Tag: diversity in living world

Balanoglossus is an ocean-dwelling acorn worm genus. They possess a long protrusible proboscis.
The tentacular apparatus, which is present in some hemichordates is of lysosomal (collar).
Balanoglossus also possess the trunk in which the gonads are present.

Balanoglossus was earlier placed in the group of the Hemichordates. But now like the other doubtful Hemichordates, such as Cephalodiscus and Rhabdopleura, Balanoglossus are now classified under non-chordates after echinoderms. It is because their notochord is doubtful. They have a short notochord which is confined to proboscis and non homologous with that of chordates.

Amphioxus also called as lancelets or cephalochordates form one of the three chordate subphyla. Amphioxus possess typical chordate characters, such as a dorsal hollow neural tube and notochord, a ventral gut and a perforated pharynx with gill slits, segmented axial muscles and gonads, a post-anal tail, a pronephric kidney. Hence, option B is correct.

The unpaired 'Hatscheck's nephridium' is the largest and most anterior of the nephridia in the body of the Branchiostoma. It is a single tubule which lies on the left side of the notochord running parallel to the left anterior aorta. It stretches from the anterior vestibule to a point immediately posterior to the velum where it opens into the endodermal pharynx. 

Hemichordata closely relates the Chordates. It contains marine deuterostome animals. They have a tubular structure known as stomochords. Stomochords arise in embryonic development as an out-pocketing from the roof of the embryonic gut anterior to the pharynx. In adults, they extend dorsally from the pharynx into the proboscis and serve to communicate with the oral cavity. Their walls are composed primarily of epithelial cells, but ciliated and glandular cells are also present.Balanoglossus belongs to the Hemichordata phylum. So, it has buccal diverticulum.

Protochordates are closely related to vertebrates. These lack some of the peculiar characteristics of chordates like the true skull, brain, skeleton. These are invertebrates. 
So, the correct answer is option A.

Balanoglossus belongs to subphylum Hemichordata, which have a short notochord present in anterior part of the body but it is only present in the larval stage.

Balanoglossus is an ocean-dwelling acorn worm, it is an "evolutionary link" between invertebrates and vertebrates. It belongs to chordates, phylum Hemichordata and order Enteropneusta.

• Balanoglossus belongs to phylum Hemichordata. They possess notochord (only in the embryonic stage) whereas earthworm, leech, series belongs to phylum Annelida and they do not possess notochord.