Detailed morphological study of more than 2600 North East Atlantic (NEA) sphaerodorids (SphaerodoridaeAnnelida) and phylogenetic analyses of DNA sequences of representatives of several identified morphospecies enforced changing the current systematic classification within the family allowed the discovery of new species provided new information about the morphological and genetic characterisation of members of this group and increased the species occurrence data to better infer their geographic and bathymetric distribution ranges. Phylogenetic analyses of nuclear (18S rRNA and 28S rRNA) and mitochondrial sequences (COI and 16S rRNA) of NEA short-bodied sphaerodorids revealed outstanding results including paraphyly of the generaSphaerodoropsisSphaerodoridium, andSphaerephesia. The number of longitudinal and transverse rows of dorsal macrotubercles is proposed as potential synapomorphies for the main clades and are consequently herein used for the genera delimitation. The new classification proposed here implies nomenclatural changes and the erection of a new genusGeminofilumgen. n.to accommodate the species previously considered asSphaerodoropsiswith two transverse rows of dorsal macrotubercles per segment. Four species are being described herein:EuritmianordicaCapa & Bakkensp. n.SphaerephesiamultichaetaCapa Moreira & Paraparsp. n.SphaerephesiaponsiCapa Parapar & Moreirasp. n.andSphaerodoridiumceliaeMoreira Capa & Paraparsp. n.Characterisation of the other 21 species including updated iconography and an identification key to all NEA short-bodied sphaerodorids are provided.

The number of described species of the genus Terebellides Sars, 1835 (Annelida, Trichobranchidae) has greatly increased in the last years, particularly in the North East Atlantic. In this context, this paper deals with several putative species recently delineated by molecular means within a well delimited clade of Terebellides. Species are characterised here by a combination of morphological characters, and a complementary nucleotide diagnostic approach. Three species were identified as the nominal species T. stroemii Sars, 1835, T. bigeniculatus Parapar, Moreira & Helgason, 2011 and T. europaeaLavesque et al., 2019. Five species are described as new: T. bakkenisp. nov., T. kongsrudisp. nov., T. norvegicasp. nov., T. ronningaesp. nov. and T. scoticasp. nov. The distinctive morphological characters refer to the branchial shape, absence or presence of papillae on lamellae of anterior margin of branchial dorsal lobes, absence or presence of ciliated papillae dorsal to thoracic notopodia, geniculate chaetae in one or two chaetigers, and the morphology of thoracic and abdominal uncini teeth. Furthermore, the description of T. bigeniculatus is revised and complemented after examination of type specimens. An updated identification key to all species of the genus in NE Atlantic and a proposal of a classification of different types of abdominal uncini to be used in taxonomy are also included.

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 genusTerebellides(Annelida). Three species were found, namelyTerebellidescf.woolawa,Terebellides hutchingsaespec. nov.(a new species fully described and illustrated), andTerebellidessp. (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 allTerebellidesspecies described in SE Indo-Pacific waters is presented.

In this paper we review the systematics, diversity, and ecology of two related annelid families: Opheliidae Malmgren, 1867 and Scalibregmatidae Malmgren, 1867. Opheliids are deposit-feeders and that are mainly found as burrowers in sandy sediments. Morphologically, opheliids are characterized by the smooth cuticle, as well as the presence of a conspicuous ventral groove, reduced parapodia, and a tubular-shaped structure often projecting from the posterior end. Scalibregmatids are also deposit-feeders, but compared to opheliids, they have a characteristic arenicoliform body, a T-shaped anterior end and a glandular, reticulated epidermis. For each family, we summarize the available information about the evolutionary relationships, taxonomic history, geographical distribution, ecological preferences and diversity of life strategies along with the techniques most commonly used for their study. By highlighting the main gaps in knowledge on each of these topics, this review ultimately aims at stimulating further research into members of these two families in the future.

Several new species of genus Terebellides Sars, 1835 (Annelida, Trichobranchidae) have been recently described from the Northeast Atlantic Ocean after the detection of a large complex of species based on DNA sequence data from previous research. Some of those species (belonging to the so-called Group A) have already been described elsewhere. In this paper, we revise several Terebellides clades belonging to Groups B, C and D resulting in the identification of five nominal species: Terebellides gracilis Malm, 1874, Terebellides atlantis Williams, 1984, Terebellides williamsae Jirkov, 1989, Terebellides irinae Gagaev, 2009, and Terebellides shetlandica Parapar, Moreira & O’Reilly, 2016, plus one new species described here as Terebellides lavesqueisp. nov. All these species are characterised by a combination of morphological features complemented with a nucleotide diagnostic approach (specific COI nucleotides in the alignment position). Morphological characters used to discriminate between taxa refer to the branchial shape, presence/absence of ciliated papillae dorsal to thoracic notopodia and the morphology of thoracic and abdominal uncinal teeth. An updated identification key to all described species of this genus in NE Atlantic waters is also included.