Animal Diversity Web

Ge­o­graphic Range

The Velella is found float­ing on the sur­face of the high seas, and is com­mon in the warm seas.

(Rick­etts, et al 1997)

• Biogeographic Regions
• atlantic ocean
  • native
• pacific ocean
  • native

Habi­tat

This hy­droid polyp re­mains afloat on the su­face 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 dis­en­te­grates. The Velella are most com­mon on the high seas, in the warmer re­gions of the South­ern and North­ern Hemi­spheres.

(Rus­sell-Hunter 1979)(Rick­etts, et al 1997)

• Aquatic Biomes
• coastal

Phys­i­cal De­scrip­tion

When tax­on­o­mists clas­si­fied the Velella velella as a Siphonophore, it was con­sis­dered 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 Hemis­pere. The dis­tri­b­u­tion of its di­mor­phic form also takes place in the At­lantic and the Mediter­ranean.

(Rus­sell-Hunter 1979, Rick­etts,et al 1997)

• Other Physical Features
• ectothermic
• radial symmetry

Re­pro­duc­tion

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.(Bayer and Hard­ing 1968)(Rick­etts, et al 1997)

• Parental Investment
• no parental involvement

Be­hav­ior

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, bea­cause 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 run­ing 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, south­ernly winds will push velella away from shore. But a strong wind will cause them to spin rapidly and fol­low the wind more closely. (Nichols, 1979; Rick­etts, et al., 1997)

• Key Behaviors
• natatorial
• motile

Food Habits

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.(Rus­sell-Hunter 1979, Nichols 1979)

Con­ser­va­tion Sta­tus

• IUCN Red List

  No special status

• US Federal List

  No special status

• CITES

  No special status

Other Com­ments

The Velella is car­niv­o­rous but is also the prey of local mol­lusks. The vi­o­let slug, a com­mon preda­tor of the Velella, floats in­de­pen­dently as it feeds on Velella. (Rick­etts,et al 1997)(Rus­sell-Hunter 1979)

Con­trib­u­tors

April Calderon (au­thor), South­west­ern Uni­ver­sity, Stephanie Fab­ri­tius (ed­i­tor), South­west­ern Uni­ver­sity.

Ref­er­ences

Bayer, F., H. Owre. 1968. The Free-Liv­ing Lower In­ver­te­brates. New York: The Macmil­lan Com­pany.

Nichols, D. 1979. The Ox­ford Book of In­ver­te­brates. Ox­ford: Ox­ford Uni­ver­sity Press.

Rick­etts, E., J. Calvin, J. Hedg­peth. 1997. Be­tween Pa­cific Tides (5th edi­tion). Stan­ford, Cal­i­for­nia: Stan­ford Uni­ver­sity Press.

Rus­sell-Hunter, W. 1979. A Life of In­ver­te­braes. New York: Macmil­lan Pub­lish­ing Co., Inc..