Investigation of nematocysts in stylasterids (Cnidaria: Hydrozoa: Stylasteridae)

<p>The type, size, shape and distribution of nematocysts represent important taxonomic characters that help to identify many hydrozoan species. The Stylasteridae is one of the most species-rich hydroid families. Nevertheless, information about the soft tissue and especially data about the nematocysts are still very scant. Scattered data about nematocysts are available in several taxonomic papers, but unfortunately without the type identification or shape description, this information is not very useful. Therefore, several questions still need answers. What types of nematocysts are present in the stylasterid family? Do nematocysts have a particular distribution in the soft tissue? Could they be considered a useful taxonomic character for the family? Is it possible to hypothesize their functions? In order to answer these questions, we analysed 15 stylasterid species belonging to seven genera. Euryteles, desmonemes, isorhizas and probably also mastigophores were identified. All examined species have euryteles and desmonemes, while isorhizas are recorded in two genera and mastigophores in only one genus. Moreover, the shape of the nematocysts in some species is very distinct. The distribution of nematocysts shows that each species contains, in the coenosarc, all nematocysts of its cnidome, while in the polyps there are only euryteles and desmonemes. Our study showed that in integrating the information about nematocyst type, size, shape and distribution, each species investigated herein has a specific cnidome. Therefore, nematocysts have a taxonomic value for stylasterids and, whenever possible, nematocysts should be included in the species descriptions. Moreover, the possible functions of stylasterid nematocysts are given in relation to their type and distribution.</p

Evolution of the characters 4 and 5.

<p>(A) Character 4, absence/presence of cyclosystems. (B) Character 5, arrangement of the cyclosystems (not in pseudocyclosystem form). I, II, and III, major clades cited in the text. The state of the analysed character is represented by a coloured pie, placed at each internal/terminal node of the tree. An enlarged multi-coloured pie is used when multiple states of a character occur at a specific node. In this latter case the size of each slice is proportional to the probability of occurrence of the state.</p

Codes and miniatures depicting the states of the ten characters analysed in present paper.

<p>Codes and miniatures depicting the states of the ten characters analysed in present paper.</p

Evolution of the characters 8 and 9.

<p>(A) Character 8, gastropore (lip presence). (B) Character 9, dactylopores (dactylostyle presence). I, II, and III, major clades cited in the text. The state of the analysed character is represented by a coloured pie, placed at each internal/terminal node of the tree. An enlarged multi-coloured pie is used when multiple states of a character occur at a specific node. In this latter case the size of each slice is proportional to the probability of occurrence of the state.</p

Maximum likelihood tree obtained from the analysis of TOT.92T data set.

<p>The ML tree (-ln = 23933.8193) was computed with IQ-TREE program. The scale bar represents 0.02 substitutions/state change per position. Black numbers represent ultrafast bootstrap values (>50%) expressed in percent, while red numbers refer to Bayesian Inference posterior probabilities. These latter values are provided in a compressed way (e.g. 1. instead of 1.00; .95 instead of 0.95) to allow a better readability of the figure.</p

Evolution of the character 10.

<p>Character 10, dactylopores (spine presence). I, II, and III, major clades cited in the text. The state of the analysed character is represented by a coloured pie, placed at each internal/terminal node of the tree. An enlarged multi-coloured pie is used when multiple states of a character occur at a specific node. In this latter case the size of each slice is proportional to the probability of occurrence of the state.</p

Evolution of the characters 3a and 3b.

<p>(A) Character 3a, arrangement of the polyps (three states). (B) Character 3b, arrangement of the polyps (six states). I, II, and III, major clades cited in the text. The state of the analysed character is represented by a coloured pie, placed at each internal/terminal node of the tree. An enlarged multi-coloured pie is used when multiple states of a character occur at a specific node. In this latter case the size of each slice is proportional to the probability of occurrence of the state.</p

Hydroid diversity of Eilat Bay with the description of a new <i>Zanclea</i> species

<p>Eilat Bay is located at the southernmost tip of Israel in the Gulf of Aqaba (Red Sea). The list of hydroids currently known from there includes 51 species, and when extending it to the entire Red Sea, it includes 157 species belonging to 41 families. Nevertheless, the information regarding hydroids in the Gulf of Aqaba, and in particular in Eilat Bay, is not exhaustive. The aim of this work is to improve knowledge of hydroid biodiversity in this area. The specimens collected during the HyDRa project (Hydroid Diversity of the Northern Red Sea) revealed the presence of 27 species, 13 Anthoathecata and 14 Leptothecata, belonging to 17 families and 20 genera. Two families, Cladonematidae and Corynidae, and five genera, <i>Cladonema</i>, <i>Slabberia</i>, <i>Campanularia</i>, <i>Nemalecium</i> and <i>Lafoeina</i>, are new findings for the Red Sea. Furthermore, <i>Nemalecium lighti</i>, <i>Zanclea gallii</i> and the new species <i>Zanclea eilatensis</i> sp. nov. have never before been recorded in the Red Sea. <i>Zanclea eilatensis</i> sp. nov. lives in association with a bryozoan, has a monomorphic colony lacking a perisarc and only has stenoteles in the polyps. The medusa stage has two prominent perradial exumbrellar nematocyst pouches and two tentacles with about 50 cnidophores having long flagella and containing macrobasic euryteles. In the present work, 54% of the species were associated with other organisms, such as hydroids, corals and bryozoans. New ecological data about the <i>Zanclea–</i>scleractinian coral association are documented. The present investigation provides new information about diversity in the Red Sea, and in particular in Eilat Bay. In addition, our data also have significance for Mediterranean and Red Sea biodiversity conservation due to the recent expansion of the Suez Canal and the consequent possible increase in the introduction of nonindigenous species in both directions.</p> <p><a href="http://zoobank.org/urn:lsid:zoobank.org:pub:C9EA7333-B9DF-4888-A643-4D45E6CD31CB" target="_blank">http://zoobank.org/urn:lsid:zoobank.org:pub:C9EA7333-B9DF-4888-A643-4D45E6CD31CB</a></p