actinotrocha

Actinotroch is the free-swimming larval stage of pterobranchs, a small and obscure group within the phylum Hemichordata. In pterobranchs such as Rhabdopleura and Cephalodiscus, the actinotroch represents the early life form that disperses from the adult, which later develops into a colonial, tube-dwelling organism. The term actinotroch derives from Greek roots meaning a “ray wheel,” referring to the larva’s radiating, tentacle-bearing apparatus.

Morphologically, the actinotroch is characterized by a crown of ciliated tentacles surrounding the mouth, forming a wheel-like feeding structure. It typically has a short trunk and a simple body plan adapted for a planktonic lifestyle. The ciliated bands and apical region facilitate locomotion and feeding in the aquatic environment. The larva is dioecious in terms of parental origin and relies on external fertilization in most species.

Ecology and life cycle, actinotrochal development and metamorphosis lead to the formation of a sessile colony. After settlement, the larva undergoes metamorphosis to produce a collection of feeding zooids organized within a chitinous or proteinaceous tube. Budding and stolon formation give rise to the colonial colony, which is the adult form that attaches to substrates and secretes the protective tube.

Significance, actinotroch larvae are important for understanding hemichordate evolution and developmental biology. Their existence supports the close relationship between pterobranchs and other echinoderm and deuterostome lineages in the tree of animal life.