BIOL212 Dissection Skills Module - Video Viewing Guide Phylogenetic Relationships No true tissues Sponges Radia symmetry Cnidarians Ancestral colonial protist Flatworms Eumetazoans True tissues Protostomes Nematodes Annelids 15% Arthropods Bilaterians Bilateral symmetry Molluscs Echinoderms Deuterostomes Chordates This figure shows a hypothesis of animal phylogeny based on morphological comparisons. You should know where each of the animals you'll be examining in the Dissection Skills Module are positioned within this phylogeny.
Dissection Specimen #1: Earthworm (video run time is 11:57) https://www.youtube.com/watch?v=1tVVVu5vY6w Introduction: 0:11 Worm is a general term for a large group of invertebrate animals. Phylum Annelida 0:37 Annelida: A large phylum of invertebrates characterized by the possession of a segmented body, movable bristles (setae), and a body cavity (coelum). Some species within this phylum include earthworms, ragworms, and leeches. External Anatomy: 0:53 annuli (plural) / annulus (singular): individual segments of the worm 0:58 setae (plural) / seta (singular) (very hard to see): tiny hairs that cover the underside of the annuli to help the worm move 1:20 When the muscles along the worm extend, these setae dig into the soil and act as anchors. Then the muscles contract and the anchored setae pull the rear part of the worm forward. 1:39 clitellum: raised band on one end of the worm, secretes viscous fluid that forms a coccon for the worms eggs 1:53 indicate how to determine anatomical orientation: · anterior: head, closer to the clitellum · posterior: rear · dorsal side: back, darker side · ventral side: stomach, lighter side Internal Anatomy: 2:23 Place the worm dorsal side up, pin the anterior and posterior ends to the tray diagonally. 2:43 Start cutting right behind (posterior to) the clitellum. Make shallow cuts so you don't damage any internal organs - you're just cutting the skin. 3:06 Once you make the incisions, lift away the skin with forceps and pin it back. Cut all the way to the posterior end of the worm. Then, starting back at the clitellum, cut all the way up to the anterior end. 3:20 septa (plural) / septum (singular): flaps attached to the skin that divide the worm into annuli 3:38 Earthworms play a crucial role in the environment, maintaining soil structure/fertility as they aerate the soil, bringing nutrients to the surface and improving drainage. 4:05 Earthworms live in the dark and are very sensitive to light. If worms are exposed to light for about an hour, they will become paralyzed. If a worm's skin dries out due to extended exposure to light, the worm will suffocate and die.
4:25 cuticle: outer layer of the worm that protects it from abrasion and drying out - looks like cling wrap 4:50 It is a common misconception that cutting an earthworm in half will result in two new worms. Although earthworms can regenerate to a certain extent, cutting an earthworm in half will most likely kill the worm 5:03 brain: at the very end of worms head, very small, 2 lobes 5:27 pharynx: beginning of digestive system, acts as a