Biology 2nd Paper (Zoology) · Classes 11-12 · Chapter 1

Practical: Identifying Nonchordate Specimens.

A specimen floats in a glass jar and the teacher asks, “What is this?” A viva answer has two halves: where the animal sits in the classification, and which marks you recognised it by. This note gives both halves for fifteen nonchordate specimens.

1. How the practical runs

The practical observes 10 animals in all: 5 nonchordates and 5 vertebrates. The teacher chooses which 10. For each one you draw a black-and-white pencil picture on a drawing sheet, showing its identifying features, and label it. This note covers the nonchordate specimens only; the vertebrates have a note of their own.

Every specimen needs two things written down: the classification line and the identifying features. The classification line always runs from the big step down to the small one.

2. A sponge and a cnidarian

Scypha (Scypha gelatinosum). Phylum Porifera; Class Calcarea; Order Heterocoela; Family Sycettidae; Genus Scypha. How to know it: a slender, vase-shaped body with a swollen middle. The body wall carries ostia. The free upper end opens by the osculum, and the closed lower end is fixed to a support by a stolon.

Hydra (Hydra viridis). Phylum Cnidaria; Class Hydrozoa; Order Hydroida; Family Hydridae; Genus Hydra. The body is tubular, one end open and the other closed. At the free end sits a cone-shaped hypostome with the mouth at its tip, ringed by thread-like tentacles. The closed end carries a round basal disc. One or more buds show on the body.

3. Flatworms and a roundworm

Pork tapeworm (Taenia solium). Phylum Platyhelminthes; Class Cestoda; Order Cyclophyllidea; Family Taeniidae; Genus Taenia. The body is a long ribbon flattened top to bottom, in three parts: scolex, neck and strobila. The small scolex has 4 suckers, a rostellum at the tip and hooks around it. The strobila holds many proglottids.

Sheep liver fluke (Fasciola hepatica). Phylum Platyhelminthes; Class Trematoda; Order Echinostomida; Family Fasciolidae; Genus Fasciola. The body is soft, leaf-like and flattened dorso-ventrally. The triangular mouth lies at the tip of the oral cone at the front end. There are two muscular suckers: the oral sucker and the ventral acetabulum. The genital pore is just in front of the acetabulum, and the excretory pore is at the hind end.

Round worm (Ascaris lumbricoides). Phylum Nematoda; Class Phasmida; Order Ascarida; Family Ascaridae; Genus Ascaris. The body is cylindrical, narrow at both ends and wide in the middle, with a smooth, tough, elastic cuticle. The mouth at the front is ringed by three lips. The excretory pore lies on the ventral side, a little behind the front end. The male's hind end is curved and carries penial setae.

4. Annelids: earthworm and leech

Earthworm (Metaphire posthuma). Phylum Annelida; Class Oligochaeta; Order Haplotaxida; Family Megascolecidae; Genus Metaphire. The tubular body is made of many segments, separated by grooves between segments. Segments 14 to 16 form the clitellum. One female pore lies on the ventral side of segment 14, and a pair of male pores on segment 18. Every segment bears setae, and the dorsal blood vessel can be seen. Touch the parts one by one in the figure below.

Leech (Hirudinaria manillensis). Phylum Annelida; Class Hirudinea; Order Gnathobdellida; Family Hirudidae; Genus Hirudinaria. The muscular body is flattened dorso-ventrally and divided into 33 segments, each with several annuli. An anterior sucker sits on the ventral side of the front end. The first 5 segments carry 5 pairs of ocelli. A plate-like posterior sucker closes the hind end.

5. Arthropods: prawn, crab, cockroach, grasshopper

Prawn (Macrobrachium malcolmsonii). Phylum Arthropoda; Class Malacostraca; Order Decapoda; Family Palaemonidae; Genus Macrobrachium. The body is elongated and bilaterally symmetrical, in two parts: cephalothorax and abdomen. The unsegmented cephalothorax is covered by a hard carapace, with a saw-like rostrum at its front. There are two pairs of antennae and a pair of stalked compound eyes.

Crab (Portunus pelagicus). Phylum Arthropoda; Class Malacostraca; Order Decapoda; Family Portunidae; Genus Portunus. Its Class and Order match the prawn's; the difference starts at Family. The oval, flattened body is covered by a hard cuticle. The carapace covers the whole body, and the abdomen lies on the ventral side of the carapace. The first of the five pairs of legs is a pincer-like chela. There are two pairs of antennae and a pair of stalked compound eyes.

Cockroach (Periplaneta americana). Phylum Arthropoda; Class Insecta; Order Dictyoptera; Family Blattidae; Genus Periplaneta. The body is slender, long, glossy and reddish-brown, divided into head, thorax and abdomen, with 3 segments in the thorax and 10 in the abdomen. The head has two compound eyes and two antennae. The thorax carries three pairs of legs and two pairs of wings. The abdomen ends in anal cerci.

Grasshopper (Poekilocerus pictus). Phylum Arthropoda; Class Insecta; Order Orthoptera; Family Acrididae; Genus Poekilocerus. The yellow-green body, covered by cuticle, is divided into head, thorax and abdomen. The triangular head has compound eyes, ocelli, antennae and chewing mouth parts. The mesothorax carries narrow hard wings and the metathorax large membranous wings. There are three pairs of jointed legs. The abdomen has 11 segments.

6. Molluscs and an echinoderm

Freshwater mussel (Lamellidens marginalis). Phylum Mollusca; Class Bivalvia; Order Unionoida; Family Unionidae; Genus Lamellidens. The soft, unsegmented body is enclosed by a two-valved shell. Each valve is convex outside and concave inside, flattened at the sides, thickest at the hind end, and joined along a hinge line. The raised part near the hinge is the umbo, with growth lines around it.

Apple snail (Pila globosa). Phylum Mollusca; Class Gastropoda; Order Mesogastropoda; Family Pilidae; Genus Pila. The soft body is enclosed by a hard, apple-shaped shell coiled in 4 whorls with an apex at the top. An operculum shaped like the Bangla numeral ‘৫’ closes the shell mouth. Growth lines mark both shell and operculum. A fleshy, lobe-like foot lies on the ventral side.

Devil fish (Octopus macropus). Phylum Mollusca; Class Cephalopoda; Order Octopoda; Family Octopodidae; Genus Octopus. The soft, oval body is covered by the mantle, with no true shell. The mouth is surrounded by 8 oral arms, longer than the body, set with suckers and joined at the base by a web. The third arm on the right is specially shaped for reproduction and is called the hectocotylus.

Starfish (Astropecten euryacanthus). Phylum Echinodermata; Class Asteroidea; Order Phanerozonia; Family Astropectinidae; Genus Astropecten. The body is radially symmetrical, flattened, star-like and spiny, with five arms at equal distances from a round central disc. The aboral surface has the madreporite and the anus. The oral surface has an ambulacral groove along each arm, with rows of tube feet on both sides.

7. Try it yourself

First, the classification. Take each common name and drop it in the right class box. The phylum is in brackets beside each class.

Now the practical table. A specimen comes up in the jar; look at its marks one by one and name it with as few as you can.

Now the other way round. In the viva you are handed a specimen and name it from one or two unique marks. Tap a mark and the specimen's name appears below.

The classification line carries marks in every answer. One specimen is picked for you; put its seven steps in the right order.

8. Check yourself

Start with the first question.

The second is about a particular specimen.

Read the last question with care.

The whole note on six cards.

Source: Biology 2nd Paper (Zoology), Classes 11-12 (NCTB), Chapter 1 “Animal Diversity and Classification”, the “Practical: Identifying Nonchordate Specimens” part.