New host for the parasitic worm Anoplodium sp . ( Rhabditophora : Platyhelminthes ) found in the sea cucumber Isostichopus fuscus ( Holothuroidea : Echinodermata )

A flatworm was discovered inside the coelomic cavity of the commercial sea cucumber Isostichopus fuscus along the Pacific coast of Mexico. Based on morphological and genetic evidence, it was determined to be Anoplodium sp. belonging to class Rhabditophora. Thus, the sea cucumber I. fuscus constitutes a new host. The flatworms were consistently found on the surface of the haemal vessels and the rete mirabile of 92% of the sea cucumbers sampled along the cost of Mazatlan, and 88% of the sea cucumbers collected in the Sea of Cortez. The infestation rate varied from 1 to 725 flatworms per individual, in both male and female sea cucumbers. When more than ~120 Anoplodium sp. were counted in a single host, the gonads of the latter were either very small (≤1.2 g wet weight, or GI <0.26) or absent, suggesting that the flatworm could be detrimental to I. fuscus and be considered parasitic. Combined with the threat of overfishing throughout its distribution range, the discovery of this parasite could seal the fate of I. fuscus in certain regions of the eastern Pacific.