[Crustacea • 2023] Limnopilos miromekong • A New Species of Furry Crown Crab, Limnopilos Chuang & Ng, 1991 (Brachyura: Hymenosomatidae) from Tonle Sap, Cambodia

Limnopilos miromekong

Ng & Chhuoy, 2023

DOI: 10.1163/15685403-bja10313 

 Researchgate.net/publication/374199389 

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Abstract

A new species of the wholly freshwater hymenosomatid crab genus Limnopilos Chuang & Ng, 1991, is described from Tonle Sap River in the lower Mekong drainage, Cambodia. This is the fourth species known, and the second one from Indochina. The type species, of Limnopilos, L. naiyanetri Chuang & Ng, 1991, was from the Chao Phraya drainage to the west in central Thailand. The new species is characterized by the presence of a rostrum, relatively shorter ambulatory legs and a different structure of the male first gonopod. Limnopilos sumatranus Naruse & Ng, 2007, is also recorded from southern Peninsular Malaysia for the first time.

Keywords: Taxonomy; new species; Hymenosomatoidea; freshwater crab; Mekong River; Indochina;

 Peter K. L. Ng and Samol Chhuoy. 2023. A New Species of Furry Crown Crab, Limnopilos Chuang & Ng, 1991 (Brachyura, Hymenosomatidae) from Tonle Sap, Cambodia.  Crustaceana. 96(9): 885–895. DOI: 10.1163/15685403-bja10313

  Researchgate.net/publication/374199389_A_new_species_of_Limnopilos_from_Tonle_Sap_Cambodia

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Résumé: Une nouvelle espèce du genre de crabe Hymenosomatidae, Limnopilos Chuang & Ng, 1991, entièrement d’eau douce, est décrit du fleuve Tonlé Sap dans le bassin versant du Mékong inférieur, au Cambodge. C’est la quatrième espèce connue, et la seconde d’Asie du Sud-Est. L’espèce-type du genre Limnopilos, L. naiyanetri Chuang & Ng, 1991, était connue du bassin versant du Chao Phraya à l’ouest dans le centre de la Thaïlande. La nouvelle espèce est caractérisée par la présence d’un rostre, de pattes ambulatoires relativement plus courtes et une structure différente du premier gonopode mâle. Limnopilos sumatranus Naruse & Ng, 2007, est aussi signalé pour la première fois dans le sud de la Malaisie péninsulaire.

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

Samarplax principe  

Husana, Tan & Kase, 2011

ABSTRACT

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 

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researchgate.net/publication/287941235_A_new_genus_and_species_of_anchialine_Hymenosomatidae_from_Samar_Philippines

[Crustacea • 2015] Aletheiana tenella • A New Genus and New Species of Freshwater hymenosomatid Crab (Decapoda: Brachyura) from Central Sulawesi, Indonesia

Aletheiana tenella

Ng, & Lukhaup, 2015

FIGURE 1. Aletheiana tenella gen. et sp. nov.. A, cascades at Puawu River, central Sulawesi, B, submerged roots at the riverbank of Puawu River where the specimens were collected; C–F, colour in life.

DOI: 10.11646/zootaxa.4039.1.4

Abstract 

A new genus and new species of free-living hymenosomatid crab, Aletheiana tenella, is described from Central Sulawesi, Indonesia. The two known Sulawesi hymenosomatid species, Cancrocaeca xenomorpha Ng, 1991, and Sulaplax ensifer Naruse, Ng & Guinot, 2008, are both from cave habitats. Aletheiana gen. nov. is most similar to Neorhynchoplax Sakai, 1938 (from freshwater and intertidal habitats in the Indo-West Pacific), and Sulaplax, but can be distinguished by its front possessing only one subventral rostral lobe, the base of the antenna is positioned between the base of the ocular peduncle and antennular fossa, the posterior margin of the epistome has two low, rounded median lobes, the merus of the third maxilliped is elongated, the ambulatory dactylus has a prominent subdistal spine, the cutting edges of the chela are armed with distinct teeth proximally, and the male abdomen is slender and elongate with the telson linguiform.

Key words: Hymenosomatidae, Aletheiana tenella, new genus, new species, taxonomy, Sulawesi

Etymology. “Aletheia” is an ancient-Greek word for disclosure and a state of not being hidden. The latinised name is used here as a genus, alluding to the present discovery of the first free-living hymenosomatid crab from Sulawesi. Gender of genus feminine. The name is derived from the Latin “tenellus” for delicate; alluding to the small size and slender appendages of the species.

Biology. Aletheiana tenella gen. et sp. nov. was found among the submerged fibrous roots of trees at the slow flowing parts of the riverbank near cascades along the Puawu River, in Central Sulawesi (Fig. 1A, B). The crabs were observed at the slow flowing parts of the riverbank among roots near cascades of the Puawu River. The water at the time of collection was muddy and had a temperature of 22°C. In the faster flowing parts of the river, no crabs were found. This is a typical habitat for many free-living hymenosomatids (e.g., see Naruse & Ng 2007). A new species of Caridina, C. boehmei (Atyidae) was also recently described from the type locality of Aletheiana tenella gen. et sp. nov. by Klotz & von Rintelen (2013).

Ng, Peter K. L. and Christian Lukhaup. 2015. Aletheiana tenella, A New Genus and New Species of Freshwater hymenosomatid Crab (Crustacea: Decapoda: Brachyura) from Central Sulawesi, Indonesia. Zootaxa. 4039(1): 118–128. DOI: 10.11646/zootaxa.4039.1.4

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