CHAP 8 (Invertebrates)

• KINGDOM ANIMALIA objectives


  Explain about animal’s origin.

  List out animal’s general characteristics.

  Describe the phyla of invertebrates, by explaining and differentiating their characteristics besides discussing their life cycle.
• Origins of animals


  * Many biologists agree that animals evolve from protists (protistan) about 900 million years ago.

  * It is hypothesized that animal may originate from different lineages. -These lineages descended from more than one group of protistan-like ancestors.
• FOUR origins of animals

  1. Choanoflagellates
  2. Ciliates
  3. Spherical Colonies
  4. Placozoans
• 1. Choanoflagellates


  A group of protists that are suspension feeder and possess(memiliki) collar cells

  
• 2. Ciliates

  Unicellular ciliates – Paramecium that possess two types of nucleus

  
• 3. Spherical Colonies

  Volvox colony that becomes mutate

  
• 4. Placozoans

  The placozoan "Trichoplax adhaerens" that is a plate-shaped, two layered animal with no symmetry and no organs.
• General characteristics of Animal

  * Animals are multicellular eukaryotes with tissues arranged in organs and organ systems. The body cell of nearly all species has a diploid chromosome number.

  * Animals are heterotrophic - obtaining carbon compound and energy by ingesting other animals/by absorbing nutrients from them.

  * Animals require oxygen for aerobic respiration.

  * Animals reproduce sexually and in some cases asexually or both.
• General characteristics of Animal

  * Most animals are motile during at least part of their life.

  * Animal life cycles include a period of embryonic development. Briefly, mitotic cell division will transform an animal zygote into a multicelled embryo. Embryonic cell will give rise to primary tissue layers (ectoderm, endoderm and in most species, mesoderm) which later will transform to tissues and organs.
• Variations in body plans.

  Comparison between the similarities and differences of animal can be made using six basic features that involve variation in their body plans.

  1. Existence of Backbone
  2. Body Symmetry and Cephalization
  3. Type of guts
  4. Body Tissue
  5. Coelom
  6. Segmentation
• Variations in body plans - Backbones

  1 Existence of backbones

  *Animals with backbones are vertebrates (about 50,000 species) while those without backbones are considered invertebrates (more than a million species)
• Variations in body plans - Symmetry

  2 Body symmetry and cephalization

  * Those with radial symmetry have body parts arranged regularly around a central axis

  
• Variations in body plans - Symmetry

  * For hydra, with a radial symmetry, a cut at the center will divide it into equal halves. Any other cut will divide them into equal quarters.

  * Radial animals live in water because their body plan is adapted to receive food drifting/swimming towards them from any direction
• Variations in body plans - Symmetry

  * Most animals are bilaterally symmetrical. Animals with bilateral symmetry have a body axis passing from an anterior end (front) to a posterior end (back). The body is separated into right and left sides along this main axis, and has a dorsal surface (backside) and ventral surface (underside).

  * These types of animals have the tendency to move head first through the environment.

  
• Variations in body plans - Symmetry

  * For animals with bilateral symmetry, there is an addition to their evolution, known as cephalization.

  * Cephalization can be defined by having a concentration of the nervous system and feeding features at the head end.

  
• Variations in body plans - Gut


  3 Type of gut

  * The place where food is digested is the gut. Some animals have saclike gut with one opening only, which is the mouth. In it, food is digested and then absorbed into the internal environment.

  * A tubular gut is a “complete” digestive tract, with two openings (mouth and anus) for continuous food processing, often through specialized regions to digest, absorb, store and get rid of material.

  
• Variations in body plans - Tissues

  4 Body tissues

  * Most animals are tripoblastic. They posses three germ layers;

  • Ectoderm – outer germ layer that give rise the skin and nervous tissue
  • Mesoderm – that give rise to most other body structures like muscles, skeletal structures and circulatory system.
  • Endoderm – forms the lining of the digestive tube and other digestive structure.

  
• Variations in body plans - Coelom

  5 Coelom

  * Triploblastic animals can be classified based on the presence and type of body cavity / coelom.

  * The body cavity or coelom is a fluid - filled space in between the gut and the body wall of most bilateral animal.

  
• Variations in body plans - Coelom

  * A coelom which is lined with peritoneum is a tissue lining located at the space between the gut and the body wall. This tissue lining helps hold the organs in place and allows internal organs to expand and operate freely. Animals with coelom are known as coelomate animals.

  
• Variations in body plans - Coelom

  * Animals such as roundworms, have a “false” coelom (pseudocoelom) which are not lined with peritoneum. Therefore, their pseudocoelom is an internal space with a direct contact with the wall of the digestive tract (gut).

  
• Variations in body plans - Coelom

  * Some animals (flatworms) do not have a coelom (acoelomate), therefore they lack body cavity. Instead, tissues fill the region between the gut and body wall.

  * Example - flatworms

  
• Variations in body plans - Segmentation

  6 Segmentation

  * A segmented animal is composed of repeating body units that may or may not be similar to one another. As an example is the earthworm, which possess similar repeated body units.

  * The segments may be grouped and modified for specialized tasks, as for example in insects.
• Animal kingdom phyla

  
• Animal kingdom phyla

  
• Phylum Porifera (Sponges)

  Calcarea and Silicea

  * Sponges are different from other animals because have an asymmetric body (no symmetry).

  * Their body only contains cells, therefore they lack any true tissues (because they do not have any germ layers) and they also lack organs.

  * Sponges (Phylum Porifera) are mostly marine animals, of widely varying size and shape while only a few are freshwater species.

  * Sponges are habitat for many other animals, such as worms and shrimps. Their sizes varies, some big enough to sit in, some as tiny as fingernails.
• Phylum Porifera (Sponges)

  Calcarea and Silicea


  * Sponges are known formerly as Porifera because they possess hundred of tiny pores.

  * The typical body of a sponge consists of hundreds of pore (ostia). * Water will enter the sponges from the ostia, and passes through the central cavity, or spongocoel and flows open through the sponge open end called the osculum.

  
• Calcarea and Silicea

  Cell types

  The sponges have four different types of cells.

  1. Flattened cell called the pinacocyte lines the exterior surface of the sponges.
  2. Tubelike cells called porocyte form the pores of a simple sponge. They can regulate a sponge diameter by contraction.
  3. Collar cells (choanocyte) that make up the inner layer. Each cell is equipped with a tiny collar surrounding the base of a flagellum.
  4. Amoeboid cells (amoebocyte) that is located in the mesohyl.

  
• Calcarea and Silicea

  Microscopic View of a Poriferan Wall

  
• Digestion in Phylum Porifera (sponges)


  • Sponges are suspension feeders. They filter a large amount of water for food.
  • Collar cells are their food-trapping structures. By means of their beating flagella; these cells move large volumes of water in through many microscopic pores and chamber in their body.
  • They trap the suspended food particles in their microvilli collars and engulf/transfer the food in the choanocyte where there are a number of food vacuoles that function in digestion.
• Digestion in Phylum Porifera (sponges)


  * The digested food product will be transferred to the amoeba-like cells (amoebocyte) in the located inside the mesohyl / matrix.

  * Amoeba-like cell will later function in further breakdown, storage and distribution of food

  
• Digestion in sponges


  1. Water moves in through microscopic pores and chambers due to beating flagella of collar cells
  2. Suspended food particles trapped in microvilli collars of collar cells
  3. Food engulfed and digested in food vacuoles of choanocytes. Choanocytes have food vacuoles that function in digestion
  4. Digested food transferred to amoeba-like cells (amoebocytes) in mesohyl/matrix
  5. Amoebocytes further break down, store and distribute food
• Protection in Phylum Porifera (sponges)


  * Between the two layers of cells (pinacocyte and choanocyte) there is a semifluid matrix (gelatin-like) called mesohyl.

  * There are a number of needle spicules (made of silica/calcium carbonate) that functions as skeletal support system

  
• Protection in Phylum Porifera (sponges)


  * These skeletal elements are the reason why sponges are successful in their survival. There are two reasons behind this;

  1. Most sponge predators dislike their taste because sampling them is equivalent of eating a mouthful of glass splinters embedded in fibrous gelatin.
  2. Furthermore, most sponges stink / are smelly
• Reproduction of Phylum Porifera (sponges)


  * Sponges reproduce sexually and sometimes asexually

  * Sexually, sperm are released into the surrounding water to be picked up by a nearby sponge and directed to the egg within the mesohyl by amoebocyte. The developing embryos are retained in the matrix. The zygote will then develops into a free swimming flagellated larvae that will attach to a substrate and settle down to its sessile life.

  
• Reproduction in Phylum Porifera (sponges)

  Asexually, sponges reproduce by :

  1. Fragmentation, where small fragments break away from the parent and grow into new sponges.
  2. Gemmules formation, formed by amoeba-like cells. These are clusters of spore-like collection of sponge cells that can survive until living conditions improve. They are protected by extreme cold or drying out. Later, when favorable condition improves, the gemmules germinate and establish new colony of sponges

  
• Phylum Cnidaria 


  1 Tissue emerge

  • Cnidarians are diploblastic, where they possess only two germ layers/tissue layers. Their body lack the mesoderm layer.
  • Cnidarians have diversified into a wide range of both sessile and motile forms including jellies, corals, and hydras.
  • Most cnidarians live in the seas; only a few species live in freshwater.

  2 Symmetry

  As adults, they possess radial symmetry
• Phylum Cnidaria


  3 Nematocyst

  • They possess unique stinging devices called nematocysts / cnidocyte.
  • When stimulated at a small projecting trigger on its outer surface, the capsules with tubular threads will be released.
  • The discharged threads have sticky prey-trapping substances to capture prey and fend off predators.
  • There are some threads that are equipped with barbs/spines that contain a toxic substance that could paralyze preys with the painful stings.

  
• Phylum Cnidaria


  4 Body plan

  • Most cnidarian consist of two body plans, the polyp and the medusa.
  • The medusa resembles an umbrella and floats in the water.
  • The oral arms surround the central mouth under the bell.
  • The polyp is tube like and is usually attached to some substrate at the other end. It may be solitary or part of a colony.

  
• Phylum Cnidaria


  4 Body plan

  • In Cnidarian, - Outer ectoderm layer form the epidermis that covers the body - Inner endoderm layer form the gastrodermis that lines the digestive cavity.
  • These thin layers are separated by a gelatinous material called mesoglea.
  • Medusa has abundant mesoglea that is helpful in providing buoyancy and serves as a skeleton.
  • Polyps have little mesoglea but use the water in their guts as a hydrostatic skeleton.
• Phylum Cnidaria


  5 Nervous system

  * They have a nerve net (with interacting nerve cells) running through both layers and it coordinates the animal’s response to stimuli.

  * Both epidermis and gastrodermis possess cells specialized to contact that are called contractile cells. Contractile cells carry out responses by contracting and lengthening itself.