Marrus Claudanielis, a New Species of Deep-sea Physonect Siphonophore (siphonophora, Physonectae)

Marrus claudanielis, a new species of deep-sea physonect siphonophore, is described from material collected by the ROV TIBURON, off California (eastern North Pacific), and the submersible JOHNSON-SEA-LINK II, off New Jersey (western North Atlantic). Marrus claudanielis is extremely fragile and all observed specimens autotomized some of their parts during observation or collection, due to the strong contraction of the stem. The siphosomal elements, the nectophoral and bracteal canals, and the pneumatophore were all deep red in life. This species is distinguished from other Marrus species by the undivided apico-lateral ridges on the nectophores, and the hook-shaped arc of enlarged ectodermal cells, including nematocysts, overlying the distal branches of the bracteal canals. Siphonophores are colonial hydrozoans found throughout the world’s oceans. Most are holoplanktonic, and none are permanently attached to a substrate. They are divided into three main groups: Cystonectae, Physonectae, and Calycophorae. The Physonectae, to which the species described here belongs, are generally linear in organization. At the apical end is a small gas-filled float known as the pneumatophore. The pneumatophore is followed by a series of asexual propulsive medusae called nectophores (swimming bells), which are grouped together to form the nectosome. Immediately adjacent to the nectosome is the siphosome, of specifically variable length, bearing the other elements, such as gastrozooids (feeding polyps, siphons), bracts (protective structures), and gonophores. Most physonects are gelatinous in consistency and many are well known for their fragility (Fewkes, 1880; Pugh, 1989). Past descriptions of many species were based on only severely damaged, and often incomplete, specimens obtained from net trawls. Technological advances over the last 25 yrs, however, have made it possible to sample organisms directly from the water column and bring them to the surface intact (reviewed by Haddock, 2004). These new methods include blue-water SCUBA diving (Hamner, 1975), and the use of sophisticated samplers mounted on manned submersibles and remotely operated vehicles (Youngbluth, 1984). These techniques have not only improved our knowledge of previously described siphonophores, but have also revealed numerous undescribed species, many being extremely delicate. Here we describe one such species, Marrus claudanielis sp. nov. It is so fragile that all of the observed specimens autotomized most of their parts upon the approach of the submersible, during the collection process, or in the sample canisters on the way to the surface. BULLETIN OF MARINE SCIENCE, VOL. 76, NO. 3, 2005 700 Marrus claudanielis new species