Experiments on food preference and chemical sense in Pycnogonida

Abstract

Food choice experiments were carried out with three species of pycnogonids: Nymphon rubrum, N. gracile, and Endeis spinosa. Running sea-water that had circulated over different possible food-sources (hydroids, actiniarians, octocorals, synascidians) was offered to the pycnogonids at one side of a basin, pure sea-water or se-water that had flowed over a different source of food at the other. The experiments, though few in number, seemed to indicate that: (1) Pycnogonids are capable of detecting the presence or absence of various coelenterate species. (2) They are able to discriminate between different food-sources, i.e. the nature of the chemical substances produced by the food determines the degree of attraction. (3) The preferential sequence for the three pycnogonids tested is: Nymphon rubrum prefers Dynamena over Tubularia and Laomedea; these are preferred over Actinia and Metridium; there is no attraction to Alcyonium. Nymphon gracile prefers Laomedea over Dynamena. Endeis spinosa prefers Laomedea over Dynamena; these are preferred over Actinia; there is no attraction to Morchellium. (4) Experimental amputation of appendages indicates a high probability that the chemo-receptors of the pycnogonids are not located on the chelifores, palps, or ovigers. They may be located (a) all over the body, possibly in innervated epidermal bristles; and/or (b) in the distal part of the proboscis, bearing sensory setae; and/or (c) on the walking legs.