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Eunice woodwardiBaird, 1869, originally described from the Ría de A Coruña (NW Iberian Peninsula), has been overlooked and never reported from the Atlantic coast of Spain after original description and the subsequent redescription of the holotype. In the present study, we revised comparatively the holotype, newly collected specimens of this species and specimens identified as Eunice vittata (Delle Chiaje, 1829) from western Mediterranean Sea. The validity of E. woodwardi is supported and previous descriptions are complemented after a throughout study of the external morphology by means of light compound microscopy and scanning electron microscopy, and that of the internal anatomy by histological sectioning and micro-computed tomography. The presence of eyes, nuchal organs, dorsal and ventral ciliary organs on parapodial cirri and paired nephridia in most segments is confirmed in E. woodwardi; the digestive tract is clearly regionalized and divided into pharynx, oesophagus, stomach, fore, mid- and hind intestine. The presence of E. woodwardi in the Ría de Ferrol is also reported, and we suggest that previous records of E. vittata in NW Iberian Peninsula should be reviewed. Eunice woodwardi is distinguished by a set of characters such as having non-articulated and non-constricted cephalic appendages, the maxillary formula, the range of branchial distribution, maximum number of branchial filaments, number of limbate and compound falciger chaetae per parapodium, the presence of an apical mucro in the guard of falciger chaetae blades and the number of teeth in pectinate chaetae. Epibiont Ciliophora on branchiae are also reported.

Background The overall anatomy of the genus Syllis (Annelida: Syllidae) has been largely studied; however, an integrative approach considering different anatomical techniques has never been considered. Here, we use micro-computed X-ray tomography (micro-CT) to examine the internal anatomy of Syllis gracilis Grube, 1840, along with other widely available techniques. Methods We studied the anatomy of the marine annelid S. gracilis through an integrative approach, including micro-CT along with stereo and light compound microscopy (STM, LCM), scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) and histological sectioning (HIS). In this manner, we evaluated the applicability of micro-CT for the examination of annelid anatomy by testing whether the images obtained make it possible to visualize the main body structures, in comparison with other current techniques, of the various elements of its internal anatomy. Results Overall external and internal body elements are clearly shown by the integrative use of all techniques, thus overcoming the limitations of each when studied separately.Any given method shows disparate results, depending on the body part considered. For instance, micro-CT provided good images of the external anatomy, including relevant characters such as the shape, length and number of articles of dorsal parapodial cirri. However, it is especially useful for the examination of internal anatomy, thus allowing for 3D visualization of the natural spatial arrangement of the different organs. The features best visualized are those of higher tissue density (i.e., body musculature, anterior parts of the digestive tract), particularly in 3D images of unstained specimens, whereas less electrodense tissues (i.e., the peritoneal lining of septa and nervous system) are less clearly visualized. The use of iodine stain with micro-CT has shown advantages against non-staining for the adequate observation of delicate elements of low density, such as the segmental organs, the connective between the ganglia, the ventral nerve cord and segmental nerves. Discussion Main external anatomical elements of S. gracilis are well shown with micro-CT, but images show lesser optical resolution and contrast when compared to micrographs provided by SEM and CLSM, especially for fine structural features of chaetae. Comparison of micro-CT and HIS images revealed the utility and reliability of the former to show the presence, shape and spatial disposition of most internal body organs; the resolution of micro-CT images at a cellular level is, however, much lower than that of HIS, which makes both techniques complementary.

The study of material collected during routine monitoring surveys dealing with oil extraction and aquaculture in waters off Myanmar (North Andaman Sea) and in the Gulf of Thailand, respectively, allowed us to analyse the taxonomy and diversity of the polychaete genus Terebellides (Annelida). Three species were found, namely Terebellides cf. woolawa, Terebellides hutchingsae spec. nov. (a new species fully described and illustrated), and Terebellides sp. (likely a new species, but with only one available specimen). The new species is characterised by the combination of some branchial (number, fusion and relative length of lobes and papillation of lamellae), and thoracic (lateral lobes and relative length of notopodia) characters and is compared with all species described or reported in the SW Indo-Pacific area, as well as with those sharing similar morphological characteristics all around the world. The taxonomic relevance of the relative length of branchial lobes and different types of ciliature in branchial lamellae for species discrimination in the genus is discussed. A key to all Terebellides species described in SE Indo-Pacific waters is presented.