Echinoids are key components of modern marine ecosystems. Despite a remarkable fossil record, the emergence of their crown group is documented by few specimens of unclear affinities, rendering their early history uncertain. The origin of sand dollars, one of its most distinctive clades, is also unclear due to an unstable phylogenetic context. We employ 18 novel genomes and transcriptomes to build a phylogenomic dataset with a near-complete sampling of major lineages. With it, we revise the phylogeny and divergence times of echinoids, and place their history within the broader context of echinoderm evolution. We also introduce the concept of a chronospace – a multidimensional representation of node ages – and use it to explore methodological decisions involved in time calibrating phylogenies. We find the choice of clock model to have the strongest impact on divergence times, while the use of site-heterogeneous models and alternative node prior distributions show minimal effects. The choice of loci has an intermediate impact, affecting mostly deep Paleozoic nodes, for which clock-like genes recover dates more congruent with fossil evidence. Our results reveal that crown group echinoids originated in the Permian and diversified rapidly in the Triassic, despite the relative lack of fossil evidence for this early diversification. We also clarify the relationships between sand dollars and their close relatives and confidently date their origins to the Cretaceous, implying ghost ranges spanning approximately 50 million years, a remarkable discrepancy with their rich fossil record.

Specimens of a new species of torquaratorid acorn worm (Hemichordata, Enteropneusta) were video recorded and subsequently collected at abyssal depths in the eastern North Pacific at sites ranging from Oregon to northern Mexico. These worms are described here as Yoda demiankoopi n. sp. by molecular and morphological methods. The new species differs from its only described congener, Yoda purpurata, in three ways. First, the lips are extremely wide and indented by a deep ciliary groove for ingesting substrate and conveying it to the mouth. Second, a connective tissue bulge of unknown significance runs mid-dorsally along the hepatic and posthepatic regions of the intestine. Third, the posthepatic intestine is strikingly sinuous and packed with gut contents presumably undergoing digestion for extended periods between infrequent defecations. Yoda demiankoopi n. sp. is hermaphroditic, a character so far known only for the genus Yoda in the entire class Enteropneusta. The gonads of each adult worm comprise hundreds of ovaries (each containing a single oocyte) and hundreds of testes located just beneath the dorsal epidermis of the anterior trunk and associated genital wings. In any given animal, at any given time, gametes of only one sex or the other become fully mature. Thus, the worm is a sequential hermaphrodite, alternately spawning purely as a female or purely as a male.

Dorvilleids belonging to Ophryotrocha Claparède & Mecznikow, 1869 are known from deep-sea hydrothermal vents in the Pacific, Atlantic, Indian and Southern Oceans. However, how they colonized and diversified in these ecosystems has not been assessed in detail. Here, a collection of Pacific hydrothermal vent Ophryotrocha was examined using morphology and DNA markers (COI, 16S and H3). Five new species were revealed, largely expanding the diversity of the group at this habitat type. They are Ophryotrocha charlottae sp. nov., O. kailae sp. nov., O. marinae sp. nov., O. pruittae sp. nov. from eastern Pacific, and O. bohnorum sp. nov. from the western Pacific. Phylogenetic analyses based on the concatenated alignments of all three genes suggest vent habitants have been colonized several times independently within Ophryotrocha. One clade of six vent species was recovered, indicative of diversification following a colonization of hydrothermal vents, likely in the eastern Pacific. An Indian Ocean species, O. jiaolongi, was nested inside this clade and was closely related to one of the new species from the Gulf of California, diverging from it by less than 4% on COI.