate legs, a transparent body, remarkable eyes and a broad tail fan. Whereas most opossum shrimps spend their lives swimming freely in the water column, Gastrosaccus spinifer
spends a major part of that time buried in the sediment. Consequently, the species is usually associated with the macrobenthos. Gastrosaccus spinifer
can reach a length of 21 mm and is characterised by a narrowing of the fifth abdomen segment with a dorsal finger-like ‘spine’ on top.