This is a Salp, or colony of Salps. Photo by Rod 01 Feb 2011 Mike's Wreck.
Location was Key Largo, FL
Siphonophore in the Order Physonecta??
<>Features: 1.
Size:  This specimen was about 5 feet long.
Description:  Salps (Subphylum Tunicata)
Audubon Field Guide (Seashore Creatures); page 727-728; 744; plate 488, 490;
Reef Fish ID 3rd ed; 

     This image shows a stained specimen of a young salp, which belongs to a group of tunicates that contains only six genera, most of which are found in tropical and semitropical waters.  Salps differ from sea squirts in having their incurrent and excurrent siphons at the opposite ends of the body.  This arrangement allows them to use the water passing through them not only to obtain food and oxygen but also for locomotion using a  type of "jet propulsion".  Some small forms are brilliantly luminescent while others range in size to over 3 meters!     
     Salps are related to the pelagic tunicate groups doliolida and pyrosoma, as well as to other bottom-living (benthic) tunicates.
Although salps appear similar to jellyfish because of the simple form of their bodies and their free-floating way of life, they are structurally most closely related to vertebrates, animals with true backbones.
     Salps appear to have a form preliminary to vertebrates, and are used as a starting point in models of how vertebrates evolved. Scientists speculate that the tiny groups of nerves in salps are one of the first instances of a primitive nervous system, which eventually evolved into the more complex central nervous systems of vertebrates.
     The salps (Class Thaliacea, Order Salpida) include the most commonly encountered pelagic tunicates.  Salps can form massive aggregations of millions of individuals that may play a significant role in marine ecosystems.  They exhibit among the fastest growth rates of any multicellular organism.  A transparent test encloses the cylindrical body, and may be relatively thick and tough with projections and keels.  Using rhythmic contractions of bands of circular muscles within the body wall, movement by jet propulsion is accomplished by regulating the action of sphincter muscles that open and close anterior and posterior openings.  This also serves to pump plankton-laden water through the body, where a mucous net is used to extract food particles.  The number and pattern of muscle bands is useful in distinguishing species. 
    Salps exhibit a complex life cycle with alternating aggregate and solitary generations.  Aggregates (the sexual gonozooids) develop asexually from an elongating stolon that buds from an area just behind the endostyle of the solitary individuals (the oozooid).  Individuals within aggregates are hermaphrodites, typically starting as females that are fertilized by older male individuals from another chain.  The resulting embryos (oozooids) then develop into the solitary asexual phase.  There is no larval stage and even before release the young oozooid often has a developing stolon.  In many species only a single embryo develops within each individual of the aggregate.  This method of asexual reproduction enables salps to quickly exploit periods of abundant food with rapid increases in population density.  With few defenses, rapid growth to maturity is the primary means to avoid predation by heteropods, jellyfish, siphonophores, ctenophores, sea turtles, marine birds and numerous types of fishes.  Hyperiid amphipods and several species of fish also use salps as traveling homes.
      The siphonophore that most people have heard of is the notorious Portuguese man-of-war, Physalia (Order Cystonecta).  The cystonects possess a gas-filled float known as the pneumatophore that keeps them at the surface with tentacles trailing below.  They lack nectophores and gelatinous bracts.  Physalia only ventures as far north as southern California, which is fortunate for swimmers and divers farther north since it packs a powerful sting.  It possesses a large number of gastrozooids that lack tentacles, with large dactylozooids endowed with long potent tentacles taking up the slack.  The tentacles can reach lengths of 20 meters or more and easily dispatch prey such as fish.  Beneath the brilliant blue gas float are clusters of smaller dactylozooids and gonozooids. 
    Siphonophores in the Order Physonecta typically form long chains with an apical pneumatophore followed by a group of muscular swimming bells (nectophores).  Posterior to this are feeding and reproductive segments known as cormidia that form the bulk of the chain.  Each cormidium typically consists of a gelatinous bract (for buoyancy or protection), a gastrozooid with a long branched tentacle, defensive dactylozooids (one or more), each with an unbranched tentacle, and male and female gonozooids.  Frequently all that you will see near the surface of species such as Apolemia is a portion of the chain that has broken away.  Even broken chains, however, must be treated with respect since the stinging capability is retained. 
    Siphonophores that lack an apical pneumatophore but possess at least 1 relatively large swimming bell are grouped in the Order Calycophora.  The apex of the stem is hidden by the posterior swimming bell.  Calycophorans have repeating cormidia that bud from an anterior growing zone (just below the last swimming bell), with the last cormidium being the oldest.  Each cormidium possesses a bract, a gastrozooid, and gonozooids (one sex only) which can also function as swimming bells.  Unlike physonect siphonophores however, the cormidia lack dactylozooids.  Cormidia can detach and then form free-swimming reproductive structures known as eudoxids.  Whereas certain calycophoran species may form chains that are in excess of 100 feet long, many are tiny, inconspicuous active swimmers with a rocket-shaped swimming bell.
    The fertilized eggs of siphonophores develop directly into planulae.  Depending on the type of siphonophore, the larva may then form what resembles a swimming bell, pneumatophore or gastrozooid.  Typically the larval swimming bell is replaced by an adult version.  Development into a complete siphonophore is initiated by a budding process that forms the steadily elongating and differentiating chain. 

Rod Bigelow
Box 13  Chazy Lake
Dannemora, N.Y. 12929
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