Review sheet 3                         Biology 4900 – Behavior          James Adams and Kristen Sanders

Invertebrates

              Be aware that the VAST majority of animal species on the planet are invertebrates, and yet we have studied the behavior of a small fraction of these animals. Certain groups (cephalopod mollusks [octopi/squid], spiders, certain insects) have been studied quite a bit, while for other groups we know virtually nothing about their behaviors. All total, there are around 31 phyla of invertebrate animals, with eight being considered major phyla because of the diversity included (both described and undescribed) and another 23 with smaller numbers known. 14 of these other 23 phyla are "worms" of various types. It should also be pointed out that there are a number of chordates that are also invertebrates (tunicates, salps, lancelets, and even hagfish).

             We will be presenting a series of short videos on some behaviors of a number of invertebrates, mostly having to do with obtaining food, avoiding predation, and reproductive behavior (where have we heard THAT before?). You will be responsible for the information contained in these videos (they are ALL linked on my website), plus additional supplementary material that I present here.

The eight major phyla of invertebrates:
        1.  Porifera -- Sponges
        2.  Cnidaria -- Jellyfish, anemones, hydra, corals
        3.  Platyhelminthes -- Flatworms (both free living and parasitic forms)
    Protostomes:
        4.  Nematoda -- Roundworms (both free living and parasitic forms)
        5.  Mollusca -- Mollusks: clams, snails, slugs, sea slugs, squid/octopi
        6.  Annelida -- Segmented worms, but incredibly variable: includes earthworms, polychaetes, leeches
        7.  Arthropoda -- Arthropods: horseshoe crabs, arachnids (spiders, ticks, scorpions, mites), millipedes
                centipedes, crustaceans (crab, lobster, shrimp, crayfish, isopods), and insects
    Deuterostomes
        8.  Echinodermata -- Sand dollars, sea biscuits, starfish and brittlestars, sea cucumbers

             The mollusks will get their own "day" of class (John Lugthart will be talking about these). The arthropods will get three days of lecture, because the diversity of arthropods far exceeds all other animal phyla combined.

             In addition to information presented on the above, I will also show short videos on Ctenophora (comb jellies), Onycophora (velvet worms) and invertebrate chordates (tunicates and salps).

             In our discussion, I will also be talking about advancements in the nervous system (from none, to net, to centralized) and digestive systems (none, to one-opening, to two-opening [protostomes and deuterostomes]) of these organisms, as these systems are vital to survival of these animals, and therefore also the evolution of various behaviors.

Porifera:
        These are considered the some of the simplest animals, with very little in the way of centralized systems. They are found in both freshwater and marine environments. These organisms can literally be separated into small cellular "globs", and, given appropriate circumstances, reassemble themselves. The videos will demonstrate feeding and reproduction (which involves release of clouds of sperm into the water).

Cnidaria and Ctenophora:
        These are the "jelly" animals, so named because there are two layers of tissue on the outside and on the inside (feeding cavity), and then the jelly-like mesoglea between them. There are free living forms (medusae) and sessile forms (polyps), with some species going through a life cycle that includes both. Reproduction (similar to sponges) involves release of clouds of sperm, oddly enough from the mouth.

Prey capture, of course, is done using cnidocytes that are armed with nematocysts (venomous harpoon-like structures), and these of course can be used for protection as well. Some of the most potent venoms in the world are produced by these organisms. Bioluminescence is also seen in some of these organisms, and we will discuss possible functions of this as well. Some of the most impressive structures built by any organism (for protection, but for attracting food as well) are produced by the corals.

Platyhelminthes:
        There are both free living and parasitic forms. This is also the first major phylum to have a centralized nervous system.

Nematoda:
        As with the flatworms above, roundworms also have free living and parasitic forms. These can be some of the most abundant animals in certain environments, with an estimated 9 million+ individuals in the top few centimeters of a m² of high quality soil. They do help with soil quality (though not as much as annelids), but many individuals are also parasites on plants as well, and therefore can cause issues with crop health.

Annelida:
        As hinted at above, humans owe a debt of gratitude to the annelids for the quality and maintenance of the agricultural soils, but annelids contain a much larger number of marine types (tube/fan worms [polychaetes]) that are filter feeders, and predatory types (such as the Bobbit worm).

Onycophora:
        Velvet worms are a small phylum found in tropical habitats. They have a unique protective and feeding mechanism involving oral papillae and sticky slime that we will discuss.

Echinodermata:
        We will discuss movement/prey capture in starfish, and a variety of behaviors in sea cucumbers.

Chordates:
        We will discuss tunicates (sea squirts), which tend to be sessile, and a variety of behaviors in their cousins the salps, which are free floating.