C. G. Di Camillo

Spatial and temporal distribution in a tropical hydroid assemblage

The hydroid assemblage of the Siladen Island coral reef (North Sulawesi, Indonesia) is made up of 107 species belonging to 51 genera and 28 families. The study of their spatial distribution has identified three different zones which are well-characterized: (1) the reef flat, where hydroids are mainly represented by cryptic species living in the shady crevices of the corals, epibiontic on sponges or sea grasses; (2) the edge of the reef characterized by hydroids growing mainly on the shady side of the corals, with the exception of the tufts of the large colonies of the stinging zooxanthellate Aglaophenia cupressina ; and (3) the vertical reef, where hydroids reach their maximum diversity and abundance and are often involved in symbiotic relationships. The number of hydroid species shows a seasonal trend with a summer minimum (July–September) and a winter maximum (November–February). The strong correlation between these variations and the abundance of rainfall suggests that food availability, strictly related to the seasonal amount of rain, represents the main abiotic factor triggering the hydroid species richness and the abundance of this tropical assemblage.

Temporal variations in growth and reproduction of Tedania anhelans and Chondrosia reniformis in the North Adriatic Sea

Most works concerning growth and reproduction of Mediterranean sponges have been performed in the oligotrophic western Mediterranean while little is known about sponge dynamics in the North-western Adriatic Sea, a basin characterized by low winter temperature and eutrophy. In order to deepen our understanding of sponges in the North Adriatic Sea and verify how its peculiar trophic and physical conditions affect sponge life cycles, temporal trend of sponge cover (%) and reproductive timing of Chondrosia reniformis and Tedania (Tedania) anhelans were studied over a 1-year period looking for a possible relation with variations of temperature or food availability. In C. reniformis, although little variations of sponge cover were evidenced around the year, the number of individuals and their size increase during spring. Asexual reproduction, via drop-like propagules, mainly occurs in spring and summer, while sexual reproduction is characterized by a maximum number of oocytes in August. T. anhelans progressively grows from spring to summer and develops propagules on its surface that reach their maximum size in July. In autumn, the sponge undergoes a process of progressive shrinkage and almost disappears in winter when temperature reaches 7–8°C. Larvae occur during summer. In the North Adriatic Sea sponges have larger sizes, higher density and a wider period of oocytes production compared with the same species from the Mediterranean Sea, suggesting these differences could be due to high food availability characterizing the eutrophic Adriatic basin. On the contrary, the sharp water temperature variations and the very low winter temperature, 5–6°C lower than what has been reported for the Mediterranean Sea, regulate temporal variations in abundance and cause the disappearance of thermophile species during winter.

Relationships between benthic diatoms and hydrozoans (Cnidaria)

Some examples of relationships between hydroids and epibionthic diatoms from the Mediterranean Sea are described, verifying the kind of interaction existing between the two partners. The athecate Eudendrium racemosum hosts an extremely rich diatom assemblage, mainly comprising Licmophora spp., Amphora spp. and Cocconeis spp. On the contrary, only adnate growth forms ( Cocconeis pseudonotata , C. dirupta ) were observed in diatom communities growing on the external side of thecate species Campanularia hincksii , Clytia linearis and Synthecium evansi . Some diatom species ( Cocconeis notata , Cylindrotheca sp. and Navicula sp.) are able to survive in the intrathecal microenvironment. They live in the narrow space between hydrotheca and polyp, receiving protection and probably using the nutrients produced by hydroid metabolism. Sunlight can penetrate through transparent thecae and reach the diatom layer, making photosynthesis possible.

Foraminifers epibiontic on Eudendrium (Cnidaria: Hydrozoa) from the Mediterranean Sea

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.

Are diatoms a food source for Antarctic sponges

Living diatoms are commonly found within Antarctic Porifera, and generally interpreted as additional food source, or as mutualists or parasites of sponge tissues. However, no data are available about temporal variations of the abundance of diatoms inside sponges especially during the winter period. In this paper we analysed the amount of diatom frustules and chlorophaeopigment concentration in six species of Antarctic sponges (Dendrilla antarctica, Homaxinella flagelliformis, Kirkpatrickia variolosa, Suberites montiniger, Haliclona dancoi, Haliclona penicillata) sampled weekly from November 2001 – before the ice melting – to February 2002. Frustule concentration in the sponge tissues was very low at the beginning of November in all the sponge species, and increased between 9 and 22 January, to reach maximum values between 29 January and 7 February. Diatom abundances were significantly higher in H. dancoi tissues, comparing to the other sponge species, reaching values up to 1217 ± 178 cells *106 g−1 dw at the end of January. Chlorophaeopigments, very low at the beginning of November, increased between 5 and 19 December, before the peak of diatoms. Maximum chlphaeo values (650.5 ± 5.9 µg g−1 dw) were observed in D. antarctica. The planktonic Fragilariopsis curta was the most common diatom species recorded inside sponges. These data clearly indicate that diatom concentration inside the sponge tissues is related to the summer phytoplankton bloom. The shift between the pigment and frustule peaks strongly suggests that diatoms are used as a food source by sponges and that their frustules are accumulated inside the sponge body. The lack of frustules at the beginning of summer indicates that diatom frustules are expelled or dissolved during the cold season.

Association between Dentitheca habereri (Cnidaria: Hydrozoa) and two zoanthids

Dentitheca habereri is a leptomedusan hydroid forming large colonies on the fringing reefs of the Bunaken National Park (North Sulawesi, Indonesia). The hydroid is generally associated with two zoanthid species, Parazoanthus gracilis and Parazoanthus sp. Colonies lacking zoanthid epibionts are rare and generally smaller (8–10 cm). When associated with Parazoanthus sp., the hydroid colonies are fan‐shaped and may exceed 1 m in width. In contrast, when D. habereri is colonised by the large polyps of Parazoanthus gracilis, the host colonies are smaller and the branching is irregular.

A tubulariid hydroid associated with anthozoan corals in the Mediterranean Sea

Abstract A solitary hydroid of the genus Ectopleura was described associated with several Mediterranean anthozoans: the black coral Antipathella subpinnata and three gorgonian species, Eunicella cavolinii, Paramuricea clavata and Paramuricea macrospina. This find represents the first record of a hydroid species epibiont of an antipatharian coral and also the first record of such association with Mediterranean gorgonians. Hydroids arise from the branches of the hosting corals and are enveloped by a thin sheet of their skeleton and by a layer of living coenenchyme up to the neck of the hydranths. The relationship causes no apparent damage to the host, while the epibiotic habitus allows the hydroid to avoid siltation and to gain in defence and support. It is hypothesised that actinulae of Ectopleura sp. are able to settle on the corals (both skeleton or tissue) and, during their growth, to be enveloped by the skeletons of their host.

The epibiontic assemblage of Geryon longipes (Crustacea: Decapoda: Geryonidae) from the Southern Adriatic Sea

The crab Geryon longipes lives in muddy bottoms of bathyal environments. Its epibiontic assemblage was studied in a population from the Southern Adriatic Sea. Four species of invertebrates were observed on the crab exoskeleton. The most abundant was the hydroid Leuckartiara cf. octona; the bryozoan Triticella flava was also quite frequent, while another hydroid, Hydractinia sp., and a bryozoan, Arachnoidea sp. were only occasionally observed. The study of the abundance and the distribution of the two most common epibionts in relation to the crab revealed a different spatio‐temporal pattern of colonisation between the hydroid and the bryozoan.

The cnidome of Carybdea marsupialis (Cnidaria: Cubomedusae) from the Adriatic Sea

Kinds and distribution of nematocysts of the cubomedusa Carybdea marsupialis were described by light and scanning electron microscopy. Three kinds of nematocysts were found in tentacles: heterotrichous microbasic euryteles, flattened holotrichous isorhizas and subspherical holotrichous isorhizas. The microbasic euryteles of the tentacles show a characteristic detachable multilayered lancet, already described in the euryteles of Carybdea alata . A possible explanation of the function of the lancet is proposed. The pedalia and the umbrella are armoured by holotrichous isorhizas together with an unidentified kind of small, drop-shaped nematocysts. Gastric cirri, characterized by a rough and ciliated surface, contain heterotrichous microbasic euryteles.

Macrorhynchia species (Cnidaria: Hydrozoa) from the Bunaken Marine Park (North Sulawesi, Indonesia) with a description of two new species

Five species of Macrorhynchia from the Bunaken National Marine Park (North Sulawesi, Indonesia) are described. Three species, M. philippina, M. spectabilis and M. phoenicea were already known for the Indo‐Pacific area, M. asymmetrica and M. fulva are described as new species. Macrorhynchia asymmetrica n. sp. is easily distinguished from the other species of the genus due to the hypertrophic lateral nematotheca that is bent downwards. Macrorhynchia fulva n. sp. is distinguishable from its congeners especially through the lateral nematothecae pointing in opposite directions, the large marginal tooth, and the presence of the well‐marked adcauline teeth. The shape and the colour of living colonies are described, thereby allowing the recognition of the species directly in situ. Generally, the observed species live on the deeper portions of the reef, but M. spectabilis occurs at more shallow depths. Almost all the recorded species have an annual cycle characterised by higher abundances during the wet season while they are absent or rare during the dry period. Only M. asymmetrica has the opposite pattern, being more abundant during the dry months.