Unless you're a diver blessed with patience and good eyesight, you have probably missed (or, sadly, ignored) a species of marine critter that is very common in our waters. I'm speaking... er, writing... about the "lowly" phoronids, also known as horseshoe worms. It has been 14 years since I last wrote about them so I think it is time to feature them once more in a "Dive Dry with Dr. Bill" column.
When I wrote the last column about them, I thought there was just a single species in our waters. My research for this week's epistle uncovered that there may be at least seven species in central and southern California and possibly a few more. For those readers fond of scientific names, they include Phoronis architecta, Phoronis muelleri, Phoronis pallida, Phoronis psammophila, Phoronis vancouverensis, Phoronopsis harmeri and Phoronopsis californica. Although they are commonly referred to as worms, they lack the segmented bodies of the annelids.
The latter is probably the species I see most commonly although it is often difficult even for ex-spurts to distinguish some of them. This species was initially described from Newport Bay back in 1930. It is locally common around several of our Channel Islands in depths from 16 to 115 feet (5-35 m). It is usually a tangerine to orange in color but we've also seen very white individuals as well. Some orange individuals may have flecks of white.
The body is about 1/5th inch (5 mm) in diameter but is topped by a larger, branched feeding structure known as a lophophore. They live in tubes which some researchers reported at over 36" in length. The tubes usually have sand or sediment stuck to the outside. I've never dug one up since I see them mostly in the marine protected area of Casino Point. The bodies are nowhere near that length though. At the lower end of the body is a swelled feature known as an ampulla that helps anchor the phoronid in its tube.
The lophophore is a unique feeding structure shared by phoronids, bryozoa and brachiopods. It is a horseshoe or circular shaped structure comprised of numerous tentacles (as many as 1,500 in Phoronopsis californica) covered in cilia and surrounding the mouth. The cilia create a current that allows the lophophore to capture food from the surrounding water. They are therefore suspension feeders. Food items which are undesirable can be removed by reversing the beat of the cilia. The digestive tract is U-shaped with the anus placed just below the lophophore.
Phoronids are preyed upon by fish, snails and nematode (round) worms although one species in California, Phoronopsis viridis, is said to be distasteful to many benthic predators. Apparently if a predator nips off the exposed lophophore extended above the surface, the phoronid can regenerate it.
The lophophore also serves as the respiratory organ. Although they have no heart, movements of the body muscles transport blood throughout the relatively small bodies. It is reported that phoronid blood may have more hemoglobin that human blood and therefore be able to transport more oxygen. This could be an adaptation to low oxygen environments.
Reproduction is varied among the different species of phoronids. At least one can reproduce asexually through budding. Most utilize sexual reproduction with some having separate sexes, others having both sexes (hermaphrodites) but not self-fertilizing. The larvae, known as actinotrochs, produced through fertilization were once thought to be separate species by biologists. They drift with the plankton for days to weeks before settling to the bottom and transforming into adults.
© 2018 Dr. Bill Bushing. For the entire archived set of over 750 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: Phoronids in the dive park (top) and images of Phoronopsis californica (orange and white) by photographer Kevin Lee.
When I wrote the last column about them, I thought there was just a single species in our waters. My research for this week's epistle uncovered that there may be at least seven species in central and southern California and possibly a few more. For those readers fond of scientific names, they include Phoronis architecta, Phoronis muelleri, Phoronis pallida, Phoronis psammophila, Phoronis vancouverensis, Phoronopsis harmeri and Phoronopsis californica. Although they are commonly referred to as worms, they lack the segmented bodies of the annelids.
The latter is probably the species I see most commonly although it is often difficult even for ex-spurts to distinguish some of them. This species was initially described from Newport Bay back in 1930. It is locally common around several of our Channel Islands in depths from 16 to 115 feet (5-35 m). It is usually a tangerine to orange in color but we've also seen very white individuals as well. Some orange individuals may have flecks of white.
The body is about 1/5th inch (5 mm) in diameter but is topped by a larger, branched feeding structure known as a lophophore. They live in tubes which some researchers reported at over 36" in length. The tubes usually have sand or sediment stuck to the outside. I've never dug one up since I see them mostly in the marine protected area of Casino Point. The bodies are nowhere near that length though. At the lower end of the body is a swelled feature known as an ampulla that helps anchor the phoronid in its tube.
The lophophore is a unique feeding structure shared by phoronids, bryozoa and brachiopods. It is a horseshoe or circular shaped structure comprised of numerous tentacles (as many as 1,500 in Phoronopsis californica) covered in cilia and surrounding the mouth. The cilia create a current that allows the lophophore to capture food from the surrounding water. They are therefore suspension feeders. Food items which are undesirable can be removed by reversing the beat of the cilia. The digestive tract is U-shaped with the anus placed just below the lophophore.
Phoronids are preyed upon by fish, snails and nematode (round) worms although one species in California, Phoronopsis viridis, is said to be distasteful to many benthic predators. Apparently if a predator nips off the exposed lophophore extended above the surface, the phoronid can regenerate it.
The lophophore also serves as the respiratory organ. Although they have no heart, movements of the body muscles transport blood throughout the relatively small bodies. It is reported that phoronid blood may have more hemoglobin that human blood and therefore be able to transport more oxygen. This could be an adaptation to low oxygen environments.
Reproduction is varied among the different species of phoronids. At least one can reproduce asexually through budding. Most utilize sexual reproduction with some having separate sexes, others having both sexes (hermaphrodites) but not self-fertilizing. The larvae, known as actinotrochs, produced through fertilization were once thought to be separate species by biologists. They drift with the plankton for days to weeks before settling to the bottom and transforming into adults.
© 2018 Dr. Bill Bushing. For the entire archived set of over 750 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: Phoronids in the dive park (top) and images of Phoronopsis californica (orange and white) by photographer Kevin Lee.
