Taxonomic review of Gallardonerisnonatoi (Ramos, 1976) comb. nov. (Annelida, Lumbrineridae), and description of a new species of Lumbrineris from the Gulf of Mexico.

The small LumbrineridaeGallardonerisiberica Martins, Carrera-Parra, Quintino & Rodrigues, 2012 was first described as new to science based on specimens from Portuguese waters. Then, it was successively reported from several south European areas, including Spain, Italy, Greece, and Cyprus. Here evidence is presented that G.iberica should be placed in synonymy with Lumbrinerisnonatoi Ramos, 1976, originally described from NW Mediterranean waters, a species that fits with the diagnosis of Gallardoneris. Based on specimens from the French coasts of the NW Mediterranean, this paper (1) redescribes the species using the new combination Gallardonerisnonatoi (Ramos, 1976) and (2) provides a morphometric analysis of its main morphological characters. The lack of recent reports of G.nonatoi comb. nov. in Mediterranean waters is presumably due to the recent redescription of the species as L.nonatoi based on specimens from the Gulf of Mexico. However, these specimens belong to Lumbrineris, as currently defined. By assessing their morphological differences, it is concluded that the specimens from the Gulf of Mexico represent a different and new species, namely Lumbrinerisjan sp. nov. Also discussed is the possible assignation of Lumbrinerislongipodiata Cantone, 1990, a poorly known species seldom recorded since its original description from the Gulf of Catania (Mediterranean Sea) to Gallardoneris, as well as on whether it is a valid species or may be an additional junior synonym of G.nonatoi comb. nov.

New light shed on the early evolution of limb-bone growth plate and bone marrow.

The production of blood cells (haematopoiesis) occurs in the limb bones of most tetrapods but is absent in the fin bones of ray-finned fish. When did long bones start producing blood cells? Recent hypotheses suggested that haematopoiesis migrated into long bones prior to the water-to-land transition and protected newly-produced blood cells from harsher environmental conditions. However, little fossil evidence to support these hypotheses has been provided so far. Observations of the humeral microarchitecture of stem-tetrapods, batrachians, and amniotes were performed using classical sectioning and three-dimensional synchrotron virtual histology. They show that Permian tetrapods seem to be among the first to exhibit a centralised marrow organisation, which allows haematopoiesis as in extant amniotes. Not only does our study demonstrate that long-bone haematopoiesis was probably not an exaptation to the water-to-land transition but it sheds light on the early evolution of limb-bone development and the sequence of bone-marrow functional acquisitions.

For many aquatic creatures, the red blood cells that rush through their bodies are created in organs such as the liver or the kidney. In most land vertebrates however, blood-cell production occurs in the bone marrow. There, the process is shielded from the ultraviolet light or starker temperature changes experienced out of the water. It is possible that this difference evolved long before the first animal with a backbone crawled out of the aquatic environment and faced new, harsher conditions: yet very little fossil evidence exists to support this idea. A definitive answer demands a close examination of fossils from the water-to-land transition including lobe-finned fish and early limbed vertebrates. To support the production of red blood cells, their fin and limb bones would have needed an internal cavity that can house a specific niche that opens onto a complex network of blood vessels. To investigate this question, Estefa et al. harnessed the powerful x-ray beam produced by the European Synchrotron Radiation Facility and imaged the fin and limb bones from fossil lobe-finned fish and early limbed vertebrates. The resulting three-dimensional structures revealed spongy long bones with closed internal cavities where the bone marrow cells were probably entrapped. These could not have housed the blood vessels needed to create an environment that produces red blood cells. In fact, the earliest four-legged land animals Estefa et al. found with an open marrow cavity lived 60 million years after vertebrates had first emerged from the aquatic environment, suggesting that blood cells only began to be created in bone marrow after the water-to-land transition. Future work could help to pinpoint exactly when the change in blood cell production occurred, helping researchers to identify the environmental and biological factors that drove this change.

Secondary ossification center induces and protects growth plate structure.

Growth plate and articular cartilage constitute a single anatomical entity early in development but later separate into two distinct structures by the secondary ossification center (SOC). The reason for such separation remains unknown. We found that evolutionarily SOC appears in animals conquering the land - amniotes. Analysis of the ossification pattern in mammals with specialized extremities (whales, bats, jerboa) revealed that SOC development correlates with the extent of mechanical loads. Mathematical modeling revealed that SOC reduces mechanical stress within the growth plate. Functional experiments revealed the high vulnerability of hypertrophic chondrocytes to mechanical stress and showed that SOC protects these cells from apoptosis caused by extensive loading. Atomic force microscopy showed that hypertrophic chondrocytes are the least mechanically stiff cells within the growth plate. Altogether, these findings suggest that SOC has evolved to protect the hypertrophic chondrocytes from the high mechanical stress encountered in the terrestrial environment.