Population co-divergence in common cuttlefish (Sepia officinalis) and its dicyemid parasite in the Mediterranean Sea.

Population structure and biogeography of marine organisms are formed by different drivers than in terrestrial organisms. Yet, very little information is available even for common marine organisms and even less for their associated parasites. Here we report the first analysis of population structure of both a cephalopod host (Sepia officinalis) and its dicyemid parasite, based on a homologous molecular marker (cytochrome oxidase I). We show that the population of common cuttlefish in the Mediterranean area is fragmented into subpopulations, with some areas featuring restricted level of gene flow. Amongst the studied areas, Sardinia was genetically the most diverse and Cyprus the most isolated. At a larger scale, across the Mediterranean, the population structure of the parasite shows co-diversification pattern with its host, but a slower rate of diversification. Differences between the two counterparts are more obvious at a finer scale, where parasite populations show increased level of fragmentation and lower local diversities. This discrepancy can be caused by local extinctions and replacements taking place more frequently in the dicyemid populations, due to their parasitic lifestyle.

First isolation of Miamiensis avidus (Ciliophora: Scuticociliatida) associated with skin ulcers from reared pharaoh cuttlefish Sepia pharaonis.

In the winter of 2015, a skin ulcer disease outbreak occurred in a pharaoh cuttlefish Sepia pharaonis population cultured on a land-based fish farm in China. Affected cuttlefish (about 60% of the population) were characterized as having developed ulcers on the dorsal skin, fin fringe, or distal mantle tip. Masses of a ciliated protozoan were isolated from skin ulcers. The ciliate was identified as Miamiensis avidus based on the morphological features of living and protargol-impregnated specimens. This identification was also supported by high sequence similarity of the small subunit ribosomal RNA gene (100%) and another ribosomal DNA region (including the 2 internal transcribed spacers and the 5.8S gene; 99%) with published sequences of fish parasitic M. avidus strains. M. avidus is known to be a histophagous marine fish parasite. This report describes the first case of M. avidus associated with skin ulcers in a cephalopod mollusk (Mollusca, Cephalopoda). This finding suggests that M. avidus may infect a phylogenetically broader range of hosts than what has previously been reported. Furthermore, M. avidus may pose a health risk to hatchery-reared cephalopods.

Diversity of apostome ciliates, Chromidina spp. (Oligohymenophorea, Opalinopsidae), parasites of cephalopods of the Mediterranean Sea.

Chromidina spp. are enigmatic apostome ciliates (Oligohymenophorea, Opalinopsidae) that parasitise the renal and pancreatic appendages of cephalopods. Only four species have been described, among which only three have been formally named. No DNA sequence has been reported so far. To investigate Chromidina spp. diversity, we sampled cephalopods in the Mediterranean Sea off Tunis, Tunisia, and identified two distinct Chromidina spp. in two different host species: Loligo vulgaris and Sepia officinalis. From haematoxylin-stained slides, we described morphological traits for these parasitic species and compared them to previous descriptions. We also re-described the morphology of Chromidina elegans (Foettinger, 1881) from Chatton and Lwoff's original materials and designated a neohapantotype and paraneohapantotypes for this species. We describe a new species, Chromidina chattoni Souidenne, Florent and Grellier n. sp., found in L. vulgaris off Tunisia, and evidence for a probable novel species, found in S. officinalis off Tunisia, although this latter species presents similarities to some morphological stages previously described for Chromidina cortezi Hochberg, 1971. We amplified, for the first time, an 18S rDNA marker for these two Chromidina species. Phylogenetic analysis supports the association of Chromidina within apostome ciliates. Genetic distance analysis between 18S rDNA sequences of representative apostomes indicates Pseudocollinia as the most closely related genus to Chromidina.

Two new dicyemids from Sepia longipes (Mollusca: Cephalopoda: Decapoda).

Two new species of dicyemid mesozoan are described from Sepia longipes, Sasaki, 1913, collected from Tosa Bay in Japan. Dicyema oxycephalum n. sp. is a medium-sized species that is about 1,800 microm in length. It lives in folds of the renal appendages. The vermiform stages are characterized as having 28-34 peripheral cells, a conical calotte, and an axial cell that extends to the base of the propolar cells. Infusoriform embryos consist of 39 cells; 2 nuclei are present in each urn cell and the refringent bodies are solid. Pseudicyema cappacephalum n. sp. is also a medium-size species; it is about 1,000 microm in length. It too lives in folds of the renal appendages. The vermiform stages are characterized as having 32-34 peripheral cells, a cap-shaped calotte, and an axial cell that extends to the base of propolar cells. Infusoriform embryos consist of 39 cells; 2 nuclei are present in each urn cell and the refringent bodies are solid. This is the first description of dicyemids from S. longipes.

A new species of Dicyemennea Whitman, 1883 (Phylum Dicyemida) from Sepia latimanus (Mollusca: Cephalopoda: Decapodidae) off Okinawa, Japan.

A new species of dicyemid mesozoan is described from a cuttlefish Sepia latimanus Quoy and Gaimard collected off Nago, Naha and Onnason, Okinawa Islands, Ryukyu Islands, Japan. Dicyemennea ryukyuense n. sp. is a large species that reaches about 5 mm in length. The vermiform stage is characterised by 23 peripheral cells, a conical calotte and an axial cell that extends to the base of the propolar cells. The infusoriform embryo consists of 37 cells; two nuclei are present in each urn cell and the refringent bodies are solid. In the type of reproductive strategy, rhombogens of D. ryukyuense form a small number of infusorigens and produce a relatively large number of gametes per infusorigen. In the family Dicyemidae, Dicyemennea Whitman, 1883 is the largest group after Dicyema von Kölliker, 1849. Other dicyemid species, including those belonging to Dicyema, were not detected. Dicyemids have never previously been detected in cephalopods living on corals and rocks off the Ryukyu Islands, even though they are benthonic in habitat. This is the first report of a dicyemid mesozoan from S. latimanus and also from off the Ryukyu Islands. S. latimanus inhabits coral reefs, often swimming over the coral but usually lying on the sandy bottom. Dicyemids cannot possibly infect cephalopods which live exclusively over coral and rock.