The association between the caprellid Pariambus typicus Krøyer (Crustacea, Amphipoda) and ophiuroids

Abstract

Caprellid amphipods are small marine crustaceans which usually live as epibionts on a variety of substrates. Apart from mostly sessile organisms such as algae, hydroids and bryozoans, they also frequently use vague fauna as substrates. Pariambus typicus (Kreyer, 1844) is a common associate of subtidal asteroids and echinoids in European seas, but has also been found free-living on the sea floor. In the German Bight, P. typicus has also been discovered regularly on ophiuroids (Ophiura albida Forbes and Ophiura ophiura (L.)), which had not been described before. Several aspects of the biology of both partners were investigated with major focus on their distribution and relation to different substrates, behavioural and morphological adaptations to their habitat and their modes of nutrition. Various behavioural and morphological adaptations enable Pariambus typicus to live on a variety of substrates, on which the amphipod settles after contact. The highly mobile ophiuroid hosts open up new habitats for the caprellid (phoresis). Extensive grooming behaviour and specialized mouthpart morphology enable P. typicus to use detritus as an important food source, which contributes also a great part to the ophiuroids' nutrition. The complex association between P. typicus and Ophiura is interpreted as a commensalism.