Limb muscles are remarkably complex and evolutionarily labile. Although their anatomy is of great interest for studies of the evolution of form and function, their homologies among major amniote clades have remained obscure. Studies of adult musculature are inconclusive owing to the highly derived morphology of modern amniote limbs, but correspondences become increasingly evident earlier in ontogeny. We followed the embryonic development of forelimb musculature in representatives of six major amniote clades and found, contrary to current consensus, that these early splitting patterns are highly conserved across Amniota. Muscle mass cleavage patterns and topology are highly conserved in reptiles including birds, irrespective of their skeletal modifications: the avian flight apparatus results from slight early topological modifications that are exaggerated during ontogeny. Therian mammals, while conservative in their cleavage patterns, depart drastically from the ancestral amniote musculoskeletal organization in terms of topology. These topological changes occur through extension, translocation, and displacement of muscle groups later in development. Overall, the simplicity underlying the apparent complexity of forelimb muscle development allows us to resolve conflicting hypotheses about homology and to trace the history of each individual forelimb muscle throughout the amniote radiations.

Background: The extremely derived body plan of turtles has sparked a great interest in studying their developmental biology. Here, we describe the embryonic development of the Stinkpot, or common musk turtle (Sternotherus odoratus), a small aquatic turtle from the family Kinosternidae. Results: We identify 20 distinct developmental stages, some comparable to stages described by previous studies on other turtles and some in between these, improving the resolution of the generalities of turtle development. We provide a detailed account of both the external morphology and skeletal development, as well as a general look at the early stages of muscular development until the attainment of the adult muscular anatomical pattern. Conclusions: Several potential skeletal and muscular apomorphies of turtles are identified or elaborated. The musk turtle, with its small size and hardshelled egg, could become an important species for the study of turtle evolution and development, suitable for in ovo experimentation and late stage imaging of well-advanced anatomical features.

No abstract

Pettalidae is a family of mite harvestmen that inhabits the former circum-Antarctic Gondwanan terranes, including

Siphonophores (Cnidaria:Hydrozoa) are abundant predators found throughout the ocean and are important components in worldwide zooplankton. They range in length from a few centimeters to tens of meters. They are gelatinous, fragile, and difficult to collect, so many aspects of the biology of these 190 species remain poorly understood. To survey siphonophore genome diversity, we performed Illumina sequencing of 32 species sampled broadly across the phylogeny. Sequencing depth was sufficient to estimate nuclear genome size from k-mer spectra in 8 specimens, ranging from 0.7-4.8Gb. In 6 specimens we got heterozygosity estimates between 0.7-5.3%. Rarefaction analyses indicate k-mer peaks can be absent with as much as 30x read coverage, suggesting minimum genome sizes range from 1.0-3.8Gb in the remaining 27 samples without k-mer peaks. This work confirms most siphonophore nuclear genomes are large, but also identifies several with reduced size that are tractable targets for future siphonophore nuclear genome assembly projects. We also assembled mitochondrial genomes for 32 specimens from these new data, indicating a conserved gene order among Hydrozoa, Cystonectae and some Physonectae, also revealing the ancestral gene organization of siphonophores. There then was extensive rearrangement of mitochondrial genomes within other physonects and in Calycophorae, including the repeated loss of atp8. Though siphonophores comprise a small fraction of cnidarian species, this survey greatly expands our understanding of cnidarian genome diversity. This study further illustrates both the importance of deep phylogenetic sampling and the utility of Illumina genome skimming in understanding genomic diversity of a clade.

Genomic data for priapulans are limited to a single species, restricting broad comparative analyses, and thorough interrogation of questions spanning phylogenomics, ecdysozoan physiology, and development. To help fill this void, we present here a high-quality priapulan genome for the meiofaunal species Tubiluchus corallicola. Our assembly combines Nanopore and Illumina sequencing technologies, and makes use of a whole genome amplification, to generate enough DNA to sequence this small meiofaunal species. We generated a moderately contiguous assembly (2547 scaffolds), with a high level of completeness (Metazoan BUSCOs n = 954, single copy complete = 89.6%, duplicated = 3.9%, fragmented = 3.5%, missing = 3.0%). We then screened the genome for homologs of the Halloween genes, key genes implicated in the ecdysis (moulting) pathway of arthropods, recovering a putative homolog of shadow. The presence of a shadow orthologue in two priapulan genomes suggests that the Halloween genes may not have evolved in a stepwise manner in Panarthropoda, as previously thought, but may have a deeper origin at the base of Ecdysozoa.

No abstract

Donacidae is a commercially important family of heterodont bivalves and one of the few bivalve lineages that has successfully colonised brackish and fresh waters. However, to date, no phylogenetic hypothesis exists for this widely distributed group. Here we turn to molecular data from the nuclear and mitochondrial genomes and combine these with the extensive fossil record of donacids to propose an evolutionary hypothesis for the family. Our analyses strongly support the monophyly of Donacidae, including Galatea, Iphigenia and ‘Plebidonax’ deltoides, but render Donax paraphyletic. The subgenus Latona is therefore elevated to genus to accommodate a clade of Indo-Pacific species, while retaining Donax for a clade of mostly Atlantic and American Pacific species, and a few Indo-Pacific species. This latter clade is sister group to Galatea + Iphigenia. The diversification of Donacidae seems to be tightly connected to the opening of the North and South Atlantic Oceans in the Cretaceous, and to the closing of the Tethys Ocean during the Oligocene. Taxonomic actions: Latona columbella (Lamarck, 1818) comb. nov., L. deltoides (Lamarck, 1818) comb. nov., L. dysoni (Reeve, 1854) comb. nov., L. madagascariensis (W. Wood, 1828) comb. nov., L. semisulcata semigranosa (Dunker, 1877) comb. nov., L. spinosa (Gmelin, 1791) comb. nov., L. sordida (Hanley, 1845) comb. nov., L. siliqua (Römer, 1870) comb. nov., L. trifasciata (Linnaeus, 1758) comb. nov. and L. victoris (Fischer-Piette, 1942) comb. nov.