Name:______________ Fish 310 Spring 2015 Animals: - Chelicerates - **LIVE** 1 big terrestrial spider - Horshoe crab - Crustaceans - Pericarida - **LIVE** Isopod - Amphipod - Pillbug - Eucarida - **LIVE** shrimp - Shrimp (large, preserved) - **LIVE** hermit crabs - Crab (large, preserved or **LIVE**) - **LIVE** Barnacles Supplies: - Dissecting scopes - Compound scopes Agenda: - Opening Comments - Station Work - Class Discussion #Introduction to Arthropods In today's lab we will examine the arthropods, a phylum that includes insects, spiders, centipedes, and crustaceans. These groups are united by some key characteristics, and as you will see are strikingly different than the cnidarians and molluskans you have already studied. A defining characteristic of arthropods is that they have a segmented, jointed, and hard chitonous exoskeleton secreted by the epidermis with intrinsic musculature between individual joints of appendages. Arthropods are divided into separate groups based on the number and structure of their segments as well as the types and number of appendages they have. Therefore, it is important to become familiar with their morphological characteristics. ####Name two layers comprising an arthropod exoskeleton. What is the function of each? ####Besides having an exoskeleton, name one other defining characteristic of arthropods. ####Draw a picture of the preserved shrimp and label the following structures: head, thorax, abdomen, telson, uropod, endopod, exopod, pleopod, pereopods, maxillipeds, second maxilla, first maxilla, mandible, second antenna, first antenna, rostrum, compound eye ####What is the function of the following structures? - Mandible: - Maxillae: - Maxillipeds: - Pereopods: - Pleopods: ##Subphylum Chelicerata The chelicerates includes spiders, scorpions, mites, horseshoe crabs, daddy longlegs and a number of other strange groups (sea spiders, wind scorpions, vinegaroons, etc.). Some defining characteristics of the chelicerates include the absence of antennae, body divided into the prosoma and opisthosoma (no distinct head), and the first pair of appendages (the chelicerae) adapted for feeding. Most chelicerates are terrestrial. However, we will be focusing on the aquatic chelicerates of the class Merostomata (horseshoe crabs) and the class Pycnogonida (sea spiders). The class Merostomata is comprised primarily of extinct species. Only 4 species are extant, including the horseshoe crab, *Limulus polyphemus* (not a true crab). All of the Merostomata are marine and have appendages on the opisthosoma known as "book gills" that are flattened and modified for gas exchange. ####Observe the morphology of the horseshoe crab. Name at least 2 characteristics that are different from those you observed in the shrimp. ####Which animal do you think is more derived? Why? They Pycnogonids are commonly known as sea spiders since all species are marine and bear very long legs that are typically 3 times the size of the body. Some species of pycnogonids have legs nearly 6 times as long as their body. Unlike other arthropods, the pycnogonids body is not divided into distinct regions. They have unique proboscis at the anterior end of the body and can have variable numbers of walking legs among species. ####How many pairs of walking legs does our species have? ####Notice the posterior pair of ovigers on the head region. Name one function of this structure? ####Observe the terrestrial spider (class Arachnida). What is one characteristic that distinguishes them from horseshoe crabs and sea spiders? ##Subphylum Mandibulata All members of the subphylum Mandibulata bear mandibles on the head segment that are modified for chewing or grinding food. In its present configuration, the Mandibulata includes 3 classes: Myriapoda (centipedes & millipedes), Insecta, and Crustacea. ##Class Crustacea There are approximately 45,000 crustacean species most of which are divided among 6 major subclasses. Some defining characteristics of crustaceans are that they have a head bearing 5 appendages including 2 pairs of antennae and their development includes a larval form called a nauplius. ####Look at the slide of a nauplius larva under your compound scope. How many pairs of appendages does it have? How many eyes? ##Subclass Malacostraca Approximately 3/4 of the known crustaceans belong to the subclass Malacostraca. In general, the animals in this group have a total of 19 body segments: 5 in the head, 8 in the thorax, and 6-7 in the abdomen plus a telson. However, this group has developed highly diverse variations on this basic body plan, and the modifications of each of these 19 body segments is the basis for the taxonomic definitions of each order within this subclass. There are 5 orders of Malacostracans: Isopoda, Amphipoda, Euphasiacae, Stomatopoda, and Decapoda. In lab today we will examine each of these orders in more detail, and you will hopefully be able to identify some of the characteristics that unite animals within this subclass as well as some of the intriguing modifications that separate them. ####Examin the displayed malacostracans. Name one characteristic that is unique to each order. *(Remember: number of appendages and segementation is super important)* - Isopods: - Amphipods: - Euphausiids: - Stomatopods: - Decapods: ####Note the gills on the pleopods of the stomatopods & isopods. Name one advantage and disadvantage to this design. ####Observe the representatives of the remaining crustacean subclasses. We will be covering these groups in detail in the coming weeks so it is important for you to be familiar with them. Which of the four subclasses do you find most interesting? Why? ##Subclass Branchiopoda Branchiopods are a diverse group of small, primarily freshwater crustaceans and include water fleas (*Daphnia*) and brine shrimp (*Artemia*). Branchiopods have thoracic appendages modified to form large flattened paddles which functions in gas exchange and locomotion, giving rise to the name of the subclass (branchio = gill; pod = foot) ##Subclass Ostracoda Ostracods are small and widespread crustaceans common in both marine and freshwater, as well as a few species exploiting terrestrial habitats. A unique feature of ostracods is that their head and body are enclosed in a partially calcified, bivalve-like carapace. Most species are free living, although some are commensal with other crustaceans or with certain echinoderms. ##Subclass Copepoda Copepods are among the most abundant animals on Earth. Most of the approximately 8,500 species are marine and feed on unicellular phytoplankton. Copepods form a major component of zooplankton and are at the base of the oceanic food chain. In contrast to many other crustaceans, copepods lack gills and abdominal appendages. ##Subclass Cirripedia Members of this subclass are exclusively marine and show a greater departure from the basic body plan than the members of any other subclass. All cirripedes (barnacles) are highly modified for attachment to hard substrates, including the outer surfaces of other animals, or for a parasitic lifestyle. Barnacles lack abdominal segments, gills, and a heart. They have modified thoracic appendages called cirri used for filter feeding and a shell composed of numerous plates.