Parenchymula

Parenchymula is a term used in developmental biology to describe a specific stage in the life cycle of certain organisms, particularly in some species of sponges (Porifera). It refers to a free-swimming larval form that develops from the fertilization of an egg and subsequent embryonic development.

The parenchymula larva is characterized by its spherical or slightly oval shape and is covered with cilia, which allow it to move through the water. These cilia also aid in feeding, as the larva can capture small particles from the surrounding water. The body of the parenchymula is composed of a layer of cells surrounding a central cavity, which will eventually give rise to the adult sponge's structure.

During the parenchymula stage, the larva undergoes significant morphological changes. It possesses a distinct anterior-posterior axis and exhibits a type of locomotion known as "creeping" or "crawling," which is facilitated by the cilia. This stage is crucial for the dispersal of the organism, as the larva can travel away from the parent sponge before settling down and undergoing metamorphosis into the adult form.

The parenchymula larva is particularly well-studied in the class Demospongiae, which represents the most diverse and abundant group of sponges. In these species, the parenchymula stage is a key part of the asexual reproduction process, ensuring the spread and colonization of new habitats. The duration of the parenchymula stage can vary depending on environmental conditions and species-specific factors, but it typically lasts for a few days before the larva settles and begins its transformation into an adult sponge.