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Some Zebrasoma tangs have serrated scalpels

By Leonard Ho - Posted Dec 11, 2017 09:00 AM
Tangs, AKA surgeonfish, are known for their scalpel-like caudal spines located on their tail peduncles. On tangs with retractable spines such as Zebrasoma and Acanthurus, the scalpels are thought to be flat blades. But researchers have found that on a few scopas tangs, the spines actually have forward-swept serrations.
Some Zebrasoma tangs have serrated scalpels

Some scopas tangs use flat blades. Some use serrated blades.

Forward-swept scalpels are conspicuously seen on the larger tangs in the genus Naso, whose spines are not retractable.  Until now, It hasn't been observed on smaller tangs from the genera Zebrasoma or Acanthurus, whose spines are much smaller and retractable.

nasospine.jpg

The pronounced, forward-swept spines of Naso lituratus.

Upon closer examination under electron microscopy, it turns that a few Zebrasoma scopas also have developed forward-pointing spikes on their retractable spines.  The researchers of a paper published in Coral Reefs found "most Z. scopas had smooth, sharp, retractable spines that came to a distinct point (Fig. b). However, some specimens had spines with distinct forward-pointing spikes (Fig. c)."  In other words, most scopas tangs exhibited the straight edge scalpels we expect, but a few specimens had unexpected serrated scalpels.

scopas_scalpel2.jpg

The discovery shows that there are intraspecific variability of morphological features that we haven't yet observed with the naked eye.  Seeing such features on Zebrasomas also reinforces the common lineage of Acanthurids and help us understand how Nasos may have evolved their pronounced forward-swept serrations.

Who knows?  In a 100,000 years, Zebrasoma scopas may all have serrated scalpels, too.  We'll keep you updated. Cool

Author: Leonard Ho
Location: Southern California

I'm a passionate aquarist of over 30 years, a coral reef lover, and the blog editor for Advanced Aquarist. While aquarium gadgets interest me, it's really livestock (especially fish), artistry of aquariums, and "method behind the madness" processes that captivate my attention.

Website: http://www.advancedaquarist.com.

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