Gorgonophilus canadensis (Copepoda: Lamippidae) a parasite in the octocoral Paragorgia arborea – relation to host, reproduction, and morphology

Abstract

The family Lamippidae (Cyclopoida) are endosymbionts mainly occurring in shallow water octocorals and records from deep-sea corals are few. Here we investigated the relationship between the lamippid Gorgonophilus canadensis Buhl-Mortensen & Mortensen, 2004 and its host the deep-sea coral Paragorgia arborea. Twenty-one specimens of G. canadensis was found inside eight gall-like structures on a P. arborea colony collected in 2010 at 318 m depth off Norway. The galls contained on average 1.6 females, 1.0 males, and 7.5 egg sacs estimated to contain 400 eggs each. Females were larger than males (4.6 mm compared to 2.0 mm). The gall volume increased with the number of egg sacs, females, and the length of females inside, the latter correlation was significant (p < 0.05). The number of egg sacs in galls was positively correlated with the abundance and length of females (p < 0.05), and by adding Canadian data from 17 galls the relation between egg sacs and numbers of females and males in galls became stronger (p < 0.01 and p < 0.05, respectively). Scanning electron microscopy revealed that this highly modified endoparasite has thoracic appendages with non-segmented flexible spines with a specialized structure at their tips through which threads are excreted. We speculate that this adaptation could relate to feeding or attachment of egg sacs inside the galls. Thread production has rarely been reported for copepods and we explore its function in the group as well as other crustaceans. The age and size of the parasite, and the introduction to and release from the host is also discussed.