By: Bryan Gonzalez

1. Chapter 33 Invertebrates By: Bryan Gonzalez

2. Key Concepts • 33.1- Sponges are sessile and have a porous body and choanocytes. • 33.2- Cnidarians have radial symmetry, a gastrovascular cavity, and cnidocytes. • 33.3- Most animals have bilateral symmetry • 33.4- Molluscs have a muscular foot, a visceral mass, and a mantle. • 33.5- Annelids are segmented worms • 33.6- Nematodes are nonsegmentedpseudocoelomates covered by a though cuticle • 33.7- Arthropods are segmented coelomates that have an exoskeleton and jointed appendages • 33.8 Echinoderms and chordates are deuterostomes

3. Overview: Life Without a Backbone • When someone first sees the marine invertebrate ,the Christmas tree worm. They may think of it as some type of alga when its actually an animal. • The two whorls are tentacles, which they use to exchange gas and to filter out small organisms in the water. The tentacles come from a tube of calcium carbonate which is secreted by the worm to protect itself. • Light sensitive parts on the tentacles can identify the shadow of a predator causing the tentacles to retract into the tube. • Christmas tree worms are invertebrates, which are animals that lack a backbone. • Invertebrates account for 95% of known animal species and all but one of the roughly 35 animal phyla that have been described. • Invertebrates occupy almost every habitat on Earth, including burning water released from hydrothermal vents to the freezing tundra of Antarctica

4. Exploring the diversity of Invertebrates • The animal kingdom is divided into about 35 phyla encompassing 1.3 million known species. • The whole number of species estimates to be around 10 million to 200 million . • We are going to discuss 24 of the 35 phyla of which include invertebrates.

5. Porifera (5,500 species) • Sponges are simple, sessile animals that lack true tissues. • They live as suspension feeders, trapping particles that pass through the internal channels of their bodies. • A sponge

6. Cnidaria (10,000 species) • Cnidarians include corals, jellies, and hydras. • These animals share a distinctive body plan that includes a gastrovascular cavity with a single opening that serves as both mouth and anus.

7. Placozoa (1 species) • When you first look at this single known species in this phylum, Trichoplaxadhaerens, it doesn’t even look anything like an animal. • It consists of a few thousand cells arranged in a double-layered plate, that measures 2 mm across. • Trichoplax feed on organic detritus. • They reproduce by dividing into two individuals or by budding off many multicellular individuals.

8. Kinorhyncha (150 species) • Almost all kinorhynhs are less than 1 mm long. • They live in sand and mud in oceans around the world, from the intertidal zone to the depths of 8,000 m. • A kinorhyncha’s body consists of 13 segments covered in plates. • The mouth is tipped with a ring of spines and can be retracted into the body.

9. Platyhelminthes (20,000 species) • Flatworms (including tapeworms, planarians, and flukes) have bilateral symmetry and a central nervous system that processes information from eyes and other sensory structures. • They have no body cavity or organs for circulation.

10. Rotifera (1,800 species) • Even though there microscopic in size, rotifers have specialized organ systems, including an alimentary canal (digestive tract). • They feed on microorganisms suspended in the water

11. Ectoprocta (4,500 species) • Ectoprocts (also known by the name bryozoans) live as sessile colonies and are covered by a though exoskeleton.

12. Phoronida (20 species) • Phoronids are marine worms. • They live in tunnels in the seafloor, theyextend there tentacles out of tunnel openings to capture food particles.

13. Brachiopoda (335 species) • Brachiopods also known as lamp shells may be easily mistaken for clams or other molluscs at first sight. • Although, most of the have a unique stalk that anchors them to their substance.

14. Nemertea (900 species) • Proboscis worms ,also called ribbon worms, swim through water or burrow in sand, extending a unique proboscis to capture prey. • Like flat worms, they also lack a true coelom, but they have an alimentary canal.

15. Acanthocephala (1,100 species) • known as the thorny-headed worms because of the curved hooks found on the proboscis at the anterior end of their body. • All species are parasites. • The larvae develop in anthropods, and the adults in vertebrates. • Some acanthocephalans manipulate their intermediate hosts in a ways that increase their chances of reaching there final hosts.

16. Ctenophora (100 species) • Ctenophores (comb jellies) are diploblastic like cnidarians, suggesting that both phyla diverged from other animals very easily in evolution. • Although they superficially resemble some cnidarians, comb jellies possess a number of distinctive traits, including a set of eight “combs” of cilia that propel the animals through the water. • They also have a unique method of catching there prey: when a small animal contacts one of the two tentacles, speicalized cells burst open and cover its prey with sticky threads

17. Mollusca (93,000 species) • Mollucs (including snails, clams, squids, and octopuses) have a soft body that in many species is protected by hard shell.

18. Annelida (16,500 species) • Annelids also known as segmented worms, are distinguished from other worms by their body segments. • Earthworms are the most familiar annelids, but the phylum also includes marine and freshwater species.

19. Loricifera (10 species) • Loriciferans are animals measuring only 0.1-0.4 mm in length that inhabit the deep-sea bottom. • A loriciferan can telescope its head, neck, and thorax in and out of the lorica, a pocket formed by six plates surrounding the abdomen. • Some species eat basteria.

20. Priapula (16 species) • Priapulans are worms with a large, rounded proboscis at the anterior end. • They range fro 0.5mm to 20cm in length, most species burrow through seafloor sediments. • Fossil evidence suggests that praipulants were among the major predators during the Cambrian period.

21. Nematoda (25,000 species) • Roundworms are enormously abundant and diverse in the soil and in aquatic inhabitants; many species parasitize plants and animals. • The most distinctive feature of roundworms is a tough cuticle that coats the body.

22. Arthropoda (1,000,000+ species) • The vast majority of known animal species, including insects, crustaceans, and arachnids, are anthropods. • All arthropods have a segmented exoskeleton and jointed appendages.

23. Cycliophora (1 species) • There is only one known species of cycliophora, Symbion Pandora was discovered in 1995 on the mouthparts of a lobster. • The tiny, vase-shaped creature has a unique body structure and a particularly starngelif cycle. • Males impregnate females that are still developing in their mother’s bodies. • The fertilized females escape and and release their offspring elsewhere on the lobster.

24. Tardigrada (800 species) • Tardigrades are sometimes called water bears for their rounded shape, stub by appendages, and lumbering, bearlike gait. • Most tardigrades are less than 0.5 mm in length. • Some live in ocenas or fresh water, while others live on plants or animals. • As many as 2 million tradigrades can be found on a square meter of moss. • Harsh conditions may cuase them to go dormant while like this, they can survive temperatures as low as -272ᵒC which is very close to absolute zero

25. Onychophora (110 species) • Onychophorans, are also called velvet worms, they orginatedfuring the Cambrian explosion. • Originally, they thrived in the ocean, but at some point they succeeded in colonizing land. • Today they live only in humid forests • Onychophorans have fleshy antennae and several dozen pairs of saclike legs.

26. Hemichordata (85 species) • Like echinoderms and chordates, hemichordates are deuterostomes. • Hemichordates also share other traits with chordates, such as gill slits and a dorsal nerve chord. • Most hemichordates are known as enteropneusts, or acorn worms. • Acorn worms are marine and generally live buried in mud or under rocks.

27. Echinodermata (7,000 species) • Echinoderms, such as sand dollars, sea stars, and sea urchins, are aquatic animals that display radial symmetry as adults. • They move and feed by using a network of internal canals to pump water to different parts of the body.

28. Chordata (52,000 species) • More than 90% of all chordate species are animals with backbones. • However, the phylum Chordata also includes three groups of invertebrates: tunicates, lancelets, and hagfishes.

29. Chapter 33.1 • Sponges are sessile and have a porous body and choanocytes. • Sponges (phylum Porifera) are so sedentary that they were mistaken for plants by the early Greeks. • Living in freshwater and marine environments, sponges are suspension feeders. • The body of a simple sponge resembles a sac perforated with holes. • Water is drawn through the pores into a central cavity, the spongocoel, and flows out through a larger opening, the osculum. • More complex sponges have folded body walls, and many contain branched water canals and several oscula.

30. Anatomy of a sponge.

31. Chapter 33.1 (cont’d) • Sponges range in height from about a few mm to 2 m and most are marine. • About 100 species live in fresh water. • Unlike eumetazoa, sponges lack true issues, groups of similar cells that form a functional unit. • The germ layers of sponges are loose federations of cells, which are not really tissues because the cells are relatively unspecialized. • The sponge body does contain different cell types. • Sponges collect food particles from water passing through food-trapping equipment. • Flagellated choanocytes, or collar cells, lining the spongocoel (internal water chambers) create a flow of water through the sponge with their flagella and trap food with their collars. • Based on both molecular evidence and the morphology of their choanocytes, sponges evolved from a colonial choanoflagellate ancestor.

32. Chapter 33.1 (cont’d) • The body of a sponge consists of two cell layers separated by a gelatinous region, the mesohyl. • Wandering though the mesohyl are amoebocytes. • They take up food from water and from choanocytes, digest it, and carry nutrients to other cells. • They also secrete tough skeletal fibers within the mesohyl. • In some groups of sponges, these fibers are sharp spicules of calcium carbonate or silica. • Other sponges produce more flexible fibers from a collagen protein called spongin.

33. Chapter 33.1 (cont’d) • Most sponges are sequential hermaphrodites, with each individual producing both sperm and eggs in sequence. • Gametes arise from choanocytes or amoebocytes. • The eggs are retained, but sperm are carried out the osculum by the water current. • Sperm are drawn into neighboring individuals and fertilize eggs in the mesohyl. • The zygotes develop into flagellated, swimming larvae that disperse from the parent. • When a larva finds a suitable substratum, it develops into a sessile adult. • Sponges produce a variety of antibiotics and other defensive compounds. • Researchers are now isolating these compounds, which may be useful in fighting human disease.

34. Chapter 33.2 • Cnidarians have radial symmetry, a gastrovascular cavity, and cnidocytes. • All animals except sponges belong to the Eumetazoa, the animals with true tissues. • The cnidarians (hydras, jellies, sea anemones, and coral animals) have a relatively simple body construction. • They are a diverse group with more than 10,000 living species, most of which are marine. • They exhibit a relatively simple, diploblastic body plan that arose 570 million years ago. • The basic cnidarians body plan is a sac with a central digestive compartment, the gastrovascular cavity. • A single opening to this cavity functions as both mouth and anus. • This basic body plan has two variations: the sessile polyp and the floating medusa.

35. A cnidocyte of a hydra This type of cnidocyte contains a stinging capsule, the nematocyst, which itself contains an inverted thread. When a “trigger” is stimulated by touch or by certain chemicals, the thread shoots out, puncturing and injecting poison into prey.

36. Chapter 33.2 (cont’d) • The cylindrical polyps, such as hydras and sea anemones, adhere to the substratum by the aboral end and extend their tentacles, waiting for prey. • Medusas (also called jellies) are flattened, mouth-down versions of polyps that move by drifting passively and by contracting their bell-shaped bodies. • The tentacles of a jelly dangle from the oral surface. • Some cnidarians exist only as polyps. • Others exist only as medusas. • Still others pass sequentially through both a medusa stage and a polyp stage in their life cycle. • Cnidarians are carnivores that use tentacles arranged in a ring around the mouth to capture prey and push the food into the gastrovascular chamber for digestion. • Batteries of cnidocytes on the tentacles defend the animal or capture prey.

37. Polyp and medusa forms of cnidarians The body wall of a cnidarian has two layers of cells: an outer layer of epidermis and an inner layer of gastrodermis.Digrstin starts in the gastrovascular cavity and is finishes inside food vacuoles in the gastrodermal cells. On the gastrodermal cells, they have flagella that keeps the content agitated and move/distribute nutrients better.

38. Chapter 33.2 (cont’d) • Organelles called cnidaeevert a thread that can inject poison into the prey, or stick to or entangle the target. • Cnidae called nematocysts are stinging capsules. • Muscles and nerves exist in their simplest forms in cnidarians. • Cells of the epidermis and gastrodermis have bundles of microfilaments arranged into contractile fibers. • True muscle tissue appears first in triploblastic animals. • When the animal closes its mouth, the gastrovascular cavity acts as a hydrostatic skeleton against which the contractile cells can work. • Movements are controlled by a noncentralized nerve net associated with simple sensory receptors that are distributed radially around the body.

39. Chapter 33.2 (cont’d) Hydrozoans • The phylum Cnidaria is divided into four major classes: Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa. • The four cnidarian classes show variations on the same body theme of polyp and medusa. • Most hydrozoans alternate polyp and medusa forms, as in the life cycle of Obelia. • The polyp stage, often a colony of interconnected polyps, is more conspicuous than the medusa. • Hydras, among the few freshwater cnidarians, are unusual members of the class Hydrozoa in that they exist only in the polyp form. • When environmental conditions are favorable, a hydra reproduces asexually by budding, the formation of outgrowths that pinch off from the parent to live independently. • When environmental conditions deteriorate, hydras form resistant zygotes that remain dormant until conditions improve.

40. The life cycle of Obelia The polyp stage is asexual, and the medusa stage is sexual; these two stages alternate, one producing the other. Both the polyp and the medusa are diploid organisms.

41. Chapter 33.2 (cont’d) Scyphozoans • The medusa generally prevails in the life cycle of class Scyphozoa. • The medusae of most species live among the plankton as jellies. • Most coastal scyphozoans go through small polyp stages during their life cycle. • Jellies that live in the open ocean generally lack the sessile polyp.

42. Chapter 33.2 (cont’d) Cubzoans • Cubozoans have a box-shaped medusa stage. • They can be distinguished from scyphozoans in other significant ways, such as having complex eyes in the fringe of the medusae. • Cubozoans, which generally live in tropical oceans, are often equipped with highly toxic cnidocytes. • Sea wasp’s poison subdue fish which is more potent than cobra venom

43. Chapter 33.2 (cont’d) Anthozoans • Sea anemones and corals belong to the class Anthozoa. • They occur only as polyps. • Coral animals live as solitary or colonial forms and secrete a hard external skeleton of calcium carbonate. • Each polyp generation builds on the skeletal remains of earlier generations to form skeletons that we call coral. • In tropical seas, coral reefs provide habitat for a great diversity of invertebrates and fishes. • Coral reefs in many parts of the world are currently being destroyed by human activity. • Pollution, overfishing, and global warming are contributing to their demise.

44. Chapter 33.3 • Most animals have bilateral symmetry • The vast majority of animal species belong to the cladeBilateria, which consists of animals with bilateral symmetry and triploblastic development. • Most bilaterians are also coelomates. • The most recent common ancestor of living bilaterians probably lived in the later Proterozoic. • During the Cambrian explosion, most major groups of bilaterians emerged.

45. Chapter 33.3 (cont’d) Flatworms • Flatworms live in marine, freshwater, and damp terrestrial habitats. • They also include many parasitic species, such as the flukes and tapeworms. • Flatworms have thin bodies, ranging in size from nearly microscopic to tapeworms more than 20 m long. • Flatworms and other bilaterians are triploblastic, with a middle embryonic tissue layer, a mesoderm, which contributes to more complex organs and organ systems and to true muscle tissue. • While flatworms are structurally more complex than cnidarians, they are simpler than other bilaterians. • Like cnidarians, flatworms have a gastrovascular cavity with only one opening (and tapeworms lack a digestive system entirely and absorb nutrients across their body surface). • Unlike other bilaterians, flatworms lack a coelom.

46. Chapter 33.3 (cont’d) Flatworms • The flat shape of a flatworm places all cells close to the surrounding water, enabling gas exchange and the elimination of nitrogenous wastes (ammonia) by diffusion across the body surface. • Flatworms have no specialized organs for gas exchange and circulation, and their relatively simple excretory apparatus functions mainly to maintain osmotic balance. • This apparatus consists of ciliated cells called flame bulbs that waft fluid through branched ducts that open to the outside. • Flatworms are divided into four classes: Turbellaria, Monogenia, Trematoda, and Cestoidea.

47. Chapter 33.3 (cont’d) Flatworms (Tubellarians) • Turbellarians are nearly all free-living (nonparasitic) and most are marine. • Planarians, members of the genus Dugesia, are carnivores or scavengers in unpolluted ponds and streams. • Planarians move using cilia on the ventral epidermis, gliding along a film of mucus they secrete. • Some turbellarians use muscles for undulatory swimming. • A planarian has a head with a pair of eyespots to detect light, and lateral flaps that function mainly for smell. • The planarian nervous system is more complex and centralized than the nerve net of cnidarians. • Planarians can learn to modify their responses to stimuli. • Planarians reproduce asexually through regeneration. • The parent constricts in the middle, and each half regenerates the missing end. • Planarians can also reproduce sexually. • These hermaphrodites cross-fertilize.

48. Chapter 33.3 (cont’d) Flatworms (Monogeneans and Tramatodes) • The monogeneans (class Monogenea) and the trematodes (class Trematoda) live as parasites in or on other animals. • Many have suckers for attachment to their host. • A tough covering protects the parasites. • Reproductive organs nearly fill the interior of these worms. • Trematodes parasitize a wide range of hosts, and most species have complex life cycles with alternation of sexual and asexual stages. • Many require an intermediate host in which the larvae develop before infecting the final hosts (usually a vertebrate) where the adult worm lives. • The blood fluke Schistosoma infects 200 million people, leading to body pains and dysentery. • The intermediate host for Schistosoma is a snail.

49. The life cycle of a blood fluke

50. Chapter 33.3 (cont’d) Flatworms (Monogeneans and Trematodes) • Living within different hosts puts demands on trematodes that free-living animals do not face. • A blood fluke must evade the immune systems of two very different hosts. • By mimicking their host’s surface proteins, blood flukes create a partial immunological camouflage. • They also release molecules that manipulate the host’s immune system. • These defenses are so effective that individual flukes can survive in a human host for more than 40 years. • Most monogeneans are external parasites of fishes. • Their life cycles are simple, with a ciliated, free-living larva that starts an infection on a host. • While traditionally aligned with trematodes, some structural and chemical evidence suggests that they are more closely related to tapeworms.