Question

Class Archiannelida is characterized by
A. Presence of setae
B. Presence of parapodia
C. Presence of both setae and parapodia
D. Absence of both setae and parapodia

Answer 1

Hint: The Archiannelida is referred to as an order of primitive bristle worms. They were considered to be a class of Annelida. All species of worms under this order lack external segments. Cilia may be present in some species that help in locomotion. Otherwise, the worms move through the contraction of body-wall muscles.

Complete answer: Archiannelida involves species of primitive types of bristle worms or polychaete worms. The organisms under this order are characterized by the complete absence of external segments. The worms move by contraction of muscles of the body wall or through the presence of cilia all over their bodies. They are mostly found living in sand. None of the members of Archiannelida bears setae or parapodia at any developmental stage. The body of Archiannelida worms is small and has no bristle-like structures as compared to polychaete worms over its epidermis. Hence, the epidermis lacks setae and may be ciliated. The segments are absent or if present not more than five. The first body segment or the prostomium has no appendages, parapodia are absent. Septa or partition is reduced or not present. The worms have a nervous system comprising the brain attached to longitudinal ventral nerve cords that are connected to the epidermis. Polygordius and Protodrilus are some common examples of Archiannelida worms.
Hence, the right answer is option D.

Note: Archiannelida is also known as Haplodrill. Zoologist Ray Lankester gave this name. They were considered to be a different phylum but now they are accepted as an order under Polychaeta. The term Haplodrill is given by Berthold Hatschek.