- Lab 2
During labs when we examine different Phyla of animals, we will use a set of tables to help compare and contrast them. The tables are constructed with the different Phyla (groups of organisms) in rows and characteristics in columns. The characteristics refer to morphological, developmental, and physiological traits. Some will be very easy to understand and you may already be familiar with them. Other will be new to you and we will go over them at the beginning of the lab.
Animal Characteristics Chart 1
Animal Characteristics Chart 2
Kingdom Animalia: a group of multicellular, eukaryotic, heterotrophic organisms. Members of the kingdom Animalia evolved from a common ancestor that would have been similar to the current choanoflagellate protozoans (Hickman et al., 2001, fig. 11-14). Members of Kingdom Protizoa are unicellular eukaryotes but often live in aggregates, called colonies. WIthin the colony, some cells can be specialized to perform certain roles (e.g., collect food, provide protection). Over long periods of time the different types of cells become dependent on each other and multicellularity develops.
Subkingdom Parazoa: The first group of organisms we will examine are separated from other animals because they are weakly multicellular. Although sponges are organisms made of many cell types that perform different tasks to help keep the individual alive, the cells can survive independent of each other for extended periods of time. Although sponges appear to be intermediate between the choanoflagellate-like ancestor to Kingdom Animalia and the rest of the kingdom Animalia, current evidence indicates that sponges branched off independently and are not ancestors to the rest of Animalia.
Phylum: Porifera - [pore bearer] sponges. (Hickman et al., chapter 12)Sponges are aquatic organisms. Most sponges occur in marine habitats although one freshwater family is found in streams of Kentucky. The body is classified as having no symmetry, or being radially symmetrical. While no true tissues are present, there are two body layers; the outer ectodermis and inner endodermis. Between these two is a middle acellular layer of jelly mesophyl. Sponges feed with speicialized cells that capture food particles and digest the material intracellularly. Support for the body comes from the spicules (spines) and proteins of the acellular mesohyl. Sponges reproduce sexually and asexually.
Specialized cells present:
outer covering - pinocytes and porocytes
middle area - amoebocytes and sclerocytes
inner channels - choanocytes (collar cells)
The Classes of Porifera are based on the type of spicules produced and body organization.
| Classes of Porifera: | Organization Categories |
| Calcarea - spicules of calcium;small, shallow ocean forms. | Ascon - simplest organization |
| Hexactinellida - glass sponges;6-ray silicon spicules; deep ocean forms. | Sycon - intermediate organization |
| Demospongiae - simple silicon spicules,95% of all sponges; all depths of oceans; 150 freshwater forms. | Leucon - most complex organization. |
| Sclerospongiae - silcon and calcium skeleton; few types in deep, hidden ocean bottoms; hard like corals. |
Subkingdom Eumetozoa: Animals with true tissues. Eumetazoa includes all of the other Phyla we will examine throughout the semester. Eumetazoans are characterized by the presence of tissues, specialized cells that act together to perform certain tasks.
Phylum Cnidaria: [nettle-like] (previously called Coelenterates), includes corals, jellyfishes, anemones. (see Hickman et al. chapter 13)
Cnidarians have radial symmetry and the body plan has two distinct layers: the outer ectodermis and inner endodermis. They are separated by a non-cellular middle layer called the mesoglea. The mouth is surrounded by soft tentacles; food enters the sac-like the gastrovascular cavity where enzymes digest it. Any undigestible material is expelled back out the mouth (there is no anus!). The nervous system consists of a branching nerve-net. When stimulated by the nervous system, contractile cells can change the shape of the body to provide for movement. Cnidarians can reproduce asexually and/or sexually with alternation of generations in some - polyp (asexual) and medusa (sexual) stages. Monoecious or dioecious ( Class Scyphozoa). Sexual reproduction results in the production of a planula larva which typically develops into the sessile (attached) polyp stage. One of the most unique, and well known, traits of Cnidarians is the presence of specialized stinging cells in the epidermis. The stinging cells, called Cnidocytes, containing Nematocysts, dart-like, structures capable of injecting a toxin into prey (or unsuspecting swimmers). Cnidocytes are responsible for the sting when you touch a jellyfish.
Cnidarian life cycles represent one or both of two life forms: the sedentary or attached polyp stage and/or the free-swimming medusa stage. Many Cnidarians exhibit an alternation of hydroid and medusa stages in the life cycle, but differ from typical plant life cycles in that both phases are diploid.
Classes of Cnidaria:
Hydrozoa - Hydra and Obelia = polyp is the dominant or only stage of the life cycle. (Physalia). Alternation of Generations common.
Scyphozoa - Aurelia = medusa is the dominant or only stage of the life cycle. Jellyfishes. Mostly marine, some freshwater forms. Alternation of Generations common.
Anthozoa - Corals and anemones. Polyp only stage in life cycle = no Alternation of Generations.
Animal Characteristics Chart 1