Question

1. How many pairs of setae are there in each segment of the worm？Does each segment have setae?
2. What body region or segment are the walking legs attached to? What about the swimmerets?
3. What is the function of these gills?
4. Try to identify and explain what the crayfish had been eating:

5. Inside the stomach locate the gastric mill, a hard serrated structure. Study it closely by running a finger along the tooth-like margin.

   What is this structure’s function?

6. What are the functions of the skin gills and pedicellariae?

Answer 1

Earthworm is a reddish brown terrestrial invertebrate that inhabits the upper layer of the moist soil. Earthworms have long cylindrical body. - The body is divided into more than hundred short segments which are similar (metameres about 100-120 in number). - The dorsal surface of the body is marked by a dark median mid dorsal line (dorsal blood vessel) along the longitudinal axis of the body. - The ventral surface is distinguished by the presence of genital openings (pores).

Answer for question 1

The first body segment is called the peristomium (buccal segment) which contains the mouth.

In a mature worm, segments 14-16 are covered by a prominent dark band of glandular tissue called clitellum.

It secretes mucus and albumen for the formation of cocoon or egg capsule.

Thus the body is divisible into three prominent regions – preclitellar, clitellar and postclitellar segments

SETAE-

1. In each body segment, except the first, last and clitellum , there are rows of S-shaped setae(four pairs), embedded in the epidermal pits in the middle of each segment.
2. Setae can be extended or retracted and their role is in locomotion.

Answer for Question 2: I believe this question is about crayfish and giving answer accordingly

Crayfish are invertebrate arthopods with a protective exoskeleton outside their body. It  has two body segments. The head fused with the thorax and forms the first segment known as cephalothorax. Carapace covers first segment to protect it like a shield. The abdomen is located behind the cephalothorax with six divided segments, whereas cephalothorax with 13 segments. Each segment of cephalothorax & abdomen contains a pair of appendages. The head region has five pairs of appendages. The first three appendages of cephalothorax are maxillipeds, which hold food during eating. The chelipeds are the large claws that the crayfish uses for defense and to capture prey. Four remaining segments contains a pair of walking legs. The first five segments of the abdomen each have a pair of swimmerets. They are smaller limbs under the tail. Function of swimmerets is to create water currents and function in reproduction.

Answer for Question 3:

In Crayfish, Gills are found in body sides and also at the base of each leg,

They are featherlike structures found below the carapace and attached to the walking legs and chelipeds.

Gills facilitate respiration.

Their feathery nature provides a larger surface area.

Gills pull oxygen into the bloodstream as water passes through them and release carbon dioxide.