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All these are animals that, in a sense, occupy the physical niche of the plants which are missing from the deeper parts of the marine environment. All are filter-feeders, straining plankton from the surrounding waters.
Corals, anemones, and hydroids are Cnidarians, ( pronounced nee-darian ) all closely related to jellyfishes. Most Cnidarians alternate a generation of the sessile polyps shown here with a generation of mobile medusae or jellyfish. Thus many medusas and polyps are actually the same species, merely in different generations. This is how seemingly fixed corals are able to disperse throughout the world's oceans, and recolonize distant areas after mass die-offs ( which may be perfectly normal, for all we know. ) In some cases, scientists have determined the relationship between a specific polyp and medusa, but for the majority it is not known.
Cnidarian lifecycle - in this case, a hydroid. Others are similar.
The actual stinging apparatus of a cnidarian is microscopic - specially developed cells.
That doesn't mean they can't hurt you !
In anemones and corals the polyp stage is dominant. Most reproduction is by asexual budding or splitting of polyps, creating colonies of clones, with only occasional long-range dispersal by the small sexual medusa stage. In Jellyfishes, the egg-laying mobile medusa stage is dominant, and the polyp stage is greatly reduced in importance and often difficult to identify. Hydroids, the most primitive cnidarians, show the most even division between polyp and medusa stages.
The rest of the ( non-cnidarian ) creatures on this page are unrelated, sharing only their fixed lifestyles.
Colorful sponges, coral, hydroids, and anemones on the Elberon Rocks
Text by Herb Segars & NJScuba.net
Click images for more galleries !
Adult (right) and immature
Frilled Sea Anemones
Sea anemones are found from the intertidal zone to extreme depths. Some live attached to solid objects, others burrow in sand or construct tubes. They feed primarily on plankton.
Sea anemones feed through a mouth located in the center of its tentacles. Waste is regurgitated through the same opening. The tentacles sting zooplankton or fish that pass too close, and the anemone swallows its prey whole. Most anemones cannot sting humans with any noticeable effect.
Small anemones may hitch a ride on a hermit crab, an arrangement that is beneficial to both. The crab is protected by the anemone's stingers, and the anemone gains a degree of mobility otherwise impossible.
The Frilled Anemone Metridium senile ( above, to 4" ) can be brown, orange, pink, or even white. It resembles a flower when its tentacles are open and extended, but it can retract these tentacles into its center. The frilled anemone can be found in the mid and upper intertidal zones, but it can also be found well below the low tide mark. Its range extends from Delaware north to the Arctic. Its body is divided into three parts: the base or pedal disc, a stalk, and numerous protruding tentacles.
The Frilled Anemone is the largest and most conspicuous sea anemone in our area, common from subtidal jetty rocks to the deepest shipwrecks. You would need to be in the right place and have a sharp eye to find the rest of the anemones depicted here:
The Lined Anemone is found in numbers great enough to carpet the bottom in places. Its range is from Cape Cod to Cape Hatteras. They live among tube worms and other growth on and under rocks; from below the low tide line to water more than 70' deep. The young are parasites on Comb Jellies. The burrowing adults grow to 1-1/2 inches.
Striped Sea Anemone
Tiny ( 1/2 " ) Striped Sea Anemones ( above and right ) are found in rivers and estuaries and other protected areas. They are not native; it is thought that they originate in Japan; they are also found in Europe. Striped Anemones reproduce asexually by budding.
Rather than living on a substrate, Burrowing Anemones ( below ) live in it, burrowing and sometimes constructing tubes in sandy or muddy bottoms, both offshore and in bays and inlets. The buried body of the animal is long and worm-like, and the tentacles are withdrawn deep down into the sediment at the slightest disturbance, much like many fan worms. In fact, fan worms and burrowing anemones are a remarkable example of convergent evolution ( for those who believe in that sort of thing. )
Most tropical corals contain photosynthetic algae which provides a substantial amount of the polyp's food. White Encrusting Coral, also known as Northern Stony or Star Coral, contains no such algae, and therefore can survive the low light conditions and temperatures of the North Atlantic where other corals would die. Instead, it is a filter-feeder, much like an anemone.
Corals are similar to anemones in many ways. Each coral polyp is like an anemone in a stony cup. Many corals are colonial ( as are some anemones ) sharing a single merged body among many polyps.
The live colony, with extended polyps, is pictured above; the skeleton below.
Northern Star Coral is found on hard substrates, subtidally to 130'. It is found in colonies of up to thirty polyps that can have a diameter up to 5". The size of a single polyp is up to 0.4". The coral's color is off-white to pink, but animals that live in some areas can be translucent.
Masses of hydroids adorn many of the offshore wrecks, mixed in with anemones, sponges, mussels, coral, and algae. Hydroids are the most primitive Cnidarians, closely related to Hydromedusae, and display the most even split between the sessile polyp stages and free-swimming medusa stages, which are quite small and common.
The common Pink-Hearted Hydroid Tubularia spp generally grows in rounded tufts up to 6" across. Siphonophores are free-living hydroids that are often highly venomous, although most attached forms are harmless to humans.
Hydroids carpeting a reef structure.
Look for tiny nudibranchs within the tufts, feeding on the hydroids.
Pink-Hearted Hydroids Tubuleria spp.
These Hermit Crabs are covered with Snail Fur - Hydractinia echinata.
"Snail Fur" is a hydroid that grows as a pinkish fuzz only on shells inhabited by hermit crabs. Living snails that plow through the sand or empty shells that tumble with the waves and currents are not suitable homes for Snail Fur because of the abrasive action of the sand. But once the shell is commandeered by a hermit crab, most of its surface, except where the shell is dragged along behind the new homeowner and scrapes the sand, is kept out of the sediments and is available for colonization by the hydroids.
Close-up of "Snail Fur"
Hydroid anatomy, greatly magnified
Bryozoans are colonial animals of uncertain evolutionary descent. They may be related to freshwater rotifers. Bryozoans are found in the lower intertidal to subtidal zones, attached to firm substrate, and also in brackish water. Individual animals are too small to see with the naked eye.
Bryozoan growth forms range from encrusting, forming coatings on hard surfaces, to bushy. An entire colony may bear a superficial resemblance to a hydroid colony, although bryozoans are internally more advanced than cnidarians. Bryozoan colonies grow to 3", and occasionally larger.
Note separate mouth and anus, unlike hydroid
Spiral Tufted Byozoans Amanthia spp
Tube worms live with their bodies buried in tubes that they construct in the soft bottom substrate. Fan Worms ( Sabella spp. and others, 1/8" to 8", right ) are among the most popular of sights on tropical coral reefs. Few people realize that they are present in temperate waters as well.
Fan Worms, or "Featherdusters", have a frill of tentacles on the head with which they feed on plankton, and occasionally larger items. Food particles are trapped in sticky mucous, and carried down into the mouth. Some Fan Worms have eye spots along the tentacles.
Despite appearances, Fan Worms are not related to any of the other tentacled creatures on this page, but are actually polychaetes, related to clam worms.
Myxicola infundibulum or something similar - note how the tentacles
are joined almost to the ends, with no eye spots.
Fan Worms are extremely sensitive, and withdraw into their tubes at the
slightest disturbance, leaving behind a ball of mucous.
The head of a terebellid worm on a subtidal mudflat in the Shark River. These are tube worms with long tentacles that spread out over the bottom. Cilia on the tentacles carry microscopic bits of food to the mouth ( see below. ) these worms do not sting like anemones.
Tube worm burrows in the side of a freshly dug hole. The dark color of the sediment indicates anoxic ( no oxygen ) conditions, which is normal in this sort of muddy bottom.
Barnacles are the strangest of crustaceans. Imagine a tiny shrimp glued down by the top of its head, with its antennae waving in the current, and you begin to understand what a barnacle really is.
Northern Rock Barnacles ( Balanus balanoides, to 1" ) grow in the intertidal zone, subtidal in places, attached to any hard surface. They are in a constant competition for living space with mussels. Mussels grow faster, but are more susceptible to drying out. Therefore, mussels quickly take over the lower wetter areas, while barnacles rule in the higher dryer reaches.
Compare with Sea Anemone
Northern Rock Barnacles
Gooseneck Barnacles are far less common - you might find them attached to the bottom of the dive boat towards the end of the season when the bottom paint is losing its potency. They are usually found on drifting flotsam offshore, or in deep water on the bottom.
Unlike typical "acorn" barnacles, Gooseneck Barnacles have a fleshy stalk by which they attach themselves. Several species range in size from 1" to 6". They are actually rather attractive creatures in life, often with purple or orange highlights.
Sponges grow at all depths, and in brackish and fresh water also. They may occur as thin encrusting coatings on rocks and wood, or as long thin branching fingers attached to the bottom, or in the typical rounded form that has been used for centuries as ... a sponge !
The Red Beard Sponge Microciona prolifera is the commonest and most colorful of several sponges that grow in the region. Sponges also occur in shades of yellow and white, and often grow in a much lower, spreading and encrusting form, especially in areas of high currents. They are the most primitive of multi-celled animals, lacking distinct tissues and organs.
A Sea Star crawls over a Red Beard sponge
Boring Sponges typically grow on mollusk shells, such as Oysters. While not parasitic, they do eat away at the shell, causing stress and sometimes death for the mollusk.
Sponges structure is based on microscopic interlocking spicules ( right ) which are built up from cell secretions. Depending on the species, these may take the form of pointed hard calcareous hooks, or flexible nets. The spicules of some tropical species can cause severe skin reactions if the sponge is touched or handled. I am not aware of any such danger with northern sponges.
Sponge "anatomy" - sponges don't really have anatomy.
Molgula manhattensis ( right )
Styela Partita ( left )
Sea Squirts are found attached intertidally to subtidally. They show an extraordinary tolerance for brackish and polluted water, which makes them highly survivable in urban areas. Sea Squirts, usually about an inch in diameter, are capable of ejecting a stream of water when agitated, hence the name. Usually found in groups of several animals. See also: Horned Salp.
Tunicates are much more advanced in the evolutionary scheme of things than anemones, having, for example, a circulatory system. The larvae actually even have several features in common with vertebrates, including the precursor of a spinal cord, but these are lost in the sac-like sessile adults.
The attractive purple growths on this Ulva weed are colonies of Golden Star Tunicates
the individual animals are almost too small to see.
Sea Squirt anatomy
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Copyright © 1996-2015 Rich Galiano
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