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UNIT 7 INVERTEBRATES PART 2 ARTHROPODS ARTHROPOD CHARACTERISTICS Largest phylum of animals Most marine arthropods are crustaceans Body is segmented, bilaterally symmetrical Jointed appendages Exoskeleton made of chitin Molt (shed exoskeleton) small CRUSTACEANS 68,000 known species Most marine Have gills 2 pairs of antennae Examples; copepods, barnacles, amphipods, isopods, krill, shrimp, lobster, crabs BIOLOGY OF CRUSTACEANS Filter feeding smaller crustaceans Use bristles on appendages to gather particles Use appendages in some for sucking and piercing Stomach has chitinous teeth Predators- decapods Stomach is two chambered; digestive enzymes Extracellular digestion; have anus Open circulatory system Gill exchange gases Simple brain; but well developed sensory organs Compound eyes Keen sense of smell Communicate with signals REPRODUCTION & LIFE HISTORY Separate sexes Internal fertilization In decapods, females carry their eggs in their pleopods or swimmerets Most have planktonic larvae SMALL CRUSTACEANS COPEPODS: planktonic; use mouthparts to filter and capture food Some parasitic Barnacles- filter feeder; live attached to surfaces; body enclosed with heavy calcareous plates; have feathery filtering appendages called cirri AMPHIPODS- have a curved body that is flattened sideways Under ¾ in Head and tail typically curve downward Ex: whale lice, beach hoppers 5000 species Beach hopper Whale lice Right whale with whale lice ISOPODS- similar in size to amphipods but have legs that are similar to each other and the body is dorsoventrally flat (flat back) Pill bugs (land) Fish lice Fish lice Giant deep sea isopod KRILL OR EUPHAUSIIDS- shrimp-like crustaceans; up to 2.5”; planktonic; head is fused with some of the body segments to form a carapace Most filter feeders Polar waters Deep water Main food source for large marine mammals krill School of krill DECAPODS Shrimps, lobsters, and crabs 10000 species Largest group of crustaceans Five pairs of legs or perapods 1st which is the heavier- the claw or cheliped 3 pairs of maxillipeds- close to the mouth; used for eating Well-developed carapace and encloses the cephlathorax (fused head and thorax) abdomen Shrimps and lobsters Laterally compressed bodies with elongated abdomens Shrimps are scavangers-some are cleaners Some burrow in muddy bottoms Lobsters are mostly nocturnal; scavangers and predators; Hermit crabs (they are not true crabs) are scavangers; hide in snail shells Mantis shrimp Giant lobster Hermit crab OTHER MARINE ARTHROPODS HORSESHOE CRABS 5 living species Last of the class Merostomata; “living fossils” Live on soft bottoms in shallow water 5 pairs of legs SEA SPIDERS 4 or more pairs of jointed legs w/small body Large proboscis w/mouth at the tip used to feed on small invertebrates Cold water Insects 3 prs of legs as an adult Rare in the sea Most live on water’s edge or high tide mark Marine water strider LOPHOPORATES BRYOZOANS, PHORONOIDS, LAMP SHELLS LOPHOPHORATE CHARACTERISTICS 3 groups Have a unique feeding structure called the lophophorate which is a set of ciliated tentacles arranged in a horseshoe shape Suspension feeders No segmentation Bilateral symmetry U-shaped gut BRYOZOANS- form colonies on seaweeds, rocks and other species 4500 species; almost all marine In phylum Ectoprocta Colonies of individuals called ZOOIDS that secrete skeletons of various shapes Lopophore is retractable U-shaped gut ends in an anus outside the edge of the lophophore PHORONOIDS-worm-like and build tubes Horseshoe-shaped or circular lophopore 20 species Burrow in sand or attach tubes to hard surfaces Very small LAMP SHELLS OR BRACHIOPODS 350 SPECIES Shell w/2 valves that are dorsal and ventral to the body Have a lophophore- w/2 ciliated and coiled arms Attached to rocks or burrowed in soft sediment ARROW WORMS CHAETOGNATHS Characteristics of Arrow worms About 100 species Transparent; streamlined; fish-like fins and tail Head has eyes, grasping spines and teeth Up to 4” carnivores Arrow worm ECHINODERMS 5-WAY SYMMETRY “spiny-skinned” movie ECHINODERM CHARACTERISTICS Radially symmetrical-adults Pentamerous – based on 5-parts Bilaterally symmetrical- planktonic larvae No head No anterior/posterior end; no ventral/dorsal side Refer to the oral and aboral side Complete digestive tract Well-developed coelom Endoskeleton Water-vascular system- waterfilled canals Tube feet- muscular extensions of canals Extended when filled with water- have muscular sacs called ampullae Used for movement, attachment, and receiving chemical and mechanical stimuli Madeporite- or sieve plate- in sea stars and sea urchins; on the aboral side; where water enters the water vascular system BIOLOGY OF ECHINODERMS Radial symmetry = sedentary life style Feeding and digestion- sea stars are carnivorous; they extend their stomach out through their mouth and excrete digestive enzymes; the food is then carried into the digestive gland and the stomach moves back into the body; if intestines are present, they are very small Brittle stars- no anus; very simple guts Crinoids- simple guts Feeding and digestion cont. Sea urchins and sea cucumbers have long coiled guts (sea urchins need this because they are herbivores and the sea cucumbers need this because they need to process sediment) In all echinoderms, nutrients are passed in the coelomic fluid within the coelom Also transports oxygen because they don’t have a circulatory system Sea cucumbers have respiratory trees- which are thin, branched tubes that are connected to the gut and extend out to the anus NERVOUS SYSTEM AND BEHAVIOR- have a nerve net- more complex actions than cnidarians though REPRODUCTION AND LIFE HISTORY Separate sexes External fertilization Zygote develops into a ciliated larva Some don’t have larva but brood their offspring in specialized pouches Some reproduce asexually by the separation of the central disc or body into two piecesREGENERATION TYPES OF ECHINODERMS 7000 KNOWN SPECIES- all marine Bottom dwellers 1. Class Asteroidea= sea stars 5 arms that radiate from central disk Amulacral groove= the radiating channels on the arms Can move in any direction Endoskeleton = interconnected plates of calcium carbonate creating very flexible arms; aboral surface may be covered with spines that are modified into pincer like organs called pedicellariae which helps to keep the surface clean Asteroidea cont. Most are predators of bivalves, snails, barnacles or other attached or slow moving animals Class Ophiuroidea= brittle stars; 5 arms are very long and brittle Most eat detritus and small animals Tube feet don’t have suckers, used for feeding No anus Most species (2000) Indian Sea Star Anthenea crassa Sunflower Sea Star Choriaster granulatus , the dough-boy star Astropectin polyacanthus Arctic Sea Stars eating a Clam Orange-banded Brittle Star (Ophiothrix) Brittle star (Ophiocoma imbricatus) Brittle star larvae CLASS ECHINOIDEA OR SEA URCHINS Endoskeleton forms a round, rigid, shell-like test with movable spines and pedicellariae Body forms a sphere Mouth on bottom; anus on top Graze on seaweeds and seagrasses Have Aristotle’s Lantern- the set of jaws and associated muscles used by sea urchins to bite food 1000 species Purple Sea urchin’s test w/o spines Purple Sea Urchin with spines Pencil Sea urchin Banded Sea urchin Class Echinoidea cont. Heart urchins and sand dollars have flattened bodies and short spines They are deposit feeders using tube feet and mucus to pick up particles Heart Urchin with and without spines Internal Sand dollar Keyhole sand dollar with and without spines CLASS HOLOTHUROIDEA OR SEA CUCUMBER Worm like No spines and no obvious radial symmetry Look stretched Lies on one side where the 5 rows of tube feet are; oral and aboral surface on the ends Endoskeleton has microscopic spicules Deposit feeders; tube feet around mouth are modified into branced tentacles Class Holothuroidea cont. Defensive mechanisms Secrete toxic chemicals in filament Might expel the gut or other internal organs; this is called evisceration Prickly red sea cucumber Orange sea cucumber Warty Sea cucumber Sea cucumber eviscerating CLASS CRINOIDEA OR CRINOIDS Suspension feeders Feathery arms 600 species of feather stars and sea lilies Sea lilies are in deep water and attached to bottom Feather stars perch and crawl in both shallow and deep water An upside down brittle star with the amulacral grooves and mouth facing upward Class Crinodea cont. Can have up to 200 arms Passion flower feather star Feather star Sea lily Sea lily reef HERMICHORDATES PHYLUM HERMICHORDATA HERMICHORDATA CHARACTERISTICS Share the same basic developmental characteristics of chordates and echinoderms With chordates…. With echinoderms… Dorsal, hollow nerve cord Openings along the anterior part of the gut Some have larvae 85 known species Acorn worms or enteropneusts- live free or in u-shaped tubes Acorn worm Acorn worm feces Acorn worm larvae Phylum Chordata 3 major groups or subphyla Vertebrata Urochordata Cephalochordata Protochordates- invertebrate Chordata- lack the backbone Chordata characteristicsSingle hollow nerve cord that runs along the dorsal length of the animal Gill or pharyngeal slits Notochord- a flexible rod for support that lies between the nerve cord and the gut In vertebrata- surrounded or replaced by the backbone Post-anal tail- a tail that extends beyond the anus Ventral heart TUNICATES Largest group of protochordates Subphylum Urochordata 3000 species; all marine Sea squirts (Class Ascidiacea) Saclike bodies; sessile; fouling organisms Body protected by a tunic- a leathery gelatinous outer covering Filter feeders; water flows through the mouth or incurrent siphon and out through the excurrent siphon Ciliated, sieve-like sac- the pharynx Can be colonial Sea squirts cont. Planktonic larvae have chordate characteristics; not the adult; known as tadpole larvae Have gill slits, dorsal nerve cord, notochord and postanal tail Has an eye as well Sea squirt Larva and adult Tunicates cont Salps (Class Thaliacea) Planktonic entire life Transparent, barrel-shaped body with muscle bands for locomotion Water through the incurrent siphon on posterior end Warm water Some colonial Tunicates cont. Class Larvacea or appendicularians Planktonic tunicate Body of tadpole larva throughout life Delicate house for protection and to filter for food LANCELETS 23 known species Subphylum Cephalochordata Body is laterally compressed and elongated like a fish; only up to 3 in long Have all chordata characteristics throughout life except for backbone Filter feeders; using gill slits to capture food Live on soft bottoms
