Porifera and Cnidaria

• Kingdom Animalia


  Metazoa - multicellular animals with at least some body organization
• Metazoa comprises


  • Parazoa - lack tissue organization, Porifera
  • Eumetazoa - cells organized into true tissues, more complex tissue organization than Parazoa, e.g. Poriferans, Cnidarians, worms, molluscs, arthropods, humans
• Scientists generally agree about the taxonomic classification of 36 animal phyla (of Kingdom Animalia)
• Scientists disagree about how these 36 animal phyla are interrelated
• Traditional reconstructions lump together phyla that share major features of body plan
• New reconstructions employ molecular comparisons of rRNA and other genes
• Major Invertebrate Phyla of Kingdom Animalia

  • Porifera - 10,000 species
  • Cnidaria - 9,500 species
  • Platyhelminthes - 25,000 species
  • Nematoda - 80,000 species
  • Annelida - 9,000 species
  • Arthropoda - 1,000,000 species
  • Mollusca - 110,000 species
  • Echinodermata - 6,000 species
• Phylum Porifera - Sponges


  Animals with pores
• Porifera is the first and most primitive phylum of the kingdom Animalia
• General Characteristics of Phylum Porifera


  • No definite symmetry or radially symmetrical
  • Body multicellular with neither tissues nor organs
  • Made up of two layers of cells, an ectoderm/epidermis and an endoderm, with a non-cellular gelatinous material called mesohyl
• General Characteristics of Phylum Porifera


  • They are full of pores and channels that lead to an inner chamber (spongocoel or atrium)
  • There is no true body cavity
  • Often have a skeleton of spicules made of silica, spongin made of collagen, or in some species exoskeleton made of calcium carbonate
• General Characteristics of Phylum Porifera

  • All sponges are sessile or sedentary
  • Reproduce sexually or asexually, with sexual reproduction being either gonochoristic or hermaphroditic
  • Have a distinct larval stage which is planktonic
• General Characteristics of Phylum Porifera


  • No nervous system
  • All are filter feeders
  • Colorful (orange, red, purple, green)
  • Size: 1 - 200cm in height
• Nutrition


  • They are filter feeders and can filter 20 litres of water daily
  • Inhalant canals, choanocytes and ostia serve as sieving system for particulate substances
  • Feed on bacteria, microscopic algae, protists and suspended organic matter
  • Food is passed on to amoebocytes and digested
  • Pinacocytes used to ingest larger particles that cannot enter inhalant canal
• Asexual reproduction in sponges


  • Regeneration - a missing part gets established and grows into an adult
  • Budding - a new sponge develops from an older one and finally breaks off to be a separate individual
  • Production of gemmules - asexual capsules (buds) containing aggregations of archaeocytes laden with food reserves and an outer hard covering
• Many freshwater sponges can produce gemmules that are resistant to freezing and drying, and release archaeocytes when conditions are favourable to organize into a new sponge
• Sponges are mostly marine, but there are some freshwater inhabitants
• Sponges can be found in deep sea or in coastal marine waters, with about 10,000 species known
• Morphology and functions of sponge cells

  • Spicules - made of silica or calcium carbonate, some sponges have a skeleton of spongin fibers made of collagenous material
  • Pinacocytes (epidermal cells) form the ectoderm/epidermis
  • Porocytes are dispersed in the pinacoderm and form the channels/ostia for water entry
• Morphology and functions of sponge cells

  • Choanocytes (collar cells) are flagellated cells that draw water in through the ostia and move it out through the osculum, trapping food particles
  • Mesohyl is the gelatinous material between the pinacoderm and choanocytes, containing amoeboid cells (amoebocytes or archaeocytes) that phagocytize and digest food
• Classes of Phylum Porifera

  • Calcarea - calcareous sponges with calcium carbonate spicules
  • Hexactinellida - glass sponges with four- and/or six-pointed silica spicules
  • Demospongiae - most diverse class with spongin and/or silica spicules
  • Homoscleromorpha - recently recognized class with small calcareous spicules or aspiculate
• Calcarea are strictly marine, found globally but mostly in shallow tropical waters
• Hexactinellida are not common, found in deep waters from 450 to 900 metres, particularly in Antarctic and Northern Pacific
• Demospongiae is the most diverse class, comprising 76.2% of all sponge species worldwide
• Homoscleromorpha has 117 species, with spiculate and aspiculate genera, and are massive or encrusting in form
• Viviparous


  Giving birth to live young
• Trichimella


  Distinct larva
• Demospongiae


  Most diverse class in the phylum Porifera, includes 76.2% of all sponge species with nearly 8,800 species worldwide
• Demospongiae


  • Predominantly leuconoid in body plan
  • Spicules made of fibers of the protein spongin, the silica, or both
  • All large sponges are in this class (the largest species are over 1 m)
  • Mostly marine
  • Reproduce both sexually and asexually
• Homoscleromorpha


  Fourth class of sponges, 117 species
• Homoscleromorpha


  • Spiculate genera (mainly) and aspiculate species (in few genera)
  • Spicules, where present, are small and calcareous with little variations
  • Massive or encrusting in form
  • Have flagellated exopinacocytes and endopinacocytes
  • Reproduce sexually and are viviparous
• Amphiblastula


  Oval, hollow flagellated larva
• Asconoid


  Simple vaselike structure, the ostia lead directly into the spongocoel
• Asconoid structure puts limitations on size; (increase in volume without a corresponding increase in the surface area for choanocytes)
• Syconoid


  The flagellated choanocyte layer has undergone folding forming finger like projections, water enters the sponge through incurrent canals then dermal pores, which pass it along to radial canals through to the spongocoel
• Leuconoid


  Have a highly branched canal system, ostia connect to branched incurrent canals which lead to numerous small chambers in which choanocytes are located, spongocoel is absent, multiple oscula exit
• Leuconoid sponges exhibit a significant increase in surface area and are, therefore, among the largest sponges
• Cnidaria


  Animals with stinging nettle (cnidos), also known as coelenterates, are the second least developed phylum of the kingdom Animalia and are the first group, according to level of advancement, to have true tissues
• Cnidocyte


  Stinging cell
• Cnidarians


  • Have blind-ending cavity called gastrovascular cavity, which function in digestion, exchange of gases and metabolic wastes as well as for discharge of gametes
  • Nervous system is made up of a nerve net
  • Usually have alternation of generations between polyp and medusa
  • Are uncephalized animals with one body opening, the mouth
  • Have radial or biradial symmetry