This is Mazon Monday post #31. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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Today, we are highlighting Fanworms. Mazon Creek fanworms were soft bodied animals and are thought to be polychaetes. They were and currently are filter feeders, which live in the ocean. Some are free swimming and some others live in tubes they construct on the ocean floor.
All of the specimens shown here were found at the Braceville spoil pile, although they have been found in other Essex localities.
Here is the text about fanworms from Creature Corner. It was first published December 1990.
Fanworms
Numerous animais have been discovered in Mazon Creek siderite concretions, but not all have been subsequently described and classified.This is the case with several (?) genera of the sedentary polychaetes (Sedentaria) that are lumped together under the descriptive term "fanworms".
Due to the excellent preservational qualities of the ironstone concretions, free-living polychaetes of the Essex biota began to be described about two decades ago, following the "glory days" of Pit 11. A rather common member of the Mazon Creek biota, the fanworm Spirorbis, was noted more than a century ago as occurring in Mazon Creek nodules. This recognition and description of Spirorbis was relatively simple due to the distinctive shape and the fact that its living, virtually unchanged descendants are found in enormous number on seaweed and nearshore debris today: it is an animal easily recognized by a student of marine life.
In contrast to the marine worms previously mentioned, our Creature, the tube-building fanworms that are found in Mazon Creek concretions are not common and are found with their unencased soft parts, the long tentacles, preserved as mere color differences on the siderite matrix. A lack of recognizable detail precludes satisfactory description of these particular polychaetes. The discovery of one or two well-preserved specimens might then make generic diagnosis a possibility.
Recent fanworms (and it is assumed their Paleozoic ancestors did likewise) build tubes made of mucus and sand grains or shell fragments or lime cemented over a mucus framework that hardens into a parchment-like protective structure. True tube-dwelling polychaetes rarely or never leave their protective shield. Reefs of fanworms have been found in the tropics, some reaching a meter in height. The several suborders of recent fanworms have some common characteristics: they have a crown of tentacles often huge, fan-like and brightly colored; they are filter or current feeders; they possess relatively enormous nerve fibers extending from one end of the body to the other within the main nerve cord; and they have well developed longitudinal muscles that retract the worm promptly into its protective tube when threatened.
Photographs of a seabed bearing a lawn or forest of fanworms, with their crown of hairy or plume-like tentacles waving in the ocean current, is strangely reminiscent of another phylum of animals that have a crown or head of plume-like appendages, the crinoids. The crinoids have evolved a column of discs that lift the feeding arms into the currents, while the worms developed a group that uses cemented particles to achieve the same lifestyle. Most interesting.
From the book "The Mazon Creek Fossil Fauna" by Jack Wittry
Mazopherusa prinosi Hay, 2002
Mazopherusa prinosi, commonly called the Fan Worm, has a tapering cylindrical body that ends in a narrow tail. The body is composed of annular segments, each adorned with six to eight sometimes visible, wart-like projections.Its fan is com- posed of long setae and is retractable.
Flabelligerids are considered to be rather sluggish animals. Modern forms are described as being mud-dwellers and surface-feeders.While resting in their burrows, they extend their fans to create eddies causing detritus to fall into their bodies which is then transported toward their mouths. The bodies of these extant forms are often covered with thick mucus in which sand, shell fragments, or other debris have become entrapped. The debris-laden mucus then hardens into a parchment-like protective structure. Mazon Creek fan worms are considered colonial animals, as evidenced by concretions containing multiple specimens. (See Figure 19.2 below and Figure 169.4, page 169.)
True tube-dwelling polychaetes rarely or never leave their protective shields.
