Exercise 12: Animal Forms

• Symmetry - association of parts with respect to a plane or an axis of reference
• Radial symmetry - is the state of having similar parts regularly arranged about a central axis, the oral-aboral axis. Thus, any plane that passes through the center will divide the animal into 2 symmetrical halves.
• Bilateral animals - one plane that divides them equally from left and right halves that are mirror images of each other.
• Biradial symmetry - uncommon in animals wherein they have exactly two planes of symmetry; body parts on opposing sides of the central axis are similar, but sections adjacent to each other are different.
• From the image, identify the type of symmetry on following species.

  A) Asymmetrical

  B) Bilateral

  C) Radial

  
• What is another word for antero-posterior axis wherein it runs from the animal's head to its tail end?

  Longitudinal axis
• What is another term for medio-lateral axis which runs from left to right of the animal and is perpendicular to the median sagittal plane?

  Transverse axis
• What is another term for dorso-ventral axis wherein runs from the back of the animal to its belly?

  Sagittal axis
• What plane is formed when longitudinal and transverse axes intersect?

  Longitudinal plane
• What plane is formed when transverse and sagittal axes intersect?

  Transverse plane
• What plane is formed when longitudinal and sagittal axes intersect?

  sagittal plane
• Median sagittal plane - plane that divides bilateral animals into symmetrical halves.
• In bipedal animals such as birds and humans what is used in place of the longitudinal plane?

  coronal plane
• What are the 8 main cardinal directions used to point to the relative location of a body part?

  Anterior, posterior, dorsal, and ventral; medial and lateral; proximal and distal
• Medial direction - describes a position that is closer to the mid sagittal plane.
• lateral direction - describes a position farther from the mid-sagittal plane
• Proximal direction - refer to locations closer to the central body mass
• Distal direction - refers to locations farther from the central body mass.
• Label the planes of despair (jk) formed from the intersection of reference axes

  A) Transverse plane

  B) Sagittal plane

  C) Longitudinal plane

  D) Transverse plane

  E) Sagittal plane

  F) Coronal plane

  
• Segmentation - refers to the presence of repeating parts called segments along the antero-posterior body axis.
• External segmentation - condition which segmentation is present in the external appearance.
• Internal segmentation - Segmentation observed in the internal organs and the body cavities.
• False segmentation - internal segmentation with absent external
• True segmentation - both internal and external segmentation
• Regionalization - condition of having distinct body structures arranged from end to end of an animal
• Head - where sensory and nervous structures are concentrated (a condition termed cephalization) can be identified at the anterior end of the animal
• The rest of the body, after the cephalization, then constitutes the trunk.
• In many segmented animals, the trunk is visibly divided into an anterior thorax and a posterior abdomen.
• In crustaceans such as crabs and shrimps, the head and thorax fuse to form the cephalothorax.
• Tail - present in some animals wherein it's found posterior to the trunk
• Neck - found between the head and trunk and it allows the former parts to move independent of each other.
• Appendages - extended outgrowths of the main body axis and mainly function for sensation, feeding and locomotion.
• What are the cephalic appendages that only occur in invertebrates?

  Antennae, eye stalks, tentacles, mouthparts, pleopods, tube-feet, uropod
• Locomotory appendages - paired structures found lateral to the trunk
• What are the locomotory appendages of most animals?

  arms, legs, wings, fins, flippers, lobopods
• Locomotion - displacement of a multicellular animal as a result of its movement against a medium
• What are the modes of locomotion for animals without appendages?

  Pedal wave locomotion, peristalsis, undulatory motion
• Pedal wave locomotion - continuous contraction of longitudinal muscles along the ventral surface of the animal.
• Peristalsis - alternating contraction of circular and longitudinal muscles throughout the body of the animal
• Undulatory motion - Lateral muscles of an animal contract in waves from head to tail. Contractions may be used by the animal to move continuously or in bursts of acceleration.