# Animal Kingdom (NEET Biology Class 11): Non-Chordate Phyla & Vertebrate Classes

Source: https://tracknation.in/story/animal-kingdom-neet-biology-class-11-non-chordate-phyla-vertebrate-classes (TrackNation — free UPSC notes with PYQs)

> NEET Class 11 Animal Kingdom, mined from NCERT: the basis of classification (symmetry, germ layers, coelom, notochord); the ten non-chordate phyla (Porifera to Hemichordata) with features, example genera, the water-canal system, polyp/medusa/metagenesis, and excretory/circulatory systems; the three chordate subphyla; and the vertebrate classes with heart chambers, reproduction and development. Includes 17 MCQs, 10 NEET PYQs and an Active Recall prompt.

## How Animals Are Classified

🎯 **NEET priority: High-yield.** *4–6 questions every year. "Match the phylum to its feature/example" and heart-chamber counts are guaranteed marks — the two tables below are the whole chapter.*

Over a million animal species are sorted using a few fundamental features. Get these axes right
and every phylum question falls into place.

- **Levels of organisation:** cellular (Porifera) → tissue (Coelenterata) →
organ → organ-system (Platyhelminthes onward).

- **Symmetry:** **radial** (Coelenterata, Ctenophora,
adult Echinodermata) vs **bilateral** (Platyhelminthes → Chordata).

- **Germ layers:** **diploblastic** (Coelenterata, Ctenophora)
vs **triploblastic** (Platyhelminthes → Chordata).

- **Coelom:** **coelomate** (true body cavity lined by mesoderm),
**pseudocoelomate** (Aschelminthes), **acoelomate** (Platyhelminthes).

- **Notochord:** **chordates** have it; **non-chordates**
(Porifera → Echinodermata) don't.

## The Ten Non-Chordate Phyla (the key table)

The ten major non-chordate phyla — the single most-asked table in the chapter:

| **Phylum**

 | **Symmetry**

 | **Coelom**

 | **Key feature**

 | **Examples**

 |
| Porifera

 | Asymmetrical

 | —

 | Canal system, spongocoel; pores (ostia)

 | Sycon, Spongilla, Euspongia

 |
| Coelenterata (Cnidaria)

 | Radial

 | Acoelomate (diploblastic)

 | Cnidoblasts/nematocysts; polyp & medusa

 | Hydra, Aurelia, Adamsia, Physalia

 |
| Ctenophora

 | Radial

 | Acoelomate (diploblastic)

 | Comb plates; bioluminescence

 | Pleurobrachia, Ctenoplana

 |
| Platyhelminthes

 | Bilateral

 | Acoelomate

 | Flatworms; flame cells (excretion)

 | Planaria, Fasciola, Taenia

 |
| Aschelminthes (Nematoda)

 | Bilateral

 | Pseudocoelomate

 | Roundworms

 | Ascaris, Wuchereria, Ancylostoma

 |
| Annelida

 | Bilateral

 | Coelomate

 | Metameric segmentation

 | Nereis, Pheretima, Hirudinaria

 |
| Arthropoda

 | Bilateral

 | Coelomate

 | Largest phylum; jointed legs, chitin exoskeleton

 | Apis, Bombyx, Anopheles, Limulus

 |
| Mollusca

 | Bilateral

 | Coelomate

 | Soft body, mantle, radula (2nd largest)

 | Pila, Sepia, Loligo, Octopus, Pinctada

 |
| Echinodermata

 | Radial (adult)

 | Coelomate

 | Water vascular system; spiny skin

 | Asterias, Echinus, Antedon

 |
| Hemichordata

 | Bilateral

 | Coelomate

 | Worm-like; proboscis

 | Balanoglossus, Saccoglossus

 |

**Memory hooks:** Porifera = canal system; Cnidaria = nematocysts; Ctenophora =
comb plates + bioluminescence; Platyhelminthes = flame cells; Aschelminthes = the only
pseudocoelomate; Annelida = segmentation; Arthropoda = largest phylum; Mollusca = radula;
Echinodermata = water vascular system.

### The Porifera water-canal system — spelled out (NEET asks the exact path)

Water enters through minute pores called **ostia** in the body wall, flows into a
central cavity, the **spongocoel**, and exits through the **osculum**. Cells
called **choanocytes (collar cells)** line the spongocoel and canals, creating the water
current and trapping food. The skeleton is made of **spicules** or the protein
**spongin** (the bath sponge *Euspongia* is spongin-based, hence soft).
Reproduction is both asexual (budding) and sexual, and Porifera show remarkable
**totipotency** — cells can regenerate a whole new sponge.

### Cnidaria — polyp, medusa & metagenesis

Cnidarians show two basic body forms: the sessile, cylindrical **polyp**
(*Hydra, Adamsia*) and the free-swimming, umbrella-shaped **medusa**
(*Aurelia*). Some species (e.g. *Obelia*) alternate between the two across
generations — polyps producing medusae asexually and medusae producing polyps sexually — a
phenomenon called **metagenesis**. **Coral reefs** are built by cnidarians
with a calcium-carbonate skeleton.

### Organ-system detail across the phyla — the exam's favourite trap zone

- **Annelida** has a **closed circulatory system** and
**nephridia** for excretion.

- **Arthropoda** has an **open circulatory system**; excretion is
via **Malpighian tubules**; respiration is by gills, book gills, book lungs or
tracheae depending on the group.

- **Arthropoda's economic importance:** *Apis* (honey),
*Bombyx* (silk), *Laccifer* (lac) — alongside vectors (*Anopheles, Culex,
Aedes*) and pests (*Locusta*).

- **Hemichordata** (*Balanoglossus*) also has an
**open circulatory system**; its body is divided into a proboscis, collar and trunk,
and it respires through gills.

- **Echinodermata** shows remarkable **regeneration capacity** —
a broken arm of a starfish can regrow.

**Exam trap:** don't swap **open** (Arthropoda, Hemichordata) with
**closed** (Annelida) circulatory systems — this exact pairing is a favourite
NEET distractor.

## Chordates & Their Three Subphyla

**Chordates** share three defining features: a **notochord**, a
**dorsal hollow nerve cord**, and **paired pharyngeal gill slits**
(non-chordates have none of these — a fourth shared trait is a **post-anal tail** at
some stage). Phylum Chordata has three subphyla:

- **Urochordata** (Tunicata) — **exclusively marine**; notochord
present only in the **larval tail**, lost after metamorphosis; e.g.
*Ascidia, Salpa, Doliolum*.

- **Cephalochordata** — notochord extends **head to tail, for life**;
e.g. *Branchiostoma* (Amphioxus / lancelet).

- **Vertebrata** — the notochord present in the embryo is
**replaced by a cartilaginous/bony vertebral column** in the adult; vertebrates also
have a **cranium (skull)** and a **ventral heart**, features
non-chordates and protochordates lack.

Urochordata + Cephalochordata together are called **"protochordates"** — chordates
without a proper vertebral column.

## The Vertebrate Classes & Heart Chambers

Subphylum **Vertebrata** splits into seven classes. **Heart chambers**
and **cold-/warm-blooded** are the favourite NEET hooks:

| **Class**

 | **Key feature**

 | **Heart**

 | **Examples**

 |
| Cyclostomata

 | Jawless; sucking mouth; no scales

 | —

 | Petromyzon, Myxine

 |
| Chondrichthyes

 | Cartilaginous fish; no air bladder (cold-blooded)

 | 2-chambered

 | Scoliodon, Pristis, Carcharodon, Trygon

 |
| Osteichthyes

 | Bony fish; air bladder; scales (cold-blooded)

 | 2-chambered

 | Labeo, Catla, Hippocampus, Exocoetus

 |
| Amphibia

 | Dual life; moist skin (cold-blooded)

 | 3-chambered

 | Rana, Bufo, Hyla, Salamandra, Ichthyophis

 |
| Reptilia

 | Dry scaly skin; lay shelled eggs (cold-blooded)

 | 3-chambered (4 in crocodile)

 | Chelone, Testudo, Naja, Calotes, Crocodilus

 |
| Aves (birds)

 | Feathers; flight; beak (warm-blooded)

 | 4-chambered

 | Crow, Pigeon, Neophron

 |
| Mammalia

 | Hair; mammary glands (warm-blooded)

 | 4-chambered

 | Ornithorhynchus, Macropus, Pteropus, Balaenoptera

 |

- **Heart chambers:** fishes **2** → amphibians & reptiles
**3** (crocodile **4**) → birds & mammals **4**.

- **Warm-blooded (homoiothermous):** only **birds and mammals**.
All others are **cold-blooded (poikilothermous)**.

### Reproduction & development across the vertebrate classes

- Most fishes and amphibians show **external fertilisation**; amphibians
additionally show **indirect development** — the aquatic **tadpole** larva
undergoes **metamorphosis** into the terrestrial adult form.

- Snakes and lizards periodically **shed their scales** as a skin
**cast** — a distinctive reptilian trait.

- Reptiles and birds lay **shelled (cleidoic) eggs**, an adaptation for
development away from water. Most mammals are **viviparous**, but
**Ornithorhynchus** (platypus) is a notable **oviparous** exception.

### Why this matters for NEET

- "Identify the phylum / class of this example" and "match feature to group" dominate —
the example genera are as testable as the features.

- Classic traps: Aschelminthes is the only **pseudocoelomate**; Arthropoda is
the **largest phylum**; only **crocodile** among reptiles has a
4-chambered heart; **Ornithorhynchus** is an egg-laying mammal.

## Test Yourself: MCQs, PYQs & Active Recall

Answer these, then close the article and do an Active Recall. Reveal each answer only after you commit to one.

## Practice Questions

**Q1.** Which phylum is characterised by the presence of a water vascular system?

- (a) Echinodermata

- (b) Mollusca

- (c) Arthropoda

- (d) Annelida

**Answer: (a)** — The water vascular system (with tube feet) is unique to Echinodermata, e.g. Asterias (starfish).

**Q2.** Nematocysts (stinging cells) are characteristic of phylum:

- (a) Porifera

- (b) Coelenterata (Cnidaria)

- (c) Ctenophora

- (d) Platyhelminthes

**Answer: (b)** — Cnidoblasts/nematocysts on tentacles are unique to Coelenterata (Cnidaria) — used for defence and capturing prey.

**Q3.** The largest phylum in the animal kingdom is:

- (a) Chordata

- (b) Mollusca

- (c) Arthropoda

- (d) Annelida

**Answer: (c)** — Arthropoda is the largest phylum — jointed appendages and a chitinous exoskeleton.

**Q4.** Flame cells, used for excretion and osmoregulation, occur in:

- (a) Platyhelminthes

- (b) Annelida

- (c) Mollusca

- (d) Aschelminthes

**Answer: (a)** — Flame cells (protonephridia) are the excretory structures of Platyhelminthes (flatworms).

**Q5.** Which group is pseudocoelomate?

- (a) Annelida

- (b) Aschelminthes (Nematoda)

- (c) Arthropoda

- (d) Platyhelminthes

**Answer: (b)** — Aschelminthes (roundworms) have a body cavity not fully lined by mesoderm — a pseudocoelom.

**Q6.** The three fundamental chordate features are notochord, dorsal hollow nerve cord and:

- (a) Water vascular system

- (b) Paired pharyngeal gill slits

- (c) Radula

- (d) Ventral nerve cord

**Answer: (b)** — Chordates have a notochord, a dorsal hollow nerve cord and paired pharyngeal gill slits.

**Q7.** Branchiostoma (Amphioxus) belongs to subphylum:

- (a) Hemichordata

- (b) Urochordata

- (c) Vertebrata

- (d) Cephalochordata

**Answer: (d)** — Branchiostoma is a cephalochordate — notochord persists from head to tail throughout life.

**Q8.** A 3-chambered heart is found in:

- (a) Birds

- (b) Amphibians and most reptiles

- (c) Mammals

- (d) Fishes

**Answer: (b)** — Amphibians and most reptiles have a 3-chambered heart (crocodile has 4); fishes have 2, birds and mammals 4.

**Q9.** Which class consists of jawless vertebrates?

- (a) Cyclostomata

- (b) Amphibia

- (c) Osteichthyes

- (d) Chondrichthyes

**Answer: (a)** — Cyclostomata (e.g. Petromyzon, Myxine) are jawless, with a circular sucking mouth and no scales.

**Q10.** Cartilaginous fishes (Chondrichthyes) must swim constantly because they lack:

- (a) An air/swim bladder

- (b) Gills

- (c) A heart

- (d) A notochord

**Answer: (a)** — Chondrichthyes lack an air bladder, so they swim continuously to avoid sinking; examples include Scoliodon and Trygon.

**Q11.** Ornithorhynchus is a unique mammal because it:

- (a) Is cold-blooded

- (b) Has no hair

- (c) Lays eggs

- (d) Has a 3-chambered heart

**Answer: (c)** — Ornithorhynchus (platypus) is an egg-laying (oviparous) mammal, yet has hair and mammary glands.

**Q12.** Comb plates for locomotion and bioluminescence are features of:

- (a) Porifera

- (b) Echinodermata

- (c) Ctenophora

- (d) Cnidaria

**Answer: (c)** — Ctenophora (sea walnuts/comb jellies) move with eight rows of comb plates (ctene) and are bioluminescent.

**Q13.** In the Porifera water canal system, water enters through the:

- (a) Choanocytes

- (b) Spongocoel

- (c) Ostia

- (d) Osculum

**Answer: (c)** — Water enters through tiny pores called ostia, passes into the spongocoel, and exits via the osculum.

**Q14.** The alternation of asexual polyps and sexual medusae in some cnidarians is called:

- (a) Metamorphosis

- (b) Metagenesis

- (c) Regeneration

- (d) Polymorphism

**Answer: (b)** — Metagenesis: polyps (e.g. Obelia) produce medusae asexually, and medusae reproduce sexually to form new polyps.

**Q15.** Excretion in Arthropoda takes place mainly through:

- (a) Malpighian tubules

- (b) Proboscis gland

- (c) Flame cells

- (d) Nephridia

**Answer: (a)** — Arthropods excrete via Malpighian tubules; flame cells belong to Platyhelminthes and nephridia to Annelida.

**Q16.** Which phylum has an open circulatory system and a body divided into proboscis, collar and trunk?

- (a) Hemichordata

- (b) Annelida

- (c) Echinodermata

- (d) Mollusca

**Answer: (a)** — Hemichordata (e.g. Balanoglossus) has an open circulatory system, respires by gills, and its body has a proboscis, collar and trunk.

**Q17.** A frog's tadpole becoming an adult frog is an example of:

- (a) Indirect development with metamorphosis

- (b) Direct development

- (c) Regeneration

- (d) Metagenesis

**Answer: (a)** — The aquatic tadpole larva undergoes metamorphosis into the terrestrial adult — indirect development, typical of amphibians.

### NEET Previous Year Questions (PYQs)

*Real NEET previous-year questions on this chapter, with explanations in our own words.*

**Q13.** Which of the following is a correct match? (NEET PYQ)

- (a) Ascaris — Aschelminthes

- (b) Taenia — Annelida

- (c) Pheretima — Arthropoda

- (d) Aurelia — Porifera

**Answer: (a)** — Ascaris (roundworm) is an aschelminth. Taenia is a platyhelminth, Pheretima an annelid, Aurelia a cnidarian.

**Q14.** Animals with a true coelom lined by mesoderm are called: (NEET PYQ)

- (a) Diploblastic

- (b) Acoelomates

- (c) Coelomates

- (d) Pseudocoelomates

**Answer: (c)** — A true body cavity fully lined by mesoderm defines coelomates (e.g. Annelida, Arthropoda, Chordata).

**Q15.** Which one is an example of a living fossil arthropod? (NEET PYQ)

- (a) Limulus

- (b) Bombyx

- (c) Pila

- (d) Apis

**Answer: (a)** — Limulus (king crab) is a living fossil; Apis (honeybee) and Bombyx (silkworm) are insects, Pila is a mollusc.

**Q16.** Diploblastic animals are found in the phyla: (NEET PYQ)

- (a) Arthropoda and Echinodermata

- (b) Porifera and Annelida

- (c) Platyhelminthes and Mollusca

- (d) Coelenterata and Ctenophora

**Answer: (d)** — Coelenterata (Cnidaria) and Ctenophora have only two germ layers (ectoderm + endoderm) — diploblastic.

**Q17.** Which feature is exclusive to phylum Echinodermata? (NEET PYQ)

- (a) Metameric segmentation

- (b) Radula

- (c) Jointed legs

- (d) Water vascular system

**Answer: (d)** — The water vascular system (with tube feet for locomotion) is unique to echinoderms.

**Q18.** Birds and mammals are warm-blooded; this means they are: (NEET PYQ)

- (a) Cold-blooded

- (b) Ectothermic

- (c) Homoiothermous

- (d) Poikilothermous

**Answer: (c)** — Homoiothermous (warm-blooded) animals maintain a constant body temperature — only birds and mammals among vertebrates.

**Q19.** Pearl is obtained from which mollusc? (NEET PYQ)

- (a) Sepia

- (b) Loligo

- (c) Octopus

- (d) Pinctada

**Answer: (d)** — Pinctada (pearl oyster) produces pearls. Mollusca is the second-largest phylum.

**Q20.** The notochord in Urochordata is present: (NEET PYQ)

- (a) Throughout life, head to tail

- (b) Only in the larval tail

- (c) Never

- (d) Only in adults

**Answer: (b)** — In Urochordata the notochord is restricted to the larval tail; in Cephalochordata it persists head to tail.

**Q21.** Which class has members with a 2-chambered heart and a cartilaginous endoskeleton? (NEET PYQ)

- (a) Cyclostomata

- (b) Amphibia

- (c) Osteichthyes

- (d) Chondrichthyes

**Answer: (d)** — Chondrichthyes (cartilaginous fishes like Scoliodon, Trygon) have a 2-chambered heart and lack an air bladder.

**Q22.** Which one is an egg-laying (oviparous) mammal? (NEET PYQ)

- (a) Macropus

- (b) Pteropus

- (c) Ornithorhynchus

- (d) Balaenoptera

**Answer: (c)** — Ornithorhynchus (platypus) is oviparous; Macropus (kangaroo) is a marsupial, the others are placental.

### Active Recall Prompt

Write everything you can recall, naming each group first. Cover: the **basis of classification** (symmetry, germ layers, coelom, notochord); the **ten non-chordate phyla** with their key feature and an example each; the **chordate features and three subphyla**; and the **vertebrate classes** with their heart chambers and examples. Begin each fact with its phylum/class and end it with a full stop.