The Gulf of Maine is home to several solitary ascidians with gelatinous bodies and translucent tunics. These species may be difficult to distinguish from each other when individuals are very young, in masses of mature individuals growing in social groups, or when morphology is masked by overgrowth of colonial ascidians such as Didemnum vexillum or Diplosoma listerianum. In Provincetown, the cryptogenic Ciona intestinalis and native Molgula sp. (probably manhattensis) are very common, whereas the invasive Ascidiella aspersa, which is common in other marinas along the coast, is less frequently seen.
Ciona is best distinguished from Ascidiella and Molgula by its elongate, vase shape which is less prominent in small individuals, and it's lemon yellow siphon rings which are visible even when young. The siphon rings are also crowned with 8 orange pigment organs that are more subtle but can be discerned by close examination. When the siphons close, muscles contract the rings and bring the pigment organs closer together at the bases of notches in the contracted opening. The pigment organs have an ocellus-like structure and probably function in light detection, although there must be additional receptors to detect light because individuals who have the siphons removed still grow towards the light.
Yellow Siphon Rings of Ciona intestinalis
Yellow Siphon Rings of Ciona intestinalis. From Adrian Gittenberger's Dutch Ascidians Homepage (www.ascidians.com).
Orange Oral Pigment Organs and Yellow Siphon Rings of Ciona
Eight orange pigment organs are seen on these individuals and can be easily distinguished when the images are enlarged. (The Ciona look like they are wearing jackets of Didemnum vexillum). Photo by Arne Kuilman.
Orange Oral Pigment Organs
Partially closed siphons with orange pigment organs brought
closer together at notches of the contracted opening.
During the process of researching images and information on the siphon rings, I came across a 2010 paper on the structure and regeneration of the siphons that was particularly interesting, filled with beautiful color photographs of the yellow rings and orange pigment organs, and available open access on the internet.
Auger, H, Y Sasakura, JS Joly, WR Jeffery. Regeneration of oral siphon pigment organs in the ascidian Ciona intestinalis. Develop. Biol. 339: 374-389, 2010 (Elsevier).
Auger and his research team examined oral siphon regeneration after surgical removal in Ciona intestinalis. After removal, the oral siphon rapidly reformed (orange) oral pigment organs (OPO) at its distal margin prior to slower regeneration of proximal siphon parts. The pattern of 8 OPOs and siphon lobes was restored with fidelity after dissecting only the end of the siphon, but as many as 16 OPOs and lobes could be reformed after dissection at the base of the siphon (complete removal).
The oral pigment organs, siphon lobes, and yellow pigment bands were the first structures to regenerate. The yellow pigment bands formed as extensions of the pigment organs, which grew together along the edge of the siphons. The rest of the siphon grew outward after the orange oral pigment organs and yellow pigment bands were formed. They concluded that the pattern of oral pigment organ regeneration is determined by cues positioned along the longitudinal axis of the oral siphon.
Anatomy and Histology of the Oral Pigment Band (PB) and Organ (OPO)
Morphology of the oral siphon. A, the tunic was removed and the pigment cells and muscles are clearly visible. B, higher magnicaiton of yellow and orange cells. D-E, the ocellus-like organs consist of receptor epithelials cells and an underlying cup-shaped aggregation of organge pigment cells. OS, oral siphon; AS, atrial siphon; OPO, oral pigment organ; PB, (yellow) pigment band; RC, receptor cells; PC, pigment cells.
PUBLICATIONS:
Hecht, S. The photo sensitivity of Ciona intestinalis. J. Gen. Physiol. 1: 147-166, 1918.
Sutton, MF. The regeneration of the siphons of Ciona intestinalis. J. Mar. Biol. Assoc. UK. 32: 249-268, 1953.
Sutton, MF. The regeneration of the siphons of Ciona intestinalis. J. Mar. Biol. Assoc. UK. 32: 249-268, 1953.
Dilly, PN, and JJ Wolken. Studies on the receptors in Ciona intestinalis. IV. The ocellus in the adult. Micron, 4: 11-29, 1973.
Chiba, S, A Sasaki, A Nakayama, K Takamura, N Satoh. Development of Ciona intestinalis juveniles (Through 2nd Ascidian Stage). Zool. Sci. 21: 285-298, 2004.
Chiba, S, A Sasaki, A Nakayama, K Takamura, N Satoh. Development of Ciona intestinalis juveniles (Through 2nd Ascidian Stage). Zool. Sci. 21: 285-298, 2004.
