Question

What is common between an earthworm, a cockroach and a centipede?
A. Sexual dimorphism
B. Metamorphism
C. Chitinous exoskeleton
D. Haemocoel

Answer 1

Hint: Arthropods and annelids are both segmented, with a pair of appendages on each segment in the annelid class Polychaeta. The neurological system of arthropods is remarkably similar to that of annelids, and both groups have a tubular, dorsal heart, which is later removed or changed in some cases. Cockroaches and centipedes belong to the phylum arthropoda while earthworms belong to the phylum annelida, thus they share some similarities with each other.

Complete answer:
Let’s solve this question by analyzing each option for potential similarities between earthworm, cockroach and centipede.
Option:A - Centipedes and earthworms do not show sexual dimorphism while cockroaches are sexually dimorphic. So, this is not a similarity between them.
Thus, Option:A is not correct.
Option:B - Earthworms do not show metamorphism as they show direct development whereas centipedes and cockroaches show incomplete metamorphism. So, this is not a similarity between them.
Thus, Option:B is not correct.
Option:C – Cockroaches and centipedes have an exoskeleton made of chitin while earthworms do not have a chitinous exoskeleton. So, this is not a similarity between them.
Thus, Option:C is also not correct.
Option:D - The only thing that cockroaches, centipedes, and earthworms have in common is that they all have haemocoel. The haemocoel is a cavity that pumps blood between the organs of arthropods and annelids. Haemolymph is the blood in the haemocoel.

Thus, Option:D is the correct answer.

Note:
Molluscs, annelids and arthropods both have an open circulatory system. Insects, mollusks, and other invertebrates have open circulatory systems that pump blood into a hemocoel, with the blood diffusing back to the circulatory system between cells. Blood is pumped from the heart into the bodily cavities, where it surrounds the tissues. In this scenario, blood flow is slow.