ORFans in Mitochondrial Genomes of Marine Polychaete Polydora.

Most characterized metazoan mitochondrial genomes are compact and encode a small set of proteins that are essential for oxidative phosphorylation, as well as rRNA and tRNA for their expression. However, in rare cases, invertebrate taxa have additional open reading frames (ORFs) in their mtDNA sequences. Here, we sequenced and analyzed the mitochondrial genome of a polychaete worm, Polydora cf. ciliata, part of whose life cycle takes place in low-oxygen conditions. In the mitogenome, we found three "ORFan" regions (544, 1,060, and 427 bp) that have no resemblance to any standard metazoan mtDNA gene but lack stop codons in one of the reading frames. Similar regions are found in the mitochondrial genomes of three other Polydora species and Bocardiella hamata. All five species share the same gene order in their mitogenomes, which differ from that of other known Spionidae mitogenomes. By analyzing the ORFan sequences, we found that they are under purifying selection pressure and contain conservative regions. The codon adaptation indices (CAIs) of the ORFan genes were in the same range of values as the CAI of conventional protein-coding genes in corresponding mitochondrial genomes. The analysis of the P. cf. ciliata mitochondrial transcriptome showed that ORFan-544, ORFan-427, and a portion of the ORFan-1060 are transcribed. Together, this suggests that ORFan-544 and ORFan-427 encode functional proteins. It is likely that the ORFans originated when the Polydora/Bocardiella species complex separated from the rest of the Spionidae, and this event coincided with massive gene rearrangements in their mitochondrial genomes and tRNA-Met duplication.

Drilling in the dorid species Vayssierea cf. elegans (Gastropoda: Nudibranchia): Functional and comparative morphological aspects.

The drilling mode of feeding is known from two clades of Gastropoda: Caenogastropoda and Heterobranchia. However, the level of convergence and parallelism or homology among these two lineages is unclear. The morphology of the buccal complex is well studied for drilling caenogastropods, but poorly known for drilling nudibranchs. It is also unclear whether the drilling feeding mechanism is similar between inside gastropods. Accordingly, a comparison between the feeding mechanisms of drilling nudibranchs and caenogastropods can help to understand the evolutional trends inside gastropods. In this study, we redescribe the morphology of the buccal complex of drilling dorid nudibranch Vayssierea cf. elegans, and compare it to that of previous investigations on this species and closely related dorid species. We describe the feeding mechanism of this species based on the obtained morphological and literature data and compare it to the feeding mechanisms described for drilling caenogastropods. The feeding apparatus of Vayssierea cf. elegans corresponds to the general morphology of the dorid buccal complex; that is, it has a similar arrangement of the buccal musculature and pattern of radular morphology. However, there are also adaptations to the drilling feeding mode similar to those found in Caenogastropoda: that is, specialized dissolving glands and lateral teeth with elongated pointed cusps; and even Sacoglossa: the specialized muscle for sucking. The feeding process of Vayssierea cf. elegans includes the same two stages as those described for drilling caenogastropods: (a) the boring stage, which is provided by mechanical and chemical activity, and (b) the swallowing stage.

Sternaspidae (Annelida, Sedentaria) from Vietnam with description of three new species and clarification of some morphological features.

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.

Molecular analysis of the Pygospio elegans group of species (Annelida: Spionidae).

Pygospio elegans Claparède, 1863, the type species of the genus Pygospio, was originally described from Normandy, France, and later widely reported from boreal waters in the northern hemisphere. Sequence data of four gene fragments (2576 bp in total) of the mitochondrial 16S rDNA, nuclear 18S and 28S rDNA, and Histone 3 have shown that individuals from California and Oregon, USA, Scotland and the White Sea, Russia were genetically similar (the average p-distances for the combined data between the four groups ranged from 0.04 to 0.16%, average p = 0.1%). These individuals are considered to be conspecific and the amphiboreal distribution of P. elegans is here confirmed. Adult morphology of the species is briefly described and illustrated. The molecular analysis revealed two genetically distant populations, Pygospio sp. 1 from the Sea of Okhotsk and Pygospio sp. 2 from Oregon. The morphological differences and high average genetic p-distances for the combined data (ranging from 3.06 to 3.18%, average p = 3.12%) between Pygospio sp. 2 and P. elegans suggest the presence of an undescribed Pygospio species co-occurring with P. elegans in Oregon. High morphological similarity and moderate genetic p-distances for the combined data (ranging from 1 to 1.11%, average p = 1.07%) between Pygospio sp. 1 and P. elegans indicate a comparatively recent genetic divergence of the Pygospio population in the Sea of Okhotsk. Taking into account the high genetic similarity of the remote European and North American populations of P. elegans and medial location of the Pygospio sp. 1 population, we suggest the latter to belong to a separate species. However, this conclusion should be verified in further studies on the morphology, reproductive biology and genetics of this population. The present findings show the need to re-examine Pygospio from the Asian Pacific and elsewhere that have been identified as P. elegans.

Giant pelagic larvae of Phyllodocidae (Polychaeta, Annelida).

The microscopic anatomy of giant pelagic larvae of Phyllodocidae was studied using routine histological, SEM, and TEM techniques. The larvae consist of two distinct regions: a large spherical trochophore measuring up to 2 mm in diameter and a posterior, long (up to 10 mm length), narrow rudiment of the adult body with up to 120 segments. The larvae have an unusual mixture of larval and adult features, including a very complex, well-developed brain and ganglia in the ventral nerve cord, and only a single pair of protonephridia located in the hyposphere of the trochophore. A muscular pharynx is not developed. The intestinal wall, especially in the trochophore region, consists of endodermal cells containing considerable nutritive material in the form of yolk-like globular inclusions. The digestive tract of all larvae was empty. The position of the frontal sensory organ and the prototroch, the structure of the parapodia and setae, and the three pairs of tentacular cirri dictate inclusion of the larvae in the family Phyllodocidae. The relatively enormous size and unusual pattern of development of the adult body may be adaptations for a long pelagic life and rapid settlement of the species, which inhabits slopes of islands and underwater mounts located far apart. J. Morphol. 238:93-107, 1998. © 1998 Wiley-Liss, Inc.