Ascidian tadpole larva

 Ascidian tadpole larva

Ascidian tadpole larva: The little tadpole larva is very active and moves around using its tail. It doesn't eat for a while during this stage, which is called the non-feeding form.

1.    The body is covered by a tunic and can be divided into an oval-shaped head and a long tail.

2.    There are three sticky bumps or warts on the chin: one in the middle on the back and two on the front sides.

3.    The tail is flattened on the sides, pointed at the end, and has a fin that connects with the dorsal and ventral fins.

4.    There are fine lines, possibly precursors to the fin rays found in fish, present on the sides.

5.    The central nervous system consists of an enlarged sense vesicle at the front, which connects to the pharynx through a neuropore, and a narrow, hollow spinal cord at the back.

6.    The sense vesicle contains a single eye with a retina, cornea, and lens, as well as a statocyst, which helps with balance.

7.    A notochord made of endodermal cells is found in the tail region, extending up to the pharynx and surrounded by a gelatinous substance.

8.    Muscles are arranged in segments on both sides of the nerve cord in the tail region.

9.    The digestive system can be divided into two parts. The front part includes a mouth, a well-developed pharynx with two pairs of gill slits, and an endo-style. The back part gives rise to the esophagus, stomach, and intestine.

10.    There are paired atrial sacs.

The tadpole larva is attracted to light and moves away from gravity. After an active period, it becomes slower and begins searching for a suitable surface to attach itself to. It prefers hard or rocky surfaces. The larva attaches itself using the sticky bumps, becomes attracted to gravity, and moves away from light, and then the metamorphosis process starts.

Metamorphosis of Ascidia:

 Ascidian tadpole larva

The metamorphosis of tadpole larvae in Ascidia is a two-way process. Some organs are lost, which is considered retrogressive, but at the same time, other structures continue to develop, which can be seen as progressive.

Changes in the larva after attachment - Retrogressive metamorphosis:

1.    The tail becomes much shorter, the number of lines reduces, and eventually, the tail disappears.

2.    The notochord coils up, becomes disorganized, and disappears along with the tail.

3.    The nerve cord is limited to the trunk region and gradually becomes a solid ganglion.

4.    The mouth shifts 90° from the point of attachment due to rapid growth between the sticky bumps and the mouth, as well as the suppression of growth on the original dorsal side.

Progressive metamorphosis:

1.    The pharynx becomes larger, and the number of gill slits increases.

2.    The atrium enlarges.

3.    The velum appears.

4.    The neural gland differentiates.

5.    Reproductive organs gradually develop.

Certainly! Here are the different types of metamorphosis other than retrogressive:

1. Progressive Metamorphosis:

Progressive metamorphosis is a type of metamorphosis in which an animal progresses in evolutionary grades during its development from a larva to an adult. The adult form possesses more advanced characteristics compared to the larval stage. This type of metamorphosis can be observed in some insects, where the larvae resemble miniature adults and undergo gradual changes as they grow.

2. Partial Metamorphosis:

Partial metamorphosis refers to a type of metamorphosis in which only certain parts of the animal's body undergo changes during its development. In this process, the overall body plan remains relatively similar, but specific structures or organs may undergo significant modifications. An example of partial metamorphosis is seen in insects that undergo incomplete metamorphosis, such as grasshoppers or dragonflies, where the immature stages (nymphs) resemble adults but lack functional wings.

3. Complete Metamorphosis:

Complete metamorphosis is a type of metamorphosis in which the entire body of an animal undergoes a drastic transformation when transitioning from the larval stage to the adult form. This type of metamorphosis involves distinct developmental stages, including the egg, larva, pupa, and adult. Examples of animals undergoing complete metamorphosis include butterflies, moths, beetles, and flies.

These different types of metamorphosis showcase the diverse strategies employed by various animal species to undergo developmental changes as they transition from immature stages to their adult forms.