Question

Besides paired series of nephridia, there is a single large nephridium known as _____ in protochordates.
A. Metanephridia
B. Hatschek’s nephridium
C. Neural gland
D. Mesonephros

Answer 1

This nephridium is the largest and the most anterior nephridia in the Branchiostoma virginiae body. This is located beside the left anterior aorta on the left side of the notochord.

Complete answer:
The organisms in the Protochordata are commonly referred to as the lower chordates. They don't constitute a "significant" taxonomic group and are labelled as such just for convenience. But they form a broad Chordata division. They're also called Acraniata because they don't have a genuine skull. Protochordates are normally found in marine water. Their body is bilaterally symmetrical, triploblastic and coelomate. At some point in their life their body grows a long rod-like structure, called the notochord. They show organizational organ system level.

A single broad Hatschek's nephridium occurs over the lateral pharynx roof to the left dorsal aorta in addition to the paired nephridia. It looked like the arrangement of coupled nephridia. It's a narrow pipe. Its front end finishes blindly before the Hatschek's pit and the back end opens into the pharynx pre bronchial area just behind the velum.

Thus, the correct answer is option B. i.e., Hatschek's nephridium.

Note: Protochordates are an informal animal group, named primarily for simplicity in order to classify animals closely linked to vertebrate species. This is a group composed of the Phylum Hemichordata, Urochordata and cephalochordata. The Phylum Hemichordata comprises marine worms which share some, but not all chordate characteristics. These animals have pharyngeal gill slits and a typically strong dorsal nerve cord.