Definition

Noun: A free-swimming larval stage of ascidians (sea squirts), characterized by a tail that resembles that of a tadpole and contains a notochord, a defining structure of chordates.

Usage

The term is used in zoology and marine biology to describe a specific, transient developmental form. It highlights a key evolutionary link, as the larva possesses a primitive backbone (notochord) that is lost in the sedentary adult form. - The ascidian tadpole swims briefly before settling and metamorphosing into an adult sea squirt. - Studying the ascidian tadpole provides insights into chordate origins.

Advanced Usage

• The ascidian tadpole is a classic example of a larval form that exhibits characteristics (like the notochord) not present in the adult organism, a concept known as "retrogressive metamorphosis."

Variants and Related Words

• Ascidian (n): The adult form, a sessile marine invertebrate of the class Ascidiacea.
• Tadpole (n): The aquatic larval stage of frogs and toads, used here by analogy due to the similar tail shape.
• Larva (n): The immature, free-living form of an animal that undergoes metamorphosis.

Synonyms

• Ascidian larva
• Urochordate tadpole larva

Related Phrases/Idioms

Not commonly used in idioms. It is a precise scientific term.

Noun

1. free-swimming larva of ascidians; they have a tail like a tadpole that contains the notochord