DIVE DRY WITH DR. BILL #768: SEE... SEA SPIDERS!
There are a few marine critters I've never been able to get an image or video of. The sea "spiders" or pycnogonids are one such group. Many of the ones in our local waters are pretty cryptic and hide easily among the turf on rocky reefs, frequently among prey such as hydroids and bryozoa. Often they are fairly small and my aging eyes make it difficult to focus on them. Interestingly, my chemo has apparently returned my vision to 20/20 so I may have better luck when I'm finally able to return to diving!
Fortunately I was able to find some excellent pictures in the public domain. They were taken by Blair Patullo at the Victoria Museum in Australia so they don't represent our local species, but do give an excellent idea of what sea "spiders" look like in general. Although they are distantly related to land spiders in the Arachnida and horseshoe crabs, they are not true spiders. They are believed to be an ancient group that evolved very early.
The body is generally very short and segmented. Some are just a silly millimeter long (1/25") while others may reach 20" in length. At the anterior end is the head (or cephalon) bearing the mouth. A protrusion on the dorsal side of the head may contain two or four eyes... or none at all in deep sea dwelling species. Most species have eight legs which in some species are very long while in others are short, but some may have five or six pairs. The pycnogonids have also been referred to as Pantopoda, meaning "all legs." I refer to humans of the fair gender as foxes if they are all legs, but then I'm occasionally politically incorrect! The pycnogonid's legs may be specialized for walking, food capture or brooding the eggs. Although both sexes may have legs adapted for brooding, usually only the males actually do so.
Mating has only been observed in a few species so making generalizations about this fascinating behavior is difficult. In those studied, the male clings to the underside of the female. The ducts (gonopores) on the legs through which the gametes are released are pressed close together. This is important because most pycnogonid sperm is not motile. No swimmers in this group! In yet another example of female liberation, the male then gathers the fertilized eggs and carries them on his egg brooding legs (called ovigers) until they hatch. The young of some species hatch as larvae while others as an immature individual.
Now that we've covered the essential act of reproduction for maintaining the species' existence, it is important to cover the dietary preferences that allow the individual to survive to reproduce. You know, munching and mating! I mentioned earlier that their prey often includes tiny hydroids and bryozoa. They are also known to chow down on sponges and polychaete worms with an occasional vegetarian taste of red algae. They use their proboscis to suck vital body fluids from their victims. Some of our local species are parasitic on sea anemones and one on mussels.
Oh, and many of my readers often wonder why I don't include respiration as one of the three primary functions of any critter. The answer is simple... how can it compare with the more thrilling functions of munching and mating? The exoskeletons of sea spiders are so thin that oxygen is taken into the body directly from the surrounding water. No need for gills in this group.
One California species that I'd like to film is Pycnogonum rickettsi. Why? Because it is named for my marine biologist icon Ed "Doc" Ricketts of Steinbeck's Cannery Row and Ed's own Between Pacific Tides fame. Although I have made the pilgrimage to Ed's lab in Monterey many times over the years, I have yet to dive the chilly waters of that region to try to find this sea spider.
Species that may be found in SoCal waters include Ammothea hilgendorfi (hmm, my paternal grandmother's maiden name was Hilgendorf), found from North Pacific to Baja California; and Nymphopsis spinsosissima (hmm, no nymphos in my family) known from Alaska to Laguna Beach.
© 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: Blair Patullo's fantastic images of pycnogonids from the Victoria Museum in Australia (used according to the Creative Commons licensing agreement)
There are a few marine critters I've never been able to get an image or video of. The sea "spiders" or pycnogonids are one such group. Many of the ones in our local waters are pretty cryptic and hide easily among the turf on rocky reefs, frequently among prey such as hydroids and bryozoa. Often they are fairly small and my aging eyes make it difficult to focus on them. Interestingly, my chemo has apparently returned my vision to 20/20 so I may have better luck when I'm finally able to return to diving!
Fortunately I was able to find some excellent pictures in the public domain. They were taken by Blair Patullo at the Victoria Museum in Australia so they don't represent our local species, but do give an excellent idea of what sea "spiders" look like in general. Although they are distantly related to land spiders in the Arachnida and horseshoe crabs, they are not true spiders. They are believed to be an ancient group that evolved very early.
The body is generally very short and segmented. Some are just a silly millimeter long (1/25") while others may reach 20" in length. At the anterior end is the head (or cephalon) bearing the mouth. A protrusion on the dorsal side of the head may contain two or four eyes... or none at all in deep sea dwelling species. Most species have eight legs which in some species are very long while in others are short, but some may have five or six pairs. The pycnogonids have also been referred to as Pantopoda, meaning "all legs." I refer to humans of the fair gender as foxes if they are all legs, but then I'm occasionally politically incorrect! The pycnogonid's legs may be specialized for walking, food capture or brooding the eggs. Although both sexes may have legs adapted for brooding, usually only the males actually do so.
Mating has only been observed in a few species so making generalizations about this fascinating behavior is difficult. In those studied, the male clings to the underside of the female. The ducts (gonopores) on the legs through which the gametes are released are pressed close together. This is important because most pycnogonid sperm is not motile. No swimmers in this group! In yet another example of female liberation, the male then gathers the fertilized eggs and carries them on his egg brooding legs (called ovigers) until they hatch. The young of some species hatch as larvae while others as an immature individual.
Now that we've covered the essential act of reproduction for maintaining the species' existence, it is important to cover the dietary preferences that allow the individual to survive to reproduce. You know, munching and mating! I mentioned earlier that their prey often includes tiny hydroids and bryozoa. They are also known to chow down on sponges and polychaete worms with an occasional vegetarian taste of red algae. They use their proboscis to suck vital body fluids from their victims. Some of our local species are parasitic on sea anemones and one on mussels.
Oh, and many of my readers often wonder why I don't include respiration as one of the three primary functions of any critter. The answer is simple... how can it compare with the more thrilling functions of munching and mating? The exoskeletons of sea spiders are so thin that oxygen is taken into the body directly from the surrounding water. No need for gills in this group.
One California species that I'd like to film is Pycnogonum rickettsi. Why? Because it is named for my marine biologist icon Ed "Doc" Ricketts of Steinbeck's Cannery Row and Ed's own Between Pacific Tides fame. Although I have made the pilgrimage to Ed's lab in Monterey many times over the years, I have yet to dive the chilly waters of that region to try to find this sea spider.
Species that may be found in SoCal waters include Ammothea hilgendorfi (hmm, my paternal grandmother's maiden name was Hilgendorf), found from North Pacific to Baja California; and Nymphopsis spinsosissima (hmm, no nymphos in my family) known from Alaska to Laguna Beach.
© 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: Blair Patullo's fantastic images of pycnogonids from the Victoria Museum in Australia (used according to the Creative Commons licensing agreement)
