Aegla brevipalma, Santos & Bond-Buckup & Buckup & Pérez-Losada & Finley & Crandall, 2012

Santos, Sandro, Bond-Buckup, Georgina, Buckup, Ludwig, Pérez-Losada, Marcos, Finley, Maegan & Crandall, Keith A., 2012, Three New Species Of Aegla (Anomura) Freshwater Crabs From The Upper Uruguay River Hydrographic Basin In Brazil, Journal Of Crustacean Biology 32 (4), pp. 529-540 : 530-532

Aegla brevipalma n. sp. Bond-Buckup and Santos

( Fig. 2 )

Type-material.— Holotype: male, Brazil, state of Santa Catarina, Matador River, BR 282 at bridge, km 136 , Bom Retiro, Canoas River sub-basin , Uruguay River basin, 27 ◦ 49 ' 02 '' S, 49 ◦ 33 ' 15 '' W; 875 m ( Fig. 1 : circle), 25.x.2000, col.: Bueno, A.; Bond-Buckup, G.; Jara, C. and Pérez-Losada, M. ( MZUSP 23465 ) .

Paratypes: 1 m, 1 f ov, 1 exuvia, same data as holotype (UFRGS 2679P) ; 1 m, same data as holotype, ( UFRGS 3005 ); 9 m, also same data as holotype ( UFRGS 3010 ) .

Diagnosis.—Anterolateral spine of carapace short, not reaching base of cornea; protogastric and epigastric lobes absent; extra-orbital sinus absent, rostrum triangular, deflected, carinate, outer proximal margin of movable finger of cheliped with lobe; palmar crest of cheliped subdisciform; anterior angle of ventral margin of epimeron 2 with modest scales; inner marginof ventral surface of ischium of cheliped with distal scaliform tubercle.

Description.—Carapace very compressed, dorsal surface scabrous, covered with punctations and scales. Front wide; PCW/FW ratio of holotype male 1.86. Rostrum triangular, low, tapered, deflected, carinate, distal portion of rostrum slightly recurved distally. Sub-rostral process very developed; in profile, rostrum with ventral portion larger than dorsal. Rostral carina begins at height of first hepatic lobe, with a row of scales reaching the apex; scales decrease in size and become more spaced as they reach the distal portion of rostrum; carina slightly elevated in median portion and very low in distal third. Lateral margins of rostrum scaly. Orbits wide, deep. Orbital margin with scales. Orbital spine absent, extraorbital sinus lacking. Antero-lateral angle of carapace projecting anteriorly in a spine, which does not reach base of cornea. Outer and inner margins of antero-lateral lobe with scales. First hepatic lobe delimited anteriorly by modest fissure; lateral margin with scales; second and third hepatic lobes not indicated; lateral margins with scales. Epigastric prominences absent, scabrous surface. Protogastric lobes absent, without indication. Transverse dorsal line slightly sinuous. Areola quadrate. AL/AW ratio of holotype male 1.58.

Epibranchial area triangular, with scales. Lateral margins of anterior branchial area with subequal scales and posterior branchial area with sparse scales.

Anterior angle of ventral margin of epimeron 2 unarmed, indicated by small scale; ventrolateral margin nearly straight; posterior angle of ventral margin obtuse, unarmed. Epimera of third to sixth segments projecting; on third and fourth segments, lateral projection ornamented with small apical scale.

Telson divided by longitudinal suture.

Anterior extremity of third sternite truncate, projected between coxae of exopods of third maxillipeds. Fourth thoracic sternite plain, tufts of long setae present anteromesially, antero-lateral angles projected by tubercle.

Chelipeds subequal, hand subquadrate. Chelae globose, covered by scales and sparse scaliform tubercles. Larger cheliped slightly more robust; outer proximal margin more inflated. Palmar crest of the minorcheliped subdisciform, especially at its proximal margin which forms an acute angle; palmar crest of major cheliped subrectangular, margin ornamented with elevations with scales, indicating lobes. Predactylar lobe forming a small step with anterior margin of propodus, with scales. Fingers thickened, covered by scales and sparse setae, and distally by scaliform tubercles. Proximal outer margin of movable finger with lobe tipped with scales. Prehensile margins of fingers with scaliform denticles along their entire length and with fitted opposed lobular teeth associated with the major cheliped. Dorsal surface of carpus scabrous, with punctuations and scales; inner margin with four spines, with the penultimate distalmost spine being most developed; last spine is reduced and situated close to basis of penultimate spine; these spines with some scales and setae on the lateral margins; inner antero-lateral angle obtuse, ornamented with scales; anterodorsal margin with scales. Distal part of dorsal surface with modest depression parallel to distal margin. Carpal crest modest, more elevated in proximal region; medial and distal parts with setae and scales clustered in clumps of three to five units on elevations of crest; outer ventral angle of carpus obtuse, with tubercle; ventral surface with conical tubercle and long setae. Dorsal margin of merus of cheliped with elevation tipped with scales decreasing in size in proximal direction, followed by long setae; antero-dorsal margin with sparse scales. Lateral surfaces with punctuations and scales. Inner ventral margin of merus with one distal spine; outer ventral margin with pronounced distal spine followed by tubercle. Dorsal margin of ischium with one tubercle, scales and long setae; inner margin of ventral surface with small distal conical tubercle and elevation bearing proximal scale.

Dorsal margin of dactylus, propodus, and carpus of second through fourth pereiopods with rows of setae and scales arranged in longitudinal series; dactyli of same pereiopods covered with scales and short setae; dorsal margins of meri covered with long setae, lending the surface a pubescent appearance.

Variations.—In some paratype specimens, the protogastric lobes are delimited anteriorly by sparse scales, although these are lacking in other specimens. Proximal outer margin of movable finger, in some specimens, bears scales suggesting a lobe. Some paratypes do not possess fitted opposed lobular teeth on the prehensile margin of the fingers, but only scaliform denticles along their entire length.

Measurements: Male holotype, CL 14.92 mm. Paratypes (n = 10) with mean CL 13.54, i.e., a small-sized species. The ovate female measured CL 12.51 mm.

PCW/FW ratio of paratypes (n = 7) ranging from 1.72 to 1.94, with mean of 1.82, i.e., a wide front in small-sized animals and narrow front in larger animals.

Paratypes (n = 4) mean ratio AL/AW 1.61, ranging from 1.47 to 1.75.

Distribution.—BRAZIL: State of Santa Catarina, Uruguay River basin, Canoas River sub-basin.

Etymology.—From Latin, brevis = short and palma = inside of the hand.

Conservation status.—Critically Endangered (CR) – B2ab(iii): Area of occupancy estimated to be less than 10 km 2; known to exist at only a single location; continuing decline, inferred from quality of habitat ( IUCN, 2001).

Biology.—Unknown.

Remarks.—The hallmark of this species, the short palm length, is shared with A. plana, a species that also occurs in hydrographic basins in southern Brazil, and with several species from Argentina including A. neuquensis, A. riolimayana, A. ringueleti and A. humauaca. It differs from A. plana, among other characters, especially by the shape of the palmar crest, which is subdisciform in the new species and subrectangular in A. plana. Similarly to A. leachi n. sp., it belongs to the small-sized group within aeglids, showing a small CL.

The new species occurs in sympatry with Aegla jarai Bond-Buckup and Buckup, 1994 as aforementioned for the sub-basins of the Upper Uruguay River ( Bond-Buckup and Buckup, 1994; Bond-Buckup et al., 2009). The type-locality is heavily impacted, with cattle and hogs being raised next to the watercourse, resulting in continuous degradation of the water quality. In a recent survey at the stream (2010), the authors did not find new specimens of the species.

Figures

Fig. 2. Aegla brevipalma n. sp. Bond-Buckup Santos (male holotype, MZUSP 23465, scale: 5 mm: A, dorsal view; B, anterior portion of carapace (lateral view); C, basis-ischium of cheliped (ventral view); D, third and fourth thoracic sternites (ventral view); E, epimeron 2 (lateral view).

Fig. 1. Upper Uruguay system, showing the sub-basins of the Canoas, Caveiras and Lava-Tudo Rivers and sampling localities (Aegla brevipalma, circle; Aegla leachi, triangle; Aegla oblata, square