Hydra, jellyfish, coral, & sea anemones I. radial symmetry II. dimorphic development III. nematocysts, specialized organelles produced by cnidocytes Radial Compass jellyfish General Characteristics • They are radially symmetrical; oral end terminates in a mouth surrounded by tentacles. • They have 2 tissue layers • Outer layer of cells - the epidermis • Inner gastrodermis, which lines the gut cavity or gastrovascular cavity (gastrodermis secretes digestive juices into the gastrovascular cavity) • In between these tissue layers is a noncellular jelly-like material called mesoglea Characteristics • Diploblastic – Epiderm & hypoderm Polymorphism : more than one body form 1. Polyp 2. Medusa Cnidarian Body Plans Polyp form • Tubular body, with the mouth directed upward. • Around the mouth are a whorl of feeding tentacles. • Only have a small amount of mesoglea • Sessile Medusa form • Bell-shaped or umbrella shaped body, with the mouth is directed downward. • Small tentacles, directed downward. • Possess a large amount of mesoglea • Motile, move by weak contractions of body Forms of Cnidarians Polyp • tentacles around the mouth • Sessile Polyp (Hydra) Polyp (sea anemone) Medusa • Umbrella shape • Tentacles around mouth • Motile, Free-swimming Dimorphic Life Cycle Colonial hydrozoan Tentacles • Have nematocysts (stinging cells) • Coiled thread discharges like a harpoon • Contains neurotoxin • Paralyzes prey Stinging Organelles • Prey capture is enhanced by use of specialized stinging cells called cnidocytes located in the outer epidermis. • Each cnidocyte has a modified cilium - cnidocil, and is armed with a stinging structure called a nematocyst. • The undischarged nematocyst is composed of a long coiled thread • When triggered to release, either by touch or chemosensation, the nematocyst is released from the cnidocyte and the coiled thread is everted • Some nematocysts function to entangle the prey; others harpoon prey and inject a paralyzing toxin Discharged nematocyst Hydrazoan stinging and capturing prey Habitat Aquatic Most Marine Few fresh-water Feeding Carnivores (predators) Process of feeding 1. Tentacles sting prey with nematocysts 2. Tentacles grab prey 3. Prey pulled into mouth 4. Prey stuffed into gastro-vascular cavity (GVC)* Lion’s mane eats another jelly 5. GVC makes enzymes, extra-cellular digestion 6. Undigested food back out mouth *incomplete digestive tract (no anus) Digestive System Nutrition • Cnidarians are carnivores with hydras and corals consuming plankton and some of the sea anenomes consuming small fishes • They use tentacles to capture prey and direct it toward the mouth so that it can be digested in the gastrovascular cavity via secretions from gland cells (extracellular digestion); some food is phagocytized by special cells and digestion occurs intracellularly • The gastrovascular cavity exists as 1 opening for food intake and the elimination of waste • There is no system of internal transport, gas exchange or excretion; all these processes take place via diffusion Respiration • Via diffusion Excretion • Via diffusion Response Sensory cells 1. Chemoreceptors (chemicals) 2. Thigmoreceptors (touch) 3. Photoreceptors (light) Ocelli (eyespots) 4. Statocysts (balance) Locomotion A. Medusa motile, free-swimming A. Polyps sessile Exceptions: 1. Hydra tumbles on tentacles 2. Sea anemones glide on pedal disc Reproduction 1. Asexual budding from polyps or medusa 2. Sexual a. Medusae release sperm & eggs b. Some monoecious, some dioecious Larvae free-swimming Cnidarian Taxonomy CNIDARIA Phylum: Cnidaria: (formerly called Coelenterata) Class: I. Hydrozoa: (hydroids) II. Scyphozoa: (jellyfish) III. Anthozoa: (corals) Class Hydrozoa: The Hydras • Polyp phase is dominant Phylum: Cnidaria Class: Hydrozoa: (hydroids) the most part colonial species that have alternating medusa and polyp stages This order has a chitinous exoskeleton Hydrozoa are colonial and create an aragonite (calcium carbonate based) skeleton The best known of these complex colonial organisms is the Portuguese man-of-war (Physalia physalis). Colonial Hydrozoans • Fire Corals – NOT TRUE CORAL • Hydrozoan colony – TRUE CORAL • Anthozoan colony Phylum: Cnidaria: (formerly called Coelenterata) Class: Scyphozoa: (Jellyfish) The class Scyphozoa is generally characterized by having a much larger medusa stage than polyp stage Scyphozoan Life Cycle Aurelia aurita (Moon jelly) Class Anthozoa Class Anthozoa: Anemones & Corals • Appear like plants but are animals. • Polyp form is dominant. Anemone • Corals build calcium shells to protect themselves • Have symbiotic relationship with algae. • Can build extensive masses which can form land masses. Coral Polyps Class Anthozoa • Exclusively marine; there is no medusa stage • At one or both ends of the mouth is a ciliated groove called the siphonoglyph; generates a water current and brings food to the gastrovascular cavity • Possess a well developed pharynx • The gastrovascular cavity is large and septa or mesenteries; increase surface area for digestion or support Class Anthozoa Corals obtain much of their energy from microscopic photosynthetic algae (zooxanthellae) or dinoflagellates that live symbiotically inside the cells of the coral Zooxanthallae is a genus among the Dinoflagellata It will loose its flagella and live in the tissue of corals Phylum: Cnidaria Class: Anthozoa: (corals) In general, the class is comprised of the vast majority of species commonly referred to as sea anemones and corals. existing exclusively as polyps, completely without a medusa life stage Anthozoa into three subclasses: I. Octocorallia, II. Hexacorallia, III. Ceriantipatharia Class: Anthozoa: (corals) Sub class: Octocorallia (Soft corals) Octocorallia: commonly known as soft corals not very closely related to the true corals (Scleractinia) The polyps of octocoralliarians have eight tentacles divided into five or six orders (Telestacea, Alcyonacea, Gorgonacea, Pennatulacea, Helioporacea, and sometimes Stolonifera) Tubipora musica (blue coral) Family Plexauridae: Menella sp. Family Plexauridae : Dendronepthya sp. Kukenthal, 1905 Colony shape: bushy Habitat : depth above 10 , with clear water ( visibility 8 m) Family Plexauridae : Echinomuricea sp. Verrill,1869 Class: Anthozoa: (corals) Sub class: Octocorallia Most do not develop skeletons Most octocorals form spicules within their tissues, and some produce calcified holdfast structures or long, rodlike internal supports. All of the octocorals are colonial, including the sea fans and sea whips (Gorgonacea). Class: Anthozoa: (corals) Sub class: Hexacorallia Order: Scleractinia (True Stony Corals) The scleractinians are the largest group of anthozoans, with approximately 3600 extant species This prominent taxon provides the calcium carbonate building blocks for the world’s coral reefs calcium carbonate skeleton is secreted by the epidermis and is present in all members of this order The order Scleractinia is usually divided into 18 families Class: Anthozoa: (corals) Sub class: Hexacorallia Order: Scleractinia (True Stony Corals) Scleractina are classified by morphological features of colony growth and various soft-tissue features The Acroporidae are mostly in two genera, Acropora and Montipora. These are fast-growing forms with both asexual and sexual reproduction. Some scleractinians, like members of the genus Fungia, are solitary and can be relatively large: up to 50 cm in diameter Acropora nasuta Montipora capricornis Fungia Class: Anthozoa: (corals) Sub class: Hexacorallia Hexacorallia is comprised of six orders, two of which are extinct, order Rugosa and Tabulata. I. order: Actinaria : sea anemones II. order: Zoanthidia : colonial anemones Class: Anthozoa: (corals) Sub class: Hexacorallia Order: Actinaria (sea anemones) I. Most of the soft-bodied anthozoans known as sea anemones are classified in the Actinaria II. Actinarians generally have column-shaped bodies with the mouth at one end and a muscular pedal disk for attachment to substrates at the other. I. Actinarians have soft bodies and do not form hard parts, some coat themselves with sand grains and/or mucuslike secretions. Sea Anemones (with sea urchins) Class Anthozoa: Sea Anemones Class: Anthozoa: (corals) Sub class: Hexacorallia Order: Actinaria (sea anemones) I. Most actinarians are relatively sessile, either not moving or moving very slowly by contractions of the pedal disk II. Some anemones burrow into sand, and a few can swim short distances III. Actinarian anemones can reproduce either sexually or asexually IV. They do not form true colonies with permanent tissue connections between members, as seen in the superficially similar zoanthiniarian anemones Class: Anthozoa: (corals) Sub class: Hexacorallia Order: Zoanthidia Small group of polypoid anthozoans that differ from most sea anemones (Actinaria) in details of internal anatomy. unlike most sea anemones, zoanthiniarians can form true colonies in which all members are connected by common tissue. Zoanthiniarians make no hard parts and leave no fossil record However, they are more closely related to extinct coral taxa (Tabulata and Rugosa) than they are to other soft-bodied anthozoans Genus: Zoanthus Class: Anthozoa: (corals) Sub class: Hexacorallia Order: Zoanthidia Sub order: Brachynemina Family: Zoanthidae Genus: Zoanthus This taxon is often referred to as intermediate in form between hard corals (Scleractinia) and sea anemones (Actiniaria), as most species lack a skeleton and yet are colonial. Zoantharians are widely distributed and