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Chapter 30 – More Invertebrates The coelom Molluscs Bivalves Cephalopods Gastropods Annelids Arthropods Crustaceans Uniramians Chelicerates Echinoderms Advantages of Coelom Protostomes vs. deuterostomes Differentiated according to three major events in embryological development 1) Cleavage Spiral cleavage in protostomes Radial cleavage in deuterostomes 2) Fate of blastopore Mouth appears near blastopore in protostomes Anus appears near blastopore in deuterstomes 3) Coelom Formation Schizocoelom forms in protostomes Enterocoelom forms in deuterstomes Mollusks (phylum Mollusca) Have three-part body plan Visceral Mass Contains internal organs Mantle May secrete shell and/or contribute to development of gills or lungs Foot Muscle adapted for locomotion, attachment, or food capture Nervous system consists of several ganglia connected by nerve cords Coelom is reduced, and largely limited to the region around the heart Heart pumps hemolymph through vessels into hemocoel Bivalves Clams, oysters, mussels, and scallops Shell of two hinged parts, closed by powerful muscles No head, no radula Circulatory system open Sexes are separate Ciliated gills hang down within mantle cavity on either side of visceral mass Beating of cilia causes water to enter cavity Filter Feeders – capture tiny food particles suspended in water 1 Bivalve Diversity Cephalopods Head Footed Force water out mantle cavity Tentacles and arms capture prey by adhesive secretions or suckers Beak used to tear prey apart Well-developed sense organs Closed circulatory system Spermatophore packets passed from males to females Cephalopod Diversity Gastropods Have elongated, flattened foot Well-developed head region Eyes and tentacles project from coiled shell Gills are found in mantle cavity in aquatic gastropods Mantle functions as lung in terrestrial gastropods Gastropod Diversity Annelids (Phylum Annelida) Segmented partitions (septa) divide the well-developed, fluid-filled coelom, which acts as hydrostatic skeleton Specialized digestive tract Closed circulatory system Ventral solid nerve cord Most are marine Setae (bristles) help in movement Polychaete Diversity Earthworms Do not have well-developed head or parapodia Setae protrude in pairs directly from surface of body Food drawn into mouth by action of muscular pharynx Digestion and absorption occur in long internal intestine Typhlosole increases surface for absorption Earthworm, Lumbricus terrestris Segmentaion evidenced by: Body rings Coelom divided by septa Setae on most segments Ganglia and lateral nerves in each segment Nephridia in most segments Branched blood vessels in each segment 2 Earthworm Reproduction Hermaphroditic Two worms lie in parallel to each other facing in opposite directions Fused midbody segment (clitellum) secretes mucus, protecting sperm from dessication Leeches Usually found in fresh water Same body plan as other annelids No setae Two additional suckers Some parasitic Keep blood flowing and prevent clotting by means of hirudin, a powerful anticoagulant Medicinal Leeches, Hirudo medicinalis Arthropods (phylum Arthropoda) have freely movable jointed appendages Very successful due to many characteristics Rigid, jointed exoskeleton Must molt as they grow Segmented, but some segments are fused into regions Head, thorax, abdomen Well-developed nervous system Arthropod Skeleton and Eye Arthropods Variety of respiratory organs Occurrence of metamorphosis Three major arthropod subphyla Crustaceans Crayfish Uniramians Centipedes Chelicerates Spiders Crustaceans Decapods are the most familiar and numerous of crustaceans Shrimp, lobsters, crayfish, and crabs Thorax bears five pairs of walking legs Head and thorax fused into cephalothorax Covered by nonsegmented carapace Abdominal segments equipped with swimmerets Respiratory system consists of gills 3 Crustacean Diversity Male crayfish, Cambarus Uniramians Include insects, millipedes, and centipedes Appendages attached to the thorax and abdomen only have one branch Head appendages include: Only one pair of antennae One pair of mandibles, and One or two pairs of maxillae Live on land and breathe by tracheae Insect Diversity Two Types of Insect Mouthparts Female Grasshopper, Romalea Centipede and Millipede Chelicerates Include terrestrial spiders, scorpions, ticks, mites, horseshoe crabs and sea spiders All appendages attached to cephalothorax; none on head First pair (chelicerae) are feeding organs Second pair (pedipalps) function in feeding or sensory Chelicerate Diversity Echinoderms Sea stars, sea urchins, sea cucumbers, and sea lilies Radial symmetry as adults (not as larvae) Internal calcium-rich plates with spines Central nerve ring with branches Water vascular system for locomotion Review The coelom Mollusks Bivalves Cephalopods Gastropods Annelids Arthropods Crustaceans Uniramians Chelicerates Echinoderms 4
