DIVELOG JUNE 406

Eubranchus sp. (sp. 19). A very long species with small cerata that are olive-shaped but still with an inflated appearance.

Eubranchus sp. (sp. 03). Among the smallest of the tropical/subtropical Eubranchus . Exhibits swollen cerata with annular constrictions.

description. Also, in the Bass Strait region of Australia for example, Bob Burn asserts that 17 await description. Yet other regions could very well have additional undescribed species. These estimates do not include any taxonomically cryptic species that are sure to be discovered when in-depth reviews, that include molecular sequencing, are eventually undertaken. What we do know with regards to external differentiating characteristics is that Eubranchus possess swollen cerata, few in number, often with annular constrictions creating a bulbous presentation that can carry from one to three circlets of tubercles sometimes giving a knobbly appearance. The cerata are usually arranged in simple rows. They are often translucent to a

degree, though usually with some opaque pigmentation, but allowing the digestive diverticulum in each to show through. Those diverticula may completely fill the cerata or they may be just a spindly thin tube. Some specimens look particularly ungainly or asymmetrical as one or two of the cerata may be two to three times more swollen than all the rest. Like most aeolids the tip of each Eubranchus ceras contains a cnidosac wherein the nudibranch concentrates, stores and maintains undischarged stinging nematocysts obtained from their hydroid prey. These are discharged in the hundreds for defence when the nudibranch’s cerata are aggravated. Rhinophores and oral tentacles are most usually smooth although a few with annular rings or tubercles on

Eubranchus virginalis. Here, several are feeding together on a hydroid. The circlets of tubercles are obvious on the translucent cerata.

Eubranchus sp. (sp. 06). This undescribed but widespread Eubranchus of the Indo-Pacific has unusual colouration and numerous crowded cerata.

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DIVE LOG Australasia #406 - June ‘24

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