Nemertean and phoronid genomes reveal lophotrochozoan evolution and the origin of bilaterian heads.

Nemerteans (ribbon worms) and phoronids (horseshoe worms) are closely related lophotrochozoans-a group of animals including leeches, snails and other invertebrates. Lophotrochozoans represent a superphylum that is crucial to our understanding of bilaterian evolution. However, given the inconsistency of molecular and morphological data for these groups, their origins have been unclear. Here, we present draft genomes of the nemertean Notospermus geniculatus and the phoronid Phoronis australis, together with transcriptomes along the adult bodies. Our genome-based phylogenetic analyses place Nemertea sister to the group containing Phoronida and Brachiopoda. We show that lophotrochozoans share many gene families with deuterostomes, suggesting that these two groups retain a core bilaterian gene repertoire that ecdysozoans (for example, flies and nematodes) and platyzoans (for example, flatworms and rotifers) do not. Comparative transcriptomics demonstrates that lophophores of phoronids and brachiopods are similar not only morphologically, but also at the molecular level. Despite dissimilar head structures, lophophores express vertebrate head and neuronal marker genes. This finding suggests a common origin of bilaterian head patterning, although different heads evolved independently in each lineage. Furthermore, we observe lineage-specific expansions of innate immunity and toxin-related genes. Together, our study reveals a dual nature of lophotrochozoans, where conserved and lineage-specific features shape their evolution.

Cheilopallene ogasawarensis, a New Species of Shallow-Water Pycnogonid (Arthropoda: Pycnogonida) from the Ogasawara (Bonin) Islands, Japan, Northwest Pacific.

A new species of pycnogonid recorded from the shallow waters of Ogasawara (Bonin) Island, Japan, Cheilopallene ogasawarensis n. sp. is described, illustrated and compared with similar species. Cheilopallene ogasawarensis is only the third pycnogonid species recorded from these islands. Morphological characters clearly distinguish the new species from its geographically closest congener C. nodulosa Hong and Kim, 1987, also recorded from Japanese waters.

Entrainment of the circatidal swimming activity rhythm in the cumacean Dimorphostylis asiatica (Crustacea) to 12.5-hour hydrostatic pressure cycles.

The cumacean Dimorphostylis asiatica (Crustacea) exhibits a circatidal swimming activity rhythm. The animals were exposed to a 12.5 hr sinusoidal change of hydrostatic pressure of 0.3 atm amplitude in the laboratory. Under constant dark conditions, most of the specimens were entrained to a daily bimodal swimming activity rhythm by the hydrostatic pressure cycle. A small number of individuals exhibited a unimodal daily rhythm, with no apparent entraining from the administered cycles. A marked feature was a flexible phase relationship between the entrained daily bimodal rhythm and the hydrostatic pressure cycles: the swimming activity of most of the specimens occurred around the pressure-decreasing phase, but for a small number of individuals it coincided with the pressure-increasing phase. Such flexibility suggests a weak entraining effect of hydrostatic pressure on the circatidal rhythm of this species. When exposed to 24 hr light-dark cycles and a hydrostatic pressure cycle simultaneously, the specimens exhibited a rhythmic activity entrained by the hydrostatic pressure cycle during the dark period, which closely resembles the temporal activity pattern of this species in the field. The light cycles entrained the swimming activity via direct inhibition and induction of activity (i.e., masking). Under light-dark conditions, the specimens exhibited activity on the pressure-increasing phase more frequently compared with specimens kept in constant darkness.