Riddle of the Y-Larvae

A fascinating article in Livescience reveals the answer to a century-old zoological mystery: what do y-larvae grow up to become? Discovered in 1899, y-larvae are clearly young crustaceans but their adult stage could not be determined. While this in itself was perplexing, the newly discovered answer is even more startling: y-larvae metamorphosize into "simple, pulsing, slug-like masses of cells... far simpler than their larval stage." In a sense, the creatures revert backwards to forms more commonly seen further down the evolutionary ladder as they mature.

Watch the process

This awesome video shows the transformation from promising young crustacean to parasitic adult slug monster. Would make a great anti-drug commercial.

As Y-larvae do not seem to be in any rush to grow into their adult form naturally (and who can blame them) the researchers used powerful hormones to induce rapid growth. The scientists theorized that adult y-larvae, or ypsigons (rolls right off the tongue...), are parasitic as they have no digestive tract or nervous system. This means that they would need to absorb nutrients from their surroundings. Some species of parasitic barnacles exhibit similar physiological changes during development.

Read more about these fascinating, infectious little guys here on Livescience or here in the journal BMC Biology.

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How can the researchers be sure that the final form has not been distorted by the hormones they use?

By Jack Aidley (not verified) on 04 Jun 2008 #permalink

This is a cool paper, these guys are so interesting...a mystery unraveling.

@Jack (and with deference to Zooilogix)

The researchers tested to see which of the several hormones known to initiate metamorphosis in crustaceans the y-larvae responded to. They used a range of concentrations as well. It was only one hormone, 20-hydroxyecdysone, in a discrete concentration range, that matched both the compound and concentration range that is known to initiate metamorphosis in the related parasitic barnacles, the Rhizocephalans.

This morphological "devolution" is not unique amongst the crustaceans, but an example of convergent evolution. The Rhizocephalans also metamorphose from a complex cyprid stage to a vermiform stage, on their way to an extremely un-crustacean like endoparasitic adult form (with out nervous system even). Like the Rhizocephalans Y-larvae adults are probably endoparasitic. Finding them will be challenging...
Massive DNA screening? Isotope tagging of larvae?

Oh noes! You have swallowed the Great Chain of Being! There is no evolutionary ladder!!!!!

Seriously, evolution has no conception of complexity or perfection, just fitness. These are no more problematic than vestigial males in cirrpedes.

By John S. Wilkins (not verified) on 04 Jun 2008 #permalink

That makes sense, thanks Eric.

By Jack Aidley (not verified) on 04 Jun 2008 #permalink

Andrew is correct. He has often been described as the hickory horned devil caterpillar of the Bleimans while I, the golden-headed scallop wing butterfly.