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?? VIDEO
<>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; Notes:
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
<
rodbigelow@netzero.net > 
