Saccoglossus

Saccoglossus is a marine, worm-like organism belonging to the phylum Hemichordata, commonly called an acorn worm, that lives in burrows within sandy or muddy coastal environments. Its soft, unsegmented body is divided into three main parts: a muscular proboscis used for burrowing and feeding, a short collar containing the mouth, and a long trunk that bears gill slits for respiration. It is a deposit feeder, ingesting sediment and extracting organic matter and microorganisms for nutrition. The organism has a simple circulatory system and a dorsal nerve cord, showing primitive similarities to chordates, which makes it evolutionarily significant. Reproduction is sexual with external fertilization, and development usually includes a free-swimming tornaria larval stage that resembles echinoderm larvae.