Phylum CNIDARIA Anemones, Corals, Jellyfish, Hydroids

Phylum CNIDARIA Anemones, corals, jellyfish, hydroids Daphne Fautin, Dennis Gordon, Dennis Opresko, Megan Oliver, Juan Sanchez, Di Tracey by impregnation of calcium carbonate, but there Phylum are no sclerites in the axis. In bamboo corals (family Isididae) the axis is conspicuously jointed, with solid CNIDARIA calcium carbonate between the joints. In isidids as well as in other highly calcified gorgonians such Anemones, corals, jellyfish, as Primnoidae and Chrysogorgiidae, the axes may give evidence of distinct growth rings in cross and hydroids section. Class Anthozoa — Corals, anemones, and kin Subclass Hexacorallia Anthozoans are the largest group of Cnidaria, Hexacorals may be solitary or colonial, soft or with about 6000 living species worldwide. All are hard, the latter having rigid calcified skeletons. marine, and there is no medusa phase. The mouth Soft hexacorals make up the Orders Ceriantharia opens into a stomach cavity that is partitioned by (tube anemones), Actiniaria (sea anemones), mesenteries (membranes) that expand the inner Corallimorpharia (coral-like anemones), and absorptive surface. There are two subclasses: Zoanthidea (zoanthid anemones). Hard hexacorals the Octocorallia (Alcyonaria), which have eight make up the Orders Scleractinia (stony corals) and mesenteries and tentacles, and the Hexacorallia Antipatharia (black corals). In the stony (or true) (Zoantharia) with tentacles and mesenteries in corals, calcification extends into the mesenteries, multiples of six. creating rigid septa that remain in the dead coral skeletons. Corals are distinguished from their soft-bodied relatives like sea anemones, jellyfish, and hydroids Order Ceriantharia by being calcified, i.e., incorporating calcium Tube anemones are solitary tube-dwelling carbonate (lime) into their bodies to create a hexacorals living in muddy bottoms. They are not skeleton. Several kinds of cnidarians do this, and a diverse group and the sole New Zealand species they can superficially resemble each other if they has not been characterised taxonomically. have a similar shape. The main kinds of calcified Order Actiniaria (sea anemones) cnidarians in New Zealand waters are hydrocorals, New Zealand has a high diversity of soft hexacorals, gorgonians (octocorals), and stony corals. especially of sea anemones (actinians). The deep- Subclass Octocorallia sea anemone fauna is widely distributed but poorly described. Sea anemones have 6 tentacles or This subclass used to be divided into a number of multiples of 6 with nettle cells that sting and capture orders, all but one colonial, in which the polyps are small or large prey. Some species are anchored in united by cords or sheets of tissue (coenenchyme). soft sediment, attached to rocks by their base, or Octocorals, so-called because polyps have an can move slowly over the seabed. Many habitually 8-fold symmetry (8 tentacles and internal body grow on other creatures, including sponges, partitions), can be relatively soft (sea pens and soft corals, and shells. Many species are distinguished corals like dead-men’s fingers) or, as in gorgonians, by attributes of the nematocysts and muscles, so have an erect axis of calcareous spicules or of if there is more than one species of a genus in hardened protein impregnated with lime. In an area, the genus name is often the only name bamboo corals and some other gorgonians the axis available. may be jointed. Octocorals also lack the distinctive vertical radial partitions that characterise stony Order Zoanthidea corals. Twelve species are listed for the New Zealand In the New Zealand EEZ, 243 octocoral species region. Zoanthids are anemone-like hexacorals (187 undescribed) are known, divided among 103 with a colonial lifestyle. One of them is Epizoanthus, genera in 28 families. These include 45 species of which settles on shells occupied by hermit crabs. Order Alcyonacea (spreading runnerlike corals and As it grows it envelopes the shell. Almost nothing soft octocorals), 167 species of Order Gorgonacea is known about zoanthid biology other than the (gorgonians including the bubblegum corals), and association of several species with sponges, 31 species of sea pens, Order Pennatulacea. The hydroids, and molluscs. A striking yellow species diversity of three families of deepwater calcified of Parazoanthus is frequently encountered on gorgonians (Isididae – bamboo corals, Primnoidae Fiordland black coral. – bottlebrush corals, and Chrysogorgiidae – golden There is also a new species of Gerardiidae from corals) is probably the highest in the world for a New Zealand, a family able to generate its single country. own skeleton. The stature of large gorgonian colonies is made Order Antipatharia (black corals) possible by the enhanced development of skeletal About 58 black coral species are known in material. In holaxonians, the axis is horny or New Zealand waters. Black corals are distinguished woodlike, owing to the presence of a scleroprotein by their erect, often bushy, habit of growth and called gorgonin, and may be further strengthened hard proteinaceous skeleton that bears tiny polyps. 49 Although the depth and geographic distribution of continue budding and even to strobilate again. the Antipatharia have not been analysed in detail, it Scyphozoans are present from the shallowest appears that most species live in the deep sea and intertidal to at least benthopelagic depths. There on seamounts at between 200 and 1000 metres are three orders — Coronatae, easily distinguished depth. All New Zealand black coral species are by the presence of a coronal groove on the outer strictly protected, (see box). umbrella surface; Semaeostomae, typically with Order Corallimorpharia long, flowing oral arms and marginal tentacles; and Rhizostomeae, which lack true marginal tentacles as Some seven species and subspecies are known well as a central mouth, instead having numerous in the New Zealand EEZ. The commonest is the tiny mouths on the edges of the oral arms. Stalked colourful jewel anemone, Corynactis australis, jellyfish (upside-down jellyfish) are now regarded as found in low-tidal rock pools and shallow a separate class (Staurozoa). depths. The species looks like a spreading colonial sea anemone. Each tentacle is tipped Class Hydrozoa — hydroids and their medusae with a characteristic white knob that is densely Hydrocorals (stylasterids) all belong to the and minutely studded with nettle cells. Other Order Hydroida family Stylasteridae. Hydroids are corallimorpharian species occur in deep water. generally small and non-calcified, so hydrocorals Order Scleractinia (stony corals) are unusual in this respect. Like other hydroids, New Zealand has a diverse fauna of 127 stony hydrocorals have tiny polyps. Some of these coral species, 110 of which are azooxanthellate, function like stomachs (gastrozooids) while the (i.e., lacking symbiotic algae) comprising non-feeding polyps are tentacle-like and used for over 16% of known azooxanthellate species. food-capture (dactylozooids) or for reproducing Azooxanthellates/ahermatypes are sometimes (gonozooids). New Zealand hydrocorals are erect called ‘deepwater corals’ or ‘solitary corals’ and are and branching, and may be white or red. usually small and slower growing, and do not form Their skeletons are distinguished from those reefs like their zooxanthellate reef counterparts. of stony corals by being generally much smaller Stony corals are calcified hexacorals, i.e., having and less robust, and minutely porous and pitted body parts in multiples of 6. Coral polyps may be with small holes for the various polyps. These thought of as skeleton-forming anemones. holes (openings) lack the distinctive vertical radial The internal membranes (mesenteries) that partition partitions that characterise stony corals. the bodies of sea anemones are calcified in corals Hydrozoans are remarkably varied. They may be so that, when all soft tissues are removed, the polyp solitary or colonial, with polyp and medusa phases, skeleton is seen to have distinctive vertical radii or either phase may be lacking altogether. (septa), often divided into cycles of major and minor ones. An entire coral, called a corallum, may consist of a PROTECTED SPECIES single individual or a colony of many individuals. The group of organisms collectively known as The skeleton (corallite) of an individual polyp has a ‘black corals’, (Cnidaria, Antipitharia pages 57 & cup-shaped opening (calyce) that is typically round 58) are currently protected under the Wildlife Act or oval as in New Zealand’s cold-water corals, but 1953. Incidental catches of black corals need to be in tropical corals neighbouring corallites can be reported via non-fish bycatch forms. fused and conjoined, resulting in large compound ‘Red corals’ are also listed as protected under the calyces. Wildlife Act 1953. At present only Errina (page Class Scyphozoa — jellyfish 67) is being interpreted as a protected species by the Ministry of Fisheries and Department of The Scyphozoa is a small group of cnidarians Conservation. Users of this guide should note that numbering only about 250 living species worldwide. the definition of “red corals” is under review by the Notwithstanding the low species diversity, this Department of Conservation at the time of writing, minor group has caused some major problems and may be extended to other species or groups, recently around the world and in New Zealand. including bubblegum coral, precious corals and Understanding of jellyfish bloom dynamics remains bamboo corals. If in

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