Ediacaran/Protezoic Survivors (2.5-0.5 billion year old critters) Once things like blue-green algae got going in the ocean they converted a lot of the carbon dioxide in the atmosphere into oxygen. The seas got a bit less soupy but a lot of oxygen-eating bacteria kept the seas a pretty hard place to live. Some slightly more complicated organisms did get going. Earth’s first multi-celled animals had soft bodies. This illustration shows a community of soft-bodied Ediacaran (edi-A-karan) animals. The Period takes its name from the Ediacaran Hills, S.A. It was a place where lots of fossils from this period were found. Some species resemble living ocean creatures. Others are unlike any known organisms. However, it was a work in progress and by the end of the period not many species survived thanks to an ice age. Cooler conditions eliminated many warm water species, and glaciation lowered global sea levels. It’s hard to find any survivors from this period, but life kept going, so something must have made it. A few mineralized animal fossils, including sponge spicules and probable worm tubes, are known. Sea Pens A body form that did survive was a species called Charnia that looked like present day sea pens. It may represent the dawn of sea pens although the current sea pen species (pennatulacean cnidarians) probably aren’t really related to species from this period. Sea pens are a diverse group with an estimated 200 or more species. They are found all over the world from polar seas to the equatorial tropics and from intertidal flats to over 6100 m in depth. Sea pens are actually colonies of polyps. One polyp has evolved to be very large and loses its tentacles, forming the central axis. The base of this primary polyp forms a bulb which may be expanded or contracted; the sea pen uses this bulb to anchor itself. Branching off this primary polyp are feeding polyps. Others polyps serve as intakes for water, which circulates within the colony and helps keep it upright. The feather-like appearance of these species gives the sea pens their common name; they look something like old-fashioned quill pens. Most species do not have polyp leaves, and look more like clubs, umbrellas, or pinwheels. Generally, sea pens don’t like being dug up by swell, so they are rare in depths less than 10M and aren’t seen very often by divers. In Australia there are a couple of reliable spots to see them in shallow water. Sea Pen Point, Tasmania On the north-eastern extremity of Rocky Cape in 10-15 metres, just south of Cave Bay. The southern shoreline of this point is strewn with bommies and boulders that harbour plenty of fish and colourful marine life. The point is special because of the large number of sea pens that can be found growing in the sand near the reef fringe. Port Stephens-Great Lakes MPA Sea pens are regularly seen over all of the dive sites in Port Stephens. This photo was taken at Fly Point in 8metres of water. Photo: Leanne & David Atkinson, Port Stephens NSW