Question

Fill in the blanks.
a. Bilateral, dorsiventral symmetry is found in ______
b. Worms causing disease elephantiasis is _____
c. The open circulatory system is found _____ where the coelomic is filled with blood.
d. _____ are known to have pseudocoelom

A.(a) Liver fluke (Fasciola hepatica)
    (b) Filarial worm ( Wuchereria bancrofti)
    (c) Arthropods
    (d) Nematodes

B.(a) Liver fluke (Fasciola hepatica)
    (b) Arthropods
    (c) Nematodes
    (d) Filarial worm (Wuchereria bancrofti)

C. (a) Filarial worm (Wuchereria bancrofti)
    (b) Liver fluke (Fasciola hepatica)
    (c) Arthropods
    (d) Nematodes

D.(a) Filarial worm (Wuchereria bancrofti)
    (b) Liver fluke (Fasciola hepatica)
    (c) Nematodes
    (d) Arthropods

Answer 1

Hint: In the open circulatory system, blood moves from the lacunae (large open spaces) and by the sinuses among the tissues. Blood contains very low pressure in this system. They are commonly found in higher invertebrates specifically insects, prawns, etc. Tissues are in direct touch with the blood. Interchange of nutrients and gasses occurs between the tissue and the blood straightly.

Complete answer:
• Bilateral, dorsiventral symmetry is found in the Liver fluke (Fasciola hepatica). Bilaterally symmetrical means left and right parts of the body have a similar design. Dorsiventrally means the front and backside/portion of the organism are flat. These two characteristics are found in the organisms belonging to the Platyhelminthes group.

• Worms causing disease elephantiasis is the Filarial worm (Wuchereria bancrofti). Elephantiasis is a condition, which is characterized by enlargement of an area of the body, specifically the limbs. Other areas usually affected include the external genitals. Elephantiasis is caused/produced by obstruction of the lymphatic system, which results in the accumulation of a fluid called lymph in the affected areas.

• All arthropods exhibit an open circulatory system, it pumps blood into a cavity called a hemocoel where it surrounds the organs and then returns to the heart(s) through Ostia (openings). The blood is found in arthropods, a mixture of blood and interstitial fluid, which is called hemolymph.

• Nematodes have pseudocoelom. The body cavity of nematodes is known as pseudocoelom because it is not totally lined by mesodermal cells as in the true coelomic cavity of all vertebrates.

Hence, the correct answer is option (A). (a) Liver fluke (Fasciola hepatica) (b) Filarial worm (Wuchereria bancrofti) (c) Arthropods (d) Nematodes.

Note:
- Peritoneum is not present in pseudocoelom, which is derived by embryonic mesoderm, whereas peritoneum is found in the inner side of the coelom.
- All arthropods have an open circulatory system and do not have differentiated blood vessels.
- Swelling of the scrotum, legs, or breasts caused by elephantiasis. Elephantiasis is considered a neglected tropical disease (NTD). It is very common in tropical and subtropical areas of the world, including Africa and Southeast Asia. Around 120 million people are suffering from elephantiasis.