Sea pens (Cnidaria: Anthozoa: Pennatulacea) constitute a distinctive group of colonial marine invertebrates. They inhabit the world`s oceans, from shallow to deep waters. Studies about this group in Argentina are scarce, and no species have been described in the area in over a decade. Based on samples collected in Mar del Plata Submarine Canyon at about 3000 m deep we describe a new species of sea pen, Umbellula pomona Risaro, Williams & Lauretta sp. nov. This is a spiculate Umbellula that differs from other species of Umbellula with sclerites, by the number, development and distribution of the autozooids in its terminal cluster, as well as the shape of its axis. Molecular data also distinguishes it from other known species. Of the forty-three described species approximately ten are considered valid for the genus Umbellula, four of them are registered for the South Atlantic Ocean and only three are described for the Antarctic region. Since sampling efforts in this area have been scarce, the number of species of sea pens from the region is likely to increase substantially in the coming years.

Corallimorpharians (Anthozoa: Corallimorpharia) from the Argentinean Sea

The Argentine continental margin is a poorly explored area as regards its benthic biodiversity. Few works have been made near the Brazil-Malvinas confluence (around 38° S) regarding corals, especially in deep waters (over 1000 m). Hitherto 17 species of stylasterids are known from southwestern Atlantic (SWA) off Argentina. Fourteen species of stylasterids collected from the Mar del Plata submarine canyon and adjacent area in years 2012 and 2013 at depths between 800 and 2200 m are discussed, including the descriptions of 13 of them. The geographic distribution of six species and bathymetric range of occurrence of two species are broadened in this work. Stations where most specimens were collected are located in areas where sedimentation is known to be scarce. Species in common between the study area and the Antarctic region, south of Chile, South Africa, New Zealand and New Caledonia suggest the Circumpolar Antarctic Current and the Malvinas Current are the means for dispersion. A key of identification of all stylasterid species off Argentina is included.

During 2007, 2008, and 2010, 23 specimens of an undescribed vermiform sea anemone were collected on Punta Pardelas and Fracaso Beach (Península Valdés, Argentina). The specimens have longitudinal rows of cinclides distally, all mesenteries perfect, tentacles hexamerously arranged without acrospheres, column not divisible into regions, no marginal sphincter and no conchula. We describe these specimens as a new species within the genus Harenactis (family Haloclavidae). Harenactis argentina sp. nov. is the second species of Harenactis; it represents the first record of this genus in the southern hemisphere and the first record of a soft bottom-dwelling sea anemone in the Argentine continental zone. Furthermore, we discuss the familial placement and relationships of the genus Harenactis and other athenarian sea anemones.

Sea anemone species of the genus Actinostella live in tropical and subtropical shallow waters. They are characterized by having a marginal ruff harboring zooxanthellae that expands during the day and retracts at night, allowing the anemone to catch prey with the tentacles. Currently, 10 or 11 species are considered valid depending on the author; however, most species within the genus were described in the 1800s or in early 1900s and, thus, most descriptions are incomplete by modern standards. In addition, several species of Actinostella have reported wide geographical distributions. We evaluate the morphology of newly collected and type material to assess potential synonymies and geographical distributions; we perform phylogenetic analysis using five standard molecular rDNA markers for sea anemones to corroborate our morphological results and to investigate the phylogenetic relationships of Actinostella, other actinioideans, and those Actinostella species present in the eastern Pacific and western Atlantic tropical region. Based on morphological and cnida differences, we find six species of Actinostella valid. We redescribe A. bradleyi, A. californica, A. digitata, and A. flosculifera and synonymize A. californica pro parte (Pacific specimens with four cycles of mesenteries and p-mastigophores A in the marginal ruff) with A. bradleyi (found in the Panamanian and Mexican Pacific and the Gulf of California). We also find that A. ornata does not belong within Actinostella. We discuss the membership of Actinostella, including species of the genus Phyllactis, and synonymize Phyllactis with Actinostella. We propose that the combination of the presence of p-mastigophores A in the marginal ruff and the arrangement and fertility of mesenteries are diagnostic characteristics to differentiate species of Actinostella from the American coasts. Finally, our phylogenetic analyses based on rDNA markers differentiated between the western Atlantic and eastern Pacific species but lacked support and resolution to elucidate relationships within species in the eastern Pacific.