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BIOLOGY XI-A WISDOM SERIES for ��������������CBSE XI Students 119 Animal Kingdom-Nonchordates Some fundamental features such as the arrangement of cells, body symmetry, nature of coelom������������������������������������������ ������������� �������� ���� ������� ��� ��������� ������������������������������������������������ ��������������� 4.1.1 Levels of Organisation The unicellular protozoan groups are the simplest animal-like organisms. The single cell is, in fact, a complete organism that performs all basic functions of life as seen in the more complex animals. Protozoans exhibit protoplasmic level of organization. All the life functions are confined within the boundaries of a single cell. Within the cell, protoplasm is differentiated into organelles capable of performing specialized functions. There is division of labour among the organelles. A metazoan’s body is composed of many kinds of cells specialized for performing different functions. Metazoan cells are not capable of independent existence. Metazoans exhibit higher levels (grades) of organisation such as cellular level, tissue level, organ level and organ system level. All animals are members of the Kingdom Animalia, also called Metazoa. All members of Animalia are multicellular eukaryotes, and all are heterotrophs. Most ingest food and digest it in an internal cavity. Animal cells lack cell walls. Collagen is a protein unique to animals. It is the main component of connective tissue, and is the most abundant protein in mammals. The bodies of most animals are made up of cells organized into tissues; each tissue specialized to some degree to perform specific functions. Most animals are capable of complex and relatively rapid movement compared to plants and other organisms. Most animals reproduce sexually. Animal kingdom is the most diverse group of organisms in comparision to the plant kingdom. It includes more than a million of living species. 4.1 BASIS OF CLASSIFICATION Despite vast differences of structural complexity of organisms ranging from simple sponges to highly evolved humans, all the animals share an intrinsic structural design (bauplan, or body plan) and fundamental functional plan. 4.1 Basis of Classification 4.1.1 Levels of Organisation 4.1.2 Symmetry 4.1.3 Primary germ layers 4.1.4 Coelom 4.1.5 Fate of Blastopore 4.1.6 Metamerism 4.1.7 Notochord 4.2 Outline Classification of Animalia 4.2.1 Porifera 4.2.2 Cnidaria 4.2.3 Ctenophora 4.2.4 Platyhelminthes 4.2.5 Nematoda 4.2.6 Annelida 4.2.7 Arthropoda 4.2.8 Mollusca 4.2.9 Echinodermata 4.2.10 Hemichordata.

BIOLOGY XI-A WISDOM SERIES for ��������������CBSE XI Students 120 Animal Kingdom-Nonchordates Fig.4.1.1(a) Levels of Organisation Organ systems in different groups of animals exhibit various patterns of complexities. For example, flatworms of the phylum Platyhelminthes have an incomplete (sac-like) gut. It has only a single opening to the outside of the body that serves as both mouth and anus. A complete gut has two openings, i.e. mouth and anus (E.g. nematodes to chordates) Similarly, the circulatory system may be of two types. In open circulatory system, blood is pumped by heart through large vessels into an open space called haemocoel. There is no distinction between the circulating fluid (blood) and the extracellular fluid of the body tissues (interstitial fluid or lymph). This fluid is thus called I. Cellular Level of Organisation This is the lowest level of organization in metazoans and is exhibited by the sponges. Individual cells differentiate during the development to perform special functions, E.g. : pinacocytes, porocytes, choanocytes, etc. Their cells are arranged as loose cell aggregates but do not form tissues. Division of labour is seen among the cells. Each cell type is specialised to perform specific function. Nerve cells and sensory cells are absent. II. Tissue Level of Organisation Diploblastic animals such as coelenterates (cnidarians and ctenophores) exhibit tissue grade of organisation. The cells performing the same function are aggregated into tissues. Nerve cells and sensory cells are present in the epidermis and the gastrodermis. The cells of a tissue together perform their common functions as a coordinated unit. The functioning of different tissues is also coordinated. The tissues are, however, not assembled into organs. The evolution of tissues is the first key transition in the animal body plan. III. Organ Level of Organisation Triploblastic animals of the phylum Platyhelminthes exhibit organ level of organisation. All the tissues are derived from three primary germ layers, i.e. ectoderm, endoderm and mesoderm. In these animals, tissues are grouped together to form functional units called organs, each specialised for a particular function. IV. Organsystem Level of Organisation Higher triploblastic animals like annelids, arthropods, molluscs, echinoderms and chordates exhibit organ-system level of organisation. In these animals, groups of organs that work together have associated to form organ systems (Fig. 4.1.1(a)). Each organ system is concerned with a specific physiological function. Highly specialized sensory and nerve cells bring about a higher level of coordination and integration among the various organ systems to lead an efficient way of life..

BIOLOGY XI-A WISDOM SERIES for ��������������CBSE XI Students 121 Animal Kingdom-Nonchordates haemolymph. The cells and tissues are directly bathed in the haemolymph. E.g Arthropods. In closed circulatory system, the circulating fluid (blood) is always enclosed within blood vessels (arteries, veins and blood capillaries) that transport the blood away from and back to a pump, the heart. Exchange of materials between the blood and the tissues occurs through interstitial fluid, or tissue fluid. Closed circulatory system is more advantageous as the flow of fluid can be more precisely regulated. E.g.vertebrates. (Fig. 4.1.1(b)). Fig.4.1.1(b) Types of blood circulation 4.1.2 Symmetry During the course of evolution animals acquired several body forms, all of which fall into few types of symmetry. Symmetry is the regular arrangement of body structures in a geometrical design, relative to the axis of the body. Symmetrical animal can be cut into two mirror image halves, or antimeres by one or more planes of symmetry. Most of the sponges (Fig.4.1.2(a)) are asymmetrical. Their body lacks definite geometrical arrangement of parts and cannot be divided into mirror image halves by any plane. Gastropods (E.g. snails) are secondarily asymmetrical. Their primary symmetry is bilateral, as can be seen in their developmental stages. I. Radial Symmetry It is also termed monaxial heteropolar symmetry. Radially symmetrical animals have an oral end that bears the mouth and the opposite aboral end. In these animals, various body parts are arranged around and along the oral-aboral axis. Any plane passing along the oral-aboral axis divides the body into antimeres (Fig. 4.1.2). Echinoderms are primarily bilateral animals (their larvae are bilateral). Most of them have secondarily become radial, exhibiting pentamerous radial symmetry in the adult stage. This type of radial symmetry has five planes of symmetry. Sea anemones and ctenophores exhibit biradial symmetry in which most of the organs are radially arranged but some are paired (E.g. tentacles of ctenophores). This type of symmetry has only two planes of symmetry. II. Bilateral Symmetry Triploblastic animals like annelids, arthropods, etc. exhibit bilateral symmetry. The body can be divided into identical left and right halves by only one plane i.e., the median sagittal plane (median dorso-ventral palne) (Fig. 4.1.2(b)). Fig.4.1.2 (a) Symmetry.

BIOLOGY XI-A WISDOM SERIES for ��������������CBSE XI Students 122 Animal Kingdom-Nonchordates Fig.4.1.2 (b) Bilateral Symmetry Evolution of bilateral symmetry is the second key transition in the animal body plan. As bilateral animals move primarily in one direction, anterior end of the animal first meets a new environment. This resulted in the concentration of sense organs and nervous tissue in the anterior end. The differentiation of the anterior part of the body into a head is termed cephalization. 4.1.3 Primary Germ Layers The fundamental cell layers formed in an early metazoan embryo are called primary germ layers. Sponges are the only metazoans that lack true primary germ layers. I. Diploblastic Organisation Diploblastic animals are the metazoans in which only two embryonic germ layers (an external ectoderm and an internal endoderm) are formed, e.g. coelenterates (cnidarians and ctenophores). Embryonic ectoderm gives rise to the epidermis, the outer layer of the body wall. Endoderm gives rise to the gastrodermis, the inner layer of the body wall that lines the gastrovascular cavity. Between the epidermis and the gastrodermis is a jelly-like substance called mesoglea. In some diploblastic animals, mesoglea may contain cells but those cells are derived either from ectoderm or from endoderm. II. Triploblastic Organisation The metazoans in which the embryo has three embryonic germ layers are termed triploblastic animals, E.g. Platyhelminthes and other higher metazoan phyla. In these animals the embryo has a third primary germ layer, the mesoderm, in between the ectoderm and the endoderm. The evolution of mesoderm resulted in structural complexity. (Fig. 4.1.3) Fig. 4.1.3 Diploblastic & Triploblastic organisation 4.1.4 Coelom A third key transition in the evolution of the animal body plan was the evolution of the body cavity. The evolution of efficient organ-systems was not possible until the evolution of body cavity around the gut. The fluid-filled body cavity acts like shock- absorber to protect the visceral organs. It provides space for expansion of visceral organs. I. Acoelomates Flatworms of the phylum Platyhelminthes are acoelomates. They exhibit a solid bauplan with a dense parenchyma between the gut and the body wall in the adults. The space around the internal organs is filled with parenchyma of mesodermal origin. Hence there is no body cavity surrounding the internal organs (Fig. 4.1.4(a)). Fig 4.1.4 (a) T.S of an Acoelomate.

BIOLOGY XI-A WISDOM SERIES for ��������������CBSE XI Students 123 Animal Kingdom-Nonchordates Fig 4.1.4 (c) T.S of a Eucoelomate The epithelium that lines the outer wall of the coelom is called the parietal, or somatic peritoneum, and the epithelium that covers the internal organs suspended within the cavity including the gut is called the visceral, or splanchnic peritoneum. A. Coelom Formation Based on the mode of formation of coelom, coelomates are classified into two types: schizocoelomates and enterocoelomates. Fig 4.1.4 (d) Modes of Coelom Formation i) Schizocoelomates Annelids, arthropods and molluscs are schizoco elomates. Coelom that arises from the splitting of mesodermal bands is termed schizocoelom (Gr. schizein = split; koilos = cavity) (Fig. 4.1.4 (d)). In arthropods and molluscs schizocoelom is reduced and the functional body cavity is haemocoel. It is formed by the fusion of the embryonic blastocoel with some coelomic spaces. II. Pseudocoelomates Animals of Aschelminthes (rotifers, nematodes, etc.) possess a pseudocoelom, or blastocoelom. It is neither formed in the mesoderm nor is lined by mesodermal peritoneum. The mesoderm is present as scattered pouches in between the ectoderm and endoderm. During their development, mesoderm occupies only a part of blastocoel adjoining the ectoderm. The unoccupied portion of blastocoel persists as pseudocoelom (Fig. 4.1.4(b)). In the evolution of animals “tube-within- a-tube” arrangement is seen for the first time in pseudocoelomates. Fig 4.1.4 (b) T.S of a Pseudocoelomate As mesoderm is confined to the body wall, musculature is confined to the body wall and the gut wall is almost entirely nonmuscular. Despite the name ‘pseudocoelom’, it is a functional body cavity. It serves as a hydrostatic skeleton, protects the internal organs from mechanical shocks, provides space for the movement of internal organs and helps in circulation of the nutrients and nitrogenous wastes. III. Coelomates (Eucoelomates) Animals possessing coelom are called coelomates, Eg: annelids, molluscs, arthropods, echinoderms, hemichordates and chordates. A true coelom (secondary body cavity) is a fluid-filled cavity that develops within the mesoderm and is lined by mesodermal epithelium called peritoneum (Fig. 4.1.4 (c))..

BIOLOGY XI-A WISDOM SERIES for ��������������CBSE XI Students 124 Animal Kingdom-Nonchordates Fig 4.1.6 Metamerism 4.1.6 Metamerism Metamerism is the serial repetition of certain organs, along the anterior-posterior axis. In some animals (E.g. earthworm), the body is externally and internally divided into segments with a serial repetition of at least some organs. The segments are also called metameres, or somites. Metamerism is observed in annelids, arthropods and chordates. (Fig. 4.1.6). 4.1.7 Notochord Notochord is a mesodermal rod-like structure formed on the dorsal side during embryonic development in some animals. Among the Metazoa some species possess a notochord, but most do not. Those that possess a notochord are called chordates and constitute the phylum Chordata. About 95% of described metazoans (Porifera to Hemichordata) do not possess a notochord and constitute the nonchordates. The fundamental features of metazoan phyla are summarized in (Fig. 4.2.1). 4.2 OUTLINE CLASSIFICATION OF METAZOA (ANIMALIA) Kingdom Metazoa is classified into two sub- kingdoms: Parazoa and Eumetazoa (Fig. 4.2.2). I. Parazoa These are multicellular animals without well- defined tissues. This subkingdom includes the phylum Porifera. ii) Enterocoelomates Echinoderms, hemichordates and chordates are enterocoelomates. Enterocoelom (Gr. enteron = gut; koilos = cavity) is formed by the evagination (out- pouching) of mesoderm from the wall of archenteron (Fig. 4.1.4 (d)). 4.1.5 Fate of Blastopore Blastopore is the external opening of the primitive gut (archenteron) in the gastrula. In protostomes (Gr. protos = first; stoma = mouth) mouth develops from the blastopore. A second opening of archenteron formed later at the opposite end becomes the anus. Fig 4.1.5 Fate of blastopore In deuterostomes (Gr. deuteros = second; stoma = mouth) blastopore forms the anus. Mouth is derived as the secondary opening of the archenteron. (Fig. 4.1.5).

BIOLOGY XI-A WISDOM SERIES for ��������������CBSE XI Students 125 Animal Kingdom-Nonchordates II. Eumetazoa These are multicellular animals with well- defined tissues. Eumetazoa is further classified into two grades: Radiata and Bilateria. i) Radiata or Diploblastica These are diploblastic and exhibit radial symmetry. This grade includes the phyla Cnidaria and Ctenophora. ii) Bilateria or Triploblastica These are triploblastic and exhibit bilateral symmetry. Bilateria is further classified into two groups: Protostomia and Deuterostomia. A. Protostomia: In these animals, blastopore develops into mouth. Protostomia includes three taxa: Acoelomata, Pseudocoelomata and Schizo-coelomata. a) Acoelomata : This includes animals without body cavity. Phylum Platyhelminthes is included under this taxon. b) Pseudocoelomata: This includes animals with pseudocoelom, which is not lined by mesodermal peritoneum. Phylum Nematoda is included under this taxon. c) Schizocoelomata : This includes protostomes in which coelom is formed by the splitting of the mesoderm. Phyla Annelida, Arthropoda and Mollusca are included under this taxon. B. Deuterostomia : In these animals, blastopore develops into anus. Deuterostomia includes the taxon Enterocoelomata. Enterocoelomata: This includes animals in which coelom is formed by the pouching of the archenteron. Enterocoelomata includes the phyla Echinodermata, Hemichordata and Chordata. 4.2.1 Porifera (L.porus = pore; ferre = to bear) The phylum Porifera includes primitive multicellular animals that are commonly called sponges. Porifera is the only metazoan phylum that includes animals without true embryological germ layers, tissues and nerve cells. Sponges are sessile and superficially resemble plants. Sponges were recognized as animals only after the nature of their internal water currents was described. Fig 4.2.1 Fundamental Features of Metazoan Phyla Kingdom Symmetry Level of Organisation Body Cavity Phylum Metazoa Radial Bilateral Organ System Level Organ Level Tissue Level Cellular Level Porifera Cnidaria Ctenophora Platyhelminthes Nematoda Annelida Arthropoda Mollusca True Coelom Echinodermata Hemichordata Chordata Asymmetry (mostly) Absent Pseudocoelom.

BIOLOGY XI-A WISDOM SERIES for ��������������CBSE XI Students 126 Animal Kingdom-Nonchordates Fig 4.2.2 Outline Classification of Animalia.

BIOLOGY XI-A WISDOM SERIES for ��������������CBSE XI Students 127 Animal Kingdom-Nonchordates Choanocytes of sponges resemble the cells in choanoflagellates. Proterospongia (protozoan) is considered a connecting link between Protozoa and Porifera. Sponges represent an evolutionary blind offshoot. GENERAL CHARACTERS Habits & Habitat : Sponges are sessile. These are mostly marine. (Families Spongillidae and Potamolepidae include freshwater sponges) Level of organisation: They are primitive multicellular animals with cellular level of organization. Symmetry : Majority of the sponges are asymmetrical with irregular shape. Some are radially symmetrical. Body Wall : Body wall consists of two cell layers: an outer pinacoderm and an inner choanoderm. Pinacoderm has porocytes which enclose minute pores called ostia. These open in to canal system. Choanoderm is composed of choanocytes. They have a collar around a flagellum. Water is pulled through the ostia by the beating of the choanocytic flagella (Fig. 4.2.3). Between the pinacoderm and the choanoderm is a gelatinous mesohyl. Mesohyl has various types of amoebocytes. Regeneration: Sponges have great powers of regeneration. Spongocoel : The central cavity is called spongocoel (also known as paragastric cavity). It opens to the outside through an osculum. Canal System : The water transport system of sponges is called canal system, or aquiferous system. It helps in food gathering, respiratory gas exchange, and excretion. Water, along with food, enters the canals through the ostia and comes out along with the excretory wastes and gametes through the osculum (Fig. 4.2.3). Endoskeleton : Mesohylar endoskeleton consists of inorganic (siliceous or calcareous) spicules or proteinaceous (spongin) fibres or both. Fig. 4.2.3 General Organisation of sponge Nutrition : Sponges are suspension feeders (filter feeders). Digestion is intracellular, and takes place in choanocytes and archaeocytes. Regeneration and Cell Aggregation: Sponge cells have remarkable powers of regeneration. Asexual Reproduction: Asexual reproduction takes place by fragmentation, budding (gemmation). During unfavourable conditions they produce gemmules. Sexual Reproduction: Most sponges are hermaphroditic (monoecious). Cross and internal fertilization occurs in the mesohyl. Development : Development is indirect and includes a flagellated free-swimming larva - (coeloblastula or amphiblastula or parenchymella (parenchymula) or trichimella). Examples: Sycon (Scypha), Spongilla (freshwater sponge) and Euspongia (bath sponge), Euplectella (Venus flower basket) 4.2.2 Cnidaria Phylum Cnidaria (Gr. knide = nettle; L. aria = like) includes diverse animals like hydra, jelly fish, sea anemones and corals. They exhibit a blind sac body plan. Cnidarians are characterized by the presence of cnidocytes, and polypoid & medusoid forms..

BIOLOGY XI-A WISDOM SERIES for ��������������CBSE XI Students 128 Animal Kingdom-Nonchordates Sycon Spongilla Fig. 4.2.4 Polyp and Medusa Fig. Sponges Euspongia Euplectella Symmetry: The body is radially symmetrical (Sea anemones show biradial symmetry). Polyp and Medusa: Cnidarians exhibit “two basic body forms: polyp and medusa (Fig. 4.2.4). Polyp is cylindrical, sessile, solitary (like Hydra and Adamsia) or colonial (Obelia). Polyp produces medusa asexually. Meudsa produces polyp bysexual GENERAL CHARACTERS Habitat: These are mostly marine. A few like Hydra live in freshwater. Habits: They are either sessile or free swimming. Many are colonial. Some are solitary (E.g. Hydra, sea anemone). Level of Organisation: They are diploblastic and show tissue grade of organization..

BIOLOGY XI-A WISDOM SERIES for ��������������CBSE XI Students 129 Animal Kingdom-Nonchordates Gastrovascular Cavity: The blind sac-like central cavity is called coelenteron, or gastrovascular cavity (hence the earlier name Coelenterata). It opens out by a mouth on hypostome and is surrounded by tentacles. Mouth serves for ingestion as well as for egestion. Coelenteron helps for digestion and circulation. Nutrition: Digestion is first extracellular in the coelenteron, and then intracellular in the nutritive- muscular cells of gastrodermis. Coordination: Neurons are interconnected to form a pair of nerve nets, one in the epidermis and the other in the gastrodermis. Sensory structures like statocysts occur in the medusoid forms. Asexual Reproduction: Asexual reproduction takes place by fission, budding and fragmentation. Sexual Reproduction: Cnidarians are generally unisexual but some are bisexual. Fertilization is external. Development is indirect and includes a free- swimming ciliated larval stage called planula. Metagenesis: In species having polyp and medusa phases (E.g. Obelia), asexually reproducing polypoid stage alternates with sexually reproducing medusoid stage. Such an alternation of asexual and sexual phases is called metagenesis. (Fig. 4.2.7) method. Medusa is umbrella- or bell-shaped, free- swimming and solitary (Aurelia). Some forms show division of labour by forming structurally and functionally different types of individual (zooids) This is called polymorphism (E.g. Physalia, Halistemma) Body Wall : Body wall (Fig. 4.2.5) is composed of an outer epithelium (the epidermis) an inner epithelium (the gastrodermis) and a gelatinous mesoglea between these two. Mesoglea often contains amoeboid cells derived from ectoderm. Mesoglea is thin in polyps. It is thick in medusae, which is important in buoyancy. Cnidocytes : Their body and tentacles contain stinging cells, or stinging capsules, or cnidoblasts, or cnidocytes\ nematocytes (hence the name Cnidaria), which contains a stinging capsule called nematocyst. Cnidocytes help in defence, adhesion, and capture of prey. (Fig. 4.2.6) Fig. 4.2.6 Cnidocyte Fig. 4.2.5 Hydra - Body plan.

BIOLOGY XI-A WISDOM SERIES for ��������������CBSE XI Students 130 Animal Kingdom-Nonchordates Fig. 4.2.7 Obelia - Life history Regeneration: Cnidarians have a remarkable ability of regeneration. Interstitial cells in the body wall are the totipotent cells. Examples : Hydra, Physalia (Portuguese man of war), Aurelia (jellyfish), Adamsia (sea anemone), Pennatula (sea-pen), Gorgonia (sea-fan) and Meandrina (brain coral). Adamsia Gorgonia Physalia Aurelia Meandrina Pennatula.

BIOLOGY XI-A WISDOM SERIES for ��������������CBSE XI Students 131 Animal Kingdom-Nonchordates Reproduction: Only sexual reproduction occurs. All are monoecious (bisexual). Sexual Reproduction: Fertilization is external. Development is usually indirect and includes a cydippid larva. Regeneration : Regeneration is common. Examples : Pleurobrachia, Ctenoplana, Beroe. Fig. 4.2.8 Pleurobrachia Beroe 4.2.4 Platyhelminthes Platyhelminthes includes the flatworms such as the planarians, flukes, and tapeworms. These are triploblastic acoelomate bilaterians. The term Platyhelminthes (Greek platys = flat; helmins = worm) refers to the dorso-ventrally flattened body. They have a solid bauplan with parenchyma between the gut and the body wall. They possess complex reproductive system. Certain anthozoans (and a few hydrozoans) in which epidermis of polyps secretes a calcareous or horny exoskeleton are called corals. Their exoskeleton is also commonly called coral. Coral reefs are the large formations of calcium carbonate laid down by certain corals in shallow tropical seas. Eg: Great barrier reef of Australia 4.2.3 Ctenophora Ctenophores (Greek cten, “comb”; phero, “to bear”) are commonly called comb jellies, sea gooseberries, or sea walnuts. They are transparent, gelatinous unsegmented animals. Most of them are planktonic. They exhibit bioluminescence. They differ from cnidarians in being monomorphic throughout their life. A phylum that includes a large number of species is termed major phylum. A phylum that includes only few species is called a minor phylum. Ctenophora, Hemichordata, etc. are minor phyla. All the other phyla which you are studying in this chapter are major phyla. GENERAL CHARACTERS Habitat : These are exclusively marine. Habits : All are solitary and free-swimming animals. Level of Organisation : They are diploblastic with tissue level of organization. Symmetry : They exhibit radial symmetry. Most of the structures are radially arranged but tentacles are paired. Comb Plates : Eight external rows of ciliated plates, called comb plates help in locomotion (Fig. 4.2.8). Gastrovascular Cavity: The gastrovascular cavity consists of a pharynx, stomach, and a system of gastrovascular canals. Digestion is extracellular and intracellular as in cnidarians. Coordination: Thy have a nerve net system similar to that of cnidarians. Statocyst is present..

BIOLOGY XI-A WISDOM SERIES for ��������������CBSE XI Students 132 Animal Kingdom-Nonchordates Taenia solium Dugesia - Flame cell Fasciola hepatica 4.2.5 Aschelminthes Aschelminthes refers to round worms which are hollow.It includes animals with pseudocoelom. GENERAL CHARACTERS Habits : These are free-living or parasitic (on plants and animals). Free-living forms may be terrestrial or aquatic. Large number of microscopic free-living nematodes, such as Rhabditis, live in soil rich in organic matter. Level of Organisation: They are triploblastic and exhibit organ-system level of organisation. GENERAL CHARACTERS Habits : These are mostly endoparasites (Flukes and tape worms). Some are free-living (Planarians). Level of Organisation: They are triploblastic, and exhibit organ level of organisation. Symmetry: They are bilaterally symmetrical and exhibit cephalization. Acoelomate Condition: They are acoelomates and lack a large fluid-filled body cavity. Connective tissue compartment between the gut and the body wall is called parenchyma. Nutrition: Gut is a blind sac. Mouth is used for ingestion and egestion. Anus is absent. In tapeworms gut is absent. They absorb nutrients from the host directly through their body surface. Parasitic adaptations: Flukes have suckers and tapeworms have hooks and suckers for attachment to the host body. Respiration and Circulation: Respiratory and circulatory systems are absent. Excretion: Protonephridia with flame cells are useful primarily for osmoregulation and secondarily for excretion. Coordination: Cerebral ganglia constitute the brain. Longitudinal nerve cords are joined by transverse commissures at regular intervals giving a ladder- like appearance. Asexual Reproduction: Many turbellarians (Planarians) reproduce asexually by fragmentation. They have remarkable power of regeneration. Sexual Reproduction: They are mostly hermaphroditic. Fertilization is internal. Development : Development is mostly indirect. Life history is complex with many larval forms in parasitic forms. Polyembryony is common in flukes. Examples: Dugesia (planarian), Fasciola (liver fluke), Schistosoma (liver fluke), Taenia (tapeworm); and Echinococcus (dog tapeworm)..

BIOLOGY XI-A WISDOM SERIES for ��������������CBSE XI Students 133 Animal Kingdom-Nonchordates Body Form: Body is cylindrical and bilaterally symmetrical. Their bodies appear circular in cross- section, hence, the name roundworm. Body Wall: Body wall consists of a thick cuticle, epidermis, and longitudinal muscles. Cuticle is transparent and collagenous. Body Cavity: Body cavity is a pseudocoelom. It is not lined by mesodermal peritoneum. It represents persistent blastocoel. Pseudocoelomic fluid acts as a hydrostatic skeleton. It is also useful in circulation. Ascaris lumbricoides Digestive System: Alimentary canal is complete with well developed muscular pharynx, Excretion: An excretory tube removes body wastes from the body cavity through the excretory pore. Renette gland is seen in some. Nervous System: They possess a circum- pharyngeal ganglionated nerve ring from which small nerves extend anteriorly and nerve cords extend posteriorly. Sense Organs: Sense organs include amphids and phasmids (chemoreceptors) Reproduction: Nematodes are unisexual (dioecious) and exhibit sexual dimorphism. Males are usually smaller than females and have a curved posterior end with cloaca and one or two copulatory spicules, or penial setae. Females are longer with anus at the posterior end and gonopore at the anterior end. Development: Fertilization is internal. These are mostly oviparous (E.g. Ascaris). Some are ovoviviparous (E.g. Wuchereria). Development may be direct (the juveniles resemble the adult) or indirect. Development includes four moults. Examples : Ascaris (roundworm), Wuchereria (filarial worm), Ancylostoma (hookworm), Rhabditis. 4.2.6 Annelida Phylum Annelida includes segmented worms. They are triploblastic bilaterally symmetrical schizocoelomate protostomes. They are metamerically segmented with organ and organ systems. GENERAL CHARACTERS Habits : Mostly free living aquatic. Some are terrestrial. Leeches are blood sucking ectoparasites. Cephalization: There is a distinct head, bearing tentacles, eyes etc. (Nereis) Metamerism: Annelids show metamerism. Body is divided into a linear series of ring like segments or metameres. Hence the phylum name Annelida (annulus : little ring) Body Wall: Body wall has both longitudinal and circular muscles which help in locomotion. Chitinous bristles that project out from the epidermis are called setae (chaetae). They provide grip on the substratum. Aquatic annelids (Nereis) have lateral appendages called parapodia. Body Cavity: The coelom develops by the splitting of mesodermal bands (schizocoel), forming a pair of coelomic compartments in each segment, one on either side of the gut. Digestive System: Alimentary canal is a straight muscular tube. Respiration: Exchange of respiratory gases takes place by diffusion through the body wall and gills. In many polychaetes parts of parapodia are modified into gills. Blood vascular system: A closed blood vascular system appeared for the first time in annelids. The common respiratory pigment of annelids is haemoglobin. Excretory System: Excretory organs are segmentally arranged metanephridia. They open into the coelom by a nephrostome. Nephridia help in excretion and osmoregulation..

BIOLOGY XI-A WISDOM SERIES for ��������������CBSE XI Students 134 Animal Kingdom-Nonchordates Arthropods are represented in every habitat on Earth and show a great variety of adaptations. GENERAL CHARACTERS They are bilaterally symmetrical, segmented schizocoelomates with organ or organ system level of organisation. Habitat: Arthropods occur in all types of habitats, i.e. marine, freshwater and terrestrial. Cephalisation: The head consists of fused segments with appendages such as antennae, mouthparts and sense organs. Exoskeleton : Their body is covered by a chitinous cuticle which forms hard plates called sclerites. It is impermeable to water. Appendages: Appendages are jointed. Hence, the name arthropoda (arthros: Jointed, poda: legs). Striated muscles first appeared in Arthropoda. Body Cavity: Coelom is reduced. Haemocoel is the functional body cavity. It is filled with blood (haemolymph). Digestive System: Alimentary canal is complete and coiled muscular tube. Respiratory System: Aquatic arthropods respire through gills and book-gills whereas terrestrial forms respire through tracheae and book-lungs. Blood Vascular System: Blood vascular system is of open type. Heart is dorsal in position. Respiratory pigment haemocyanin is present in some (spiders, scorpions, prwns and crabs). Excretory System: Excretory organs include Malpighian tubules (in terrestrial forms), coxal glands and green glands (in aquatic forms). Nervous System: The central nervous system consists of a nerve ring and a solid double ventral nerve cord, which contains segmental ganglia and nerves. Sense organs include antennae, simple eyes, compound eyes, statocysts, etc. Reproduction: Most arthropods are unisexual. Fertilization is usually internal. Nervous system: Nervous system consists of paired ganglia connected by lateral nerves to a double ventral nerve cord. Reproduction: Reproduction is sexual. Polychaetes are unisexual. Earthworms and leeches are bisexual. Development: Fertilisation is external, except in leeches. Development is direct in earthworms and leeches. In polychaetes, development is indirect and includes a Trochophore larva. Examples: Nereis, Pheretima (earthworm) and Hirudinaria (blood-sucking leech). Nereis Hirudinaria granulosa 4.2.7 Arthropoda Arthropoda is a successful group of animals on earth. They have conquered land, sea and air. With more than one million described species, Arthropoda is the largest metazoan phylum. Over two thirds of all named species on earth are arthropods. Arthropoda is an incredibly diverse group of taxa such as insects, crustaceans, scorpions, and centipedes..

BIOLOGY XI-A WISDOM SERIES for ��������������CBSE XI Students 135 Animal Kingdom-Nonchordates Development: They are mostly oviparous. In many arthropods, development is direct. The young, hatched from eggs, resemble the adult and often occupy the same habitat. They grow by moulting. Indirect development occurs in others. The egg hatches into an independent larva. The process of transformation of a larva into an adult is called metamorphosis. Economically important insects – Apis (honeybee), Bombyx (silkworm), Laccifer (lac insect) Vectors – Anopheles, Culex and Aedes (mosquitoes) Gregarious pest – Locusta (locust) Living fossil – Limulus (king crab). It is considered living fossil as it has remained without evolutionary change over millions of years. Palamnaeus Laccifer Bombyx Locusta Limulus (King crab) Penaeus.

BIOLOGY XI-A WISDOM SERIES for ��������������CBSE XI Students 136 Animal Kingdom-Nonchordates 4.2.8 Mollusca Molluscs form an ancient group Mollusca (L. mollusca = a soft nut) includes the familiar soft- bodied animals such as snails, slugs, mussels, oysters, octopuses, etc. Phylum Mollusca is the second largest animal phylum. Mantle and radula are characteristic of molluscs. Molluscs are triploblastic, bilaterally symmetrical, unsegmented schizocoelomates. Architeuthis (Giant Squid) is the largest extant invertebrate. Pearls are obtained from pearl oyster- Pinctada sps. GENERAL CHARACTERS Habitat: Molluscs are chiefly marine. Some gastropods and bivalves live in freshwater. Some gastropods are terrestrial. Level of Organisation: They exhibit organ-system level of organisation. Symmetry: These are bilaterally symmetrical. Gastropods are secondarily asymmetrical. Shell: Body is covered by a calcareous shell secreted by the mantle epithelium. Body Divisions: The body is unsegmented and is divided into an anterior head, a large dorsal visceral mass or hump, and a muscular ventral foot. Foot is useful in locomotion. Anterior region of head bears sensory tentacles (Fig. 4.2.9). Mantle and Mantle Cavity: A soft and spongy layer of skin forms a mantle, or pallium over the visceral hump. The space between the mantle and the visceral mass is called mantle cavity, or pallial cavity. It contains feather-like gills, osphradium, anus, nephridiopores, and gonopores (Fig. 4.2.9). Digestive System: Buccal cavity contains a file-like rasping organ called radula (Fig. 4.2.9), except in the bivalves. Respiratory System: Gills of molluscs are called ctenidia. They have respiratory and excretory function. ADDITIONAL READING MATERIAL • All insects included under the taxon Pterygota undergo metamorphosis. • In paurometabolous (gradual) metamorphosis, the life history includes egg, nymph (young), and imago (adult). The nymph resembles the adult in its mode of life but differs from it in structure. The nymph is without wings. Examples: cockroaches, grasshoppers, etc. • In hemimetabolous (incomplete) metamorpho- sis, the life history includes egg, naiad (young), and imago (adult). The naiad differs from the adult in both mode of life and structure. Ex- amples: dragon flies and may flies. • In holometabolous (complete) metamorphosis, the life history includes egg, larva, pupa� and imago (adult). Examples: butterflies, moth, beetles, house flies, mosquitoes, fleas, honey bees, ants and wasps. • The statocyst is a balance sensory receptor present in some aquatic invertebrates, including, cnidarians, echinoderms, molluscs and crustaceans. The statocyst consists of a sac-like structure containing a mineralised mass (statolith) and numerous sensory cells. Statocyst.

BIOLOGY XI-A WISDOM SERIES for ��������������CBSE XI Students 137 Animal Kingdom-Nonchordates Blood Vascular System: Blood vascular system is of open type, except in cephalopods (squids, Octopus). Respiratory pigment is haemocyanin. Excretory System: Pair of metanephridia, often called kidneys or organs of Bojanus are present. Nervous System: Nervous system consists of pairs of ganglia. Sense organs include eyes, tentacles, statocysts and osphradia. Osphradium is a chemoreceptor in bivalves and gastropods, which helps in detection of the quality of water. Reproduction and Development: Molluscs are mostly unisexual (dioecious) and oviparous. Development is mostly indirect with trochophore larva or veliger larva. In most species, it develops into a veliger larva. Development is direct in some (E.g. cephalopods). Examples: Pila (apple snail), Pinctada (pearl oyster), Sepia (cuttlefish), Loligo (squid), Octopus (devil fish), Aplysia (sea hare), Dentalium (tusk shell) and Chaetopleura (chiton). Octopus Sepia Fig. 4.2.9 Generalised Mollusc.

BIOLOGY XI-A WISDOM SERIES for ��������������CBSE XI Students 138 Animal Kingdom-Nonchordates Aplysia Chiton Pila Dentalium Loligo Pinctada 4.2.9 Echinodermata GENERAL CHARACTERS Habits & Habitat: All are free-living; parasites are absent. Echinoderms are marine animals. A few can occur in brackish waters also (E.g. Synapta similis). Level of Organisation: They are triploblastic, unsegmented animals with organ-system level of organisation. Symmetry: Their larvae are free-swimming and bilaterally symmetrical. Adults exhibit (pentamerous) radial symmetry. The body parts occur along five axes. Skeleton: Skeleton consists of calcareous ossicles located in the dermis. Ossicles project outward as spines or warts (hence the name Echinodermata). Coelom: Body cavity is enterocoelom, formed by the pouching of archenteron. Water Vascular System: It is the most distinctive feature of echinoderms. Tube feet associated with this system are useful in locomotion, food capture, gas exchange and excretion (Fig. 4.2.10). Fig. 4.2.10 Starfish-Water vascular system.

BIOLOGY XI-A WISDOM SERIES for ��������������CBSE XI Students 139 Animal Kingdom-Nonchordates Digestive System: Digestive system is complete with mouth on the lower oral (ventral) side and anus on the upper aboral (dorsal) side. Gas Exchange: In addition to tube feet, respiratory trees and special outgrowths of body wall, such as papulae (dermal branchiae), are useful in gas exchange. Circulation: Echinoderms rely chiefly on coelomic circulation. Blood vascular system is of open type and is poorly developed. Heart and blood vessels are absent. Excretion: Specialized excretory organs are absent. Nervous System: Nervous system is poorly developed. Reproduction and Development: Reproduction is sexual. These are mostly unisexual, without sexual dimorphism. Fertilization is usually external. Development is indirect with a free-swimming larva. Regeneration: Echinoderms have remarkable power of regeneration. Many species exhibit autotomy (auto = self; tome = cut) when captured by a predator. The lost body parts are regenerated. Examples: Asterias (star fish or sea star), Echinus (sea urchin), Antedon (feather star), Cucumaria (sea cucumber) and Ophiura (brittle star), Echinocardium (heart urchin). Asterias Cucumaria Echinus Ophiura.

BIOLOGY XI-A WISDOM SERIES for ��������������CBSE XI Students 140 Animal Kingdom-Nonchordates Fig. 4.2.11 Balanoglossus Circulatory System : Circulatory system is simple and is of open type. Excretory System : Excretion occurs by a single proboscis gland, or glomerulus. Nervous System : Nervous system is primitive consisting mainly of two nerve cords: dorsal and ventral. Reproduction and Development : Sexes usually separate. Fertilization is external, takes place in sea water. Development is direct or indirect with a free-swimming tornaria larva. Examples: Balanoglossus, Saccoglossus, Rhabodpleura (colonial), and Cephalodiscus. Antedon 4.2.10 Hemichordata It was earlier considered as a sub-phylum under Chordata. But, now it is treated as separate phylun under non-chordates. GENERAL CHARACTERS Habitat: Exclusively marine, solitary or colonial, mostly tubicolous. Body: Body is soft, wormlike, unsegmented and bilaterally symmetrical. Body is divided into three regions: anterior proboscis, middle collar and posterior long trunk. (Fig. 4.2.11). Level of Organisation: They are triploblastic with organ-system level of organisation. Coelom: Coelom is enterocoelom. Digestive System: They are ciliary filter-feeders. Digestive tube is complete, straight or V-shaped. Foregut gives out a hollow buccal diverticulum that extends into proboscis, which was earlier considered homologous to “notochord”. Respiratory System: It includes one to several pairs of dorso-lateral pharyngeal gill-slits..