What organ is in amphioxus?

The wheel organ is a prominent and specialized structure found within the oral cavity of an adult amphioxus, also known as a lancelet.

The Wheel Organ in Amphioxus

The wheel organ is a unique and essential component of the feeding apparatus in amphioxus. It is not an internal organ in the traditional sense, but rather a specialized epithelium located in the roof and sides of the animal's oral cavity. This structure plays a crucial role in creating water currents necessary for filter feeding.

Structure and Characteristics

The cells forming the wheel organ are highly specialized, exhibiting distinct features that enable their specific function:

• Tall and Strongly Ciliated: The cells are elongated and possess numerous cilia, which are hair-like projections that beat rhythmically to create water currents.
• Dark, Heterochromatin-Rich Nuclei: Their nuclei are dense and contain a high concentration of heterochromatin, suggesting a tightly regulated genetic activity characteristic of highly specialized cells.
• Bordering Oral Epithelium: The wheel organ precisely borders the main oral epithelium, forming a continuous and efficient surface for generating the feeding current.

Function and Significance

The primary function of the wheel organ is to generate a strong, constant water current that draws water, along with suspended food particles, into the oral cavity of the amphioxus. This process is vital for its filter-feeding lifestyle. The rhythmic beating of the cilia creates a vortex-like motion, hence the name "wheel organ." This mechanism allows the lancelet to efficiently capture microscopic organisms and detritus from the water column, which are then filtered by other structures like the pharyngeal gill slits.

The presence and specific characteristics of the wheel organ underscore the adaptive strategies of amphioxus as an invertebrate chordate, providing insights into the evolutionary development of feeding mechanisms in early chordates.

What is Amphioxus (Lancelet)?

Amphioxus, or lancelet, is a small, fish-like marine animal that belongs to the subphylum Cephalochordata. It is widely studied in biology because it possesses many fundamental characteristics of chordates (like a notochord, dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail) but lacks a vertebral column, making it an important model organism for understanding the evolutionary origins of vertebrates. These creatures spend most of their lives buried in the sand, filter-feeding on microscopic organisms.

For more detailed information on lancelets and their anatomy, you can explore resources like the University of Wisconsin-La Crosse's information on lancelets or various zoology textbooks.

Key Features of the Wheel Organ