Search Results (3)

The Humboldt Current System (HCS) off southwest America is known for its strong upwelling and the resulting high primary production and associated oxygen minimum zones (OMZs). Macrozoobenthic species represent a group of organisms that are affected by the low oxygen concentrations in the OMZ. In January 2023, benthic diversity was investigated at 8 stations on a transect off Concepción, central Chile (in the centre of the OMZ) in a water depth range from 56 to 912 m. The measured oxygen values ranged from 0 µmol/L in the OMZ to 144.64 µmol/L outside the OMZ. At each station, 3 van Veen grabs were taken, the species identified, counted and weighed. The mean abundance, biomass and diversity were calculated for each station. This analysis provided an overview of the changes in the species communities at different oxygen concentrations. The species communities at the stations with low oxygen levels differed greatly from those with higher oxygen levels. Species diversity at the stations increased during the transition from low (<2 µmol/L) to higher oxygen levels (>100 µmol/L). In contrast, species abundance and, to a lesser extent, biomass tended to be higher at low oxygen concentrations. The species composition at the various stations showed a high occurrence of polychaetes. The spionid polychaete Paraprionospio pinnata played an important role as a central key species within the OMZ. In addition to Paraprionospio, Ampelisca araucana, Magelona phyllisae, Nephtys ferruginea and Cossura chilensis were found in high abundance in the oxygen minimum zone (50–200 m water depth). At the edge and presumably below the oxygen minimum zone (300–912 m), where the oxygen concentration rises again, the dominance of individual species decreased, and the total number of species increased. In addition, the species composition changed and the abundance of other polychaete families (Cirratulidae, Amphinomidae, Oweniidae and Capitellidae) amplified. The proportion of polychaetes in the total abundance decreased from almost 100% at the low-oxygen stations to around 60% at the stations below the oxygen minimum zone. Bivalvia of the families Thyasiridae, Nuculidae and Yoldiidae were of particular importance at the deeper stations with a share of up to 20% of the total abundance. The study of benthic communities is of central importance to better understand the future changes in the structure and function of marine ecosystems in hypoxic waters. Full article

Dinophiliformia is a newly revealed clade within Annelida that is a sister group to Pleistoannelida. Dimorphilus gyrociliatus is a representative of this clade that has fascinated scientists with its high degree of sexual dimorphism. Both males and females are small, worm-like creatures that have specific ciliary structures: anterior ventral, posterior ventral, and dorsal ciliary fields in males, and prototroch, metatroch, and ventral ciliary fields in females. There are data on the morphology and development of the nervous system in Oweniidae, Sipunculida, Pleistoannelida, and even Dinophiliformia. However, data on the neuromorphology and development of D. gyrociliatus dwarf males are limited. Here, we present data on the distribution of cilia, sensory neurons, and the 5-HT-like immunoreactive system in 3D reconstructions and cross-sections. Immunochemical labeling with anti-acetylated tubulin and anti-5-HT antibodies and confocal microscopy were used to visualize the ciliary structures and neurons. The male has three ciliary fields: anterior ventral, posterior ventral, and dorsal. These include frontal ganglia, five commissures, two ventral and two dorsal bundles, and penial nerves. A total of fifty-seven neurons and only five 5-HT-like immunoreactive cells were described. Although the sensory neurons were not 5-HT-like immunoreactive, they had 5-HT innervation, which may indicate the role of 5-HT in perception. There may be homology between male and female ciliary structures. The dwarf male of D. gyrociliatus may have a reduced apical organ consisting of two sensory neurons and a 5-HT-like immunoreactive cell. Full article

Palaeoannelida Weigert and Bleidorn, 2016 is an old clade branching off at the base of the Annelida radiation. It includes two morphologically and ecological divergent groups of sedentary burrowers and tube-dwellers: Magelonidae Cunningham and Ramage, 1888, and Oweniidae Rioja, 1917. Magelonids are characterised by a flattened, shovel-shaped prostomium and a pair of ventral papillated palps. Oweniids have simplified bodies lacking parapodia or appendages and are easily distinguished by the presence of oval patches of packed uncini, each with two distal curved teeth. The present review aims to summarise available information about the diversity of forms and life strategies displayed in the group, providing some guidelines for species identification and the techniques commonly used for their study. In addition, the assumed geographic distributions of some taxa are critically discussed. A brief introduction about the evolutionary relationships, systematics, and taxonomic history is given for both Magelonidae and Oweniidae. The motivation of this review is to highlight the main knowledge gaps from a taxonomic, methodological, and geographic perspective, aiming at stimulating further research into members of this clade. Full article