Bio Lab Practical 2

• Invertebrates are those animals who evolved before an internal bony skeleton evolved
• Invertebrates have other characteristics of animals :

  1. Has eukaryotic and diploid cells
  2. being multicellular
  3. acquiring energy through hetrotrophy
  4. Most have some form of sexual reproduction, but many also reproduce asexually
  5. Most animals are motile to find food and mater
• Asymmetrical - lack symmetry
• animals that have asymmetrical bidy symmetry are sponges
• Radial Symmetry : body parts are arranged around a central axis

  • some may be divided in half through central axis at any angle to produce identical halves
• Organisms with Radial symmetry have a top (dorsal) and bottom (ventral) surface, but no left or right side, and no front or back sides
• Bilateral Symmetry : have body shape which can be divided in half at only one point, midline, to produce identical left and right halves
• Type of symmetry animal has is adapted to its body structure and type of motility
• Animals that are asymmetrical are mostly immobile or sessile
• Animals with bilateral symmety are also typically cephalized and have body parts which propel movement in an anterior direction so that head encounters and senses environmental stimuli which signal food or danger first before thr=e rest of the body is in range
• Cephalized : have an anterior region with sensory and neural structures
• Eumetazoa : having true tissues
• True Tissue are specialized tissue layers that form at an early stage during embryo development that are referred to germ layers
• Animals that form three germ layers are called triploblastic
• Triploblastic :

  1. Endoderm is innermost layer of tissue
  2. Mesoderm forms in middle layer
  3. ectoderm is outermost layer of tissue
• Animals that form only two germ layers are called diploblastic
• Diploblastic :

  Have endoderm and ectoderm but lack mesoderm
• Diploblastic organisms evolved before triploblastic organisms, only multicellular animal that is diploblastic are the Cnidarians
• Triploblastic animals are further classified according to whether they have one of two types of embryonic body plan development : protosome or deuterosome
• Protostomes : first opening of embryo to form is the mouth
• Deuterostomes : first opening of an embryo to form is anus, and the mouth is second opening to develop
• Another development characteristics of triploblastic animals is type of coelom or body cavity they have
• Acoelomate : Animals that lack a body cavity
• Coelomate : Animals with a body cavity that is fully lined with mesoderm tissue
• Pseudocoelomate : Animals that have a body cavity partly lined with mesoderm tissue
• Sponges evolved from an ancestral protist that was single celled

  • lived in closely organized colonies
  • selective benefits of colonal organization gave rise to multicellular organisms
• Sponges

  extant protist group most closely related to animals are choanoflagellates
• Sponges

  Choanoflagellates : Free living single-celled organisms have a collar-like feeding structure composed of microvilli surrounding a flagellum that assists in filter feeding and propels cell movement
• Sponges are thought to be first type of multicelluar animal to evolve, and choanoflagellates are grouped as sister taxa within animal clade Choanozoa
• Sponges

  • Do not have tissue germ layers
  • Cell function is not fixed or determinded during development, each individual cell in a sponge can migrate or be moved to other location in sponge and take on different function based on where new location is required there
• Sponges

  • are totipotent : have potential to differentiate into different cell types
  • Archeocytes : sponge cells in undifferentiated state
  • Aquatic
  • May live singly or in colonies
  • lack typical animal properties of symmetry and motility
  • typically sessile (immobile and often fixed to a subtrate)
• Sponges

  • Reproduction in sponges occurs both asexually by budding or fragmentation, or sexually by the production of eggs or sperm
• Sponges

  acquire food by filter feeding : water flow is generated by flagellated choanocytes or collar cells that line that cavity of their osculum

  • draw water in through propcyte cells which form pores
• Sponges

  Water flows over villi of collar cells which trap food particles and continues out opening of osculum cavity

  • Trapped food particles are engulfed by phagocytosis, and digested by nearby ameobocytes
• Porifera : Sponges

  A) Amoebocytes

  B) Epidermal Cells

  C) Porocytes

  D) Osculum

  E) Spicules

  F) Choanocytes

  G) Amoebocytes

  
• Sponges

  1. Porocytes : Form pores, small openings in walls of sponge that allow water to flow in
  2. Epidermal Cells : Form body or wall of a sponge
  3. Spicules : hard, sharp spiky structures made of calcium carbonate or silica, provide structure and defense
• Sponges

  4. Amoebocytes : ingest and digest food particles by phagocytosis, form spicules, may differentiate into other cell types

  5. Choanocytes : flagellated collar cells that generate water flow and function for filter feeding

  6. Osculum : Hollow interior cavity of a sponge, how water exits a sponge
• Cnidaria : Soft bodied aquatic invertebrates which include jellyfish, anemones, and corals.
• Cnidarians

  • Have true tissues
  • are Diploblastic, means they have two tissue layers
  • Since they lack mesoderm, they lack any type of coelom or body cavity
  • Typically exhibit a form of radial symmetry
• Cnidarian

  • Reproduction may be accomplished by asexual budding or strobilation ( sexually by production of gametes and fertilization)
  • Highly mobile larval stage Cnidarian is formed by fertilization and is termed a planula
  • Two basic body forms in Cnidarian lifecycles, a polyp form and a highly mobile medusa form