Larvae of ~100 species of benthic invertebrates were obtained from the vicinity of Tomales Bay and Dillon Beach, California, over a 6-year period (1971–1977). This study reports on larvae of 14 species in eight families of polychaetes: Micronereis nanaimoensis, Nereis vexillosa, Sthenelais fusca, Nephtys caecoides, Nephtys californiensis, Boccardia berkeleyorum, Polydora pygidialis, Polydora spongicola, Dipolydora cardalia, Mediomastus californiensis, Ampharete labrops, Phragmatopoma californica, Sabellaria cementarium and Pectinaria californiensis. Some species were cultured from embryos obtained from laboratory fertilizations or field-collected egg masses or capsules. Larvae of other species were obtained from meroplankton and some of these were cultured through metamorphosis. A summary table is presented documenting seasonal occurrence of 60 polychaete taxa in the meroplankton.

Species definition is not an easy task, when considering the more than 27 known species concepts. Among them, the morphospecies concept has been one of the most applied since it is based on the use of observable morphological features. Morphometry has been used to delimitate morphospecies or similar taxa complementing the morphological observations and contributing to clarify taxonomic problems. Specimens from the sympatric species Perinereis anderssoni and Perinereis ponteni, collected from the north-eastern to southern coast of Brazil and considered synonymous by some authors, were compared through morphometric analyses for the evaluation of their taxonomic status. Morphometric analysis indicates that notopodial cirri lengths in the median and posterior regions on the body clearly allowed differentiation between the two species. Our results indicate that the number and arrangement of paragnaths demonstrate a pattern of variation that effectively differs and could be used to discriminate these two Perinereis species. This distinction was confirmed by the restricted among-population variability within each species, even when populations that are geographically very distant from each other were considered.

Rullierinereis ancornunezi is recorded for the first time from British waters. Specimens were discovered at two sites: near the Isles of Scilly at the extreme south-west of the country and near the Isle of Wight in the English Channel.

Karyotypes of the hermaphroditic polychaete Hediste limnicola were examined using an air-drying method and genetic material prepared from regenerating tail and newborn juveniles. Materials were obtained from a lineage of cultured worms originating from Watsonville Slough (California, USA) and maintained for six years in the laboratory. Giemsa-stained preparations were analysed by a computer-assisted image-analysing system for the identification of each chromosome pair. A diploid chromosome number of 26 was obtained from well-spread metaphase chromosomes of mitotic cells, consisting of metacentric (N = 11), submetacentric (N = 1) and telocentric (N = 1) chromosomes. It is possible that hermaphroditism in this species evolved through loss of a pair of sex chromosomes, which are present in closely related congeneric species.