Featured Invertebrate Data
Velella velella is considered to be commonly seen on Okinawa, especially during the Summer. I've only collected the single above featured animal but have seen huge numbers of individuals over many years of Okinawa diving. It is commonly known by the names: by-the-wind sailor, sea raft, purple sail, little sail, or simply Velella.
The following description of Velella velella is from the Animal Diversity Web (ADW).
The Velella is found floating on the surface of the high seas, and is common in the warm seas.
This hydroid polyp remains afloat on the surface of the Pacific Ocean for most of its life. It never touches or even comes close to the ocean bottom, and the only stage in its life when it is completely submerged under water is the larval stage. The Velella velella begins its life in the middle of the Pacific Ocean, is brought by the wind to the shores, and is usually cast up on a beach where it dies and disintegrates. The Velella are most common on the high seas, in the warmer regions of the Southern and Northern Hemispheres.
When taxonomists classified the Velella velella as a Siphonophore, it was considered to be a much smaller species then most which comprise the order. Although these animals are tiny, they were described as having a complex body structure just as any other Siphonophore. The Velella is sometimes mistakenly called a 2 cm "portuguese man-of-war" and has cellophane-like floats and erect triangular sails. The invertebrate is described as an upside-down polyp of a hydrozoa which did not settle to the bottom and grow sessile, but instead settled on the surface of the water and grew a float. The Velella is blueish to purple with a flat oval transparent float and an erect sail projecting vertically at an angle to the axis of its body. The projection of the sail is so that the animal can take the best advange of the wind, at any given moment. Older zoological opinions thought the Velella was a colony of specialized individuals like the "man-of -war", and that beneath its disk there was a single large feeding polyp surrounded by many reproductive polyps and a fringe of stinging polyps. More recent studies, however, have classified the Velella velella as a highly modified individual hydroid polyp, and not a colonial hydrozoa. Older zoological opinions classified the Velella velella as a Siphonophore, along with the Portuguese man-of-war and other colonial creatures. In contrast, recent taxonomists have classified the animal as a Chondrophore along with two or three uncommon relatives.
Within the species of Velella, the offspring show polymorphism in the orientation of their sails. A portion of the progeny have sails located from left to right away from the parent, and others have the sail from right to left. Both forms of Velella velella commonly occur. It is hypothesized that the different forms of this marine animal are mixed in the middle of the Pacific Ocean as larva, and that wind and wave patterns during development and growth cause them to move towards the coast. (Each form sending them in opposite directions). Near the end of spring, and early summer they arrive on the shores and are commonly cast up on the beaches of the Northern and Southern Hemisphere. The distribution of its dimorphic form also takes place in the Atlantic and the Mediterranean.
When biologists looked at the Velella velella as a colonial hydrozoan, the colonies were said to be hermaphroditic and the gonophores dioecious. The reproductive polyps were thought to produce medusa, which would break away from the colony and reproduce sexually, giving rise to planula larva. In recent studies, as biologist have examined the Velella as a single hydroid, reproduction still consists of an alternate generation between polyp and medusa stages. The life cycle: polyp-medusa-egg-planula-polyp.
The order Siphonophora, to which the Velella velella was originally placed, consists of highly polymorphic, free-swimming or floating colonies. The Velella, in accordance, was not considered to be a single animal but rather organisms which are linked together. When describing the behavior of the Velella it does not matter if one refers to the old definition (a colony of specialized polyps) or the new (a single highly modified polyp). The most striking aspect of the Velella velella is the direction of its sail, because it represents the direction the Velella is going and eventually to what shore it will arrive. The sail, which is situated on a diagonal to the long axis of the Velella's body, is found to be diagonal in the direction of the northwest to southeast on specimens cast upon northeast Pacific beaches. The other form of velella, which occur on the western side of the Pacific and in the Western Hemisphere have the sail running from northeast to southwest. Since the geographic range of velella also includes the Southern Hemisphere, the same strange distribution of the two forms takes place, although here they are reversed. Biologists speculate that both forms are mixed up in the middle of the Pacific Ocean, and are sorted by action of the wind. Due to the angle of the sail, which is 45' to the wind, southerly winds will push velella away from shore. But a strong wind will cause them to spin rapidly and follow the wind more closely.
The Velella velella is a carnivorous hydroid polyp, feeding on small prey and fish that can be caught only immediately below the surface of the water. The Velella is limited to surface food because it is not a very big animal and its tentacles do not reach very far. Its mouth is located in the middle of the underside of its body and lacks tentacles.
There are numerous on-line sites with photographs and videos of Velella velella. Several of these sites are:
Google. (Numerous photos).
By-the-wind sailors (aka Velella velella) wash up on the Oregon Coast.
The secret life of Velella: Adrift with the by-the-wind sailor. Monterey Bay Aquarium Research Institute (MBARI)
Velella velella: US west coast invaded by millions of jellyfish like creatures
I've added a second page w/ a series of images of the species.
In addition, I've added a link to the current and past featured invertebrates via a list and thumbnails.
*Wrack Line: The wrack zone or "wrack line" is a coastal feature where organic material (e.g kelp, seagrass, shells) and other debris is deposited at high tide. This zone acts as a natural input of marine resources into a terrestrial system, providing food and habitat for a variety of coastal organisms.