Plant-like Animals
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.
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.
Text by Herb Segars & NJScuba-net
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.
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Most tropical corals contain photosynthetic algae which provide 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.
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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.
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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 a 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 are occasionally larger.
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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 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 eyespots along the tentacles.
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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 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.
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Sponges grow at all depths, and in brackish and freshwater 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.
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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.
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