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

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

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

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

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

Description of <i>Turritopsoides marhei</i> sp. nov. (Hydrozoa, Anthoathecata) from the Maldives and its phylogenetic position

<p><i>Turritopsoides marhei</i>, a new species of the hydrozoan family Oceaniidae, is described from the Maldives. This species can be distinguished from the only other member of the genus by the presence of more branched colonies, branches not being adnate to pedicels, longer pedicels, larger nematocysts, nematocyst-rich nematophore-like outgrowths from pedicels, smaller male gonophores, and a different geographic distribution. This finding represents the first record of the genus outside the type locality of its type species, in Belize. Molecular phylogenetic analyses show that, as expected, <i>T. marhei</i> belongs to the clade Filifera IV. However, the phylogenetic hypothesis based on both mitochondrial and nuclear DNA sequences reveals that most of the families of this group are polyphyletic, including Oceaniidae, and suggests that the morphological characters used to discriminate among filiferan families need to be revised thoroughly.</p> <p><a href="http://zoobank.org/urn:lsid:zoobank.org:pub:CE901E0D-B125-4A87-BB97-8020C0658B5D" target="_blank">http://zoobank.org/urn:lsid:zoobank.org:pub:CE901E0D-B125-4A87-BB97-8020C0658B5D</a></p

Morphological differences among clades.

<p>^a present study;</p><p>^b Fontana et al. 2012;</p><p>^c Montano et al. 2015.</p><p>Morphological characters of the clades resulted from the molecular analyses.</p

Phylogenetic tree based on the nuclear gene 28S inferred by Bayesian inference.

<p>The clade support values are <i>a posteriori</i> probabilities, bootstrap values from Maximum Likelihood, and bootstrap values from Maximum Parsimony, in this order. The node supporting the scleractinian-associated <i>Zanclea</i> clade is highlighted in red.</p