Exam 2 material

• Phylum Placozo— all marine, asymmetrical adults, low level or organization (no nervous system, no muscles, no digestive system) Possibly diploblatic, small ind. Swim, large ind. Crawl or cilary gliding. Do phagocytotic feeding (endocytosis)

  • No anterior or posterior but does have dorsal and ventral
  • Double layer plate that has several thousand cells
• Placozoa Dorsal cells:

  • Flattened
  • Shiny spheres (lipid droplets that help arrange themselves)
  • Extracellular and positive toxins
  • Monociliate
  • Singe cilium per cell
• Placozoa ventral cells-

  • Columnar cells
  • Most monociliate
  • No shiny spheres
  • May be vaginated for feeding
• Mesenchyme in Placozoa

  • Between dorsal and ventral
  • Non-living gel
  • Ameboid cells
  • Use Pseudopodia to move
• Placozoa Reproduction:

  • Asexual:
  • Binary fission and budding (flagellated buds)
  • Sexual:
  • Not understood
  • eggs in mesenchyme
  • fertilization never observed
  • No survival past 64 cells in lab
• Phylum Porifera: multicellular, sessile, and filter feeders (FLAGELLATED CHOANOCYTES)

  • Have an Aquiferous system
  • Totipotents cells (cells that change form and function)
  • 3 classes of Porifera:
  • Calcarea
  • Hexactinellida (glass sponges)
  • Demospongiae: most sponges
• Porifera body plan- simple tissues, aquiferous system, and totipotent cells

  • Are like a rigid perforated bag
  • Have a spongocoel: cavity inside bag that is lined with choanoderm (collar cells for water flow)
• Choanoderm: generate water currents and circulation

  • Used for food capture (filter feeding)
  • Sperm capture
  • Gas exchange
  • Waste removal
• Pinacoderm- outside of sponge that is lined with pinacocytes

  • Internal cavities of the aquiferous system are called endopinacocytes and lead into the spongocoel
• Ostia are small holes in the pinacoderm that are entrances to the aquiferous system

  • Holes on outside that allow water in
• Osculum- opening where water leaves aquiferous system
• Choanoderm and pinacoderm are both a single cell in thickness
• Mesohyl: between the pinacoderm and choanoderm

  • Acellular, non-living, and gelatenous
  • Contains living cells and spicules (made of silicon and provide structural support)
• Functions of the mesohyl: found in Porifera

  • Digestion
  • Gamete production
  • Skeletal formation
  • Transport of waste and nutrients
• Choanoderm increases folding and therefore increases surface area to volume ratio

  • Helps with absorption of materials and things the cells need
• Asconoid condition:

  • Unfolded Choanoderm

  Synconoid condition:

  • Folded Choanoderm

  Leuconoid condition:

  • Multiple independent chambers of Choanoderm (more contact with water)
• Porocytes (porifera): make up the pores and form the ostia

  • Contractile: can squeeze water to help it move through the aquiferous system
• Choanocytes are not coordinated

  • Flagella move independently
  • Distinct morphology
  • Do phago and Pinocytosis
• Sclerocytes: provide structure and produce spicules

  • Are found in mesohyl
• Archaeocytes: ameboid cells that can differentiate into different types

  • Are motile
  • Functions:
  • Digestion
  • Transportation
  • Reproduction
• Organic poriferan support:

  • Collagen - linked to spongin
  • Calcium- Calcarean sponges
  • Silicon- in spicules
• Inorganic poriferan support: spicules

  • Some lack spicules and are softer
  • Spicules come in a variety of sizes and shapes (# of axes or rays)
• Nutrition in porifera:

  • Intracellular digestion
  • Use archaeocytes for larger particles as it is the lining of intake tubes
  • Choanocytes used for smaller particles and microvilli (partial digestion)
• Excretion and Gas exchange in Porifera:

  • Simple diffusion
  • Choanoderm: helps get rid of metabolic waste from intracellular digestion
  • Release from choanocytes and minimize contact between good and bad
  • Freshwater sponges use contractile vacuoles
  • Do osmoregulation (controls water in and out)
• Poriferan reproduction: both asexual and sexual

  • Asexual: fragmentation, pieces fall off and spread to new areas
  • Gemmules
  • Sexual: gametes
• Gemmule formation: archaeocytes in mesohyl that are doing rapid mitosis

  • Nurse cells (can change what they are to overcome environmental struggles)
  • Are engulfed by archaeocytes and act as food stores
  • Archaeocytes are surrounded by spongin
  • Spicules are integrated and gemmule’s form
• Sexual reproduction in Porifera (broadcast spawning)

  • Most are hermaphroditic (totipotent cells)
  • Won’t self fertilize because cross fertilization is better
  • Choanocytes
  • Look like sperm in a skirt
  • Sperm enter aquiferous system
  • If cross choanoderm, will fertilize mesohyl
  • If captured by choanocytes: lose collar and flagellum and carry sperm to mesohyl
• Poriferan larvae are released into the environment

  • Must go through metamorphosis
• Class Calcarea: calcium based spicules (synapomorphy)

  • Asconoid, synconoid, and leuconoid
  • All Marine
• Class Hexactinellida: glass sponges that have 6-rayed silicon-based spicules

  • Lacks pinacoderm
  • Single plasma membrane and multiple nuclei
  • 1 big cell and lots of nuclei (cyncytial)
• Class Demospongia: 80% of all species

  • Most of these are leuconoid (type of complex sponge)
  • Spongin and silica for support
  • Some without spicules
• Phylum Cnidaria: corals, jellyfish, sea anemonies

  • Dimorphic life cycle
  • Polypoid are sessile and do asexual reproduction
  • Medusoid form (jellyfish): sexual reproduction
• Body plan of Cnidarians:

  • Diploblastic (no mesoderm)
  • Cnidae (stinging cells)
  • Tentacles
  • Gastrovascular cavity
  • Incomplete gut and no anus
  • Mesenchyme and mesoglea are derived from the ectoderm
  • No cephalization (nerve net instead)
  • No organs
• Most Cnidarians are marine

  • Polyp is sessile
  • Medusae is errant
• Synapomorphies of Cnidarian:

  • unique polyp form
  • Planula larva (bilateral)
  • Stinging cells (Cindae)
• Calcification

  • Class Hydrozoa (hydra)
  • Class Anthodoa: anemonies, corals, sea pems
  • Class Cubozoa sea wasps, box jellyfish
  • Class Scyphozoa: jellyfish
• Cnidarian body plan:

  • Ectoderm (adult epidermis)
  • Entoderm: adult gastodermis
  • Mesoglea: mostly acellular gelatinous middle layer
  • Radial symmetry
  • Ring of tentacles that interact in all directions (feeding)
  • Dimorphic life cycle
• Mesoglea is acellular whereas mesenchyme is cellular

  • Hydrozoa has mesoglea
  • Schyphozoa and cubozoa
  • Thick and scattered cells in mesenchyme
  • Anthozoa: thick and many cells in mesenchyme
• Polypoid form is reduced in Scyphozoa and Cubozoa

  • Oral end faces environment

  Aboral end (attache to ventral side)
• Tentacles: surrounded mouth

  • A filiform tentacle tapers to tip. A capitate tentacle has a rounded knob at tip and is composed of cnidae