Sabellastarte Krøyer, 1856 (Sabellidae), a morphologically homogeneous group distributed in warm and temperate coasts of the Indo-Pacific and Caribbean Sea, is characterized by the presence of a unique combination of features. To date, the genus comprises eight species, but morphological characters traditionally used in diagnostics have shown intra-specific variability, making species boundaries and distributions unclear. The present study constitutes the first attempt to test the monophyly of Sabellastarte and its relationships to other sabellid genera by combining molecular (COI and 16S) and morphological data. Results include placement of a clade containing Stylomma, Sabella, Branchiomma and Bispira as the sister group to Sabellastarte. Phylogenetic analyses and genetic divergence among specimens from several localities around the world indicate the presence of at least six lineages within Sabellastarte. In the context of a discussion of species boundaries and diagnostic features, the distribution of some of those lineages can be explained by the presence of cryptic species and potential introductions.

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The South American sabellid polychaete worm collections of Phyllis Knight-Jones and José María Orensanz were recovered, curated and specimens identified, comprising fourteen species grouped in nine genera. Five species belonging to the genera Chone Krøyer, 1856, Acromegalomma Gil and Nishi, 2017, Notaulax Tauber, 1879, Parasabella Bush, 1905, and Pseudopotamilla Bush, 1905, are described as new to science from the Patagonian Shelf (Argentina). Jasmineira crumenifera Hartmann-Schröder, 1986, Myxicola sulcata Ehlers, 1912, Parasabella columbi (Kinberg, 1867), Perkinsiana antarctica (Kinberg, 1867) and Perkinsiana assimilis (McIntosh, 1885) are redescribed and reported from several Patagonian localities. Three new combinations are made: Sabella tilosaula Schmarda, 1861, is transferred to Notaulax, Sabella magalhaensis Kinberg, 1867, to Perkinsiana Knight-Jones, 1983, and Potamilla platensis Hartman, 1953, to Pseudopotamilla. Potamethus littoralis Hartman, 1967, was synonymized with Perkinsiana magalhaensis. Notaulax tilosaula, Perkinsiana antarctica and P. magalhaensis are reported from the biogeographical subregion Humboldt Current System, whereas Bispira sp., Chone orensanzi sp. nov., Jasmineira crumenifera, Acromegalomma schwindtae sp. nov., M. sulcata, Notaulax salazari sp. nov., Parasabella columbi, P. yonowae sp. nov., Perkinsiana assimilis, Pseudopotamilla platensis, and P. knightjonesae sp. nov., are reported from the Patagonian Shelf.

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The use of live algae and preserved algal products was examined as to their utility in supporting growth and survival of the feather duster worm, Sabellastarte spectabilis. Hatchery‐reared 4‐mo‐old worms were provided the same cell densities of live T‐Iso, preserved T‐Iso, live Nannochlropsis sp., and preserved Nannochloropsis sp. over the course of 132 d. A group of worms placed in a water table that received a continuous flow of raw seawater served as controls. Live and preserved T‐Iso resulted in the highest survival (86.7 ± 6.2% and 78.3 ± 16.5%, respectively) compared to all the other treatments. Live T‐Iso fed worms resulted in significantly larger worms than all other treatments with the preserved T‐Iso treatment supporting similar growth to those being fed live Nannochloropsis sp. and exposed to raw seawater. The preserved Nannochloropsis sp. resulted in significantly lower survival and growth when compared to all the other treatments. Fatty acid profiles of the algal diets and worm carcasses obtained during the current investigation suggest that T‐Iso outperformed Nannochloropsis because of its higher energy or fatty acid content.

Understanding the reproductive characteristics of Sabellastarte spectabilis (Grube, 1878), an economically important polychaete worm collected for the aquarium trade, is essential to the development of artificial propagation and conservation of coral reefs. The purpose of this study was to determine whether S. spectabilis is hermaphroditic. Using histological techniques, 180 individuals were examined for gametes. Gametes were present only in abdominal segments. Primary oocytes were 7-8 mm in diameter in histologically prepared sections. Sperm appeared as round black dots about 2 mm in diameter on histologically prepared slides. Most individuals sampled had only one type of gamete in the coelom, but both eggs and sperm were seen in the coelom of 15% of individuals, demonstrating the occurrence of hermaphroditism in Hawaiian populations of S. spectabilis. The sex ratio of males to females was skewed significantly toward males in both the small (6-8 mm diameter) and medium (9-10 mm diameter) sized worms. Among the largest worms (11-13 mm diameter), the sex ratio did not diverge significantly from 1 : 1. There was a significantly higher proportion of hermaphrodites (30%) in the large size class. Worms of unknown gender, although present in all size classes examined, were most frequent (33%) in the medium size class. These patterns are consistent with sequential (protandrous) hermaphroditism.

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