Monday, March 14, 2016

[Crustacea • 2011] Samarplax principe • A New Genus and Species of Anchialine Hymenosomatidae (Decapoda, Brachyura) from Samar, Philippines

Samarplax principe  
Husana, Tan & Kase, 2011

A new genus and species of brachyuran crab, Samarplax principe (family Hymenosomatidae) is described from an anchialine cave in Samar Island, Philippines. This cavernicolous species lacks rostrum and has degenerated eyes, possesses two small spines at the lateral margin of the carapace, has a proportionally shorter projected merus of the third maxilliped, an almost flat epistome and brush-like setae instead of teeth along the cutting edges of the chelae. The complete loss of visual organs and pigmentation, the long but slender ambulatory legs and large egg size suggest a completely hypogeal lifestyle for this species. This is the first species of Hymenosomatidae recorded from an anchialine cave in the Philippines exhibiting true troglomorphic adaptations.

Key words: Samarplax principe new genus, new species, taxonomy, Philippines, Samar, Principe Cave, anchialine cave, troglobite

Hymenosomatidae Macleay, 1838 

Samarplax new genus 

Diagnosis. Carapace sub-polygonal, as long as wide to slightly longer than wide; dorsal surface uneven due to regions, surrounded by continuous rim, regions slightly inflated, separated by deep grooves. Rostrum absent; frontal margin gently bilobed. Posterolateral margin entire. Antennular fossa very shallow. Epistome almost flat, not visible from dorsal view. Eyes strongly reduced, visible as vestigial structure only under scanning electron microscopy (SEM) (Fig. 7); cornea absent. Male sterno-abdominal cavity relatively narrow; abdominal locking button indistinct. Male abdomen-pleotelson with somites 3–5 fused; somites 1, 2 with rounded lobes on disto-lateral angle on both sides; fused somites narrowed distally; pleotelson distinctly narrower than half width of abdomen; tip of pleotelson reaching to mid-point of abdominal somite 4. Female abdomen dome-shaped, with undivided plate formed by fusion of somite 2 to pleotelson, somite 2 and pleotelson marked by shallow suture on outer side. G1 slender, slightly sinuous, twisted at base, tapering at tip, curving inwards, distal portion with long stiff setae. G2 short, about half length of G1. 

Etymology. The genus name Samarplax is derived from the locality, Samar province and plax for “plate”, the suffix of the cavernicolous genera, Sulaplax and Guaplax, alluding to their superficial resemblance. Gender feminine.

Samarplax principe new species

Etymology. This species, principe, was named after the cave locality, Principe Cave. The name is used as a noun in apposition. 

Habitat. Samarplax principe new species, was discovered in Principe Cave, an anchialine cave, located approximately 200 meters away from the shoreline, with the surface salinity ranging from 1.5 to 3.5‰. 

Distribution. Samarplax principe new species, is currently known only from Principe Cave, Calicoan Island, Guiuan, Eastern Samar, Philippines.

 Daniel Edison M. Husana. Swee Hee Tan and Tomoki Kase. 2011. A New Genus and Species of Anchialine Hymenosomatidae (Crustacea, Decapoda, Brachyura) from Samar, Philippines. Zootaxa. 3109: 49–59