A small lot of fossil whale barnacles from the Upper Pleistocene of California and the Middle Pleistocene (Chibanian) of Oregon (United States West Coast), described in a 1972 unpublished MA thesis, are formally described and illustrated herein. In that thesis, a new genus and species name were proposed; however, according to the International Code of Zoological Nomenclature, they have no taxonomic standing and are thus unavailable. Based on our reappraisal, two specimens in this lot belong to a new, extinct species that can be assigned to the purportedly extant genus Cetopirus. Cetopirus polysyrinx sp. nov. differs from congeners in that its secondary T-shaped flanges are multitubiferous internally, that is, they are perforated by a high number of irregularly-sized and irregularly-spaced tubules that result in a spongy aspect in transverse section. Whether or not this peculiar condition had any adaptive significance is difficult to determine. Considering that Cetopirus is currently known as an obligate epibiont of right whales (including the North Pacific form Eubalaena japonica (Lacépède 1818)), the host of C. polysyrinx sp. nov. was E. japonica or some other species of Eubalaena. The Plio-Pleistocene deposits of the Pacific coast of North America have yielded a rather idiosyncratic fossil whale barnacle fauna, inclusive of the genera Cetolepas, Cryptolepas and now Cetopirus, which seemingly contrasts with all other coeval assemblages worldwide, the latter being in turn dominated by Coronula spp.

The present study reports for the first time the association between the decapod Thymops birsteini (Nephropidae) and the amphipod Caprella ungulina (Caprellidae). A benthic biodiversity survey was carried out to explore the Mar del Plata Submarine Canyon, off the Argentine coast, in the South-western Atlantic Ocean. A total of 205 caprellids (181 juveniles, 4 males and 20 not-classified individuals) were found attached to 7 specimens of T. birsteini caught between 1087–2212 m depth. The epibiotic parameters showed that the prevalence of C. ungulina on T. birsteini was 50%; the mean abundance was 14.64 and the intensity value was 29.29. In addition, specimens of C. ungulina were recorded mainly on mouthparts of T. birsteini (31.22%), followed by chelipeds (18.05%), cephalothorax (4.88%) and pereiopods (0.98%). Our finding of C. ungulina provides the deepest record until now; additionally, this epibiont is reported in a new host belonging to an infraorder and a family of crustacean that had not previously been found as basibionts. The potential mechanisms implied in the wide distribution of C. ungulina are discussed.

Macroalgal communities of coastal ecosystems play a key role in maintaining overall coastal biodiversity. In this study, habitat preference (macroalgal host preference) and temporal changes (season) of epifaunal communities associated to five macroalgal species such as Padina, Sargassum, Ulva, Acanthophora and Gracilaria were observed at seasonal intervals (summer and winter) for 2 years from May 2012 to March 2014 on the Jeddah coastal waters of the Red Sea. Major epifaunal groups observed included polychaetes, amphipods, isopods, gastropods, mussels and crabs. Polychaetes were represented by 10 species followed by amphipods with five species. The abundance of gastropods, polychaetes and mussels showed significant variation between the macroalgae irrespective of morphology. Generally, the abundance of these taxa were high on Padina and low on Sargassum. Significant seasonal changes were observed on the abundance of polychaetes, amphipods and isopods. The abundance of some epifaunal groups showed a significant relationship with environmental parameters such as surface water temperature, salinity, pH and dissolved oxygen content.

In this study we examined the epibiont assemblage on shells of the living limpet Patella aspera. Limpets were collected at two sites at each of the nine islands of the Azores, totalling 707 individuals examined. Shells were measured and all the epibiota identified to the lowest taxonomic resolution possible. 190 taxa were recorded, of which 97% were algae, including 17 new records for the Azores. Only five shells were devoid of fouling organisms. The assemblage was dominated by a few algal taxa, whereas the majority of species occurred on less than 10% of the shells. A significant and positive relationship was generally found between basibiont size (shell length) and epibiota richness. The strength (slope) of the relationship, however, varied between islands and sites. These results suggest that a range of processes operating at multiple spatial scales influenced epibiont assemblages. Many features identified in these assemblages resemble, in many ways, those examined in island biogeography, suggesting that basibionts may be considered as ‘islands’ and may provide a suitable model system to test ecological hypotheses about ecosystems that are not so amenable to experimentation.

The structure of sessile epibiotic assemblages fouling the shells of farmed populations of the common Mediterranean mussel Mytilus galloprovincialis, a species known to be involved in ecosystem engineering processes, was investigated in the north Aegean Sea. Mussel samples were collected from three aquaculture installations and all sessile organisms were examined. Fifteen species were recorded, one macroalga and 14 macro-invertebrates. Four colonial species covered up to 20% of the mussel shell. Among solitary organisms, polychaetes dominated followed by barnacles. The diversity of sessile epibionts associated with farmed mussel populations was comparable to that observed on natural mussel beds in contrast to their abundance/cover, which was higher in the former, possibly due to the higher trophic status in the farming areas. The structure of epibiotic assemblages exhibited limited variability at the spatial scale, in general. On the contrary, strong temporal variability with decreased diversity and abundance/cover values during the cold period of the year was assessed, in accordance with the life cycles of species involved and prevailing environmental conditions. Mussel epibionts appeared to have a negative impact on their basibiont since a reduced condition index was detected; however this impact was rather weak and further data are required to generalize the consequences of epibiosis on farmed mussels.

The presence of a diverse range of epibionts was found on Pagurus bernhardus from the west coast of Scotland. The invertebrate species found on the shell inhabited by the crab were the hydrozoans Hydractinia echinata and Dycorine conferta, the cirripeds Balanus balanus and Balanus crenatus, the polychaetes Hydroides norvegica, Pomatoceros triqueter and Circeis armoricana, and the molluscs Hiatella arctica and Anomia ephippium. On the crab were observed the polychaete Circeis armoricana and the amphipod Podoceropsis nitida. In addition, on the gastropod shells occupied by P. bernhardus, ciliate protozoan species were found attached to the hydrozoan Dycorine conferta, this being hyperepibiosis. These ciliates were 6 suctorian (Conchacineta constricta, Corynophrya anisostyla, Actinocyathula homari, Actinocyathula crenata, Acineta sulcata and Acineta corophii), and one peritrich species (Zoothamnium sp.). This is the first time that this hyperepibiosis was observed. In contrast to the epibiont communities observed in previous surveys in the same sampling area, basibiont specimens without D. conferta did not show ciliate epibionts. The ciliate epibionts also were not present on the surface of the shell and crab in specimens with D. conferta; they only appeared in hyperepibiosis on the surface of the hydrozoan. The spatial distribution and abundance of the invertebrate epibiont species were analysed, as well as the morphology, taxonomy and distribution of the ciliate hyperepibionts.

Temporal and spatial fluctuations of environmental parameters are normally assigned as causes of variations in morpho-phenological characters of seaweeds and in their epibionts, but formal tests of such hypotheses are lacking, especially in narrow gradients. The present study evaluated the influence of a very small depth gradient (1 to 3 m) and of subtle seasonality characteristic of tropical areas on morpho-phenological traits and on the occurrence of sessile epiphytic organisms using a controlled orthogonal sampling design in a sublittoral population of the tropical brown alga Sargassum cymosum. Four temporal samples were obtained over a one-year period at three depths using nine replicates. The wet weight, maximum length, number of primary and secondary branches, and proportion of secondary branches with receptacles were recorded. Epibiosis was estimated by visual evaluation of percentage cover on secondary branches. Algal morphology varied as a function of the period of the year (weaker effect) and depth (stronger effect) but in different ways for each variable analysed. In general, fronds tended to be shorter, heavier, and more ramified in shallower areas. In relation to time, the morphological characters tended mostly to present higher values in January (summer) and/or April (autumn). Frequency of receptacles did not depend on algal morphology and depth at all but varied in time, although only in the deepest area. Epibiosis also did not depend on algal morphology but varied in relation to time (stronger effect) and, to a lesser extent, depth (weaker effect). The effect of time upon epibiosis also depended on the biological group analysed. These data support the hypothesis that algal morphology varies in relation to period of the year and depth, even under small temporal and spatial environmenal gradients.

Some specimens of the blue crab are bearing barnacles which have been identified as Chelonibia patula. Although generally known in the Mediterranean Sea this is the first report of C. patula from the Turkish coasts. It has been photographed and some morphometric measurements are provided.

The prevalence and infestation intensities of Octolasmis lowei in the branchial chambers of Libinia spinosa were evaluated according to the host's sex, size, and moult condition. Epibionts were classified as cyprid larvae, non-ovigerous or ovigerous according to their developmental stage. A median intensity of infestation of 21 epibionts/host was found (range = 1–644; Q3 = 81). Epibiont prevalence values (88%) were higher on ovigerous female hosts than on males (55%) or on non-ovigerous females (31%). Intensity of infestation was positively correlated with host size in both sexes for non-ovigerous and ovigerous epibionts. No preference between host sex by cyprid larvae was observed, nor any correlation between cyprid abundance and host size. Cyprid larvae abundance was positively correlated with settled epibionts on both host sexes. The duration of the intermoult phase was the main factor linked to the establishment of sessile epibionts. These observations are important in relation to crabs that have a terminal moult, because these animals cannot eliminate their epibionts in future moults, thus increasing the importance of density-dependent mechanisms on epibiont establishment; in that way, prevalence of infestation alone can underestimate the real impact of infestation on the host's life cycle.

Several hydroid species have an epibiontic lifestyle, living associated with organisms of many different phyla. On the other hand, hydroids can also host dense assemblages of microflora and microfauna, mainly composed of protists and bacteria. Among protists, diatoms are the most abundant and diversified group, followed by foraminifera and sessile ciliata such as Vorticella and suctorians. Regarding the spatial distribution of epibionts, hydroid colonies represent a mosaic of different microhabitats: in some species, each colony portion (base of the stem, branches, pedicels, inner space between the polyp and the theca) hosts different diatom species. Moreover, three foram species have been shown to occupy different positions according to the plasticity of their shell. A host specificity has been also observed: some epibionts are typical of only one or a group of species, such as Vorticella living on the teeth of the Aglaophenia thecae or coralline algae that cover mainly Aglaophenia and Sertularella colonies. The microassemblage associated to Eudendrium racemosum showed a typical seasonal cycle and a vertical distribution which reflects the selective advantage of the different life forms. Experiments with plastic structures miming hydroid colonies demonstrated that the living hydroid affects the assemblage structure. Probably, the perisarc composition and secondary metabolites play a crucial role in the relationships between hydroids and their microassemblage.

Epibiotic interactions between macroalgae and crustaceans have rarely been described. We examined the interaction between the mole crab, Emerita analoga and the opportunistic algae Enteromopha spp. in a sandy beach of the central coast of Peru. Enteromorpha spp. was found fouling the carapace of the mole crab that provides the only stable substrate to spore settlement in the beach environment. Epibiosis prevalence was up to 2.1%, and affected mainly larger, ovigerous females. Prevalence presented a seasonal pattern, with peaks during summer. Mole crab body condition was higher when fouled, whereas fecundity was not affected. Fouled mole crabs burrowed at lower speed, which was reversible by the removal of epibiotic algae. The burrowing depth was not affected by epibiosis. Contrary to the expected, the effects of algal epibiosis on demographic and life history parameters of mole crabs, with the exception of body condition, were mainly neutral but important on behavioural traits.

Four species of foraminifers Rosalina globularis, Lobatula lobatula, Acervulina inhaerens and Miniacina miniacea were observed as epibionts on some species of the athecate hydroids of the genus Eudendrium—E. armatum, E. glomeratum, E. moulouyensis and E. racemosum—from the Mediterranean Sea. The abundance and the distribution of the protozoans were determined for each hydroid and considered in relation to the shape and size of the Eudendrium branches. Results revealed differences in the composition of the epibiontic assemblage among different species of Eudendrium which were dependent on several factors, but were mainly related to the habitat and to the morphology of the host.

The interactions between Eudendrium and its epibionts were considered to emphasize the role of the Eudendrium colonies as a hotspot not only of poorly known species but also of co-evolutionary relationships and life histories.