The symbiotic relationship between the syllid polychaete, Haplosyllides floridana Augener, 1922, and the barrel-shaped sponge Xestospongia muta (Schmidt, 1870), originally documented solely in the Caribbean, is presumed to be species-specific. Recently, the host sponge has been found as a single species distributed across approximately 8000 km (from 26°N to 22°S). Herein we addressed new spatial and bathymetric population records of H. floridana to question the persistence of the association with X. muta, and whether, in the case of an association, the polychaete remains as a single species throughout this extensive distribution. Our findings change the restricted distribution of H. floridana, revealing a remarkable association with X. muta from Tropical north-western to south-western Atlantic including records in the Fernando de Noronha Archipelago and the Almirante Saldanha Seamount, at 270 m deep. The populations analysed in this study are morphologically consistent. The study underscores the need for further investigations into the connectivity of Xestospongia species, the presence of Haplosyllides in other ocean basins, and the shared evolutionary history between Xestospongia and Haplosyllides. The observed life cycle completion of H. floridana within the host sponge suggests a potential co-evolutionary relationship, offering insights into the intricate dynamics of symbiotic associations in marine ecosystems.

Coastal tide pools in southern Japan are inhabited by the rock-boring sea urchin Echinostrephus molaris, which excavate pits in the substrate. These pits are subsequently used by non-boring sea urchins such as Anthocidaris crassispina and Echinometra sp. B, and the recolonized pits are often inhabited by a commensal limpet-like trochid snail species, Broderipia iridescens. We explored the population and community dynamics of these sea urchins and the limpet-like snail by monitoring occupancy of 512 pits in tide pools in Shirahama, Japan from May 2017–May 2019. Initially, nearly all pits were occupied by any one of the three sea urchin species, but an unusual cold event in February 2018 caused a mass die off of these sea urchins. After this event, occupancy decreased from 99% to 15%, and the tropical species Echinometra sp. B disappeared from the study pools. We observed slow population recovery of E. molaris and A. crassispina, provably via migration of sub-adults from the subtidal zone. Turnover rate of the pit-occupying sea urchin species was <1.0% before the cold event, but drastically increased after the cold event. Population size of the commensal snail decreased along with those of their host, but the rate of commensalism was constant at 50–55% throughout the study period, suggesting that these snails followed their host sea urchins repeating inter-pit migration. Despite mass mortality and slow recovery, the sea urchin density remained high enough to maintain persistent sea urchin barrens throughout the study period.

The hamadryas baboon (Papio hamadryas hamadryas) is the only indigenous species of non-human primates (NHP) found in the Kingdom of Saudi Arabia (KSA). There are no peer-reviewed publications on viral infections of the baboons of KSA. Apart from camels, other animals are likely sources of the novel Middle East Respiratory Syndrome coronavirus (MERSCoV) for humans. We investigated evidence of highly pathogenic coronavirus infections including MERSCoV in a large group of commensal baboons accompanied by feral dogs, on the outskirts of Ta'if city, KSA, in February 2013. Fifty baboons (16 juveniles and 34 adults) were screened for serum antibodies to human coronaviruses (HCoV-043/-NL63/-229) and canine coronaviruses (CCoV-1-3) using direct Enzyme-linked Immunosorbent Assay (ELISA) technique and for MERSCoV antibodies using Serum Neutralization Test (SNT). Of the 50 sampled baboons, 22% (n = 11) were seropositive to HCoVs, 10% (n = 5) were seropositive to CCoVs, while none had detectable MERSCoV antibodies. These findings bear potentially significant implications for public health, canine health and baboon conservation efforts, necessitating follow-up investigations and preventive measures at locations where baboons frequent human habitations, or are regarded as tourist attractions, in KSA.

Bacteraemia caused by Escherichia coli are particularly frequent and severe, contrasting with the commensal character of the strains found in the digestive tract. A better understanding of the relationships between strains of both origins is needed to unravel the pathogenesis of this disease. Two hundred and forty-three commensal strains were compared to 243 bacteraemic strains isolated from adult hosts matched in terms of gender and age, and from similar location and epoch. Phylogenetic grouping, O-type determination, virulence factor content and antibiotic resistance were compared. Compared to commensal strains, the bacteraemic strains were characterized by a higher proportion of B2, C and D phylogroups, and a lower proportion of A, E and F phylogroups. They also had a lower proportion of the B2 subgroup IV (STc141), a higher proportion of virulence factors, and a higher frequency of antibiotic resistance. These differences were more marked for the bacteraemic strains of urinary tract origin with the presence of specific clones, whereas the bacteraemic strains of digestive origin remained non-significantly different from the commensal strains, except for their antibiotic resistance. Thus, two levels of specialization from commensal strains were demonstrated in the bacteraemic strains: resistance to antibiotics in all cases, and virulence for those of urinary tract origin.

The decapod Hippolyte prideauxiana is a cryptic commensal of the crinoid Antedon bifida, giving rise to its common name ‘the feather star shrimp’. In 2010 and 2013 H. prideauxiana was recorded in the Shetland Islands and the Orkney Islands (‘north isles’), northern Scotland. These observations widen the known geographical distribution of this species by 400 km north from the west coast of Scotland where it was first recorded in 1997. Whilst it is possible that these new records are the result of a range expansion due to climate change it is more likely that this species has been overlooked due to its cryptic coloration, limited awareness of this species and increase in survey effort in the north of Scotland using SCUBA.

We describe a new genus and a new species of Polycladida, Namyhplana henriettae (Platyhelminthes, Euplanidae), which lives associated with the tubes of the bivalve Bankia martensi in the fjords of the South Pacific Ocean in Chile. This species is characterized by a ribbon-like body, light brown colour, anterior region devoid of pigment, few eyes, no tentacles, pharynx in the anterior region of the body with few folds, independent gonopores anterior to the medial body line, seminal vesicle strongly muscularized, digitiform penian papilla oriented posteroanteriorly, a curled vagina, and a large Lang's vesicle ventral to the intestine. A phylogenetic analysis of the Euplanidae, based on morphological characters, is presented. With the dataset used, the family Euplanidae does not seem to be a monophyletic group. The new species is closely related to Taenioplana teredini (also discussed here) which presents life-habit characteristics that are similar to those of the new species.

Acrothoracican barnacles of the genus Trypetesa are obligate symbionts of hermit crabs that burrow into the gastropod shells occupied by their hosts. In the present study, hermit crabs were examined for the presence of trypetesids, based on collections from the United States, Jamaica, and the Philippines made between 1997 and 2008. Shells from Jamaica and New York contained Trypetesa lateralis, a trypetesid previously documented from central California. Trypetesa lateralis is redescribed based on light and scanning electron microscopy, showing the presence of an external mantle flap and asymmetrical opercular bars diagnostic for this species. The mean prevalence of trypetesids in Jamaica was 8.3% and most barnacles were associated with Calcinus tibicen; in New York the barnacles were found in 1.6% of shells occupied by Pagurus longicarpus. Specimens from the Philippines were identified as Trypetesa spinulosa (formerly known only from Madagascar) based on the presence of their diagnostic orificial palps. The mean prevalence of T. spinulosa in the Philippines was 3.7% and most barnacles were associated with Calcinus spp. Hermit crab eggs were observed in the guts of T. lateralis from Jamaica and T. spinulosa from the Philippines. In both of these regions the trypetesids were found significantly more often in shells occupied by female hermit crab hosts (80–87% with females). These findings suggest the barnacles be classified as transient parasites. The biology of trypetesids is reviewed and a key to the family is provided. Further studies are needed to determine if egg predation occurs in all trypetesids and the impacts on hosts.

In the past half century, a number of studies have described the general composition of the mesozooplankton of Southampton Water, but little attention has been paid to the occurrence of parasitic and commensal species. In order to fill this gap, the occurrence and distribution of parasitic/commensal species was investigated in three fixed stations along the estuary in 2001/2002. A total of 16 parasitic taxa were identified, including 11 new records for the zooplankton of Southampton Water. The most frequent and abundant parasitic taxa observed in the estuary were Peltogaster paguri, Sacculina carcini, Siphonostomatoida copepodites and cryptonistic forms of isopods. This study is the first report on ‘free-forms’ of parasitic/commensal species within the mesozooplankton of Southampton Water being also a reasonable indicator of the presence of the infected/associate host in the estuary or surrounding areas.

Here we report direct underwater observations of the pom pom anemone Liponema multicornis at sites in the western Gulf of Maine. The paucity of records from historic collections as well as recent studies suggest this species is widespread but numerically rare across the region. We found this species hosts high numbers of the commensal amphipod Stenothoe brevicornis amongst the tentacles. In addition, pandalid shrimp were observed using the anemone for shelter by occupying space around the distal edges of the tentacles and as a food source by feeding on bits of mucous. Krill were also observed feeding on amphipods occurring amongst the tentacles. A long history of using bottom contact fishing gear in the region may have reduced abundance, thereby reducing the functional role of L. multicornis as a source for refuge and prey of several crustacean species.

This study of the little known north-eastern Atlantic mytilid Modiolarca subpicta suggests a more intimate relationship with ascidians and, especially, Ascidiella aspersa, than has hitherto been appreciated. Both live for ~18 months and the reproductive cycle of both is approximately co-ordinated so that juvenile ascidians become available as hosts to the settling spat of the symbiotically epizoic M. subpicta each summer. Settling spat of M. subpicta are thought to be attracted to the exhalant flow from the ascidian's anal siphon. After the ascidian's death, the liberated mussels may adopt a wandering, free-living, lifestyle they have occasionally been reported to pursue. Anatomically, M. subpicta is of the typical mytilid plan, albeit simplified commensurate upon its normal lifestyle of protective envelopment within the host's tunic. The foot, however, is highly mobile and in addition to being used for locomotion, especially in juveniles, is responsible for the planting of byssal threads, typically dorsally above the shell, so that each individual stimulates the ascidian to produce an epidermal pocket into which it manœuvres itself and reposes, securely attached, but dorsal side down Modiolarca subpicta, epizoic in the tests of ascidians, could have evolved from a more isomyarian, equivalve, ancestor via a nestling, epibyssate, Trichomusculus-like shaped intermediary with ventral flattening and, hence, stability characteristic of the more familiar heteromyarian mytilids of rocky shores and lotic freshwaters being achieved through living dorsal side down.