Phylum Porifera
Primitive multicellular animals with cellular grade of organisation.
Free living aquatic, mostly marine, sedentary forms either solitary or colonial.
Body with a large number of incurrent pores called ostia leading into a spongocoel through a system of canals, Spongocoel opening out by one or two large excurrent pores called oscula.
Canals and spongocoel are lined by flagellated cells called choanocytes or collar cells.
Body wall with two layers of loosely arranged cells and a mesenchyme in between.
Body has an endoskeleton made up of spicules. Composed of calcareous or silicious spicules or spongin fibres.
Digestion is intracellular.
Respiration and excretion by simple diffusion.
Reproduction by asexual (external or internal buds) or sexual methods.
fig. 10.5 - Some Common Sponges
The phylum is divided into three classes.
fig. 10.6 - Generalised Sponge Anatomy
Phylum Platyhelminthes
Bilaterally symmetrical, triploblastic true multi-cellular animals with organ grade of organisation.
Free living (aquatic or terrestrial) or parasitic (ecto- or endoparasites).
Body is dorso-ventrally compressed, leaflike.
A body cavity is absent. Space between body wall and alimentary canal is filled with mesenchyme (connective tissue).
Digestive system is incomplete. Anus is absent.
Respiration by simple diffusion.
Excretion with the help of specialised cells called flame cells or solenocytes.
Nervous system is ladder-like consisting of a brain and a pair of longitudinal nerves connected by many transverse nerves.
Reproduction is usually by sexual methods. Majority of the forms are bisexual (hermaphrodites). Development is direct or indirect.
Body is triploblastic.
They have blind sac body plan.
fig. 10.9 - Examples of PlatyhelminthesThe phylum is divided into three classes
fig. 10.10 - Planarian Anatomy
Phylum Aschelminthes
Mostly parasitic (in animals and plants), a few free living called as flukes.
Body is long, cylindrical, fusiform (pointed at both the ends).
Body wall is composed of cuticle, epidermis and musculature.
Presence of a false body pseudocoelom not lined by epithelium.
Digestive system is complete.
Respiration by simple diffusion.
Nervous system consists of a nerve ring and many longitudinal nerve cords.
Only sexual reproduction. Sexes are separate with sexual dimorphism. Males are usually shorter than females.
fig. 10.8 - Examples of Nematodes
Common examples of nematodes, a major group of Aschelminthes.
1. Rhabditis (free living)
2. Ascaris (round worm) (parasitic)
3. Dracuculus (guinea worm)
4. Enterobium (pin worm)
5. Trichiuris (whilp worm)
6. Wuchereria (filarial worm)
7. Loa loa (eye worm)
fig. 10.12 - Roundworm Anatomy
Phylum Annelida
Free-living, terrestrial or aquatic form (freshwater or marine).
Body is long, cylindrical and metamerically segmented.
Body wall consists of cuticle, epidermis and musculature.
Body cavity is a true coelom, lined by epithelium.
Digestive system is complete.
Respiration is either through skin or through gills.
Excretion with the help of characteristic nephridia.
Presence of a circulatory system (closed type). Hemoglobin dissolved directly in the plasma.
Nervous system consists of a nerve ring and a double ventral nerve cord with segmental ganglia.
Locomotion with the help of setae or parapodia.
Reproduction by sexual methods. Either unisexual or bisexual development may be direct or indirect.
Body has a true coelom.
fig. 10.13 - Examples of Annelida
The phylum is divided into four classes
fig. 10.14 - Anterior Segments of Nereis
fig. 10.15 - Earthworm Anatomy
Phylum Arthropoda
This phylum is the largest in the animal kingdom comprising of more than 75% of the animal species that have been identified.
Free living forms, aquatic (fresh water or marine) or terrestrial or aerial. Some parasitic forms also.
Body is elongated and segmented, usually distinguished into regions like head, thorax and abdomen.
Body has exoskeleton made up of a hard, impermeable substance called chitin.
Digestive system is complete.
Circulatory system is of open type. Blood flows freely in the body cavity (hemocoel).
Respiration through gills, or trachea or book lungs.
Excretion through coxal glands or malpighian tubules.
Nervous system consists of a nerve ring and a double ventral nerve cord.
Locomotor organs represented by segmentally arranged many jointed appendages.
Cilia are totally absent in any part of the body.
Reproduce sexually, sexes are separate. Development may be direct or indirect.
fig.10.16 - Examples of Arthropoda
The phylum is divided into six classes
Class (habital) / Respiratory organs / Walking legs / Common examples1.Diplopoda (terrestrial) / Trachea / Many-two pairs in each segment / Millipede
2.Chilopoda (terrestrial) / Trachea / Many one pair in each segment / Centipede
3.Crustacea (aquatic) / Gills / Five pairs / Crab, Prawn, Lobster
4.Arachnida (terrestrial) / Book lungs / Four pairs / Scorpion, Spider
5.Insecta (terrestrial) / Trachea / Three pairs / Cockroach, Butterfly
6.Onychophora (terrestrial) / Trachea / Many unjointed / Penpatus
fig.10.17 - Grasshopper Anatomy
Mollusca
Free living aquatic forms (freshwater or marine), some amphibious.
Body is soft and unsegmented enclosed in a glandular mantle covered by usually a shell.
Coelom is reduced to a pericardial cavity around the heart.
Digestive system is complete.
Respiratory organs are in the form of gills called ctenidia.
Locomotor structure is represented by muscular foot.
They have soft-body, which is differentiated into three regions - head, visceral hump and foot.
Visceral hump is covered by a thin, fleshy fold called mantle.
Mantle secretes a calcarious shell, which may be external or internal.
Reproduction is sexual. Either unisexual or bisexual, development is direct.
fig.10.18 - Examples of Mollusca
The phylum is divided into six classes
fig. 10.19 - Snail Anatomy
Echinodermata
Free living exclusively marine forms.
Adults are radially symmetrical while larvae are bilaterally symmetrical.
Body is represented by a central disc covered by ossicles with spines called pedicellaria.
Disc may bear extensions called arms.
Digestive system is complete.
A unique ambulacral or water vascular system is present.
Tube feet are present for locomotion and respiration. Tube feet are extended and retracted by variation in hydraulic pressure of the fluid in them and contraction of their muscles.
Nervous system has a central nerve ring with five radiating nerves.
Reproduction is sexual. Sexes are separate. Development is indirect.
Show very high power of regeneration.
Tube feet are for feeding as well.
fig. 10.20 - Examples of Echinodermata
The phylum is divided into five classes.
fig. 10.21 - Starfish Anatomy
Chordata
Presence of a solid supporting structure on the dorsal side of the body called notochord.
Presence of a dorsal hollow, tubular nerve cords.
Presence of pharyngeal gill slits at least in the embryonic stages.
The phylum is divided into 4 sub phyla.
Hemichordata, Urochordata, Cephalochordata (together called as Protochordates) and Vertebrata.
Characteristics of Protochordates
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fig. 10.22 - Classification of Vertebrata
The phylum is divided into six classes.
fig. 10.23 - Examples of Pisces
fig. 10.24 - Examples of Amphibians
fig. 10.25 - Examples of Reptilia
fig. 10.26 - Examples of Aves
fig. 10.27 - Examples of Mammalia
Note
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Mammals exhibit the following unique features also.
Presence of mammary glands to nourish the young ones.
Presence of muscular diaphragm that separates thorax from abdomen.
Presence of external ear called pinna.
Presence of seven vertebrae in the neck region.
fig. 10.28 - Fish Anatomy
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