Hesionidae Grube, 1850 currently comprises over 175 species in 28 genera, placed in several subfamilies. Discoveries in recent years have largely been of deep-sea taxa. Here we describe a further four new hesionid species, mainly from methane 'cold' seeps at around 1000–1800 m depths off the Pacific coast of Costa Rica and new record of another species. Several of these taxa also occur at methane seeps in the Guaymas Basis (Mexico) and off the USA west coast (California and Oregon). The phylogenetic relationships within Hesionidae are reassessed via maximum parsimony and maximum likelihood analyses of DNA sequences from nuclear (18S rRNA and 28SrRNA) and mitochondrial (16SrRNA and Cytochrome c oxidase I) loci for the new samples. On the basis of these results, we refer one of the new species to
Gyptis Marion & Bobretzky in Marion, 1874, one to
Neogyptis Pleijel, Rouse, Sundkvist & Nygren, 2012, and two to
Sirsoe Pleijel, 1998. The new species [are]
Gyptis robertscrippsi n. sp.,
Neogyptis jeffruoccoi n. sp.,
Sirsoe dalailamai n. sp. and
Sirsoe munki n. sp. We refer to a collection of individuals from seeps ranging from Oregon to Costa Rica as
Amphiduropsis cf.
axialensis (Blake & Hilbig, 1990), even though this species was described from hydrothermal vents off Oregon.
Neogyptis jeffruoccoi n. sp. was generally found living inside the solemyid clam
Acharax johnsoni (Dall, 1891). The position of
Hesiolyra bergi Blake, 1985 is resolved on the basis of newly-collected specimens from near the type locality and, as a result, Hesiolyrinae Pleijel, 1998 is synonymized with Gyptini Pleijel, 1998 (and Gyptinae Pleijel, 1998).
