BIOL 51 Arthropods Lecture notes 2007

BIOL 51 Arthropods Lecture notes 2007 - BIOL 51 THE...

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BIOL 51 Page 1 BIOL 51: Lecture – Arthropods and their relatives FALL 2007 THE LOPHOPHORATES: The lophophorates are a collection of three odd phyla. They are called lophophorates because all members of these 3 phyla posses an unusual feeding apparatus: the lophophore : •A “horseshoe”-shaped fold of ciliated tentacles surrounding the mouth • Cilia whip about and create a water current, drawing water and food particles into mouth. Food particles adhere to mucus coating the tentacles, then the cilia sweep the mucus into the mouth. • All lophophorates are aquatic substrate / filter feeders . All lophophorates also possess a U-shaped complete gut , with the mouth positioned in the middle of the lophophore and the anus positioned just outside of the lophophore. Other lophophorate traits: • Body is NOT segmented Nervous system: Ganglia or nerve ring for brain and two ventral solid nerve cords Skeletal system: none (they are sessile), but shelled spp can use muscles to close valves. Respiratory system : surfaces of lophophore are used as a gill. Circulatory system : varies in each group (see below) Excretory system : Metanephridia Reproductive systems : Vary within and between groups Lophophorates have a eucoelom , but they differ from other eucoelomates in that they do not fit the traditional Deuterostomate-Protostomate dichotomy . Lophophorates have: 1. Radial cleavage, indeterminate development , and enterocoelom (Deuterostomate traits) 2. In most spp, the blastopore becomes the mouth and they have metanephridia for excretory organs (Protostomate traits) In the past, the lophophorates have been set apart taxonomically from Deuterostomates and Protostomates, but recent data, and molecular evidence, place them in the Protostomate lineage.
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BIOL 51 Page 2 BIOL 51: Lecture – Arthropods and their relatives FALL 2007 PHYLUM BRACHIOPODA : Brachiopods or Lamp shells • < 500 spp., all sessile, solitary (not colonial), marine animals. Open circulatory system with heart • Body is protected by a split shell ( valves ). Brachiopods resemble molluscan bivalves (clams), except: 1. The brachiopod body is divided into dorsal and ventral halves (not left and right). 2. The two valves of the brachiopod shell are not symmetrical w/ each other . 3. Brachiopod valves are made of calcium carbonate (as in bivalve mollusks, or of a mix of calcium phosphate and chitin . PHYLUM PHORONIDA : Phoronid worms or Horseshoe worms • ~20 spp., all marine (SW) Tube-dwelling worms (up to 50 cm long!); burrowed in sand. • Some spp form a protective outer chitinous tube . • Superficially resemble tube-dwelling polychaete worms. • Simple closed circulatory system and blood (but no heart) PHYLUM ECTOPROCTA : Bryozoans , Sea mosses or Sea mats • ~ 5,000 spp. Mostly marine, few FW • Colonial spp that resemble corals (Cnidaria) or mats of mosses (Bryophyta); Commonly called “Bryozoans” for that reason. • Colonies of many species form protective hard
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BIOL 51 Arthropods Lecture notes 2007 - BIOL 51 THE...

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