Larva of Herdmania is called as tadpole larva. After hatching it leads a free-swimming life for 90-180 seconds and then undergoes retrogressive metamorphosis.

1. Tadpole larva

Comments:

• Larva is minute, transparent and 1.2 mm long. Body divisible into head or trunk and a long posterior tail.
• Anteriorly trunk contains 2 dorsolateral and 1 ventral median adhesive papillae.
• Tail contains tail fin which is extension of thin covering of the body. Along tail fin striations are present giving impression as fin rays. In the axis of tail notochord is present.
• Structures seen adhesive papillae, stigmata, heart rectum, ganglia of trunk, atrium on ciliated funnel.
• Various internal organs comprise sensory vesicle with otolith, visceral ganglion, mouth, pharynx, endostyle, stomach, intestine, atrium and atriopore.
• Tail is a powerful locomotory organ. It has notochord, nerve cord and tail fin.

2. Metamorphosis

• During metamorphosis, tadpole larva undergoes both retrogressive and progressive changes. Retrogressive changes : The just hatched tadpole larva immediately attaches to substratum by adhesive
  papillae. It undergoes following degenerative changes 
• Larval tail with tail fin shortens and later on disappears along with notochord and nerve cord.
• Anterior region expands. Sense organs and adhesive papillae disappear.
• Other structures seen are rectum, atrium, nerve ganglion, ciliated diverticulum, oral aperture, endostyle, stigmata or gill slits, heart and notochord.

3. Progressive changes

• Larva undergoes progressive changes. Young adult becomes without tail. Branchial and atrial apertures become functional, pharynx develops gill slits. Young adult undergoes following progressive changes :
• Body becomes surrounded by test or tunic all over. Tail completely degenerates. Branchial and atrial apertures become functional 
• Pharynx enlarges and develops gill slits. Stomach, intestine and liver develop. Heart, pericardium and gonads appear.
• Other structures seen are nerve ganglion, neural duct, endostyle, dorsal tubercle, atrial cavity, stolon, ciliated groove, atrium, and rectum.
  Special features : All chordate characters are found only in tadpole larva of Herdmania. Adults are without any chordate characters. Larva shows unique combination of retrogressive and progressive metamorphosis.