Category: Biology Second Paper

Nephridia is a type of excretory organ. nephridia It collects nitrogenous wastes. Passes waste material to the intestines. Plays a role in osmoregulation.

Leech- Hirudinaria medicinalis
Nereis- Nereis/Neanthes caudata
Spectacular insect – Amphrite figulus
Arenicola – Arenicola marina
Earthworm- Metaphire posthuma
Terebella lapidaria
Haemopis- Haemopis terrestris
Pontopdella- Pontopdella muricata
Hairy Worm- Hediste diversicolor
Blood worm- Glycera convoluta
Lumbricus- Lumbricus terrestris
Parchment worm- Chaetopterus variopedatus
Red worm – Eisenia foetida
Tubifex – Tubifex tubifex
Sea Lice – Aphrodite aculeata
Ornate Worm- Aphrodite ornata
Fan worm- Serpula vermicularis

The order Annelida is divided into 3 classes.
1. Polychaeta: Their body parts are covered with hairs. locomotion parapodia. Sensory organ is nucell organ. They are mostly marine. For example, Nereis caudata.
2. Oligochaeta: These are leech-like creatures. They live by digging holes. For example, Metaphire posthuma.
3. Hirudinia: They have clitellum. There is a substance called hirudin in the body. For example, Hirudinaria medicinalis.

1. Body long, cylindrical, bilaterally symmetrical and with true cylomes.
2. The body is segmented and composed of many segments or metameres similar to rings.
3. Movement organs are chitinous seatae or parapodia.
4. Patchy excretory organs called nephridia are located in almost every segment. It is called segmental organ.
5. The body contains the clitellum and secretes mucus.
6. The alimentary canal is cylindrical and complete and consists of oral and anal openings.
7. Blood is red. Plasma contains hemoglobin, heme-erythrin or chloroquine.
8. The body is composed of chitinless and soft cuticle.
9. The larval stage of the life cycle consists of trochophores.
10. They are unisexual or bisexual. Reproduction occurs sexually and asexually.

[Key words to remember features: metamere, seatae, parapodia, nephridia, trochophore]

The word Annelida is derived from the Latin word annelus meaning small ring and eidos meaning shape. Animal bodies that are triploblastic, cylindrical, ring-like segments or metameres are called Annelida. The animals of this phase are known as ringworms or segmented worms. Phlebotomy is the process in which a starved leech is attached to the body to suck the contaminated blood from the body. The number of species in this category is about 17,338. Lamark (1809) identified soft-bodied animals as Annelida.

The word Mollusca is derived from the Latin word molluscus meaning soft. Mollusca are the animals whose body is soft, asymmetrical or bilaterally symmetrical, segmentless, ciliated, fleshy legs and exoskeleton made of calcium carbonate. Mollusca is the second largest phylum of fauna. But it is the largest marine episode. 23% of the ocean is molluscs. Precious pearls, Tyrian purple dye, sea silk, lime etc. are obtained from animals of this phase. The giant squid of this episode is 12 meters long and weighs 270 kg. Land snails (Achatina fulica) and snails cause extensive damage to crops and are known as crop pests. The number of species in this category is about 1,00,000. Johnston (1650) named the order Mollusca.

Characteristics of the Mollusca
1. Their bodies are soft, fleshy and unsegmented.
2. They are cylomates, asymmetrical or bilaterally symmetrical and have a conspicuous head.
3. At the base of the body are muscular fleshy legs.
4. The body is covered by a thin covering called mantle. Calcareous material secreted from the mantle forms the shell.
5. Respiration occurs by gills and mantle membrane. Pulmonary sacs are developed in terrestrials.
6. The digestive tract consists of sand-tongues or radulas made of chitin.
7. The body cavity is very short and turned into a hemocele. Circulatory system is semi-free type.
8. The alimentary canal is straight, curved or U-shaped.
9. Blood contains hemocyanin (meat and copper) and amoebocytes.
10. Siloam is limited only to the sides of the heart, the genital cavity and the kidneys.
11. A unisexual or bisexual animal. They have sex.
12. The life cycle consists of trochophore, velizar or gochidium larvae.
13. They live in sea salt water, fresh water, ditches or pits.

[key words to remember features: soft body, head, fleshy leg, mantle, radula, hemosyl, hemocyanin, trochophore, velizer, glochidium]

Classification of Mollusca
The order Mollusca is divided into 5 classes.
1. Caudofovita: They are 2–140 mm long. Body covered with chitinous cuticle. They are marine.
2. Polyplacophora: They are 8 mm to 33 cm long. Body covered by chitin.
3. Gastropods: Their bodies are soft, fleshy and unsegmented. Body covered by mantle.
4. Bivalvia: They have hemolymph fluid. There are two shells made of calcium carbonate.
5. Cephalopoda: These are marine animals with eight arms. There is no hard shell on the body. Has eight legs (cephalopods). They are nocturnal.

Some animals of Mollusca
Snail – Pila globosa
Octopus – Octopus macropus
Mussel – Lamellidens marginalis
Dentalium – Dentalium kernedei
Loligo – Loligo edulis
Cattle fish – Sepia aculeata
Neopilina – Neopilina galatheae
Teredo – Teredo navalis
Mussel – Unio marginalis
Pearl oyster – Pinctada vulgaris
Chiton – Chiton tuberculatus
Chiton – Ischnochiton evanida
Chaetoderma – Chaetoderma nitidulum
Solen – Solen ensis
Garden Snail – Helix pomatia
King Scallop– Pecten maximus

Devil fish
Eight armed marine animals belonging to the Mollusca family are called devil fish. It is called Octopus. They grab prey by their arms and kill them with poisonous saliva secreted from their mouths. For example – Octopus macropus.
Cuttle fish
Sepia and Loligo belong to Mollusca group called cuttlefish. Cuttlefish are edible animals. Their body is shield-shaped. Shells exist on the body. For example – Sepia aculeata.
Radula
The radula is a sand tongue. The radula or sand tongue is a toothed tongue-like organ in the digestive system of molluscs. It is made of chitin. It helps in taking and chewing food. For example – Snail (Pila globosa).

Ctenidia
Pteridia are respiratory organs. The gill-like breathing organs in the molluscs are called taenia. It resides in the mantle or mantle cavity or on the body surface of animals.

Pteridia are respiratory organs. The gill-like breathing organs in the molluscs are called taenia. It resides in the mantle or mantle cavity or on the body surface of animals.

The radula is a sand tongue. The radula or sand tongue is a toothed tongue-like organ in the digestive system of molluscs. It is made of chitin. It helps in taking and chewing food. For example – Snail (Pila globosa).

Sepia and Loligo belong to Mollusca group called cuttlefish. Cuttlefish are edible animals. Their body is shield-shaped. Shells exist on the body. For example – Sepia aculeata.

Eight armed marine animals belonging to the Mollusca family are called devil fish. It is called Octopus. They grab prey by their arms and kill them with poisonous saliva secreted from their mouths. For example – Octopus macropus.