Parathelphusa cabayugan, Freitag & Yeo, 2004

Freitag, Hendrik & Yeo, Darren C. J., 2004, Two New Species Of Parathelphusa H. Milne Edwards, 1853, From The Philippines (Crustacea: Decapoda: Brachyura: Parathelphusidae), Raffles Bulletin of Zoology 52 (1), pp. 227-237 : 228-232

Parathelphusa cabayugan , new species

( Figs. 1-4 )

Material examined. – Holotype - male (32 by 25.3 mm) ( PNM 17259 ), Cabayugan River , Puerto Princesa, Palawan, coll. H. Freitag, 5 Jun.2001.

Paratypes - 2 males (larger 19.3 by 16.4 mm), 1 female (21.6 by 17.8 mm) ( ZRC2004.0622 ) , 2 males (larger 20.7 by 17.2 mm) ( ZIH) , 2 males (largest 17.2 by 14.7 mm) ( SPCP-ASTD) , Cabayugan River , Puerto Princesa, Palawan, coll. H. Freitag, 2001.

Others (designated for ecological studies) - 38 males (largest 14.6 by 12.4 mm), 28 females (largest 26.4 by 21.6 mm),> 100 juveniles (smallest 5.0 by 4.5 mm) ( SPCP-ASTD), same data as paratypes .

Diagnosis. – Carapace low, dorsal surface flat; cervical grooves distinct, deep, broad; epibranchial teeth well developed, sharp, directed forwards. Merus of ambulatory legs with well developed subdistal spine on dorsal margin. Male sixth abdominal segment elongated, relatively slender, longer than telson (segment 7). G1 gently sinuous, proximal part broader than distal part; tip truncate, gently curved outwards, with distinct subdistal notch on outer margin.

Etymology. – The species is named for the type locality, Cabayugan River and Barangay Cabayugan of Puerto Princesa City. The name is a noun in apposition.

Colour. – In life, dorsal carapace and walking legs dirty greyish brown, the latter with a slight cross-stripe pattern. Ventral parts (sternum and abdomen) a dirty-white colour. Eleven out of 71 specimens with blackened fingers of the chelipeds, while the rest with greyish brown fingers. In alcohol, all brown parts become a light orange-brown.

Remarks. – Parathelphusa cabayugan , new species, superficially resembles several known species of Philippine Parathelphusa . For example, the sharp, well-developed epibranchial teeth of P. cabayugan resemble those of P. palawanensis ( Bott, 1969) , P. saginata Ng & Takeda, 1993 , P. mindoro Ng & Takeda, 1993 , and P. manguao , new species (present study). In addition, the truncate tip of the G1 of P. cabayugan resembles that seen in P. obtusa ( Bott, 1969) and P. rasilis Ng & Takeda, 1993 ; and the overall form of its G1 is similar to that of P. nana Ng & Takeda, 1993 . Parathelphusa ovum Ng, 1994 , from Sabah, Borneo, also possesses a G1 with a truncate tip that is similar to that of P. cabayagan .

Parathelphusa cabayugan , however, can be immediately separated from these and all other Parathelphusa species by the presence of a distinct subdistal notch on the outer margin of the tip of its G1, in addition to a unique combination of external and other G1 characters (see Tables 1A, B).

The diagnostic subdistal notch on the outer margin of the tip of the G1 and the sharp, well-developed epibranchial teeth are also present in juvenile specimens of P. cabayugan ( Figs. 2C, D, G, H ).

Ecological notes. – The habitats where P. cabayugan occur are in the Cabayugan River catchment (10 09’N, 118 51’E), which has an area of approximately 3,683 ha ( PAMB of Puerto Princesa City, 1998, unpublished). The catchment is surrounded by mountains up to 1028 m high, but all permanent tributaries and sites sampled are lowland waters. The soils drained are yellowish to deep red clays on ultrabasic subsoils at the peripheral headwaters; alluvial soils on shale and sandstone at the upper to middle river course; and karst soils on limestone at the lower and subterranean course of Cabayugan/Underground River. This results in the pH being generally basic, ranging from 7.1 to 8.7, and the conductivity being relatively high, ranging from 140 to 740 S/cm.

Highest abundance of P. cabayugan was found in undisturbed first to third order headwaters with moderate to low turbidity (> 120 cm light penetration). The specimens were collected from the river bed and in colonization baskets situated between stony and course organic substrates. Within such river sections, the crabs were found in different micro-habitats such as under small falls, in riffles, and in pools. Applying drift nets at all sites, several specimens were caught only at a spring brook running out off limestone rocks. Dissolved oxygen was occasionally found decreasing to 60% saturation in this site. All other sites sampled had generally higher values.

Lower abundance of P. cabayugan was found in the middle river course that is influenced by anthropogenic activities (paddy fields, settlements). Those result in higher temperature fluctuations (26 C 3 C), raised turbidity and slightly increased BOD 2+5 (max: 2.6 mg /l, n=5). In paddy fields and their draining channels, no individuals of the species were found. This is in contrast to other parathelphusid crabs such as members of Sayamia , Esanthelphusa and Somanniathelphusa that occur in rice fields in many parts of Indochina and China (see Ng & Naiyanetr, 1993; Naiyanetr, 1994; Ng, 1995; Dai, 1999; Yeo & Nguyen, 1999). It is possible that the absence or low abundance of P. cabayugan in the middle parts of the river may be due to natural physical/ environmental variables. However, the use of pesticides and fertilizers in the nearby paddy fields may also have played a part.

The species was not detected in the other stretches of the river, viz., the subterranean course and the estuary.

The species appears to be primarily aquatic in habits, as majority of the specimens were collected from within the river. However, a single specimen caught on the river bank about 1 metre above the water surface, in an emergence trap for eclosing aquatic insects, suggests that the members of the species actively leave the water body for short times at least.

Juvenile stages (<5 by 4.5 mm) assigned to this species were found several times throughout the year at the same stream courses as the adults. One female (26.4 by 21.6 mm) was found carrying 54 juveniles of 2.0 by 1.9 mm size. Juveniles of the same size were detected as smallest among the released free living ones.

The data from this semi-quantitative collection seems to indicate that P. cabayugan has an affinity for small and undisturbed headwater streams, with clear and unpolluted water. The preferred habitats overlap in parts with those of the potamid genus Insulamon Ng & Takeda, 1992 .

Figures

Fig. 1. Parathelphusa cabayugan, new species, holotype male (32 by 25.3 mm) (PNM 17259). A, dorsal view of carapace; B, frontal view of carapace; C, right third ambulatory merus; D, right fourth ambulatory merus; E, left chela; F, abdominal segments 5-7. Scales = 10.0 mm.

Fig. 2. Parathelphusa cabayugan, new species, left G1. A, B, E, F, holotype male (32 by 25.3 mm) (PNM 17259); C, D, G, H, paratype juvenile male (15.2 by 13.1 mm) (SPCP-ASTD). A, C, ventral view; B, D, dorsal view; E, G, ventral view of distal part; F, H, dorsal view of distal part. Scales = 1.0 mm.

Fig. 3. Parathelphusa cabayugan, new species, holotype male (32 by 25.3 mm) (PNM 17259).A, dorsal view; B frontal view; C, ventral view.

Fig. 4. Parathelphusa cabayugan, new species, paratype female (26.4 by 21.6 mm) (ZIH).