The annelid body wall generally comprises an outer layer of circular muscle fibres and an inner layer of longitudinal muscle fibres as well as parapodial and chaetal muscles. An investigation of Dysponetuspygmaeus (Chrysopetalidae) with confocal laser scanning microscopy showed that circular muscles are entirely absent. Further studies indicate that this feature is characteristic for all Chrysopetalidae. A scrutiny of the literature showed a similar situation in many other polychaetes. This lack of circular muscle fibres may either be due to convergence or represent a plesiomorphic character. Since circular muscles are very likely important for burrowing forms but not necessary for animals which proceed by movements of their parapodial appendages or cilia, this problem is also related to the question of whether the ancestral polychaete was epi‐ or endobenthic.

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Abstract. The morphology of the obligately ectoparasitic polychaete Asetocalamyzas laonicola was studied by light and electron microscopy, and its taxonomic position was determined using molecular methods. The parasite has an extensive coelomic cavity, complete septae, and well‐developed segmental nephridia, circulatory, and digestive systems. The nervous system is rudimentary and without ganglia. The parasite's anterior region penetrates the tissues of the host, and opens into the host's body cavity. The epidermal tissues of the parasite and the host are highly integrated in the area of contact, and the parasite's cuticle is continuous with that of the host. Blood vessels of the parasite and the host may interlace in the fusion zone. The dorsal side of the parasite faces the dorsal side of the host. All parasites were males, but all hosts were females. In order to elucidate the uncertain systematic position of the parasite, molecular systematic studies were conducted. Parasite and host 18S rDNA sequences were virtually identical and revealed that both belong to the spionid cluster. These sequences differed from those of Scolelepis squamata and Scolelepis bonnieri by 2.7% and 0.9%, respectively. In addition, of seven partial sequences of the mitochondrial COI gene obtained from three parasites and four hosts, six were identical, and in one host–parasite pair, COI sequences differed by one substitution. Partial ITS2 sequences from one host–parasite pair were analyzed and also found to be similar but not identical, with two indels in a 645‐bp alignment. We conclude that the parasite is in fact a dwarf male of its conspecific spionid female host. Consequently, A. laonicola is transferred to Scolelepis (Spionidae), forming the new combination Scolelepis laonicola.

Five sternaspid species were found near Vietnam shores: Sternaspis britayevi sp. nov., S. costata von Marenzeller, 1879, S. nana sp. nov., S. papillosa sp. nov., and S. spinosa Sluiter 1882. Sternaspis britayevi is described from the shallow water in Vietnam inhabiting soft bottoms; it resembles S. spinosa described from Java and S. thorsoni Sendall & Salazar-Vallejo, 2013 described from the Persian Gulf, but differs in having a medially projected and markedly ribbed fan of the ventro-caudal shield and nearly parallel, distally widened and rounded branchial plates. Sternaspis nana sp. nov. is described from Nha Trang Bay; it differs from the other known species by the combination of the following characters: small size, evenly distributed micropapillae and regular rows of long cirriform papillae; posterior chaetal fascicles consisting of single thick chaeta; a ventral shield with smooth integument, without ribs and usually without concentric lines. Sternaspis papillosa sp. nov. is also described from Nha Trang Bay; it resembles S. africana Augener, 1918 and S. andamanensis Sendall & Salazar-Vallejo, 2013 by having similar ventro-caudal shields but differs by body papillation and details of the ventro-caudal shield. Based upon observations of different species some morphological features are clarified: 1) notochaetae are present in introvert chaetigers as delicate capillaries; 2) peg-chaetae are really a dense group of more than 100 thin individual chaetae, embedded in a fibrous matrix, and covered by a common sheath; 3) the pharynx is an eversible, lobed, axial non-muscular proboscis with a ciliated surface; 4) the body cavity is divided by three septa in the anterior body region, and there are no other septa; and 5) an eversible anal peduncle is confirmed, as has been shown by early taxonomists.

SUMMARY:The sperm ultrastructure and spermatogenesis of the ectoparasitic polychaete Asetocalamyzas laonicola Tzetlin, 1985 (Calamyzidae) is investigated. The male cells are located freely in the coelom. The spermatocytes are large cells of irregular shape; their nuclei have condensed chromatin in the periphery. Spermatocyte cytoplasm is granular and electron-dense with several spherical mitochondria. During early developmental stages spermatids are aggregated into a rosette (four cells). The early spermatids have a tiny acrosomal vesicle at one side of the cell, a few round mitochondria at another, and electron dense nuclei. The late spermatids have elongated mitochondria, a well-developed acrosome and a flagellum. The mature sperm are threadlike with a round acrosomal vesicle, an electron-dense structure. The elongated nuclei have anterior and posterior depressions. The supporting root zone of the acrosome is located behind the acrosomal vesicle in the anterior invagination of the nuclei. Six elongated mitochondria surround the flagellum and form the midpiece of the sperm. A single centriole lies in the posterior depression of the nucleus. The middle part of the flagellum possesses a normal (9+2x2) pattern. Probably, the terminal part of flagellum is modified. The sperm structure suggests internal fertilization or another type of specialized sperm transfer in A. laonicola. SIKORSFI, 1994, DEL MAR BLANCO. -La ultraestructura del esperma y la espermatogénesis del poliqueto ectoparásito Asetocalamyzas laonicola Tzetlin, 1985 (Polychaeta) ha sido investigada. Las células masculinas están localizadas libres en el celoma. Los espermatocitos son células grandes de forma irregular cuyos núcleos presentan cromatina condensada en su periferia. El citoplasma de los espermatocitos es granular y presenta alta densidad a los electrones, así como distintas mitocondrias esféricas. Durante el desarrollo inicial, las espermatidas se encuentran agregadas en rosetas de cuatro células. Las espermatidas iniciales presentan una minúscula vesí-cula acrosomal a un lado de la célula, unas pocas mitocondrias redondas y un núcleo denso a los electrones. En su fase más tardía, las espermátidas contienen mitocondrias alargadas, un buen desarrollado acrosoma y un flagelo. El esperma maduro parece estar enebrado con una vesícula acrosomal redonda y una estructura densa a los electrones. El núcleo alargado presenta depresiones posteriores y anteriores. La zona raiz de soporte del acrosoma se encuentra localizada detrás de la vesícu-la acrosomal, en una invaginación anterior del núcleo. Seis mitocondrias alargadas rodean el flagelo y forman la pieza central del esperma. Un centriolo único descansa en la depresión posterior del núcleo. La parte central del flagelo posee un patrón normal (9+2x2). Probablemnente la parte terminal de dicho flagaleo está modificada. La estructura del esperma sugiere una fertilización interna u otro tipo de transferencia del esperma muy especializada en A. laonicola.

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The fauna of Orbiniidae (Annelida: Errantia) from the Lizard Island has been studied. Five species were found and each was redescribed and illustrated using light microscopy and SEM. Scoloplos acutissimus Hartmann-Schröder, 1991 and Scoloplos dayi Hartmann-Schröder, 1980 collected for the first time since their original descriptions and confirmed through re-examination of their type materials. Molecular analyses were carried out using nuclear 18S rDNA and mitochondrial 16S rDNA and CO1 gene sequences with evolutionary distances and the Neighbor-Joining Method. The molecular analyses did not support the monophyly of the genera Scoloplos, Leitoscoloplos, Leodamas, and Naineris, and its results are incongruent with morphological data.