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ResearchBlogging.org

My second post for Earth week 2012 is  about a lone new species in a new genus that is most probably found only in Principe cave at the southern tip of Samar island.

Recently, the world was awed by the 5 new species of purple crab found in Palawan (link here and here).  Here, I present the first reported anchialine cave* species of crab which is totally colorless. (* and **,  see below)

Samarplax principe described by the authors in Zootaxa, is “the first species of hymenosomatid formally recorded from an anchialine cave and exhibiting true troglomorphic adaptations** [1].”  Hymenosomatidae is a family of crabs with about 110 described species in 20 genera.

The diagnostic characters of this new species new genus are:

    • the absence of rostrum and eyes,
    • well-defined dorsal (back) surface of the carapace with two small spines or sharp teeth on its lateral (side) margin,
    • proportionally shorter projected merus of the third maxilliped (merus is a segment of a crab’s leg),
    • an almost flat epistome (a plate that lies in front of the mouth),
    • long chelipeds (the leg bearing the pincers) without cutting teeth but lined instead with brush-like setae,
    • a four-segmented pleotelson (seen in the abdominal area),
    • eggs that are held in the brood cavity.

Picture of the vestigial eyes. The crab lost its eye function as a result of its adaptation to its environment.  Courtesy: Husana, D.E.M, Tan, S.H., & Kase T. Zootaxa 3109, 2011.

The authors say that “the brush-like setae along the inner margin of palm and finger in the chelipeds (instead of cutting teeth) of the new species, is an unusual character, suggesting that it uses its cheliped to brush/scrape off objects to obtain food.”

“This chela structure is not known in other hymenosomatids so far. It is armed with brush-like setae along the inner margin of its fingers instead of cutting teeth.” Courtesy: Husana, D.E.M, Tan, S.H., & Kase T. Zootaxa 3109, 2011.

A picture of a live sample from the authors is shown below.

This tiny crab (~4 mm) is truly colorless. The yellowish coloration seen here is due to sediments adhering to its body.  Courtesy: Husana, D.E.M, Tan, S.H., & Kase T. Zootaxa 3109, 2011.

Crabs that are similar in habitat to and are relatives of Samarplex principe are very sensitive to human activities. The authors add that “the apparent rarity of this new species, its low natality, (its) restriction to the cave habitat and endemism to the island poses an immediate conservation concern.”

This crab will probably not turn red when cooked, Jerome. But more importantly, you may not eat this crablet.

GALLERY (Click an image below to go to Gallery view.)

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*An achialine cave is a cave that has a mixture of freshwater and salt water.

**Troglomorphic adapataions refer to adaptations to a cave environment.

[1] Husana, D.E.M, Tan, S.H., & Kase T. (2011). A new genus and species of anchialine Hymenosomatidae(Crustacea, Decapoda, Brachyura) from Samar, Philippines Zootaxa , 3109, 49-59.

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