Phylum Cnidaria PDF Fall 2024

Phylum Cnidaria BZ 212 Animal Biology - Invertebrates Fall 2024 Zach Grochau-Wright, PhD  Diploblastic Body Plan Only two germ layers with a layer of mesoglea between. Mesoglea is mostly extracellular matrix but could include some cells depending on the organism The...

Phylum Cnidaria BZ 212 Animal Biology - Invertebrates Fall 2024 Zach Grochau-Wright, PhD  Diploblastic Body Plan Only two germ layers with a layer of mesoglea between. Mesoglea is mostly extracellular matrix but could include some cells depending on the organism The only diploblastic animals are Cnidaria and Ctenophora  What can we learn from resolving relationships? Were early animals Placozoan-like, with Cnidarians and Bilaterian later evolving muscles and neurons? Did the ancestor of Placozoans have muscles and neurons then lose them? Did diploblastic development evolve before or after sponges diverged from other animals? Did nervous systems evolve independently in Ctenophora and Cnidaria + Bilateria or are nervous Laumer et al. 2018 eLife systems homologous among these groups?  Cnidaria Characteristics Radial symmetry or variations thereof Diploblastic, tissue-level organization Gelatinous mesoglea between the epidermal and gastrodermal tissue layers, acellular or with scattered ectodermally derived cells. Single gastrovascular cavity. Nerve cells organized into subepidermal and subgastrodermal nerve nets Specialized cells, called cnidocytes, used in defense, feeding and Nerve net attachement Most are predators Circulation, Gas Exchange, Excretion, Osmoregulation No specialized circulation, gas exchange, excretion, or osmoregulatory systems. Circulate water and nutrients through gastrovascular cavity. May be folded into mesenteries (i.e. Anthozoa) or branched into radial canals (i.e. Medusozoa) to increase surface area. Freshwater species periodically expel excess water through gastrovascular cavity Alternation of Generations Many (but not all) Cnidarians exhibit an alternation of generations with a sexual medusa stage and an asexual polyp stage Cnidarian Phylogeny  Class Anthozoa ~7,200 species Colonial or solitary polyps Medusae absent Cnidocytes present in epidermis & Anthopleura sola gastrodermis Acropora cervicornis Tripartite series of flaps on cnidae Gametes gastrodermal in origin Gastrovascular cavity divided by mesenteries that bear nematocysts Thick mesenchyme Marine. Anemones and corals. Subclass Octocorallia ~3,000 species Soft corals, sea fans, sea pens Polyps with 8 hollo tentacles, and 8 mesenteries Subclass Hexacorallia ~4,300 species Order Actiniaria Sea anemones (Order Actiniaria) Order Scleractinia Stony corals (Order Scleractinia) Mesenteries in multiples of 6. Reef forming coral anatomy From USGS  Coral Reef Symbiosis Corals form a symbiotic partnership with a type of algae called “Zooxanthellae”. The algae perform photosynthesis and provide sugars to coral. Coral provides protection, nitrogen, and carbon dioxide to algae. Cnidarian Phylogeny Subphylum Endocnidozoa – Class Myxozoa Highly reduced endoparasitic Cnidarians One species Henneguya salminicola has no mitochondrial genome and does not require oxygen! Typically have an Annelid and a Vertebrate host. Cnidarian Phylogeny Subphylum Medusozoa ~3,900 species Class Hydrozoa Class Staurozoa Class Cubozoa Class Syphozoa  Physalia physalis Class Hydrozoa ~3,500 species Cnidocytes present in the epidermis Gametes produced epidermally and always released to the outside of the body Hydra spp. Mesoglea is largely acellular Medusae usually with a velum Many polyps colonial Obelia longissima Gonionemus vertens Some with medusae capable of asexual reproduction. Mostly marine with some freshwater species. Hydra, Obelia. Gonionemus, Physalla. Class Staurozoa “Stalked jellyfish” – Sessile Stauromedusae Develop from benthic planula larvae Eight tentacles surrounding the mouth Attachment to substrate by adhesive disk Sexual reproduction only Marine only Class Scyphozoa Medusa prominent in the life history Polyp small or absent Gametes gastrodermal in origin and released into the gastrovascular cavity Cnidocytecs present in the gastrodermis as well as epidermis Medusa lacks a velum Mesoglea with scattered cells of epidermal origin Aurelia aurita Marine Scyphozoan Reproduction  Class Cubozoa Box jellyfish or Sea wasps Chironex fleckeri Medusa prominent in life history, with velarium Polyps small, directly metamorphize into medusae Highly toxic venom, potentially deadly to humans! Medusa cuboidal in shape with tentacles that hang from each corner of the bell Marine only Scyphozoan & Cubozoan Sensory Structures Rhopalia with multiple sensory structures for detecting light and in some cases images (Ocelli), orientation and pull of gravity (Statocyst), and chemosensory organs.