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Station 1
Introduction to the Kingdom Animalia
There are well over 1 million extant species of animals. Many of these forms are very familiar to us like birds, earthworms, or snails. Others may not be as easily recognized as animals at first glance, like a colorful sponge or a slow-growing staghorn coral.
Members of the animal kingdom are:
- eukaryotic
- heterotrophic by ingestion
- multicellular
- composed of cells not surrounded by a cell wall and rely on structural proteins (like collagen) for support
- composed of specialized tissues (exception : sponges) which arise from embryonic germ layers
- typically motile; not sessile like plants
- diploid and reproduce sexually
Most zoologists agree that the ancestors to animals were colonial choanoflagellates (cells with a flagellum surrounded by a collar) and that the first animals lived some 700 million years ago.
Animals may be classified based on grades of body plans ; a set of morphological or developmental characteristics. The processes of evolution have altered the generalized body plans to allow each particular animal to be successful in its environment.
During the next few lab exercises, you will be closely examining various animal forms. Therefore, it will be important that you understand how to describe the locations of various animal body parts. Listed on page 2 are anatomical terms that you should become familiar with to fully understand animal anatomy.
In this exercise, we will use the human skeleton and the bone position to illustrate the anatomical terms. Using the human skeleton and laminated sheets locate and label each of the human bones.
The Animal Kingdom and Sponges
Laboratory
Anatomical terms
Dorsa l - near or towards the back Ventral - near or towards the belly Lateral - near or towards the sides; right and left Median – near or towards the middle Anterior – near or towards the front end Posterior – near or towards the hind end Caudal – refers to the tail Cranial – refers to the head
Longitudinal – parallel to the long axis from head to tail Transverse – perpendicular to the long axis from head to tail Superficial – near the surface Deep – below the surface; under Pectoral – relates to the chest Pelvic – relates to the hips region Proximal – directional term; close to main part of the body Distal – directional term; far from the main part of the body
Station 2
Animal Phylogeny
In this exercise, we will examine the different morphological features commonly used to classify animals.
Tissues By definition, most animals have a body composed of tissues. However, the sponges (Phylum Porifera) are an exception as they lack such tissues and are known as parazoans. Animals classified as eumetazoans develop from an embryo that develops through a process known as gastrulation. During gastrulation, the embryo develops distinct tissue layers (called germ layers ). These germ layers ( endoderm, ectoderm or mesoderm ) will give rise to the more complex tissues and organs as the animal develops. Endoderm tissue forms the lining of the digestive tube; ectoderm tissue forms the outer covering of the animal and in some cases, the central nervous system. Mesoderm tissue may produce muscle and the remaining tissues and organs. Some eumetazoans are diploblastic and only develop endoderm and ectoderm (i.e. Hydra). Others are triploblastic possessing a mesoderm layer between the ectoderm and endoderm (i.e. earthworms and frogs).
Symmetry Animals are also classified based on symmetry. Parazoan sponges lack symmetry and are known as asymmetrical. Eumetazoans may exhibit radial symmetry or bilateral symmetry. Radial symmetry produces only dorsal and ventral sides; no anterior or posterior; no lateral sides. Bilateral symmetry produces right and left lateral sides as well as dorsal and ventral sides. Many animals that exhibit bilateral symmetry also have an anterior and posterior orientation. Sensory structures are normally positioned anteriorly forming the head (the development of a head is an evolutionary trend known as cephalization ). Most diploblastic animals are radially symmetrical while triploblastic animals are bilaterally symmetrical.
Label the figures above- radial symmetry, bilateral symmetry, dorsal, ventral, anterior, posterior
Body Cavities Triploblastic animals may be further broken into three distinct groupings based upon the presence or absence of a body cavity.
Acoelomate animals (i.e. planarian) do not have a body cavity positioned between their digestive cavity and the outer body wall. Their bodies are a solid mass of tissue.
Pseudocoelomate ( pseudo = false) animals (i.e. a roundworm) have a hollow cavity located deep to their outer body wall. This cavity is filled with fluid and surrounds the digestive tract. It is known as a false cavity (pseudocoelom) because mesoderm tissue only surrounds the cavity on one side; the endoderm tissue forms the other cavity boundary.
Coelomate animals (i.e. earthworms and frogs) have a hollow cavity which is completely lined with mesodermally-derived tissues. There are advantages to having a coelomic cavity. For example, muscle (derived from mesoderm) may move food through the digestive system independently from the movements of the outer body. Coelomates may be categorized as protostome sor deuterostomes based upon embryonic development events. For example, in protostomes, the blastopore becomes the anterior opening of the digestive tract (mouth). In deuterostomes, the blastopore becomes the anus, while the mouth forms secondarily.
Label the figures above – ectoderm, endoderm, mesoderm, acoelomate, pseudocoelomate, coelomate
- List the three germ layers that develop in a bilaterally symmetrical animal.
- Fill in the chart below by listing the type of symmetry observed in each specimen:
- Name a triploblastic organism you examined today.
- Name a diploblastic organism you examined today.
- Define cephalization.
- What is the difference between a pseudocoelomic cavity and a coelomic cavity?
- Fill in the chart below by listing at least one representative organism for each of the nine phyla.
Phylum name Examples
Animal Type of symmetry
Sponge
Flatworm
Insect
Jellyfish
Human
Station 3
The Phylum Porifera – The sponges
Sponges are parazoans that live in marine or aquatic habitats. They are the simplest animals as their body does not consist of true tissues but rather a loose colony of organized cells. Typically, a sponge consists of amoebocytes , choanocytes , porocytes and epidermal cells with each cell having a particular function. The amoebocytes may digest food and distribute the food to other cells, as they are capable of locomotion throughout the sponge’s body. The epidermal cells form the outer protective surface of the sponge and surround the porocytes, which form the openings into the sponge’s body.
As sessile organisms, sponges grow attached to rocks, coral, shells, or other large submerged objects relying upon their food coming to them. Sponges obtain nutrients by filtering the water column using flagellated collar cells (choanocytes) to assist with the movement of water through their porous bodies. As the flagella move, water is drawn through the porocytes and suspended nutrients are collected in the collars and phagocytized.
Spicules or a framework of a fibrous protein called spongin forms the extracellular matrix and determines a sponge’s shape. Spongin in bath sponges makes them useful in cleaning things and for absorbing water.
Use the drawing below to label choanocyte, spicule, amoebocyte, porocyte, epidermal cell, extracellular matrix
Sponge anatomy
Review Questions
- Compare the texture of a bath sponge to a glass sponge.
- Define sessile.
- How do sponges obtain nutrients?
- What type of spicules are found in a glass sponge?
- What is the composition of Grantia’s spicules?
