Ophiothrix

Abstract: Ophiotrichidae Ljungman, 1867 comprises brittle stars diagnosed by the absence of oral papillae and presence of a cluster of dental papillae covering at least half the height of the dental plate. Ophiothrix Muller & Troschel, 1840 is the largest genus in the family and is composed of many species with a highly variable morphology. Ophiothrix angulata is one species with descriptions showing morphological variation in many of the diagnostic characters stated by Say (1825) in the original description. Say's (1825) type material and specimens studied by him could be located. Thus, in order to elucidate the taxonomic identity of O. angulata and following Article 75 of the International Code for Zoological Nomenclature, here we propose the neotype designation of O. angulata based on topotype specimens from South Carolina, United States. A discussion of the records of O. angulata from the Atlantic Ocean is included. Taxonomic comments on the genus Ophiothrix are also provided.

Abstract: . The relationship between a sponge, Callyspongia vaginalis, and an associated brittlestar, Ophiothrix lineata, was examined for mutualistic symbiotic interaction. Cinematography, feeding experiments, and analyses of stomach contents reveal that O. lineata (unlike other Ophiothrix species) is a non-selective deposit feeder. Its diet consists of detrital particles adhering to the sponge, which are too large to be utilized by the sponge as food. Thus, the brittlestar cleans the inhalent surface of the sponge as it feeds. Since siltation interferes with sponge pumping-activity, it is suggested that the cleaning behavior of O. lineata may enhance the filtration capability of C. vaginalis. In situ elapsed-time films show that brittlestars expose their arms when they feed, suggesting that they feed only at night because of a need to avoid diurnal predators. Manipulative experiments show that residence in C. vaginalis protects O. lineata from predatory fish. A comparison of the incidence of arm regeneration for brittlestars residing on C. vaginalis, and on a toxic sponge, Neofibularia nolitangere, indicates that factors other than sponge toxicity are involved in protecting sponge-dwelling brittlestars.

Abstract: The frequency of sublethal damage was examined in two ophiuroid species, Palaeocoma milleri and ?Ophioderma tenuibrachiata (Ophiodermatidae), from a shallow-water Jurassic "starfish bed." None of 60 specimens was regenerating arms, a result that agrees with four previous studies of Paleozoic and early Mesozoic ophiuroids. By contrast, 66.1 percent of a living Ophioderma brevispinum population from Belize were regenerating one or more arms. For living populations of Ophiothrix oerstedi, the natural injury frequency was high at sites where the field mortality of tethered individuals was high. All predators that have been observed feeding on ophiuroids cause sublethal injuries, which would appear as regenerating arms in the fossil record. These results support the hypothesis that predation pressure on ancient ophiuroid populations was low and increased after the Jurassic.

Abstract: Perez-Portela, R., Almada, V. & Turon, X. (2012). Cryptic speciation and genetic structure of widely distributed brittle stars (Ophiuroidea) in Europe. —Zoologica Scripta, 42, 151-169. The development of molecular techniques has led to the detection of numerous cases of cryptic speciation within widely distributed marine invertebrate species and important tax- onomic revisions in all the major marine taxa. In this study, we analysed a controversial marine species complex in the genus Ophiothrix, a widespread taxon in European waters traditionally assigned to two nominal species, Ophiothrix fragilis and O. quinquemaculata. These species are important components of the rocky shores and deep marine benthos along the North Atlantic and Mediterranean littoral. Their status (including variants of both species) has remained contentious due to overlapping variability in morphological characters. In this study, we analysed the genetic and morphological differences of Ophio- thrix lineages along the Atlantic and Mediterranean coasts. We also assessed population genetic structure in the Atlantic and Mediterranean basins by sequencing two mitochon- drial genes, the 16S rRNA gene and COI gene, of 221 specimens from 13 locations. Phy- logenetic analyses demonstrated the existence of two genetically distinct lineages, attributable to two different species although unrelated to previous taxonomic distinctions. Morphological differences could also be detected between these lineages. Samples from the Northeast Atlantic and one from the deep Mediterranean grouped within Lineage I, whereas Lineage II pooled together the southern Atlantic and rocky shallow Mediterranean samples. In the northern region of the Iberian Peninsula and at a deep locality in the Mediterranean, both lineages overlap. Speciation processes likely happened during the Mio-Pliocene transition (about 4.8-7.5 million years ago), when marine-level oscillations led to the blockage of major marine corridors in Europe and promoted genetic isolation by vicariance. Secondary contact between lineages following sea-level increases and recol- onization during the refilling of the Mediterranean after the Miocene salinity crisis could explain the present-day distribution of genetic variability. No barriers to gene flow along the Atlanto-Mediterranean area were detected for Lineage II, and the lack of genetic struc- ture could be caused by a mixture of several factors, such as wide dispersal potential, recent demographic expansion and large population size.