It looks like an apodid-type holothurian to me. Species might be Chiridota cf. albatrossii. However, as far as I know apodids are deposit feeders, not filter feeders.
It does resemble a holothuroid. But, it also could be a sipunculan. It definitely is not an echiurid. I can't really see the details clearly enough in this photograph. Also, dissection or careful examination of the internal organs would definitely differentiate between the two.