Coelomate Invertebrates Chapter 33

Outline Coelomates Mollusks Segmented Animals Classes of Annelids Lophophorates Arthropods Crustaceans Arachnids Insects Echinoderms

Coelomates Coelomates have a new body design that allows for the development of complex tissues and organs. allows wider array of body architectures and increased body size

Mollusks Mollusks (Mollusca) extremely diverse characterized by a coelom great economic significance pearls mother of pearl economic / environmental costs zebra mussel invasion intermediate hosts for parasites

Body Plan of the Mollusks Distinct bilateral symmetry Digestive, excretory, and reproductive organs are all concentrated in a visceral mass and a muscular foot. May have differentiated head Folds constituting a mantle gills - increased surface area for gas exchange

Body Plan of the Mollusks Shells serve primarily for protection Radula - rasping tongue-like organ used for feeding Circulatory system (except cephalopods) consists of a heart and an open circulatory system. Nitrogenous wasted removed by nephridia nephrostome lined with cilia

Mollusk Body Plans

Body Plan of the Mollusks Reproduction in mollusks most have distinct male and female individuals most engage in external fertilization many have free-swimming larvae (trochophores) which closely resemble larval stage of many marine annelids veliger stage follows trochophore stage

Classes of Mollusks Polyplacophora: chitons oval bodies with eight overlapping calcareous plates Gastropoda: snails and slugs heads of most have pair of tentacles with eyes at the ends undergo torsion during embryological development.

Classes of Mollusks Bivalvia: bivalves clams, scallops, mussels and oysters two lateral shells hinged together dorsally mantle secretes shell and ligaments most are sessile filter-feeders

Classes of Mollusks Cephalopoda: octopuses, squids, nautilus most intelligent of the invertebrates active marine predators foot evolved into a series of tentacles equipped with structures to capture prey highly developed nervous systems

Segmented Animals Building of body from series of similar segments small change in existing segment can produce new kind of segment with different function Annelids three characteristics: repeated segments specialized segments connections

Segmented Animals Body plan of the annelid tube within a tube internal digestive tract within the coelom specialized for different functions hydrostatic skeleton for locomotion each segment typically possesses setae, that help anchor during locomotion most have closed circulatory system nephridia collect and transport wastes

Classes of Annelids Polychaeta: polychaetes well developed head with specialized sense organs parapodia on most segments usually lack permanent gonads Oligochaeta: earthworms hermaphroditic

Classes of Annelids Hirudinea: leeches occur mostly in fresh water hermaphroditic develop clitellum during breeding season unable to self-fertilize secrete anticoagulant into wounds

Lophophorates Lophophore - circular or U-shaped ridge around the mouth bearing one or two rows of ciliated, hollow tentacles functions as surface for gas exchange and as food-collection organs use cilia to capture food

Lophophorates Phylum Phoronida: phoronids

Lophophorates Phylum Ectoprocta: bryozoans

Lophophorates Phylum Brachiopoda: brachiopods

Jointed Appendages and Exoskeleton All arthropods have jointed appendages. Rigid external skeleton (exoskeleton) protects animal and provides sites for muscle attachment brittle, thus arthropod body size limited due to exoskeleton thickness estimates of a quintillion insects alive at any one time 1,000,000 species

Arthropod Body Plan Exoskeleton tough outer covering that also serves to anchor muscles Molting (ecdysis) shedding of outer cuticular layer

Arthropod Body Plan Compound eye composed of many ommatidia each covered with a lens and linked to a complex of eight retinal cells and a light sensitive core rhabdom Simple eyes (ocelli) have single lenses. function in distinguishing light from darkness

The Compound Eye

General Characteristics of Arthropods Circulatory system greatly reduced coelom open circulatory system Nervous system double chain of segmented ganglia running along the animal’s ventral surface brain appears to be inhibitor rather than stimulator

General Characteristics of Arthropods Respiratory system no single major respiratory organ small branched air ducts - tracheae branch into tracheoles air passes into trachea through spiracles Excretory system Malpighian tubules

Crustaceans Most crustaceans have two pairs of antennae, three types of chewing appendages, and various numbers of leg pairs. all pass through nauplius larval stage mandibles likely originated from a pair of limbs that took on chewing function during course of evolution

Crustaceans Decapod crustaceans “ten footed” exoskeleton usually reinforced with calcium carbonate most body segments are fused into cephalothorax covered by carapace Lobsters and crayfish have swimmerets and uropods to aid in swimming, and may have a telson (tail spine).

Decapod Crustacean

Crustaceans Terrestrial and freshwater crustaceans about half of estimated 4,500 species are terrestrial and live in moist habitats pillbugs sowbugs isopods Sessile crustaceans barnacles free-swimming larvae

Class Arachnida Largest of three classes have a pair of chelicerae, a pair of pedipalps, and four pairs of walking legs most are carnivorous, except for mites many spiders have book lungs

Class Arachnida Order Araneae: spiders about 35,000 named species of spiders many do not spin webs, but actively hunt have poison glands leading through their chelicerae used to bite and paralyze prey

Class Arachnida Order Acari: mites and ticks largest in terms of number of species and most diverse of arachnids about 30,000 named species diverse in structure and habitat found in virtually every habitat known ticks can carry many diseases

Class Chilopoda and Diplopoda Centipedes and millipedes both have bodies that consist of a head region followed by numerous segments centipedes have 30+ legs carnivorous millipedes have 60+ legs herbivorous

Class Insecta Largest group of organisms on earth More than half of all named species on earth are insects. hectare of lowland tropical rainforest is estimated to be inhabited by as many as 41,000 insect species

Class Insecta External features three body segments head, thorax, and abdomen three pairs of legs one pair of antennae modified mouthparts solid wings

Class Insecta Internal organization tubular digestive system dilute digestive enzymes trachea extends throughout body fat body for food storage Sense receptors sensory hairs - linked to nerve cells tympanum - found with tracheal air sacs pheromones – communication signals

Insect Life Histories Metamorphosis simple immature stages complete larvae pupa (chrysalis)

Deuterostome Development Echinoderms ancient group of marine animals consisting of about 6,000 living species name refers to hard, calcium-rich endoskeleton beneath the skin unique water-vascular system is a fluid-filled system used to aid in movement and feeding

Echinoderm Body Plan Secondary radial symmetry bilaterally symmetrical during larval development, but become radially symmetrical as adults. Five part body plan Nervous system - nerve ring

Echinoderm Body Plan Endoskeleton delicate epidermis containing thousands of neurosensory cells continuous growth body plates often pierced to allow tube foot extension

Echinoderm Body Plan Water vascular system radiated from a ring canal that encircles esophagus five radial canals extend into each of the five body parts water enters through madreporite radial canals extend into the hollow tube feet ampulla located at base

Echinoderm Water-Vascular System

Echinoderm Body Plan Body cavity coelom connects with tubular systems and helps provide circulation and respiration Reproduction many echinoderms have the ability to regenerate most reproduction is sexual and external

Major Classes of Echinoderms Extant classes Crinoidea - sea lilies and feather stars Asteroidea - sea stars Ophiuroidea - brittle stars Echinoidea - sea urchins and sand dollars Holothuroidea - sea cucumbers Concentricycloidea - sea daisies

Class Asteroidea Sea stars abundant in intertidal zone important marine predators body composed of central disc that merges gradually with the arms

Class Ophiuroidea Brittle stars largest and probably most abundant class slender branched arms groove running down each arm is closed and covered with ossicles tube feet lack ampullae and are used for feeding, not locomotion

Class Echinoidea Sea urchins and sand dollars lack distinct arms, but still have five-part body plan walk on tube feet or movable spines

Summary Coelomates Mollusks Segmented Animals Classes of Annelids Lophophorates Arthropods Crustaceans Arachnids Insects Echinoderms