DIVE DRY WITH DR. BILL #754: A NUDI BY ANY OTHER NAME
For some reason I've had nudis on my mind lately. No, I haven't been looking at the centerfolds in Playboy... haven't seen one of those in many years and I hear they no longer feature them anyway. Besides almost all the critters I deal with as a marine biologist are unclothed anyway so what's the big deal? Yep, I'm thinking naked gills... nudibranchs... the beautiful shell-less snails.
This week the specific one I have in mind is Hermissenda opalescens. Back when I first arrived on the island in the late 1960s, it was one of the first nudis I learned in the days of no Internet and few field guides. Today, the resources to identify and learn about nudibranchs are quite extensive, but back then it involved a lot of time and research.
In the 1960s and throughout much of my early career as a marine biologist, this species was known as Hermissenda crassicornis. Its common name was the opalescent nudibranch due to the white or bluish lines. There is a prominent orange streak above and behind the head. It has a shag carpet like mass of gills (cerata) along its dorsal surface that may be orange to brown in color. Each one is tipped in white. The body length may reach two to three inches.
In those daze... er, days... this nudi was believed to reside from Alaska to Baja California, and from Japan to the far eastern Russian coast. A year ago divers started seeing this species along with other nudis on Doug Aitken's underwater pavilions in the dive park. Michael Francisco, a dive instructor at Craig Yeaton's Sharky's Eco Dive center, took a number of pictures of the critters on the pavilions and I am sharing some of his with this column.
Although nudis are frequently seen off the mainland coast and further north, it has been my experience here on the island that they are more common at depths exceeding 100 ft. A few species are observed on shallower rocky reefs here, but I usually have to descend further to observe and film them. I'm not sure if this is due to a preference for cooler water or that their preferred prey lives at greater depth here.
In the past taxonomists, the biologists that try to identify the many different species on our planet, have had to rely on physical, physiological and behavioral characteristics of individuals to create distinctions between species. Of course this is a judgment call since the characteristics they use may simply reflect variation within a species rather than differences between two species. Regardless of whether you have blonde, brunette or red hair or blue, brown or green eyes we humans are all members of the same species.
With the development of molecular biology, taxonomists now have a more fundamental set of characteristics with which to classify critters. I'm referring to their genes. Years ago I dated identical twins (several years apart though, not simultaneously). Even though their genes were the same, they exhibited some different physical features and behavior. Of course occasionally they wore the same genes... er, I mean jeans.
Earlier this year taxonomists split the nudibranch formerly known as Prince... er, Hermissenda crassicornis... into three different species. Individuals found from Alaska to northern California retain the original name, but those living from northern California down into Baja are now known as Hermissenda opalescens while the ones in Japan and Russia were given the name Hermissenda emurai.
Distinctions like this and other species name changes have made this old geezer's scientific studies more difficult. My senescing brain has to throw out the old tried and true names from its memory banks and adopt the new ones. Of course I often revert to the names I learned first, so please pardon me when I do.
© 2017 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: Opalescent nudibranch on Eagle Reef (Catalina); eggs and an individual imaged by Michael Francisco on the pavilions exhibiting the brown gill clusters.
For some reason I've had nudis on my mind lately. No, I haven't been looking at the centerfolds in Playboy... haven't seen one of those in many years and I hear they no longer feature them anyway. Besides almost all the critters I deal with as a marine biologist are unclothed anyway so what's the big deal? Yep, I'm thinking naked gills... nudibranchs... the beautiful shell-less snails.
This week the specific one I have in mind is Hermissenda opalescens. Back when I first arrived on the island in the late 1960s, it was one of the first nudis I learned in the days of no Internet and few field guides. Today, the resources to identify and learn about nudibranchs are quite extensive, but back then it involved a lot of time and research.
In the 1960s and throughout much of my early career as a marine biologist, this species was known as Hermissenda crassicornis. Its common name was the opalescent nudibranch due to the white or bluish lines. There is a prominent orange streak above and behind the head. It has a shag carpet like mass of gills (cerata) along its dorsal surface that may be orange to brown in color. Each one is tipped in white. The body length may reach two to three inches.
In those daze... er, days... this nudi was believed to reside from Alaska to Baja California, and from Japan to the far eastern Russian coast. A year ago divers started seeing this species along with other nudis on Doug Aitken's underwater pavilions in the dive park. Michael Francisco, a dive instructor at Craig Yeaton's Sharky's Eco Dive center, took a number of pictures of the critters on the pavilions and I am sharing some of his with this column.
Although nudis are frequently seen off the mainland coast and further north, it has been my experience here on the island that they are more common at depths exceeding 100 ft. A few species are observed on shallower rocky reefs here, but I usually have to descend further to observe and film them. I'm not sure if this is due to a preference for cooler water or that their preferred prey lives at greater depth here.
In the past taxonomists, the biologists that try to identify the many different species on our planet, have had to rely on physical, physiological and behavioral characteristics of individuals to create distinctions between species. Of course this is a judgment call since the characteristics they use may simply reflect variation within a species rather than differences between two species. Regardless of whether you have blonde, brunette or red hair or blue, brown or green eyes we humans are all members of the same species.
With the development of molecular biology, taxonomists now have a more fundamental set of characteristics with which to classify critters. I'm referring to their genes. Years ago I dated identical twins (several years apart though, not simultaneously). Even though their genes were the same, they exhibited some different physical features and behavior. Of course occasionally they wore the same genes... er, I mean jeans.
Earlier this year taxonomists split the nudibranch formerly known as Prince... er, Hermissenda crassicornis... into three different species. Individuals found from Alaska to northern California retain the original name, but those living from northern California down into Baja are now known as Hermissenda opalescens while the ones in Japan and Russia were given the name Hermissenda emurai.
Distinctions like this and other species name changes have made this old geezer's scientific studies more difficult. My senescing brain has to throw out the old tried and true names from its memory banks and adopt the new ones. Of course I often revert to the names I learned first, so please pardon me when I do.
© 2017 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: Opalescent nudibranch on Eagle Reef (Catalina); eggs and an individual imaged by Michael Francisco on the pavilions exhibiting the brown gill clusters.
