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n. pl.1.(Zool.) A kind of embryo of certain hydroids (Tubularia), having a stellate form.
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A Copepod eggs 76.2% Unknown 0.9% Barnacle nauplii 1.1% Copepod nauplii 9.8% Polychaete larvae 1.8% Rotifera 3.6% Cladocerans 0.2% Actinula larvae 2.3% Veliger larvae 0.2% Cyprids 0.7% Spiricules 0.5% Pieces of sponge 0.9% Unknown nauplii 2.0% Note: Table made from pie chart.
Instead of a planula larva, Tubularia hydroids produce the uniquely shaped actinula larva as the dispersive stage in their life cycle.
In this study, to understand actinular settlement, we extensively examined larval behavior, morphological transformation, and nematocyte dynamics in the actinula larvae of Tubularia mesembryanthemum.
Actinula larvae were obtained by placing female branches or polyps in small plastic baskets in 2- or 3-1 beakers filled with fresh FSW (about 10 polyps/1)
After the actinula larvae were released from the maternal gonophores, their behavior and morphogenesis were observed on either clean or microbial-filmed glass petri dishes under a stereoscopic microscope.
Fertilized eggs developed to star-shaped embryos, preactinulae, and then to actinula larvae that were released from the maternal gonophore (Fig.
Maintenance and culture were dependent on the physiological state of the colonies collected; colonies without degeneration of the hydocaulus stayed mature for 1-2 months in running seawater and released actinula larvae repeatedly, every 1-2 weeks.
Ascidian tadpole larvae and hydroid actinula larvae were found regularly in samples during spring and summer.
The actinula larvae are believed to be those of Tubularia spp.
Actinula hydroid larvae had significantly higher densities 1-5 cm from wall compared to 1 m from the wall on days of low-flow speed but showed no significant differences on days of high flow.
The results of this study show a clear horizontal pattern of distribution away from vertical rock substrata for ascidian tadpole larvae, mussel pediveligers, veliconcha-stage mussel larvae, Anomia veligers, hydroid actinula larvae, and others.
Hydroid actinula larvae, also short-distance dispersers, showed a similar strong pattern; they were found primarily close to invertebrate-covered substrata with abundant Tubularia colonies.