Morphological and molecular analysis of Aggregata aspera n. sp. (Apicomplexa: Aggregatidae) in Amphioctopus ovulum and Amphioctopus marginatus (Mollusca: Cephalopoda) from the Western Pacific Ocean.

Aggregata Frenzel, 1885 (Apicomplexa) are dangerous protozoan parasites that cause malabsorption syndrome in wild and reared cephalopod species, resulting in significant economic loss to fishery and aquaculture industries. The new parasitic species, Aggregata aspera n. sp., in the digestive tract of Amphioctopus ovulum and Amphioctopus marginatus from an area in the Western Pacific Ocean was identified, it is the second two-host parasite species of Aggregata. Mature oocysts and sporocysts were spherical to ovoid in shape. Sporulated oocysts were 380.6-1,158.4 µm in length and 284.0-1,090.6 µm in width. The mature sporocysts were 16.2-18.3 µm in length and 15.7-17.6 µm in width, with irregular protuberances on the lateral wall of the sporocysts. Sporozoites within mature sporocysts were curled in shape and measured 13.0-17.0 µm in length and 1.6-2.4 µm in width. Each sporocyst contained 12-16 sporozoites. Phylogenetic tree analysis, based on 18S rRNA gene partial sequences, indicated that Ag. aspera forms a monophyletic cluster within the genus Aggregata and has a sister relationship with Ag. sinensis. These findings will provide the theoretical basis for the histopathology and diagnosis of coccidiosis in cephalopods.

Histologic lesions of cestodiasis in octopuses.

Parasitism of cephalopods is common, including infection with Aggregata spp., Ichthyobodo spp., dicyemids, cestodes of the orders Tetraphyllidea and Trypanorhynchidea, and various crustaceans. Cestodiasis in octopuses is reported, although a full histologic description of lesions has not been previously described. Cestodiasis was identified in 10 octopuses of 4 different species, which included 4 common octopuses (Octopus vulgaris), 3 Caribbean reef octopuses (Octopus briareus), 2 two-spot octopuses (Octopus bimaculoides), and 1 giant Pacific octopus (Enteroctopus dofleini). Larval cestodes were present in the cecum (n = 5), intestines (n = 4), digestive gland (n = 3), chitinous alimentary tract (n = 2), renal appendage (n = 1), and salivary duct (n = 1). In 5 cases, larval cestodes invaded tissue and were associated with hemocytic inflammation and tracts of necrotic tissue in the intestines (n = 3), digestive gland (n = 3), and/or renal appendage (n = 1). When present in the chitinous alimentary tract (esophagus, stomach) or cecum, larval cestodes were in the central lumen and not associated with lesions. One adult cestode was identified in the mantle cavity and was not associated with lesions. Other common concurrent parasitic infections included enteric Aggregata spp. infection, branchial Rickettsia-like organism infection, enteric nematodiasis, and an arthropod-associated branchitis.

Dicyema sphyrocephalum (Phylum Dicyemida: Dicyemidae) isolated from Korean common octopus Callistoctopus minor in Korea.

BACKGROUND: Dicyemids are parasites found in the renal sac of cephalopods. The first species of dicyemid was found from kidneys of the Korean common octopus Callistoctopus minor. OBJECTIVES: This study aimed to identify the dicyemid and investigate the effect on renal sac of host. METHODS: In this study, we compared the morphological characteristics of isolate to dicyemids (Dicyema sphyrocephalum, Dicyema clavatum, and Dicyema dolichocephalum) reported from C. minor in Japan. We compared the 18S ribosomal RNA (rDNA) and cytochrome c oxidase subunit I (COI) sequences of isolate to the sequences of D. shyrocephalum and D. clavatum. The infected octopuses renal tissues were histologically compared with the tissues of uninfected individuals. RESULTS: The morphological characteristic of this isolated species corresponds to D. sphyrocephalum. The sequences similarities of 18S rDNA and COI gene of isolate are 99.7% and 98.1% with D. sphyrocephalum. We observed morphological changes in the epithelia folds of kidney at the dicyemids attached areas. CONCLUSIONS: The present study identified the isolate as D. sphyrocephalum and this is the first report of dicyemid species from Republic of Korea. Further studies on the effects of dicyemids on growth and health status of cephalopods will be needed.

Larval ascaridoid nematodes in horned and musky octopus (Eledone cirrhosa and E. moschata) and longfin inshore squid (Doryteuthis pealeii): Safety and quality implications for cephalopod products sold as fresh on the Italian market.

The aim of this study was to evaluate the occurrence, infection level and distribution of ascaridoid larvae in cephalopod products sold in Italy. Data on the species most commonly commercialized as whole and fresh on the Italian market were collected. After comparing commercial and literature data, Eledone spp., comprising E. cirrhosa and E. moschata (horned octopus and musky octopus, respectively) and Doryteuthis pealeii (longfin inshore squid) were selected, as they had been rarely investigated. Overall, 75 Eledone spp. caught in the Mediterranean Sea (FAO area 37) and 70 D. pealeii from the Northwest Atlantic Ocean (FAO area 21) were examined by visual inspection and artificial digestion (viscera and mantle separately). Parasites were submitted to morphological and molecular analysis. Prevalence (P), mean intensity (MI) and mean abundance (MA) were calculated. In D. pealeii, 2 nematode larvae molecularly identified as Anisakis simplex s.s. were found in the viscera and in the mantle of two specimens (P: 2.9% 95% CI: 0-6.8%; MI: 1; MA: 0.028). In Eledone spp. 9 nematode larvae molecularly attributed to Hysterothylacium spp. were found in the mantle of 5 specimens (P: 6.7% 95% CI: 1-12.3%; MI: 1.8; MA: 0.12). This is the first report of A. simplex s.s. in D. pealeii. Considering the zoonotic and allergenic potential of these larvae and their localization also in the edible part (mantle), a potential public health issue exists.

Octopicola huanghaiensis n. sp. (Copepoda: Cyclopoida: Octopicolidae), a new parasitic copepod of the octopuses Amphioctopus fangsiao (d'Orbigny) and Octopus minor (Sasaki) (Octopoda: Octopodidae) in the Yellow Sea.

A new species of parasitic copepod, Octopicola huanghaiensis n. sp., collected from the octopuses Amphioctopus fangsiao (d'Orbigny) and Octopus minor (Sasaki) (Octopoda: Octopodidae) in the Yellow Sea (off Qingdao, Shandong Province, China), is described. The new species is most similar to O. superba Humes, 1957, but can be distinguished from the latter by: (i) the third antennal segment having a different ornamentation; (ii) the fourth antennal segment of females much shorter than that in O. superba (49 vs 94 µm); (iii) males much smaller than females (mean body length 1.3 vs 2.0 mm, respectively) (vs similar male and female body size in O. superba, 1.9 mm and 1.8 mm respectively); and (iv) the presence of a spike at the posterior tip of each labrum flap. Octopicola huanghaiensis n. sp. is the first species of Octopicola Humes, 1957 reported from A. fangsiao and O. minor and is the only species of the family Octopicolidae Humes & Boxshall, 1996 known in North Pacific waters.

Octopus maya parasites off the Yucatán Peninsula, Mexico. I. Faunal assemblages.

The red octopus Octopus maya Voss et Solís-Ramírez, 1966 is an endemic species found exclusively off the coast of the Yucatán Peninsula, Mexico; its fishery is one of the most important along the Atlantic coast of Mexico and the Caribbean Sea. To date, the parasite fauna of Octopus spp. in southern Mexico remains unknown. In this study, we present the parasite fauna of O. maya from 8 localities along the Yucatán Peninsula. From August 2009 to June 2010, a total of 1202 specimens of O. maya were caught by artisanal fisheries and examined. Twenty parasite taxa were recorded from all octopus examined: 7 cestodes, 8 digeneans, 3 nematodes, 1 copepod and 1 coccidian. All taxa are new records for this host species, and the sampled locations represent new records of the geographic distribution of these parasite taxa. The gills and the intestine were the micro-habitats in which the highest number of taxa were found. More than half of the parasites (13 taxa) that we found infected O. maya via its feeding habits, although a high number of taxa (n = 9) colonized via active transmission. Cestoda and Digenea were the taxonomic groups with the highest number of taxa. Prochristianella sp. showed the highest prevalence and mean abundance values in the localities where it was present. This work represents the first study on the parasite fauna of any cephalopod species in Mexico.

Octopus maya parasites off the Yucatán Peninsula, Mexico. II. Salivary gland damage by cestodes.

The red octopus Octopus maya Voss et Solís-Ramírez, 1966 is an endemic species and one of the most important fishery resources of the Yucatán Peninsula, Mexico. Due to its economic importance and the fact that in recent years interest in farming this species has increased, several initiatives have been implemented to study its biology and requirements for cultivation. Parasites represent an important component of the biology of the red octopus, as they can have an impact on both wild and cultivated populations. A total of 44 O. maya specimens were sampled from the fishing ports of Ría Lagartos and Dzilam de Bravo, Yucatán; specimens were measured and subsequently subjected to histological analysis of the buccal masses where cestode larvae (Prochristianella sp.) were found in the anterior salivary glands. Results of a chi-squared test showed that specimen size class and infestation levels (parasite abundance) were significantly correlated, with parasite damage levels more pronounced in larger animals. The damage caused to the anterior salivary glands by this parasite could have serious implications for feeding and reproductive success of O. maya.

Morphological and Molecular Characterization of Aggregata spp. Frenzel 1885 (Apicomplexa: Aggregatidae) in Octopus vulgaris Cuvier 1797 (Mollusca: Cephalopoda) from Central Mediterranean.

Coccidian parasites of the genus Aggregata are known to parasitize cephalopods as definitive hosts, however one of the genus members, A. octopiana, has shown an unresolved phylogeny within the same definitive host, the common octopus (Octopus vulgaris). Our study represents a large-scale investigation aimed at characterizing morphological traits and phylogeny of A. octopiana isolated from O. vulgaris inhabiting three distinct geographic areas of the central Mediterranean: The Adriatic, Ionian and Tyrrhenian Seas. The morphology of sporogonic stages of the parasite in octopus tissues was assessed by light and electron microscopy; molecular characterization has been carried out using the 18S rRNA locus. Our results support the hypothesis that two morphologically and genetically different A. octopiana infect O. vulgaris in the investigated areas of the Mediterranean Sea. Additional nuclear and mitochondrial markers for Aggregata should provide further information and better resolution of its phylogeny.

Redescription of Dicyemennea eledones (Wagener, 1857) (Phylum Dicyemida) from Eledone cirrhosa (Lamarck, 1798) (Mollusca: Cephalopoda: Octopoda).

Dicyemids are common parasites found in the kidneys of many cephalopods. Species identification previously relied on old species descriptions containing considerable confusions, casting doubt on taxonomy and identification. Detailed morphological description and genotyping of all developmental stages are required for an exact taxonomy. To this end, we undertook the redescription of the dicyemid Dicyemennea eledones (Wagener, 1857), infecting the cephalopod Eledone cirrhosa (Lamarck). Samples were collected off Concarneau in the Bay of Biscay, France, and off La Goulette in the Gulf of Tunis, Tunisia. Dicyemennea eledones is a large species, with adults reaching c.7,000 µm in length. The vermiform stages are characterised by having 23 peripheral cells, a conical calotte and an axial cell that extends to the base of the propolar cells. An anterior abortive axial cell is present in vermiform embryos. Infusoriform embryos consist of 37 cells; a single nucleus is present in each urn cell and the refringent bodies, which were not always seen, are possibly liquid. For the first time, an 18S rDNA sequence is generated for D. eledones, illustrating genetic differences with the other dicyemid 18S rDNA sequences available in databases. This sequence can now be used for D. eledones barcoding, making the identification of the species easier and more reliable.

Two new species of dicyemid mesozoans (Dicyemida: Dicyemidae) from Octopus maya Voss & Solis-Ramirez (Octopodidae) off Yucatan, Mexico.

Two new dicyemid species are described from the endemic cephalopod Octopus maya Voss & Solis-Ramirez collected off Yucatan, Mexico. The renal sacs of 40 juvenile and adult octopuses from four localities were examined. Dicyema hochbergi n. sp. is a medium-sized species that reaches 2,245 µm in length. The vermiform stages consist of 18-24 peripheral cells, a conical calotte and the extension of the axial cell between the base and middle of the metapolar cells. Infusoriform embryos consist of 39 cells with urn cell containing one germinal cell, two nuclei and solid refringent bodies. Dicyema mexcayae n. sp. is a relatively small species that reaches 1,114 µm in length. The vermiform stages are constituted by 14-16 peripheral cells, an elongate calotte and the axial cell extending forward to the middle of the metapolar cells. The infusoriform embryos consist of 37 cells, two solid refringent bodies and urn cells with two nuclei each. The present study represents the first description of a dicyemid species from O. maya and increases the number of described species from Mexican waters to 11.

De novo transcriptome sequencing of the Octopus vulgaris hemocytes using Illumina RNA-Seq technology: response to the infection by the gastrointestinal parasite Aggregata octopiana.

BACKGROUND: Octopus vulgaris is a highly valuable species of great commercial interest and excellent candidate for aquaculture diversification; however, the octopus' well-being is impaired by pathogens, of which the gastrointestinal coccidian parasite Aggregata octopiana is one of the most important. The knowledge of the molecular mechanisms of the immune response in cephalopods, especially in octopus is scarce. The transcriptome of the hemocytes of O. vulgaris was de novo sequenced using the high-throughput paired-end Illumina technology to identify genes involved in immune defense and to understand the molecular basis of octopus tolerance/resistance to coccidiosis. RESULTS: A bi-directional mRNA library was constructed from hemocytes of two groups of octopus according to the infection by A. octopiana, sick octopus, suffering coccidiosis, and healthy octopus, and reads were de novo assembled together. The differential expression of transcripts was analysed using the general assembly as a reference for mapping the reads from each condition. After sequencing, a total of 75,571,280 high quality reads were obtained from the sick octopus group and 74,731,646 from the healthy group. The general transcriptome of the O. vulgaris hemocytes was assembled in 254,506 contigs. A total of 48,225 contigs were successfully identified, and 538 transcripts exhibited differential expression between groups of infection. The general transcriptome revealed genes involved in pathways like NF-kB, TLR and Complement. Differential expression of TLR-2, PGRP, C1q and PRDX genes due to infection was validated using RT-qPCR. In sick octopuses, only TLR-2 was up-regulated in hemocytes, but all of them were up-regulated in caecum and gills. CONCLUSION: The transcriptome reported here de novo establishes the first molecular clues to understand how the octopus immune system works and interacts with a highly pathogenic coccidian. The data provided here will contribute to identification of biomarkers for octopus resistance against pathogens, which could improve octopus farming in the near future.

Egg number-egg size: an important trade-off in parasite life history strategies.

Parasites produce from just a few to many eggs of variable size, but our understanding of the factors driving variation in these two life history traits at the intraspecific level is still very fragmentary. This study evaluates the importance of performing multilevel analyses on egg number and egg size, while characterising parasite life history strategies. A total of 120 ovigerous females of Octopicola superba (Copepoda: Octopicolidae) (one sample (n=30) per season) were characterised with respect to different body dimensions (total length; genital somite length) and measures of reproductive effort (fecundity; mean egg diameter; total reproductive effort; mean egg sac length). While endoparasites are suggested to follow both an r- and K-strategy simultaneously, the evidence found in this and other studies suggests that environmental conditions force ectoparasites into one of the two alternatives. The positive and negative skewness of the distributions of fecundity and mean egg diameter, respectively, suggest that O. superba is mainly a K-strategist (i.e. produces a relatively small number of large, well provisioned eggs). Significant sample differences were recorded concomitantly for all body dimensions and measures of reproductive effort, while a general linear model detected a significant influence of season*parasite total length in both egg number and size. This evidence suggests adaptive phenotypic plasticity in body dimensions and size-mediated changes in egg production. Seasonal changes in partitioning of resources between egg number and size resulted in significant differences in egg sac length but not in total reproductive effort. Evidence for a trade-off between egg number and size was found while controlling for a potential confounding effect of parasite total length. However, this trade-off became apparent only at high fecundity levels, suggesting a state of physiological exhaustion.

Numerical and functional responses to the presence of a competitor--the case of Aggregata sp. (Apicomplexa: Aggregatidae) and Octopicola superba (Copepoda: Octopicolidae).

Evidence of interference competition between the eimeriorin coccidian Aggregata sp. and the octopicolid copepod Octopicola superba at the level of the gills of naturally infected Octopus vulgaris is evaluated. Numerical and functional responses are considered for analysis, and the fundamental and realized spatial niches (FSNs and RSNs) are measured as part of the study. While it was not possible to measure the FSN of Aggregata sp., the analysis of the infection levels of O. superba recorded for non-concomitantly and concomitantly infected hosts suggests that the gills and body skin constitute, respectively, the main and accessory sites of infection of the parasite. According to the evidence found, the gills function mainly as an accessory site of infection of Aggregata sp., in specimens in which the caecum and intestine are massively infected. Evidence for a negative interaction between Aggregata sp. and O. superba has been found while controlling for a potential confounding effect of host size. Furthermore, the presence of O. superba on gill lamellae appears to have been negatively affected by the presence of Aggregata sp., while this latter remained mostly undisturbed. The mean number of oocysts of Aggregata sp. in the gills was higher in spring and summer, which were also the seasons presenting the broadest RSN for O. superba.

Proteomic characterization of the hemolymph of Octopus vulgaris infected by the protozoan parasite Aggregata octopiana.

The immune system of cephalopods is poorly known to date. The lack of genomic information makes difficult to understand vital processes like immune defense mechanisms and their interaction with pathogens at molecular level. The common octopus Octopus vulgaris has a high economic relevance and potential for aquaculture. However, disease outbreaks provoke serious reductions in production with potentially severe economic losses. In this study, a proteomic approach is used to analyze the immune response of O. vulgaris against the coccidia Aggregata octopiana, a gastrointestinal parasite which impairs the cephalopod nutritional status. The hemocytes and plasma proteomes were compared by 2-DE between sick and healthy octopus. The identities of 12 differentially expressed spots and other 27 spots without significant alteration from hemocytes, and 5 spots from plasma, were determined by mass spectrometry analysis aided by a six reading-frame translation of an octopus hemocyte RNA-seq database and also public databases. Principal component analysis pointed to 7 proteins from hemocytes as the major contributors to the overall difference between levels of infection and so could be considered as potential biomarkers. Particularly, filamin, fascin and peroxiredoxin are highlighted because of their implication in octopus immune defense activity. From the octopus plasma, hemocyanin was identified. This work represents a first step forward in order to characterize the protein profile of O. vulgaris hemolymph, providing important information for subsequent studies of the octopus immune system at molecular level and also to the understanding of the basis of octopus tolerance-resistance to A. octopiana. BIOLOGICAL SIGNIFICANCE: The immune system of cephalopods is poorly known to date. The lack of genomic information makes difficult to understand vital processes like immune defense mechanisms and their interaction with pathogens at molecular level. The study herein presented is focused to the comprehension of the octopus immune defense against a parasite infection. Particularly, it is centered in the host-parasite relationship developed between the octopus and the protozoan A. octopiana, which induces severe gastrointestinal injuries in octopus that produce a malabsorption syndrome. The common octopus is a commercially important species with a high potential for aquaculture in semi-open systems, and this pathology reduces the condition of the octopus populations on-growing in open-water systems resulting in important economical loses. This is the first proteomic approach developed on this host-parasite relationship, and therefore, the contribution of this work goes from i) ecological, since this particular relationship is tending to be established as a model of host-parasite interaction in natural populations; ii) evolutionary, due to the characterization of immune molecules that could contribute to understand the functioning of the immune defense in these highly evolved mollusks; and iii) to economical view. The results of this study provide an overview of the octopus hemolymph proteome. Furthermore, proteins influenced by the level of infection and implicated in the octopus cellular response are also showed. Consequently, a set of biomarkers for disease resistance is suggested for further research that could be valuable for the improvement of the octopus culture, taken into account their high economical value, the declining of landings and the need for the diversification of reared species in order to ensure the growth of the aquaculture activity. Although cephalopods are model species for biomedical studies and possess potential in aquaculture, their genomes have not been sequenced yet, which limits the application of genomic data to research important biological processes. Similarly, the octopus proteome, like other non-model organisms, is poorly represented in public databases. Most of the proteins were identified from an octopus' hemocyte RNA-seq database that we have performed, which will be the object of another manuscript in preparation. Therefore, the need to increase molecular data from non-model organisms is herein highlighted. Particularly, here is encouraged to expand the knowledge of the genomic of cephalopods in order to increase successful protein identifications. This article is part of a Special Issue entitled: Proteomics of non-model organisms.

First descriptions of dicyemid mesozoans (Dicyemida: Dicyemidae) from Australian octopus (Octopodidae) and cuttlefish (Sepiidae), including a new record of Dicyemennea in Australian waters.

Three new species of dicyemid mesozoans are described for the first time from Australian octopus and cuttlefish species. Dicyemennea floscephalum sp. n. is described from Octopus berrima Stranks et Norman (southern keeled octopus) collected from Spencer Gulf and Gulf St. Vincent, South Australia, Australia and represents the first description of a species of Dicyemennea Whitman, 1883 from Australian waters. Dicyema papuceum sp. n. and D. furuyi sp. n. are described from Sepia papuensis Hoyle (Papuan cuttlefish) collected from Shark Bay, Western Australia, Australia. Dicyemennea floscephalum sp. n. is a medium to large species that reaches approximately 4.9 mm in length. The vermiform stages are characterised by having 23-28 peripheral cells, and a disc-shaped, flower-like calotte in larger individuals. An anterior abortive axial cell is absent in vermiform embryos and verruciform cells were not observed in nematogens and rhombogens. Infusoriform embryos comprise 37 cells; one nucleus is present in each urn cell. Dicyema papuceum sp. n. is a small species that reaches approximately 1.1 mm in length. The vermiform stages are characterised by having 30-33 peripheral cells and a relatively small, cap-shaped calotte. An anterior abortive axial cell is absent in vermiform embryos and verruciform cells were occasionally observed in nematogens. Infusoriform embryos comprise 37 cells; two nuclei are present in each urn cell. Dicyema furuyi sp. n. is a large species that reaches approximately 5.3 mm in length. The vermiform stages are characterised by having 22-24 peripheral cells and an elongate calotte. An anterior abortive axial cell is absent in vermiform embryos and verruciform cells were not observed in nematogens and rhombogens. Infusoriform embryos comprise 37 cells; one nucleus is present in each urn cell. Three secondary nematogens were also observed in the right renal appendages of two host individuals, confirming the occurrence of this form.

Coccidian infection may explain the differences in the life history of octopus host populations.

The prevalence of coccidian parasites in three Octopus tehuelchus populations from San Matías Gulf (Patagonia, Argentina) is compared. The prevalence was similar between sexes, but varied between seasons (being highest during cold months) and sites. Islote Lobos had the highest prevalence (42.7-100%) followed by San Antonio Bay (0-66%) and El Fuerte (0-24.5%). Octopuses under 27 mm of dorsal mantle length showed a low prevalence (less than 50%), which increased with size. We hypothesize that the high prevalence of parasites, which affect the three populations differentially, could account for the observed variability in life-span and growth, size-frequency distributions, reproduction and densities of O. tehuelchus populations.

Revisiting the octopicolid copepods (Octopicolidae: Octopicola Humes, 1957): comparative morphology and an updated key to species.

A review of the present state of knowledge on the octopicolid copepods (Octopicolidae: Octopicola Humes, 1957) is presented. Characteristic morphological features are illustrated with scanning electron micrographs of Octopicola superba superba Humes, 1957. Comparative morphology analysis led to the conclusion that there is sufficient evidence to justify raising the two subspecies of O. superba to full species rank. A new identification key for the four species of Octopicola Humes, 1957, i.e. O. superba Humes, 1957, O. antillensis Stock, Humes & Gooding, 1963, O. stocki Humes, 1963 and O. regalis Humes, 1974, is proposed after evaluation of the morphological characters which vary more markedly between them. Among other characters, these species differ in the ornamentation of the third antennal segment, maxilla and male maxilliped. They are further distinguished by a combination of several character states concerning the fifth pedigerous somite.

Molecular phylogenetic analysis of the coccidian cephalopod parasites Aggregata octopiana and Aggregata eberthi (Apicomplexa: Aggregatidae) from the NE Atlantic coast using 18S rRNA sequences.

The coccidia genus Aggregata is responsible for intestinal coccidiosis in wild and cultivated cephalopods. Two coccidia species, Aggregata octopiana, (infecting the common octopus Octopus vulgaris), and A. eberthi, (infecting the cuttlefish Sepia officinalis), are identified in European waters. Extensive investigation of their morphology resulted in a redescription of A. octopiana in octopuses from the NE Atlantic Coast (NW Spain) thus clarifying confusing descriptions recorded in the past. The present study sequenced the 18S rRNA gene in A. octopiana and A. eberthi from the NE Atlantic coast in order to assess their taxonomic and phylogenetic status. Phylogenetic analyses revealed conspecific genetic differences (2.5%) in 18S rRNA sequences between A. eberthi from the Ria of Vigo (NW Spain) and the Adriatic Sea. Larger congeneric differences (15.9%) were observed between A. octopiana samples from the same two areas, which suggest the existence of two species. Based on previous morphological evidence, host specificity data, and new molecular phylogenetic analyses, we suggest that A. octopiana from the Ria of Vigo is the valid type species.

A new dicyemid from Octopus hubbsorum (Mollusca:Cephalopoda:Octopoda).

A new species of dicyemid mesozoan is described from Octopus hubbsorum Berry, 1953, collected in the south of Bahia de La Paz, Baja California Sur, México. Dicyema guaycurense n. sp. is a medium-size species that reaches about 1,600 µm in length. It occurs in folds of the renal appendages. The vermiform stages are characterized as having 22 peripheral cells, a conical calotte, and an axial cell that extends to the base of the propolar cells. Infusoriform embryos consist of 39 cells; 1 nucleus is present in each urn cell and the refringent bodies are solid. This is the first of a dicyemid species from a host collected in the Gulf of California.

A new dicyemid from Benthoctopus sibiricus (Mollusca: Cephalopoda: Octopoda).

A new species of dicyemid mesozoan is described from Benthoctopus sibiricus Loyning, 1930, collected in the eastern Chukchi Sea. Dicyemennea chukchiense n. sp. is a medium species that reaches about 2,000 µm in length; it lives in folds of the renal appendages. The vermiform stages are characterized in having 23 peripheral cells, a conical calotte, and an axial cell that extends to the base of the propolar cells. An anterior abortive axial cell is present in vermiform embryos. Infusoriform embryos consist of 37 cells; a single nucleus is present in each urn cell and the refringent bodies are solid. This is the first dicyemid described from the Arctic waters.