Annelid functional genomics reveal the origins of bilaterian life cycles.

Indirect development with an intermediate larva exists in all major animal lineages1, which makes larvae central to most scenarios of animal evolution2-11. Yet how larvae evolved remains disputed. Here we show that temporal shifts (that is, heterochronies) in trunk formation underpin the diversification of larvae and bilaterian life cycles. We performed chromosome-scale genome sequencing in the annelid Owenia fusiformis with transcriptomic and epigenomic profiling during the life cycles of this and two other annelids. We found that trunk development is deferred to pre-metamorphic stages in the feeding larva of O. fusiformis but starts after gastrulation in the non-feeding larva with gradual metamorphosis of Capitella teleta and the direct developing embryo of Dimorphilus gyrociliatus. Accordingly, the embryos of O. fusiformis develop first into an enlarged anterior domain that forms larval tissues and the adult head12. Notably, this also occurs in the so-called 'head larvae' of other bilaterians13-17, with which the O. fusiformis larva shows extensive transcriptomic similarities. Together, our findings suggest that the temporal decoupling of head and trunk formation, as maximally observed in head larvae, facilitated larval evolution in Bilateria. This diverges from prevailing scenarios that propose either co-option9,10 or innovation11 of gene regulatory programmes to explain larva and adult origins.

Unearthing the diversity of Japanese Magelona (Annelida: Magelonidae); three species new to science, and a redescription of Magelona japonica.

Whilst seven species of magelonids have been originally described from the North-Western Pacific Ocean, only two have been from Japanese waters. Given the often high diversity of magelonid species within relatively small regions, the number of Japanese Magelona species is likely to be higher. The validity of several recorded species from the region has been additionally called into question, and the urgent need for a review of magelonids of Japan highlighted. Newly collected samples of magelonids have emphasised the presence of three species new to science occurring off Japan, herein described: Magelona alba sp. nov., Magelona armatis sp. nov., and Magelona boninensis sp. nov. A redescription of Magelona japonica is additionally provided, along with notes on a fifth species, which approaches Magelona cornuta. A dichotomous identification key to magelonid species of the North-Western Pacific Ocean, along with a table of characters for all five observed species is provided.

Who's who in Magelona: phylogenetic hypotheses under Magelonidae Cunningham & Ramage, 1888 (Annelida: Polychaeta).

Known as shovel head worms, members of Magelonidae comprise a group of polychaetes readily recognised by the uniquely shaped, dorso-ventrally flattened prostomium and paired ventro-laterally inserted papillated palps. The present study is the first published account of inferences of phylogenetic hypotheses within Magelonidae. Members of 72 species of Magelona and two species of Octomagelona were included, with outgroups including members of one species of Chaetopteridae and four of Spionidae. The phylogenetic inferences were performed to causally account for 176 characters distributed among 79 subjects, and produced 2,417,600 cladograms, each with 404 steps. A formal definition of Magelonidae is provided, represented by a composite phylogenetic hypothesis explaining seven synapomorphies: shovel-shaped prostomium, prostomial ridges, absence of nuchal organs, ventral insertion of palps and their papillation, presence of a burrowing organ, and unique body regionation. Octomagelona is synonymised with Magelona due to the latter being paraphyletic relative to the former. The consequence is that Magelonidae is monotypic, such that Magelona cannot be formally defined as associated with any phylogenetic hypotheses. As such, the latter name is an empirically empty placeholder, but because of the binomial name requirement mandated by the International Code of Zoological Nomenclature, the definition is identical to that of Magelonidae. Several key features for future descriptions are suggested: prostomial dimensions, presence/absence of prostomial horns, morphology of anterior lamellae, presence/absence of specialised chaetae, and lateral abdominal pouches. Additionally, great care must be taken to fully describe and illustrate all thoracic chaetigers in descriptions.

A further review of European Magelonidae (Annelida), including descriptions of Magelona equilamellae and Magelona filiformis.

Following on from the partial review of European Magelonidae by Fiege et al. (2000), a dichotomous identification key, a table of characters and images of all nine known European magelonid species are provided. Magelona equilamellae is redescribed highlighting several features not reported originally by Harmelin. Notably the thoracic neuropodial lamellae, which are initially prechaetal but become distinctly postchaetal by chaetiger 7, an additional character allowing separation from the morphologically similar Magelona alleni. Records suggest that M. equilamellae is a Mediterranean species, more commonly occurring in shallow, transitional waters. Several new characters for Magelona filiformis are additionally highlighted as well as a number of corrections to the existing description, including the number of prostomial ridges, presence of abdominal lateral pouches, morphology of chaetiger 9, and the presence of smaller abdominal hooded hooks adjacent to lateral lamellae. The first image of M. filiformis minuta is provided, and its synonymy with M. filiformis further supported.

Redescription of Magelona minuta Eliason, 1962 (Annelida), with discussions on the validity of Magelona filiformis minuta.

Since Magelona minuta was described in 1962 our understanding of the key features required to distinguish between magelonid species has increased. The original description contains only four illustrations and vital information on many key characters is not included. This re-assessment of the holotype and material from the type locality includes several features not previously described, specifically related to thoracic and abdominal lamellae. Comparative material from Britain and the Southern Irish and Celtic Seas is examined, adding information on the posterior region. Diet is discussed based on the gut contents of a specimen originally identified by Eliason. Information on numbers of thoracic chaetae and the angle between teeth of abdominal hooded hooks for several magelonid species is investigated. The validity of the dwarf species Magelona filiformis minuta is herein examined.

Shallow marine benthic invertebrates of the Seychelles Plateau: high diversity in a tropical oligotrophic environment.

Soft sedimentary biotopes are extensive in the shallow Western Indian Ocean, especially on the Seychelles Plateau and Mascarene Ridge, yet pro rata compared with coral reefs the research effort devoted to them has been minimal. In this study we examine the benthic mollusc and polychaete worm assemblages of the shallow waters (11-62 m) around Mahe, in the Seychelles, and make direct comparisons with the temperate Irish Sea area and subtropical waters of Hong Kong, China (using identical methodology). Two assemblages were recognized, characterized by depth and sediment type. Of these, assemblage A (in shallow carbonate sands) was the most diverse, with diversity and richness measures exceeding those from the Irish Sea or Hong Kong. Hong Kong generally had the poorest fauna. Considering the Bivalvia alone, estimates of taxonomic distinctness showed this to be least for Seychelles assemblage A. The degree of conformity of the results to the concept of the latitudinal gradient in species richness and the possible underlying causes are discussed. Comparisons with other data suggest that the Seychelles support a benthic fauna at least as diverse as any other described from the tropics. A tentative examination of total bivalve species richness suggests a total of 400-500 for the Seychelles. This is in keeping with other Indian Ocean localities, but higher than known figures for continental east Africa. The findings of this paper support the case for widespread ecological and taxonomic studies of the Western Indian Ocean benthic invertebrates.