Gregarious pest: A pest is an animal that is detrimental or harmful to humans or human concerns. Locusta (locust) is a pest that is dangerous to crops. It causes heavy damage to the vegetation. As it lives in groups of the same individuals but does not help one another, hence called gregarious.
Body symmetry of Echinoderms: The adult echinoderms are radially symmetrical, but their larvae are bilaterally symmetrical. The echinoderms are unique in this feature that the larvae are bilaterally symmetrical (an advanced feature) while the adults developing from them are radially symmetrical (a primitive feature). Examples: Asterias (Starfish), Echinus (Sea urchin), Antedon (sea lily), Cucumaria (sea cucumber), and Ophiura (Brittle star).
Book-lungs: Present in scorpions, spiders, etc. These are the modified book-gills.
Bioluminescence: Bios means living and lumen means light. Bioluminescence is the property of production and emission of light by a living organism and hence shines in the dark background. It is a naturally occurring phenomenon. This property is well-marked in Ctenophores as they emit light and hence shine against the dark backgrounds. Examples: Pleurobrachia, Ctenoplana.