Animal Diversity and Classification

Animal Diversity and Classification carries 4 of the 40 Zoology questions, all from one syllabus line: the diagnostic features and classification of animals from Protozoa to Chordata. The questions are of three kinds — "which phylum or class has this feature" (flame cells, choanocytes, water vascular system, placoid scales), "which animal is this" (the scientific name behind a common name), and "which statement is true of this group" (coelom, symmetry, excretory organ, heart). Learn the tables in this chapter column by column.

2.1 Diagnostic features and classification of animals from Protozoa to Chordata

The bases of classification

Basis	States	Found in
Level of organisation	protoplasmic (one cell does everything)	Protozoa
	cellular (cells with division of labour, no true tissues)	Porifera
	tissue	Coelenterata, Ctenophora
	organ	Platyhelminthes
	organ-system	Aschelminthes to Chordata
Symmetry	asymmetrical	most sponges; adult snails (after torsion)
	radial (any plane through the oral–aboral axis halves the body)	Coelenterata; adult Echinodermata (pentaradial)
	biradial	Ctenophora, sea anemones
	bilateral (one plane only)	Platyhelminthes to Chordata; echinoderm larvae
Germ layers	diploblastic (ectoderm + endoderm, non-cellular mesogloea between)	Coelenterata, Ctenophora (Porifera are usually grouped here)
	triploblastic (mesoderm added)	Platyhelminthes onwards
Coelom	acoelomate (space packed with mesodermal parenchyma)	Platyhelminthes
	pseudocoelomate (cavity not fully lined by mesoderm — a blastocoel remnant)	Aschelminthes
	eucoelomate, schizocoelous (mesoderm splits)	Annelida, Arthropoda, Mollusca
	eucoelomate, enterocoelous (pouches from the gut)	Echinodermata, Hemichordata, Chordata
Segmentation	metameric (true, repeated organs)	Annelida, Arthropoda, Chordata
	pseudometamerism (proglottids budded off)	tapeworms
Embryo	protostome: blastopore → mouth; spiral, determinate cleavage	Annelida, Arthropoda, Mollusca
	deuterostome: blastopore → anus; radial, indeterminate cleavage	Echinodermata, Hemichordata, Chordata
Notochord	absent (non-chordates) / present (chordates)	—

The true coelom is a cavity lined on both sides by mesoderm: the outer parietal (somatic) layer on the body wall and the inner visceral (splanchnic) layer on the gut. In Arthropoda and Mollusca the coelom is reduced and the main body cavity is a blood-filled haemocoel.

The phyla at a glance

Phylum	Level	Symmetry	Coelom	Gut	Circulation	Respiration	Excretion	Nervous system
Protozoa	protoplasmic	various	—	food vacuoles	—	diffusion	contractile vacuole, diffusion	—
Porifera	cellular	asymmetrical / radial	none	none (canal system)	none	diffusion	diffusion	none
Coelenterata	tissue	radial	none (coelenteron)	blind sac, one opening	none	diffusion	diffusion	nerve net
Platyhelminthes	organ	bilateral	acoelomate	incomplete (no anus) or absent	none	diffusion	flame cells	ladder-like
Aschelminthes	organ-system	bilateral	pseudocoel	complete	none	diffusion	renette cells / canals	circum-pharyngeal ring + cords
Annelida	organ-system	bilateral	schizocoel	complete	closed	skin, gills	nephridia	ventral, double, ganglionated
Arthropoda	organ-system	bilateral	haemocoel	complete	open, dorsal heart	gills, tracheae, book lungs	Malpighian tubules, green glands	ventral, double, ganglionated
Mollusca	organ-system	bilateral (snails asymmetrical)	reduced (pericardial)	complete, radula	open (closed in cephalopods)	gills (ctenidia), pulmonary sac	kidneys / organ of Bojanus	ganglia
Echinodermata	organ-system	pentaradial adult, bilateral larva	enterocoel	complete	haemal system	tube feet, dermal branchiae	none	nerve ring, no brain
Chordata	organ-system	bilateral	enterocoel	complete	closed, ventral heart	gills or lungs	kidneys	dorsal, hollow

Protozoa (kingdom Protista)

In the five-kingdom system the protozoans are the animal-like protists; the syllabus begins animal classification with them.

• Unicellular eukaryotes at the protoplasmic level; free-living or parasitic.
• No cell wall; body covered by plasma membrane or a firm pellicle.
• Nutrition holozoic, holophytic (Euglena), saprozoic or parasitic.
• Locomotion by pseudopodia, flagella or cilia; Sporozoa have none.
• Osmoregulation by contractile vacuoles in fresh-water forms; respiration and excretion by diffusion.
• Asexual reproduction by binary or multiple fission; sexual by syngamy or conjugation; cysts survive bad conditions.

Class	Locomotion	Examples (and diseases)
Rhizopoda (Sarcodina)	pseudopodia	Amoeba proteus; Entamoeba histolytica (amoebic dysentery); E. gingivalis (in the gums); Elphidium (Polystomella, a foraminiferan)
Mastigophora (Flagellata)	flagella	Euglena viridis; Trypanosoma gambiense (African sleeping sickness, by the tsetse fly Glossina); Leishmania donovani (kala-azar, by the sandfly Phlebotomus — endemic in Nepal's Terai); Giardia intestinalis (diarrhoea); Trichomonas vaginalis; Noctiluca (sea luminescence); Trichonympha (digests cellulose in termites)
Sporozoa (Apicomplexa)	none in the adult; all parasites; form spores	Plasmodium (malaria, by female Anopheles); Monocystis (seminal vesicles of earthworm); Eimeria (coccidiosis of poultry); Toxoplasma
Ciliata	cilia; two kinds of nuclei (macronucleus, micronucleus)	Paramecium caudatum (slipper animalcule); Vorticella (bell animalcule); Balantidium coli (the only ciliate parasite of man, dysentery); Nyctotherus (rectum of frog)

Phylum Porifera — sponges

• Aquatic, mostly marine, sessile; asymmetrical or radial; cellular level.
• Body perforated by many small pores, the ostia (incurrent), and one large osculum (excurrent); the body cavity is the spongocoel.
• Canal (water-current) system — ostia → canals → spongocoel → osculum — brings food and O₂ and removes waste. Types: ascon (Leucosolenia), sycon (Sycon), leucon (Spongilla, Euspongia).
• Choanocytes (collar cells) line the spongocoel or chambers and drive the current; digestion is intracellular.
• Skeleton of spicules (calcareous or siliceous) and/or spongin fibres.
• No mouth, gut, muscles, nerves or organs. Hermaphrodite; fertilisation internal; larva amphiblastula or parenchymula. Asexual by budding, fragmentation and gemmules (internal buds of fresh-water sponges). Great power of regeneration.

Class	Skeleton	Examples
Calcarea (Calcispongiae)	calcareous (CaCO₃) spicules	Sycon (Scypha), Leucosolenia, Grantia
Hexactinellida (Hyalospongiae) — glass sponges	six-rayed siliceous spicules	Euplectella (Venus' flower basket), Hyalonema (glass-rope sponge)
Demospongiae	spongin fibres with or without siliceous spicules	Euspongia (bath sponge), Spongilla (fresh-water sponge), Cliona (boring sponge), Chalina (dead man's fingers)

Phylum Coelenterata (Cnidaria)

• Aquatic, mostly marine (Hydra is fresh-water); solitary or colonial; radial symmetry; tissue level; diploblastic with a non-cellular mesogloea.
• One cavity, the coelenteron (gastrovascular cavity), opening by the mouth on a raised hypostome; no anus. Digestion extracellular, then intracellular.
• Cnidoblasts (cnidocytes) with nematocysts (stinging capsules) on the tentacles — the diagnostic feature; for prey capture, defence and anchorage.
• Two body forms: the sessile, cylindrical polyp (asexual) and the free-swimming, umbrella-shaped medusa (sexual). Their alternation is metagenesis (Obelia). Polymorphism: different zooids in one colony (Physalia).
• Nerve net, no brain; no respiratory, circulatory or excretory organs. Larva planula. Corals secrete a CaCO₃ skeleton and build reefs.

Class	Dominant form	Examples
Hydrozoa	polyp, medusa or both; medusa with a velum	Hydra (polyp only), Obelia (sea fur, metagenesis), Physalia (Portuguese man-of-war), Velella
Scyphozoa	medusa dominant (true jellyfish)	Aurelia (moon jelly), Rhizostoma, Cyanea
Anthozoa (Actinozoa)	polyp only, no medusa	sea anemones Metridium, Adamsia (on the hermit crab's shell); corals Corallium (red coral), Madrepora, Meandrina (brain coral), Fungia (mushroom coral); Gorgonia (sea fan), Pennatula (sea pen)

Ctenophora (comb jellies) are a small marine phylum close to the Cnidaria: biradial, diploblastic, with eight rows of comb plates (ctenes) of fused cilia for swimming, colloblasts (lasso cells) instead of nematocysts, and strong bioluminescence: Pleurobrachia (sea gooseberry), Ctenoplana.

Phylum Platyhelminthes — flatworms

• Dorsoventrally flattened; bilateral, triploblastic, acoelomate (parenchyma fills the body); organ level; head present.
• Mostly endoparasites with hooks and suckers; thick tegument resists host enzymes.
• Gut incomplete (mouth, no anus) or absent (tapeworms absorb food through the body surface).
• Excretion and osmoregulation by flame cells (protonephridia).
• Mostly hermaphrodite; internal fertilisation; complicated life cycles with one or two hosts. Planaria regenerates whole worms from small pieces.

Class	Features	Examples (and diseases)
Turbellaria	free-living, ciliated epidermis	Dugesia (Planaria)
Trematoda (flukes)	parasitic, suckers, branched gut	Fasciola hepatica (liver fluke of sheep; snail Lymnaea is the intermediate host; larvae miracidium → sporocyst → redia → cercaria); Schistosoma (blood fluke, schistosomiasis)
Cestoda (tapeworms)	ribbon-like; scolex with suckers (± hooks); chain of proglottids; no gut	Taenia solium (pork tapeworm: scolex armed with hooks; pig is the intermediate host; its larva in man's brain causes neurocysticercosis); T. saginata (beef tapeworm, scolex without hooks); Echinococcus granulosus (dog tapeworm; hydatid cyst in man)

Phylum Aschelminthes (Nemathelminthes, Nematoda) — roundworms

• Cylindrical, unsegmented, tapering at both ends; tough cuticle; bilateral, triploblastic, organ-system level.
• Pseudocoelomate — the first body cavity.
• Complete gut (mouth and anus) with a muscular pharynx — the first "tube within a tube".
• Only longitudinal muscles in the body wall (whip-like movement). No circulatory or respiratory organs; excretion by excretory canals / renette cells.
• Sexes separate (dioecious) with sexual dimorphism: the male is smaller with a curved tail bearing penial spicules. No cilia anywhere.

Worm	Common name	Disease / note
Ascaris lumbricoides	common roundworm	ascariasis (small intestine)
Enterobius vermicularis	pinworm (seat worm)	children; anal itching
Ancylostoma duodenale	hookworm	larvae enter through the skin of bare feet; blood-sucking → anaemia
Wuchereria bancrofti	filarial worm	filariasis (elephantiasis); vector Culex mosquito
Dracunculus medinensis	guinea worm	intermediate host Cyclops (in drinking water)
Trichinella spiralis	trichina worm	trichinosis from undercooked pork
Loa loa	eye worm	under the skin and over the eye
Caenorhabditis elegans	—	free-living model organism of genetics

Phylum Annelida — segmented worms

• Elongated, metamerically segmented — the first true segmentation; bilateral, triploblastic, coelomate (schizocoelous).
• Thin moist cuticle; locomotion by setae (chaetae), parapodia or suckers, with circular and longitudinal muscles working on the coelomic fluid (hydrostatic skeleton).
• Closed circulatory system; haemoglobin dissolved in the plasma.
• Excretion by nephridia; respiration through the moist skin (gills in some polychaetes).
• Ventral, double, ganglionated nerve cord with a nerve ring.
• Hermaphrodite (earthworm, leech) or dioecious (Nereis); polychaetes have a trochophore larva.

Class	Diagnostic	Examples
Polychaeta	marine; parapodia with many setae; no clitellum; dioecious; trochophore	Nereis (sandworm, clam worm), Aphrodite (sea mouse), Chaetopterus, Arenicola (lugworm)
Oligochaeta	few setae, no parapodia; clitellum; hermaphrodite; direct development	Pheretima posthuma (Indian earthworm), Lumbricus terrestris, Tubifex
Hirudinea (leeches)	no setae or parapodia; fixed number of segments (about 33); anterior and posterior suckers; hermaphrodite; coelom filled by botryoidal tissue	Hirudinaria granulosa (cattle leech), Hirudo medicinalis (medicinal leech — saliva has the anticoagulant hirudin), Haemadipsa (land leech of the monsoon hills)

Phylum Arthropoda — jointed-legged animals

The largest phylum: more than two-thirds of all named animal species.

• Jointed appendages; chitinous exoskeleton shed by moulting (ecdysis).
• Body segmented and grouped into head, thorax and abdomen or cephalothorax and abdomen.
• Coelom reduced; body cavity a blood-filled haemocoel; open circulation with a dorsal heart.
• Respiration by gills, book gills (Limulus), book lungs (scorpions, spiders), tracheae (insects, myriapods) or the body surface.
• Excretion by Malpighian tubules (insects, myriapods, arachnids), green (antennal) glands (crustaceans) or coxal glands (arachnids).
• Compound eyes; ventral double nerve cord; sexes usually separate; fertilisation internal; often metamorphosis.

Class	Body	Antennae	Legs	Respiration / excretion	Examples
Crustacea	cephalothorax (with carapace) + abdomen	2 pairs	many, biramous	gills / green glands; nauplius larva	Palaemon (prawn), Astacus (crayfish), Cancer (crab), Daphnia (water flea), Cyclops, Balanus (barnacle), Sacculina (parasite of crabs), Eupagurus (hermit crab)
Chilopoda (Myriapoda) — centipedes	head + many trunk segments	1 pair	1 pair per segment; first pair are poison claws	tracheae / Malpighian tubules	Scolopendra
Diplopoda (Myriapoda) — millipedes	head + many trunk segments	1 pair	2 pairs per segment	tracheae / Malpighian tubules	Julus, Spirostreptus
Insecta (Hexapoda)	head, thorax, abdomen	1 pair	3 pairs; usually 2 pairs of wings	tracheae / Malpighian tubules	Periplaneta americana (cockroach), Musca domestica, Anopheles, Aedes, Culex, Apis (honey bee), Bombyx mori (silk moth), Laccifer (Kerria) lacca (lac insect), Locusta, Pediculus (louse), Cimex (bed bug), Xenopsylla (rat flea, plague), Lepisma (silverfish, wingless)
Arachnida	cephalothorax + abdomen	none	4 pairs; chelicerae and pedipalps	book lungs or tracheae / Malpighian tubules, coxal glands	Palamnaeus and Buthus (scorpions), Aranea (spider), Sarcoptes scabiei (itch mite, scabies), ticks
Merostomata	cephalothorax with horseshoe carapace + abdomen	none	5 pairs + book gills	book gills	Limulus (king crab, a living fossil — not a true crab)
Onychophora	worm-like, soft cuticle	1 pair	unjointed stumpy legs	tracheae / nephridia	Peripatus (Annelida–Arthropoda link)

Insect vector	Disease it spreads
female Anopheles	malaria
Aedes aegypti	dengue, chikungunya, yellow fever
Culex	filariasis, Japanese encephalitis
Phlebotomus (sandfly)	kala-azar
Glossina (tsetse fly)	sleeping sickness
Xenopsylla cheopis (rat flea)	plague
Musca domestica (housefly)	mechanical carrier of typhoid, cholera, dysentery

Phylum Mollusca — soft-bodied animals

The second largest phylum.

• Soft, unsegmented body (except Neopilina) of head, muscular foot and visceral hump; bilateral, but snails become asymmetrical by torsion (180° twisting of the visceral mass).
• The mantle (pallium) covers the hump and secretes the calcareous shell; the mantle cavity holds the gills (ctenidia).
• Radula — a rasping, file-like tongue with chitinous teeth (absent in bivalves).
• Coelom reduced to the pericardial cavity and gonad cavities; open circulation (closed in cephalopods); respiratory pigment haemocyanin (copper).
• Excretion by kidneys (the organ of Bojanus in bivalves such as Lamellidens); osphradium tests the water entering the mantle cavity.
• Sexes usually separate; larvae trochophore and veliger.

Class	Diagnostic	Examples
Monoplacophora	single cap-like shell; serially repeated gills and nephridia	Neopilina (living fossil; Annelida–Mollusca link)
Polyplacophora (Amphineura)	8 dorsal shell plates	Chiton
Aplacophora	worm-like, no shell, spicules in the skin	Neomenia, Chaetoderma
Scaphopoda	tusk-shaped tubular shell open at both ends	Dentalium (tusk shell)
Gastropoda	torsion; coiled shell (or none); distinct head with tentacles	Pila globosa (apple snail), Helix (land snail), Limax (slug, no shell), Aplysia (sea hare), Doris (sea lemon), Patella (limpet), Lymnaea (pond snail)
Pelecypoda (Bivalvia, Lamellibranchiata)	two hinged valves; no head, no radula; filter feeders	Lamellidens and Unio (fresh-water mussels), Mytilus (sea mussel), Ostrea (edible oyster), Pinctada (pearl oyster), Teredo (shipworm, bores wood), Pecten (scallop)
Cephalopoda	foot modified into arms/tentacles around the head; closed circulation; large eyes; ink gland; shell internal or absent (external only in Nautilus)	Sepia (cuttlefish), Loligo (squid), Octopus (devil fish), Nautilus, Architeuthis (giant squid, among the largest invertebrates)

Phylum Echinodermata — spiny-skinned animals

• All marine; adults pentaradial, larvae bilateral; triploblastic, enterocoelous deuterostomes.
• Endoskeleton of calcareous ossicles with spines (from mesoderm) — hence "spiny skin".
• Water vascular (ambulacral) system — sea water enters by the madreporite and works the tube feet (podia) for locomotion, food capture and respiration — the diagnostic feature.
• No head, no brain, no excretory organs; open haemal system; pedicellariae clean the surface.
• Sexes separate; external fertilisation; many free-swimming larvae; great regeneration (starfish).

Class	Diagnostic	Larva	Examples
Asteroidea (starfishes)	star-shaped; arms not sharply marked off from the disc; tube feet with suckers in open ambulacral grooves	bipinnaria, brachiolaria	Asterias, Pentaceros (Oreaster)
Ophiuroidea (brittle stars)	long slender arms sharply set off from a round disc	ophiopluteus	Ophiura, Ophiothrix
Echinoidea (sea urchins, sand dollars)	globular or flat; no arms; movable spines; chewing Aristotle's lantern	echinopluteus	Echinus, Clypeaster (sand dollar), Echinocardium (heart urchin)
Holothuroidea (sea cucumbers)	elongated, leathery; ossicles microscopic; respiratory trees; evisceration	auricularia	Cucumaria, Holothuria
Crinoidea (sea lilies, feather stars)	cup-shaped, feathery arms; stalked or free; mouth faces up	doliolaria	Antedon (feather star), Metacrinus (sea lily)

Hemichordata

Worm-like marine burrowers with a body of proboscis, collar and trunk, pharyngeal gill slits and a dorsal nerve cord in the collar. Their stomochord (buccal diverticulum) was once taken for a notochord, so older books made them a subphylum of Chordata; today they are a separate non-chordate phylum. The tornaria larva resembles echinoderm larvae. Examples: Balanoglossus (acorn worm), Saccoglossus.

Phylum Chordata

Four fundamental characters, present at least in the embryo:

1. a notochord — a flexible rod of vacuolated cells dorsal to the gut;
2. a dorsal, hollow, single nerve cord;
3. paired pharyngeal gill slits;
4. a post-anal tail.

Character	Non-chordates	Chordates
Notochord	absent	present (at least in the embryo)
Nerve cord	ventral, solid, double, ganglionated	dorsal, hollow, single
Pharyngeal gill slits	absent	present
Heart	dorsal (if present)	ventral
Post-anal tail	absent	present
Blastopore	usually becomes mouth (protostomes)	becomes anus (deuterostomes)

Subphylum	Notochord	Features	Examples
Urochordata (Tunicata)	only in the larval tail	marine, sessile adult in a tunic of tunicin; free-swimming tadpole larva; retrogressive metamorphosis	Herdmania, Ascidia (sea squirt), Salpa, Doliolum
Cephalochordata	from head to tail, throughout life	small, fish-like, burrowing filter feeders; no head, no paired fins	Branchiostoma (Amphioxus, the lancelet)
Vertebrata (Craniata)	replaced by the vertebral column in the adult	cranium round the brain; paired appendages; muscular ventral heart with chambers; kidneys	fishes to mammals

Urochordata and Cephalochordata together are the protochordates. Every vertebrate is a chordate, but not every chordate is a vertebrate.

Vertebrata divides into Agnatha (jawless — class Cyclostomata) and Gnathostomata (jawed — super-class Pisces with the two fish classes, and super-class Tetrapoda with four-limbed Amphibia, Reptilia, Aves and Mammalia).

Class	Skin / exoskeleton	Skeleton	Heart	Respiration	Body temperature	Excretion	Reproduction	Examples
Cyclostomata	soft, no scales	cartilaginous; notochord persists	2-chambered	6–15 pairs of gill slits	cold-blooded	ammonia	migrate to fresh water to spawn (lamprey); larva ammocoete	Petromyzon (lamprey, ectoparasite of fish), Myxine (hagfish)
Chondrichthyes (cartilaginous fish)	placoid scales	cartilaginous	2-chambered	5–7 pairs of separate gill slits, no operculum; no air bladder	cold-blooded	urea	claspers in males; internal fertilisation; many viviparous; heterocercal tail; ventral mouth	Scoliodon (dogfish), Pristis (sawfish), Torpedo (electric ray), Trygon (stingray), Carcharodon (great white shark)
Osteichthyes (bony fish)	cycloid or ctenoid scales	bony	2-chambered (venous)	4 pairs of gills under an operculum; air (swim) bladder	cold-blooded	ammonia	mostly oviparous, external fertilisation; terminal mouth; homocercal tail	Labeo rohita (rohu), Catla catla, Clarias (magur), Hippocampus (sea horse), Exocoetus (flying fish), Anabas (climbing perch), Pterophyllum (angel fish), Betta (fighting fish), Protopterus (lungfish)
Amphibia	moist, glandular, no scales	bony	3-chambered (2 atria + 1 ventricle)	gills (larva), lungs, skin, buccopharynx	cold-blooded	urea (adult)	cloaca; external fertilisation in water; tadpole larva, metamorphosis; tympanum	Rana (frog), Bufo (toad), Hyla (tree frog), Salamandra, Ichthyophis (limbless), Necturus
Reptilia	dry, cornified, epidermal scales or scutes	bony	3-chambered; 4 in crocodiles	lungs	cold-blooded	uric acid	internal fertilisation; cleidoic (shelled, amniotic) eggs; direct development; snakes and lizards moult	Chelone (turtle), Testudo (tortoise), Calotes (garden lizard), Hemidactylus (wall lizard), Chamaeleo, Draco (flying lizard), Crocodylus, Alligator, Gavialis (gharial), Naja (cobra), Bungarus (krait), Vipera (viper), Python
Aves	feathers; scales on legs; only the oil (preen) gland	bony, pneumatic (air-filled)	4-chambered	lungs + air sacs	warm-blooded	uric acid	beak without teeth; crop and gizzard; syrinx; oviparous; right aortic arch	Columba livia (pigeon), Corvus (crow), Psittacula (parrot), Struthio (ostrich), Pavo cristatus (peafowl), Aptenodytes (penguin), Neophron (vulture), Lophophorus impejanus (Danfe, national bird of Nepal)
Mammalia	hair; sweat and sebaceous glands; mammary glands	bony; 7 neck vertebrae	4-chambered	lungs; diaphragm	warm-blooded	urea	external ear (pinna); teeth heterodont and replaced once; viviparous (except monotremes); left aortic arch; RBCs without nuclei	see below

Mammal sub-class	Diagnostic	Examples
Prototheria (monotremes)	lay eggs; cloaca; no nipples	Ornithorhynchus (duck-billed platypus), Tachyglossus (spiny anteater, Echidna)
Metatheria (marsupials)	young born very early and reared in a pouch (marsupium)	Macropus (kangaroo), Didelphis (opossum), Phascolarctos (koala)
Eutheria (placentals)	true placenta	Homo, Rattus, Canis, Felis, Elephas, Pteropus (flying fox), Balaenoptera (blue whale, largest animal), Delphinus (dolphin), Panthera tigris (tiger), Rhinoceros unicornis (one-horned rhinoceros), Ailurus fulgens (red panda)

Formula and fact sheet

One feature, one group

Feature	Group
Choanocytes, ostia, osculum, spicules, gemmules	Porifera
Cnidoblasts / nematocysts, mesogloea, polyp and medusa	Coelenterata
Comb plates, colloblasts	Ctenophora
Flame cells, hooks and suckers, proglottids	Platyhelminthes
Pseudocoel, cuticle, renette cells, sexual dimorphism	Aschelminthes
Metameric segmentation, setae, parapodia, nephridia, clitellum	Annelida
Jointed legs, chitin, haemocoel, Malpighian tubules, tracheae	Arthropoda
Mantle, shell, radula, ctenidia, osphradium, organ of Bojanus	Mollusca
Water vascular system, tube feet, madreporite, Aristotle's lantern	Echinodermata
Notochord, dorsal hollow nerve cord, gill slits, post-anal tail	Chordata
Placoid scales, claspers	Chondrichthyes
Operculum, air bladder	Osteichthyes
Feathers, pneumatic bones, air sacs, syrinx	Aves
Hair, mammary glands, diaphragm, pinna	Mammalia

Common name → scientific name

Common name	Animal (group)
Venus' flower basket / bath sponge / fresh-water sponge	Euplectella / Euspongia / Spongilla (Porifera)
Portuguese man-of-war / sea fur / moon jelly	Physalia / Obelia / Aurelia (Coelenterata)
Sea anemone / sea fan / sea pen / red coral	Metridium, Adamsia / Gorgonia / Pennatula / Corallium
Liver fluke / pork tapeworm / dog tapeworm	Fasciola / Taenia solium / Echinococcus
Roundworm / pinworm / hookworm / filarial worm / guinea worm	Ascaris / Enterobius / Ancylostoma / Wuchereria / Dracunculus
Sea mouse / sandworm / earthworm / cattle leech	Aphrodite / Nereis / Pheretima / Hirudinaria
Prawn / crayfish / water flea / barnacle	Palaemon / Astacus / Daphnia / Balanus
Centipede / millipede / silverfish / king crab	Scolopendra / Julus / Lepisma / Limulus
Apple snail / slug / tusk shell / chiton	Pila / Limax / Dentalium / Chiton
Pearl oyster / shipworm / cuttlefish / squid / devil fish	Pinctada / Teredo / Sepia / Loligo / Octopus
Starfish / brittle star / sea urchin / sea cucumber / feather star	Asterias / Ophiura / Echinus / Cucumaria / Antedon
Acorn worm / sea squirt / lancelet	Balanoglossus / Herdmania, Ascidia / Branchiostoma
Lamprey / hagfish / dogfish / sawfish / electric ray / stingray	Petromyzon / Myxine / Scoliodon / Pristis / Torpedo / Trygon
Rohu / sea horse / flying fish / climbing perch	Labeo rohita / Hippocampus / Exocoetus / Anabas
Toad / tree frog / limbless amphibian	Bufo / Hyla / Ichthyophis
Garden lizard / wall lizard / turtle / cobra / gharial	Calotes / Hemidactylus / Chelone / Naja / Gavialis
Pigeon / ostrich / penguin / Danfe	Columba / Struthio / Aptenodytes / Lophophorus impejanus
Platypus / spiny anteater / kangaroo / flying fox / blue whale	Ornithorhynchus / Tachyglossus / Macropus / Pteropus / Balaenoptera

Larvae

Larva	Group
Amphiblastula	sponges (Sycon)
Planula	Coelenterata
Miracidium, sporocyst, redia, cercaria	liver fluke
Cysticercus (bladder worm)	Taenia
Trochophore	Polychaeta, Mollusca
Veliger	Mollusca
Nauplius	Crustacea
Bipinnaria / echinopluteus / auricularia	starfish / sea urchin / sea cucumber
Tornaria	Balanoglossus
Tadpole	ascidians, frogs
Ammocoete	lamprey

Chapter summary

• Animals are classified by level of organisation, symmetry, germ layers, coelom and segmentation: cellular → Porifera; tissue, radial, diploblastic → Coelenterata; acoelomate → Platyhelminthes; pseudocoelomate → Aschelminthes; schizocoelous protostomes → Annelida, Arthropoda, Mollusca; enterocoelous deuterostomes → Echinodermata, Hemichordata, Chordata.
• Protozoa are grouped by locomotion: pseudopodia (Amoeba, Entamoeba), flagella (Euglena, Trypanosoma, Leishmania), none (Sporozoa: Plasmodium), cilia (Paramecium, Balantidium).
• Porifera: ostia, osculum, canal system, choanocytes, spicules or spongin, gemmules; Calcarea, Hexactinellida (Euplectella), Demospongiae (Euspongia, Spongilla).
• Coelenterata: radial, diploblastic, coelenteron, nematocysts, polyp and medusa, metagenesis in Obelia; Hydrozoa, Scyphozoa, Anthozoa.
• Platyhelminthes (flame cells; Fasciola, Taenia) and Aschelminthes (pseudocoel, complete gut, separate sexes; Ascaris, Wuchereria, Ancylostoma, Enterobius).
• Annelida: metameres, setae/parapodia, closed circulation, nephridia; Polychaeta (Nereis), Oligochaeta (Pheretima), Hirudinea (Hirudinaria).
• Arthropoda, the largest phylum: jointed legs, chitin, haemocoel, open circulation; Crustacea (2 pairs of antennae, gills, green glands), Myriapoda, Insecta (3 pairs of legs, tracheae, Malpighian tubules), Arachnida (4 pairs of legs, book lungs, no antennae).
• Mollusca: mantle, shell, radula, ctenidia; seven classes from Neopilina to Sepia; Echinodermata: pentaradial adults, water vascular system, tube feet; Asteroidea to Crinoidea.
• Chordata: notochord, dorsal hollow nerve cord, gill slits, post-anal tail; Urochordata (larval notochord), Cephalochordata (Branchiostoma), Vertebrata — Cyclostomata, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves, Mammalia, each with its skin, heart, temperature and egg in the table.

Practice questions

Set A — Recall (30 questions)

1. Choanocytes (collar cells) are characteristic of the phylumaCoelenteratabPoriferacPlatyhelminthesdCtenophora
2. Venus' flower basket is the common name ofaEuspongiabSpongillacEuplectelladHyalonema
3. Nematocysts are found inaCoelenteratabPoriferacCtenophoradEchinodermata
4. The Portuguese man-of-war isaAureliabAdamsiacPennatuladPhysalia
5. Alternation of a polyp generation with a medusa generation (metagenesis) is seen inaHydrabObeliacMetridiumdPleurobrachia
6. Flame cells are the excretory structures ofaMolluscabAnnelidacPlatyhelminthesdArthropoda
7. The tapeworm whose scolex bears both hooks and suckers, and whose intermediate host is the pig, isaTaenia soliumbTaenia saginatacEchinococcus granulosusdFasciola hepatica
8. Elephantiasis is caused byaAncylostoma duodenalebEnterobius vermiculariscAscaris lumbricoidesdWuchereria bancrofti
9. A pseudocoelom is the body cavity ofaPlatyhelminthesbAschelminthescAnnelidadMollusca
10. Parapodia are the locomotory organs ofaPheretimabHirudinariacNereisdTubifex
11. Kala-azar, endemic in the Terai of Nepal, is caused byaLeishmania donovanibTrypanosoma gambiensecGiardia intestinalisdEntamoeba histolytica
12. The only ciliate known to parasitise man isaParamecium caudatumbVorticellacNyctotherusdBalantidium coli
13. The largest phylum of the animal kingdom isaMolluscabArthropodacChordatadAnnelida
14. Green glands are the excretory organs ofacockroachbscorpioncprawndcentipede
15. Book lungs are the respiratory organs ofascorpionbcockroachcprawndmillipede
16. Two pairs of legs on each trunk segment are found inaScolopendrabPeriplanetacPalaemondJulus
17. A radula is found in most members ofaEchinodermatabAnnelidacMolluscadArthropoda
18. The pearl oyster isaOstreabPinctadacUniodTeredo
19. The cuttlefish isaSepiabLoligocOctopusdNautilus
20. A water vascular system with tube feet is the diagnostic feature ofaPoriferabCoelenteratacMolluscadEchinodermata
21. Aristotle's lantern is the chewing apparatus ofastarfishbbrittle starcsea urchindsea cucumber
22. The feather star isaAsteriasbAntedoncOphiuradCucumaria
23. Retrogressive metamorphosis is shown byaHerdmaniabBranchiostomacPetromyzondBalanoglossus
24. Placoid scales are found inaLabeobHippocampuscCatladScoliodon
25. Among reptiles a four-chambered heart is found inaNajabCalotescCrocodylusdChelone
26. Pneumatic bones and air sacs are features ofaReptiliabAvescMammaliadAmphibia
27. An egg-laying mammal isaOrnithorhynchusbMacropuscPteropusdDidelphis
28. A muscular diaphragm separating the thorax from the abdomen is found only inaAvesbReptiliacAmphibiadMammalia
29. The Danfe, the national bird of Nepal, isaPavo cristatusbColumba liviacLophophorus impejanusdPsittacula krameri
30. The limbless amphibian among the following isaHylabIchthyophiscSalamandradBufo

Answers and explanations — Set A

1. (b) — collar cells with a flagellum line the spongocoel of sponges and drive the water current. Ctenophores have colloblasts, not choanocytes.

2. (c) — Euplectella, a glass sponge with six-rayed siliceous spicules; Hyalonema is the glass-rope sponge.

3. (a) — nematocysts in cnidoblasts are the diagnostic feature of Cnidaria; Ctenophora have adhesive colloblasts instead.

4. (d) — Physalia is a polymorphic floating hydrozoan colony; Aurelia is the moon jelly, Adamsia a sea anemone.

5. (b) — Obelia alternates an asexual colonial polyp with a sexual medusa. Hydra and Metridium have no medusa; Pleurobrachia is a ctenophore.

6. (c) — flame cells (protonephridia) of flatworms; Annelida have nephridia, Arthropoda Malpighian tubules or green glands, Mollusca kidneys.

7. (a) — T. solium, the pork tapeworm, has an armed scolex; T. saginata (beef) has suckers only.

8. (d) — the filarial worm Wuchereria, carried by Culex, blocks lymph vessels.

9. (b) — the roundworm cavity is not lined by mesoderm on the gut side: a pseudocoel. Flatworms are acoelomate.

10. (c) — Nereis, a polychaete, has paired lateral parapodia with many setae; earthworms have only setae, leeches suckers.

11. (a) — Leishmania donovani, a flagellate spread by the sandfly Phlebotomus. Trypanosoma causes sleeping sickness.

12. (d) — Balantidium coli causes balantidial dysentery; Nyctotherus lives in the frog's rectum.

13. (b) — arthropods make up more than two-thirds of all named animal species.

14. (c) — crustaceans excrete by antennal (green) glands; cockroach, scorpion and centipede have Malpighian tubules.

15. (a) — scorpions and spiders breathe by book lungs; insects and millipedes by tracheae, prawns by gills.

16. (d) — Julus, a millipede (Diplopoda), has two pairs per segment; Scolopendra, a centipede, has one.

17. (c) — the radula is the molluscan rasping tongue; bivalves lack it.

18. (b) — Pinctada; Ostrea is the edible oyster, Teredo the shipworm.

19. (a) — Sepia; Loligo is the squid, Octopus the devil fish.

20. (d) — the ambulacral system works the tube feet of echinoderms.

21. (c) — Aristotle's lantern is the five-jawed feeding apparatus of sea urchins (Echinoidea).

22. (b) — Antedon is a crinoid; Asterias starfish, Ophiura brittle star, Cucumaria sea cucumber.

23. (a) — the tadpole larva of Herdmania loses its tail, notochord and most of its nerve cord when it settles: a step backwards in organisation.

24. (d) — Scoliodon, a cartilaginous fish; the bony fishes have cycloid or ctenoid scales.

25. (c) — the crocodile's ventricle is fully divided; other reptiles have an incompletely divided ventricle.

26. (b) — hollow, air-filled bones and air sacs lighten birds and supply the lungs.

27. (a) — the platypus is a monotreme; Macropus and Didelphis are marsupials, Pteropus a placental bat.

28. (d) — only mammals have a muscular diaphragm.

29. (c) — Lophophorus impejanus, the Himalayan monal; Pavo cristatus is the peafowl.

30. (b) — Ichthyophis is a caecilian, a burrowing limbless amphibian.

Set B — Understanding (18 questions)

1. Which of the following is a true fish?ajellyfishbsilverfishcsea horsedcuttlefish
2. The silverfish (Lepisma) belongs to the classaInsectabOsteichthyescCrustaceadArachnida
3. An enterocoelous coelom is found inaAnnelidabArthropodacMolluscadEchinodermata
4. In which pair of phyla does the blastopore become the anus?aAnnelida and ArthropodabEchinodermata and ChordatacMollusca and AnnelidadPlatyhelminthes and Aschelminthes
5. True metameric segmentation is NOT found inaPheretimabPeriplanetacTaeniadNereis
6. Which of the following is NOT a fundamental character of chordates?anotochordbdorsal hollow nerve cordcpharyngeal gill slitsdventral solid double nerve cord
7. In Urochordata the notochord is presentaonly in the tail of the larvabfrom head to tail throughout lifecas a vertebral column in the adultdas a stomochord in the proboscis
8. Which of the following is NOT a mollusc?aDentaliumbLimuluscChitondTeredo
9. The mesogloea of Hydra isaa cellular mesodermbthe body cavityca non-cellular jelly between ectoderm and endodermda layer of spicules
10. The body cavity of a cockroach is called a haemocoel because itais filled with blood from an open circulatory systembis lined by mesoderm on both sidesccontains coelomic fluid but no blooddis absent, the body being solid
11. Among molluscs a closed circulatory system is found inaPilabUniocDentaliumdOctopus
12. The shelled (cleidoic) egg of reptiles and birds is an adaptation foraexternal fertilisation in waterbdevelopment on land without free waterclarval metamorphosisdfaster hatching in ponds
13. Which pair of animals has neither a circulatory nor a respiratory system?aearthworm and leechbcockroach and prawncHydra and Taeniadfrog and toad
14. Which group excretes mainly uric acid?abirds and reptilesbbony fishes and tadpolescmammals and adult frogsdsharks and rays
15. The duck-billed platypus is placed among mammals because italays eggsbhas a cloacachas a beakdhas hair and mammary glands
16. Which pair is correctly matched?aFasciola — tapewormbEnterobius — pinwormcTaenia — liver flukedAscaris — filarial worm
17. Sponges are said to be at the cellular level of organisation because their cellsalive singlybform true tissues and organscdivide labour but form no true tissuesdlack nuclei
18. Which feature separates Osteichthyes from Chondrichthyes?aan operculum covering the gillsbpaired finsca two-chambered heartdjaws

Answers and explanations — Set B

1. (c) — Hippocampus is a bony fish with gills, fins and an operculum; the others are a cnidarian, an insect and a mollusc.

2. (a) — Lepisma is a primitive wingless insect (three pairs of legs, one pair of antennae).

3. (d) — echinoderms (with hemichordates and chordates) form the coelom from gut pouches; the other three are schizocoelous.

4. (b) — they are deuterostomes; in annelids, arthropods and molluscs (protostomes) the blastopore becomes the mouth.

5. (c) — the proglottids of Taenia are budded off from the neck and do not repeat organs in a true metameric way: pseudometamerism.

6. (d) — a ventral, solid, double nerve cord is the non-chordate (annelid, arthropod) pattern.

7. (a) — "uro" = tail: the notochord lies in the larval tail and is lost at metamorphosis. (b) is Cephalochordata, (d) Hemichordata.

8. (b) — Limulus, the king crab, is an arthropod (Merostomata); the others are a tusk shell, a chiton and the shipworm.

9. (c) — Cnidaria are diploblastic; the mesogloea is jelly, not a germ layer.

10. (a) — arthropod blood leaves the vessels and bathes the organs in the body cavity; the true coelom is reduced.

11. (d) — cephalopods are active predators with a closed system and accessory branchial hearts.

12. (b) — the shell and the amnion keep the embryo in its own pond, so reptiles and birds can breed away from water.

13. (c) — cnidarians and flatworms exchange gases and wastes by diffusion through the body surface.

14. (a) — uric acid saves water (uricotely); fishes and tadpoles are ammonotelic, mammals and adult frogs ureotelic, sharks retain urea.

15. (d) — hair and milk glands define mammals; egg-laying and a cloaca are reptilian features it retains.

16. (b) — Enterobius vermicularis is the pinworm; Fasciola is a liver fluke, Taenia a tapeworm, Ascaris the roundworm.

17. (c) — sponge cells specialise (pinacocytes, choanocytes, amoebocytes) but never form true tissues.

18. (a) — bony fishes have an operculum (and air bladder); paired fins, a two-chambered heart and jaws are common to both.

Set C — Application (12 questions)

1. An animal has jointed legs, two pairs of antennae, a cephalothorax covered by a carapace and breathes by gills. It belongs toaInsectabCrustaceacArachnidadMyriapoda
2. An animal has four pairs of walking legs, no antennae and breathes by book lungs. It belongs toaInsectabCrustaceacChilopodadArachnida
3. A specimen is radially symmetrical with tentacles bearing stinging cells round the only opening of its gut. It belongs toaCoelenteratabPoriferacEchinodermatadCtenophora
4. A worm is cylindrical and unsegmented, with a complete gut, a body cavity not lined by mesoderm on the gut side, and separate sexes. It belongs toaPlatyhelminthesbAnnelidacAschelminthesdHirudinea
5. A student collects Hydra, Fasciola, Ascaris, Nereis, Pila and Asterias. How many of them are triploblastic and truly coelomate?a3b2c4d5
6. Which of these animals would you expect to have a closed circulatory system?acockroachbearthwormcPiladprawn
7. A pond organism has a pellicle, a flagellum, an eyespot and chloroplasts, and feeds saprophytically in the dark. It isaParameciumbAmoebacPlasmodiumdEuglena
8. A vertebrate has moist glandular skin without scales, a three-chambered heart, external fertilisation and a larva with gills. Its class isaReptiliabOsteichthyescAmphibiadCyclostomata
9. An animal has dry skin with epidermal scales, a four-chambered heart, lays shelled eggs and is cold-blooded. It isaCrocodylusbColumbacOrnithorhynchusdNaja
10. A marine animal has a sessile adult enclosed in a tunic; its free-swimming larva has a notochord only in its tail. It belongs toaCephalochordatabUrochordatacHemichordatadCyclostomata
11. A fish has a ventral mouth, five pairs of uncovered gill slits, placoid scales and claspers, and no air bladder. It isaLabeo rohitabHippocampuscExocoetusdScoliodon
12. A spiny-skinned animal with tube feet, no head and a pentaradial body has a bipinnaria larva. It isaEchinusbHolothuriacAsteriasdAntedon

Answers and explanations — Set C

1. (b) — two pairs of antennae, carapace and gills mark a crustacean such as the prawn; insects have one pair of antennae, arachnids none.

2. (d) — four pairs of legs, no antennae and book lungs: a scorpion or spider.

3. (a) — radial symmetry, cnidoblasts and a blind-sac coelenteron: a cnidarian such as Hydra. Ctenophores lack stinging cells.

4. (c) — a pseudocoel, complete gut and separate sexes describe a nematode such as Ascaris.

5. (a) — Nereis (annelid), Pila (mollusc) and Asterias (echinoderm). Hydra is diploblastic, Fasciola acoelomate, Ascaris pseudocoelomate.

6. (b) — the earthworm's blood stays in vessels (closed system); cockroach, Pila and prawn have open systems.

7. (d) — Euglena, a flagellate that photosynthesises in light and absorbs organic food in the dark.

8. (c) — moist naked skin, three chambers and an aquatic gilled tadpole mark an amphibian.

9. (a) — the crocodile is the reptile with a four-chambered heart; Columba is warm-blooded, Naja has three chambers, Ornithorhynchus has hair.

10. (b) — a tunic and a larval tail notochord are the marks of a tunicate such as Herdmania.

11. (d) — all are features of a cartilaginous fish; Scoliodon is the dogfish. The other three are bony fishes with an operculum.

12. (c) — the bipinnaria is the starfish larva; Echinus has an echinopluteus, Holothuria an auricularia, Antedon a doliolaria.