Ecology
Habitat
The habitat of E. godeffroyi is seagrass beds and reef flats, up to 80m in depth (Granja-Fernández et al., 2013). The species has been found inhabiting areas that consisted of sand, seagrass, rocks, calcareous material, coral rubble and coral reefs (Granja-Fernándezet al., 2013).
The species displays nocturnal behaviour and generally hides under rocks and boulders during the day, exhibiting little activity and emerges into the water column at night to feed.
Feeding
The species has been previously observed to show nocturnal habits, consistent with the behaviour that was observed on Heron Island (Granja-Fernándezet al., 2013). E. godeffroyi was observed to shelter under a rock during the day, in which it displayed little activity, and typically emerged into the water column (from beneath the boulder to the surrounding aquarium) at approximately 7-8pm at night, after which it was regularly moving and feeding.
Euapta godeffroyi is a deposit feeder (Granja-Fernández et al., 2013). It feeds actively by extending its buccal tentacles into the sediment or water column (Granja-Fernándezet al., 2013). The buccal tentacles move independent of each other.
Vision
Synaptids are the only family within holothurians that have been found to have ocelli or optic cups, which are ‘small patches of pigmented cells at the base of their buccal tentacles that enclose photosensitive cells’ (Yamaotoand Yoshida, 1978; Kerr, 2001). Species that have been found to have photoreceptor organs include the ocelli (photoreceptor organs) of Opheodesoma spectabilis, and the statocysts (mechanoreceptor organs) and ciliated cups (chemoreceptor organs) of Leptosynapta inhaerens (VandenSpiegal et al, 1998).
Opheodesoma spectabilis, which is a closely related synaptidae to E.godeffroyi, has been found to possess a functional ocelli which responds to changes in exposure to light and thus displays phototactic behaviour (Yamaoto and Yoshida, 1978). Several physical changes were observed; ‘the microvilli became shorter and irregularly arranged’, the microvilli was engulfed to plasmalemmal invaginations, ‘coated vesicles of varying appearances and membranous fragments became abundant, microtubules are less evident in the apical part, and small flat vesicles appear along the plasma membrane in the middle part’ (Yamaoto and Yoshida, 1978; Kerr, 2001).
In Opheodesoma spectabilis, the ocelli consist of paired pigmented patches which enclose the receptive cells situated at the base of the each tentacular nerve near the nerve ring (Yamaoto and Yoshida, 1978).
Further studies are needed to determine if E. godeffroyi firstly possess functional ocelli, and, if so, whether the species display phototactic behaviour and how this would relate to the ecology of a primarily nocturnal organism.
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