Chapter 8 Lower Invertebrates Karleskint Turner Small Key

Chapter 8 Lower Invertebrates Karleskint Turner Small

Key Concepts • Sponges are asymmetric, sessile animals that filter food from the water circulating through their bodies. • Sponges provide habitats for other animals. • Cnidarians and ctenophores exhibit radial symmetry. • Cnidarians possess a highly specialized stinging cell used to capture prey and for protection.

Key Concepts • Most marine animals exhibit bilateral symmetry. • Turbellarians are free-living flatworms; flukes and tapeworms are parasitic flatworms. • Ribbon worms are marine predators that somewhat resemble flatworms. • Phoronids, bryozoans and brachiopods have a specialized feeding structure called a lophphore.

What Are Animals? • Animals: 1. are multicellular – distinguishes them from bacteria and most protists 2. have eukaryotic cells without cell walls – distinguishes them from bacteria, fungi, algae and plants 3. cannot produce their own food, depend on other organisms for nutrients 4. can actively move (with the exception of adult sponges) 5. invertebrates = animals that lack a vertebral column (backbone 6. vertebrates – animals with a vertebral column 7. majority of animals in sea are invertebrates

Sponges • Phylum Porifera • Basic characteristics: – simple – asymmetric – sessile: permanently attached to a solid surface – have many shapes, sizes and colors – shape often determined by shape of bottom sediments, material on which they are growing and local water currents

Sponge Structure and Function • Body is built around a system of water canals – ostia: tiny holes or pores through which water enters the sponge’s body – spongocoel: spacious cavity in the sponge into which water flows – osculum: large opening through which water exits from the spongocoel

Water exits through osculum Spicule Archaeocyte Water enters through small pores (ostia) Pinacocyte Spongocoel Pore cells Spongocoel Collar cell (choanocyte) Collar Ostium Flagellum Food particles Stepped Art Fig. 8 -1, p. 193

Sponge Structure and Function • Lacking tissues, sponges have specialized cells – collar cells (choanocytes) use their flagella to provide force for moving water through the sponge’s body – pinacocytes in a layer provide an outer covering for the sponge – archaeocytes: cells that resemble amoebas, and can move through sponge body • can assume any of the other cell forms • transport materials • important role in repair and regeneration

Sponge Structure and Function • Structural materials – spicules: skeletal elements that give support to a sponge’s body, produced by specialized cells and composed of calcium carbonate, silica or spongin – spongin: a protein that forms flexible fibers

Sponge Structure and Function • Sponge size and body form – size is limited by water circulation – asconoid: simplest form; tubular and always small, found in clusters – syconoid: sponges that exhibit the first stages of body-wall folding – leuconoid: sponges with the highest degree of folding, which have many chambers lined with collar cells

Sponge Structure and Function • Nutrition and digestion – sponges are suspension feeders – feed on material suspended in seawater – sponges are also referred to as filter feeders – they filter food from the water – large particles are engulfed and digested by pinocytes and archaeocytes – collar cells trap ~ 80% of food which consists of small particles (0. 1 to 1. 0 micrometers in size) – sponges are one of the few animals that can capture such small sized particles

Sponge Structure and Function • Reproduction in sponges – asexual reproduction • budding: a group of cells on the outer surface of the sponge develops and grows into a tiny new sponge, which drops off and establishes itself • fragmentation: production of a new sponge from pieces that are broken off by physical processes, e. g. , waves, storms, predators – sexual reproduction • most sponges are hermaphrodites • eggs usually develop from archaeocytes and sperm from modified collar cells • larval stage is called a planktonic amphiblastula

Fertilization Sperm cell engulfed by a collar cell Egg cell Sperm cell (modified collar cell) Asexual reproduction Bud Embryo Sexual reproduction Planktonic amphiblastula larva New sponge Larva settles and attaches to bottom or other surface Stepped Art Fig. 8 -3, p. 195

Ecological Roles of Sponges • Competition – compete aggressively with corals and bryozoans for attachment space • Predator-prey relationships – few species eat sponges • spicules are like needles • some produce chemical deterrents – a few species of bony fish and molluscs and sea turtles (especially the hawksbill) will eat sponges

Ecological Roles of Sponges • Symbiotic relationships – sponges are mutualistic or commensalistic hosts to many organisms • e. g. symbiotic cyanobacteria – many organisms (shrimp, fish) live within the canals or spongocoel, for protection and to take advantage of water flow

Ecological Roles of Sponges • Sponges and nutrient cycling – boring sponges (family Clionidae) recycle calcium as they burrow into coral and mollusc shells

Cnidarians: Animals with Stinging Cells • Phylum Cnidaria • Include jellyfish, hydroids, corals and sea anemones • Named for their cnidocytes—stinging cells • Cnidocytes are used to capture prey and protect the animal

Organization of the Cnidarian Body • Radial symmetry: many planes can be drawn through the central axis that will divide the animal into equivalent halves • Often exhibit 2 body plans within their life cycles: – polyp: benthic form characterized by a cylindrical body with an opening at 1 end, i. e. , the mouth which is surrounded by tentacles – medusa: a free-floating stage (jellyfish) • Many cnidarians have both body plans, corals and sea anemones exist as polyps

Stinging Cells • Cnida: stinging organelle within a cnidocyte, which may function in locomotion, prey capture, or defense – nematocysts: spearing type cnida, which are discharged when the cnidocill—a bristle-like trigger—contacts another object

Stinging Cells • Stinging cells also triggered by certain chemical substances released by prey • Dangerous species – Portuguese man-of-war (painful stings) – box jellyfish (can kill within 3 -20 minutes)

Types of Cnidarians • Hydrozoans (class Hydrozoa) – mostly colonial – colonial forms contain 2 types of polyp: • gastrozooid = feeding polyp—functions in food capture • gonangium = reproductive polyp—specialized for reproduction – hydrozoans known as hydrocorals secrete a calcareous skeleton, e. g. , fire coral – some produce floating colonies • e. g. Portuguese man-of-war

Types of Cnidarians • Jellyfish and box jellyfish – scyphozoans—true jellyfish (class Scyphozoa) • considered members of the plankton • medusa is predominant life stage • photoreceptors: sense organs that can determine whether it is dark or light – box jellyfish (class Cubozoa) • • box-shaped bells relatively strong swimmers tropical voracious predators, primarily of fish

Types of Cnidarians • Anthozoans (class Anthozoa) – include sea anemones, corals and gorgonians – sea anemones • benthic, all adults are sessile • polyps with a gastrovascular cavity divided into compartments radiating from the central one • though sessile, many can change locations

Types of Cnidarians • Anthozoans (class Anthozoa) – coral animals • polyps that secrete a hard or soft skeleton • scleractinian corals = hard, stony corals • form reefs along with coralline red algae and calcified green algae

Types of Cnidarians • Anthozoans (class Anthozoa) – soft corals • polyps that form plant-like colonies

Nutrition and Digestion • Gastrovascular cavity: central cavity where cnidarians digest their prey – functions in digestion and transport – waste products forced back out mouth • Many hydrozoans and anthozoans are suspension feeders • Jellyfish and box jellyfish are carnivorous, eat fish and larger invertebrates • Sea anemones generally feed on invertebrates, some large species feed on fish, shallow water species have symbiotic algae

Reproduction • Hydrozoans – generally exhibit asexual polyp stage and sexual medusa stage in the life cycle – reproductive polyps form medusa-like buds which grow into adults after release – adults release gametes into the water column, where they are fertilized and form larvae • planula larva: planktonic larva disperses and grows in the water column, then settles

Medusae Sperm Egg Planula larva Polyp colony Young polyp colony Stepped Art Fig. 8 -15, p. 204

Reproduction • Scyphozoans – in adult jellyfish and box jellyfish, sexes generally separate – medusae (sexual stage) release gametes into the water column for fertilization – planula larvae settle, grow into polyps, and reproduce medusa-like buds asexually – immature buds are released into the water column to grow into mature medusae

Young medusa Adult medusa Gastrovascular cavity Gonad Bell Asexual reproduction Tentacles Radial canal Mouth Oral arms Egg Sexual reproduction Young polyp Planula Stepped Art Fig. 8 -16, p. 205

Reproduction • Anthozoans – asexual reproduction IS COMMON • pedal laceration: leaving parts of the pedal disk (base) behind to grow into new animals • fission: the anemone splits in two and each half grows into a new individual • budding produces large colonies of identical hard corals asexually – sexual reproduction • corals usually have male and female forms, gametes are released into water column • larval stage is a planula larva

Ecological Relationships of Cnidarians • Predator-prey relationships – cnidarians are predators – stinging cells discourage predation – sea turtles, some fish and molluscs prey on hydrozoans and jellyfish • Habitat formation – coral polyps form complex 3 -dimensional structures inhabited by thousands of other organisms – coral reefs provide a solid surface for attachment, places for pelagic animals to rest and hide and buffer waves and storms

Ecological Relationships of Cnidarians • Symbiotic relationships – Portuguese man-of-war and man-of-war fish – reef-forming corals and zooxanthellae • Algae provide food and oxygen to coral through photosynthesis • Coral provides nutrients and carbon dioxide to algae through respiration – sea anemones. . . • and clownfish • and the hermit crab

Ctenophores • Phylum Ctenophora • Planktonic, nearly transparent • Ctenophore structure – named for 8 rows of comb plates (ctenes) which the animal uses for locomotion • ctenes are composed of large cilia – exhibit radial symmetry – lack stinging cells – bioluminescent

Ctenophores • Digestion and nutrition – carnivorous, feeding on other plankton, larval fish and fish eggs – may use branched tentacles in a net pattern, adhesive cells, jellyfish stingers to capture prey

Ctenophores • Reproduction – almost all are hermaphroditic – fertilization may be in the water column, or eggs may be brooded in the body – cydippid larva: free-swimming larva resembling the adult ctenophore

Ctenophores • Ecological Role – can effect zooplankton abundance directly and fish populations by preying on fish larvae and eggs

The Evolution Of Bilateral Symmetry • Bilateral symmetry – body parts arranged such that only one plane through the mid-line of the central axis divides animal into similar right and left halves – allowed for streamline body shape increasing mobility – favored concentration of sense organs at one end of animal (cephalization)

Flatworms • Have flattened, bilaterally symmetrical bodies with a definite head and posterior end • Trubellarian flatworms (class Turbellaria) are free-living • Flukes (class Trematoda) and tapeworms (class Cestoda) are parasitic

Flatworms • Types of flatworm – turbellarians are mostly pelagic, and are common members of meiofauna (invertebrates living between sediment particles) – turbellarians have sensory receptors in head region to detect light, chemicals, movement and help maintain balance – flukes usually have complex life cycles – tapeworms live in the host’s digestive tract

Flatworms • Reproduction – can reproduce asexually and regenerate missing body parts – sexual reproduction • reciprocal copulation—when hermaphrodites mate and fertilize each other • some have no larval stage; others have freeswimming planktonic larva • turbellarians produce few eggs • parasitic flatworms produce 10 to 100 thousand times more eggs than turbellarians

Flatworms • Ecological role of flatwroms – Turbellarians: • turbellarians funnel nutrients to higher trophic levels • prey for higher-level consumers – Parasitic flatworms: • can regulate population size by lowering fitness of host

Ribbon Worms • Phylum Nemertea – most are benthic – resemble flatworms but are longer with thicker bodies – sexes are separate, fertilization external – carnivorous – feed on annelids and crustaceans – capture prey with proboscis (tube extending from mouth)

Ribbon Worms • Ecological role of ribbon worms – prey organisms for higher consumers – burrowing in sediment moves nutrients to surface – abandoned burrows can serve as habitat

Lophophorates • Lophophorates are sessile animals that lack a distinct head • Possess a lophophore: arrangement of ciliated tentacles that surround the mouth, used for feeding, gas exchange • 3 phyla of lophophorates: – Phoronida (phoronids) – Ectoprocta (bryozoans) – Brachiopoda (brachiopods)

Phoronids • Small, worm-like animals • Secrete a tube of leathery protein or chitin that can be attached or buried in bottom sediments • Catch plankton and detritus with mucuscoated tentacles • Can reproduce sexually or asexually (budding, transverse fission) • Have a planktonic larval stage

Bryozoans • Small, abundant, colonial animals • Most live on rocks, shell, algae, mangroves, etc. in shallow water • Along with hydroids, rank among the most abundant marine epiphytic animals • Colonies are composed of zooids (tiny individuals), each inhabiting a box-like chamber it secretes • Most are hermaphroditic brooders • Larvae are planktonic, settle to form new colonies

Brachiopods • Most brachiopods (lamp shells) are benthic and live in shallow water • changed little since they evolved 400 million years ago • Have mollusc-like, bivalve shells – valves differ in size and shape, and are dorsal and ventral – a pedicle (fleshy stalk) attaches the shell or is buried • Gather detritus/algae with lophophore • Generally have separate sexes; larvae are planktonic and settle in 24 -30 hrs.

Ecological Roles of Lophophorates • As a group, they are filter feeders • Food for many invertebrates, especially molluscs and crustaceans • Largely responsible for fouling ship bottoms