DIVE DRY WITH DR. BILL #895: MEET YOUR RELATIVES!

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drbill

The Lorax for the Kelp Forest
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Rest in Peace
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DIVE DRY WITH DR. BILL #895: MEET YOUR RELATIVES!

Many of my readers know that human beings (species Homo sapiens sapiens) share a large percentage of our DNA (99%) with chimpanzees. The behavior of some of us illustrates that we have not evolved as far from them as we claim. Many feel a kinship with other vertebrates such as pigs, goats, horses, etc. But how many of you recognize our "close" ties to a group of invertebrates known as tunicates?

Yes, this group is a member of our very own phylum Chordata... yet few recognize the family resemblance. I don't either, but as a marine biologist I am aware that these spineless critters have a notochord during their youth and that is what qualifies them to be in the phylum. Some are sessile (attached bottom dwellers) as adults and may be solitary or colonial. The body is encased in a tunic from which the phylum gets its name. Others are planktonic and are known as salps and pyrosomes (fire salps).

Tunicates are filter feeders. They take in water from an incurrent siphon, filter out the munchables using a structure, the branchial basket, that evolved from their larval gills and expel it through an excurrent siphon. In the pelagic pyrosomes, the flow of water from these siphons is ejected out of the body to give the critter what Lil Eva referred to as "locomotion." Open water salps use body contractions for propulsion.

Reproduction is accomplished in two ways. Sexual reproduction involves the fertilization (often internal) of an egg by sperm from another individual. Asexual reproduction through budding is what causes many of these species to multiply in number very quickly. Humans accomplish that using the first method.

One local species of sessile tunicate that has been of interest to some of my diver friends is the orange social tunicate (Metandrocarpa taylori). One individual posted an abalone that was covered with them. Almost everyone though it was some sort of sponge, but I pointed out the two siphons on each zooid and identified it. I have seen them growing on rocks, abalone and wavy top snail shells in the dive park.

Another attached form I find interesting is the Pacific white crust (Didemnum carnulentrum). As its common name suggests, it is usually white in color. There is one "large" opening and many small ones as can be seen in the accompanying image.

A third bottom dwelling species that many divers recognize is the light bulb tunicate (Clavelina huntsmani). Individuals are rarely more than 2" tall and the two "filaments" within the translucent body look like the ones in an old fashioned light bulb. With LEDs replacing incandescents, we may have to come up with a new common name in the future!

While doing blue water dives to look for our vanishing blue sharks or out on the oil rigs, I often encountered Cyclopsalpa affinis drifting nearby. It has a solitary generation and an aggregate generation (pictured) that can be quite beautiful (at least in my eyes).

Another pelagic species is the twin-sailed salp (Thetys vagina). They are seen somewhat frequently in our waters, often in very large numbers. I had to explain to some lady-go-divers that the species name did not refer to a certain part of their anatomy. The word vagina is based on its ancient Latin meaning, a sheath. One can easily identify them by the two brownish "tails." They begin life as females, generate an aggregate generation and then transform into males. Hmmm.

The final example is yet another pelagic species, a pretty common pyrosome known scientifically as Pyrosoma atlanticum. It will bioluminesce which resulted in giving it the common name fire salp. I have observed large numbers of these entering shallow water and dying, often "littering" the ocean floor and even washing ashore on our beaches. A related species may reach as long as 60 feet!

So there you have it... new additions to your family album along with those from Ancestry.com! And they may be lifesavers for us. Several anti-tumor chemicals have been extracted from a few species and are in clinical trials. Who knows... maybe through all my diving I may have absorbed some of these from our local tunicates. My oncologist was surprised to see one of my most serious cancers "disappear" after 200 dives last year!

© 2021 Dr. Bill Bushing. For the entire archived set of nearly 900 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page

Image caption: The Pacific white crust and orange social tunicate; the light bulb tunicate and Cyclopsalpa; the twin sailed salp and a pyrosome.

DDDB 895 tunicates sm.jpg
 
Just curious, but what size scale are we talking about for the lightbulb tunicate?
 

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