Phreatobius dracunculus, Shibatta, Oscar Akio, Muriel-Cunha, Janice & Pinna, Mário C. C. de, 2007

Shibatta, Oscar Akio, Muriel-Cunha, Janice & Pinna, Mário C. C. de, 2007, A new subterranean species of PHREATOBIUS Goeldi, 1905 (Siluriformes, INCERTAE SEDIS) from the Southwestern Amazon basin, Papéis Avulsos de Zoologia 47 (17), pp. 191-201 : 192-195

Phreatobius dracunculus , new species

( Figs. 1 , 3 and 5 )

Holotype: MZUSP 93955 , 36.0 mm SL, Brazil, State of Rondônia, hand-dug well in settlement of Rio Pardo, approximately 90 km south of the City of Porto Velho ; area of Rio Branco drainage (tributary to Rio Jaci-Paraná , itself tributary to Rio Madeira , Amazon basin), 63°58’08.2”W 9°34’10.7”S, Coll. J.M. Cunha, J. Zuanon & Z. V. P. Siqueira, 01-03 Nov 2006.

Paratypes: All from type locality. MZUSP 93956 , 1 ex, 35.8 mm SL ; MZUSP 93957 , 1 ex, 29.7 mm SL ; MZUSP 93958 , 1 ex, 31.2 mm SL, collected with holotype ; MZUSP 91680 , 1 ex, 38.1 mm SL , MZUEL 4761 , 2 ex (20.1 and 29.8 mm SL), Coll. Z . V.P. Siqueira, 05-27 Sep 2005 .

Diagnosis: Distinguished from its only congener, P. cisternarum , by the following characteristics: 1) eyes absent (vs. small eyes present); 2) ventral procurrent rays 11-13 (vs. 22 to 26), dorsal procurrent rays 29-31 (vs. 42 to 50); 3) vertebrae 52 or 53 (vs. 59-64); 4) five pectoral-fin rays (vs. four); 5) long pectoral fin (50-60% HL; vs. 20-25%); 6) posterior insertion of dorsal-fin approximately at vertical through third anal-fin ray (vs. at vertical through origin of anal-fin); 7) first dorsal-fin pterygiophore inserted immediately posterior to neural spine of free vertebra 12 or 13 (vs. vertebra 17-19); 8) First anal-fin pterygiophore inserted immediately posterior to hemal spine of free vertebra 16 or 17 (vs. vertebra 22-24); 9) no integumentary dark pigmentation (vs. some faint dark pigment always present); 10) pseudotympanus large, visible in dorsal, lateral and ventral views (vs. pseudotympanus small, visible in lateral view only); and 11) posterior (and only) pores of infraorbital canal nearly aligned transversely on head with posterior nasal pores (vs. posterior infraorbital pores markedly posterior to transverse line through posterior nasal pores); cf. fig. 2, compare with fig. 1 in Muriel-Cunha & de Pinna (2005).

Description: Morphometric data given in Table 1. Cross-section of body at trunk approximately round, becoming more compressed posterior to base of dorsal-fin. Caudal penducle region strongly compressed. Caudal region expanded dorsally and ventrally by procurrent caudal-fin rays ( Fig. 1 ).

Integument thin, hyaline in live specimens, with vertical folds regularly disposed along sides of trunk in preserved specimens. Myotomes and skeletogenous septa evident externally along most of body except in region along anal fin, thickly covered with adipose tissue.

Head longer than broad, its lateral profile convex in dorsal view. Eyes absent. Anterior naris small, close to upper lip, as long as wide, with a tube of integument prolonged anterodorsally. Posterior nares round and small. Snout round in dorsal view. Mouth as wide as head and prognathous, lower jaw extending further anteriorly than upper one ( Fig. 1 ). Corners of mouth strongly curved posteriorly, reaching slightly beyond vertical through posterior margin of posterior nares in lateral view. In lateral view cleft of mouth straight, located on dorsal fourth of head depth ( Fig. 1 ). Lower jaw projected dorsally, its ventral profile slightly convex. Upper jaw strongly depressed, its depth one-third that of lower one in lateral view. Lips large and thick, well defined laterally by fold of integument. Branchial membranes mostly free, narrowly attached to isthmus. Posterior attachment of branchial membranes immediately dorsal to origin of pectoral fin.

Proportional barbel lengths varying markedly among specimens and on different sides of same specimen. Maxillary barbel, when abducted, not reaching posterior limit of dorsal head musculature in MZUSP 91680 , MZUEL 4761 (2 exs), reaching that point in holotype ( MZUSP 93955 ) and reaching anterior third of pectoral fin in MZUSP 93956 , MZUSP 93957 and MZUSP 93958 . Base of maxillary barbel close to anterolateral corner of upper jaw, at mid distance between corner of mouth and tip of snout. Outer mental barbel slightly shorter than maxillary one, not reaching to vertical through pectoral-fin base in holotype ( MZUSP 93955 ), MZUSP 93956 , MZUSP 91680 and MZUEL 4761 (29.8 mm SL), but reaching pectoral-fin base in MZUSP 93958 and anterior third of pectoral-fin in MZUSP 93957 . Outer mental barbel broken on right side of MZUEL 4761 (29.8 mm SL) and absent or broken on both sides of MZUEL 4761 (20.1 mm SL). Inner mental barbel shortest and not reaching vertical through corner of mouth in MZUSP 91680 and MZUSP 93956 , reaching vertical through the middle distance between corner of mouth and pectoral-fin base in the holotype ( MZUSP 93955 ), almost reaching pectoral-fin base in MZUSP 93958 and reaching that point in MZUSP 93957 . Origin of inner mental barbel slightly anterior to that of outer mental barbel. All barbells with fine round tips .

Six cephalic latero-sensory canal pores present dorsally on anterior snout region posterior to nares, corresponding to pores of the supraorbital latero-sensory canal associated with nasal bone. Anterior pair of pores close to each other, located mesial to base of anterior nares. Posterior pair less widely apart than in P. cisternarum . Posterior pores at infraorbital canals nearly aligned, tranversely with posterior nasal pores. Latero-sensory canal system absent on most of body, restricted anteriorly to short tube with two pores representing remnant of lateral line.

Pectoral-fin rays all soft, i+4 (n=5, holotype) or i+3+i (n=1), a single specimen with 5 branched rays on one side and i+3+i on the other. Fin large, its length about 50-60% of HL and its base narrow. Pelvic fin reaching or covering anal opening, but not reaching anal fin (almost reaching that point in small specimen, MZUEL 4761 , 20.1 mm SL). Pelvic-fin bilaterally and intraspecifically variable: MZUSP 93957 , both fins v; MZUSP 93955 (holotype) left fin with 5 branched rays, right one i+3; MZUEL 4761 (20.1 mm SL specimen) and MZUSP 93956 , both fins with 5 branched rays; MZUEL 4761 (29.8 mm SL specimen), both fins with 5 rays, left one ii+3 and right one i+4; MZUSP 91680 , left fin ii+2+i, right one i+2; MZUSP 93958 , left pelvic fin i+2+i, right fin i+3+i. Dorsal-fin short, its origin closer to tip of snout than to base of caudal-fin, its base extending posteriorly to vertical through origin of pelvic-fins, its posterior insertion approximately at vertical through the third anal-fin ray and at middle of SL. Seven dorsal-fin rays, all soft, i+6 (n=4), ii+5 (n=2, holotype), ii+4+i, i+1+i+4. First dorsal-fin pterygiophore inserted posterior to neural spine of vertebra 13 (n=6, holotype) or vertebra 12 (n=1). Anal-fin long, with 20 (n=1), 21 (n=1), 22 (n=4, holotype), or 24 (n=1) soft rays, all unbranched. Origin of anal-fin slightly posterior to anal opening. First anal-fin pterygiophore inserted posterior to hemal spine of vertebra 17 (n=6, holotype) or 16 (n=1). Anal-fin continuous posteriorly with ventral procurrent caudal-fin rays, but two regions distinguishable by abruptly shorter procurrent rays, marked by clear indentation and by slightly more closely-positioned procurrent rays, when compared to more widely spaced anal-fin rays (fig. 1). Caudal-fin round (n=3, holotype) or symmetrically lanceolate (n=4), continuous dorsally and ventrally with procurrent rays. Procurrent caudal-fin rays more numerous dorsally (29-31) than ventrally (11-13). Principal caudal-fin rays 10 (n=4) or 11 (n=3, holotype), all soft, 6 to 10 middle rays branched. Dorsal procurrent caudal-fin rays, principal caudal-fin rays, ventral procurrent caudal-fin rays and anal-fin rays joined as single extended fin. Vertebrae 52 (n=1) or 53 (n=6, holotype). Two (n=1) or three (n=6, holotype) pairs of pleural ribs, on vertebrae 7 and 8 or 6, 7 and 8, respectively. In holotype, anterior pleural rib (on vertebra 6) present on one side only. Last pair of pleural rib smaller than preceding ones, associated with hypertrophied parapophysis on vertebra 8. ( Fig. 5 ) Swimbladder occupying entire body width and reaching posterior limit of vertebra 8 .

Coloration

Live specimens are light pink, slightly darker alongside the vertebral column due to dorsal aorta ( Fig. 1 ). Numerous adipose bodies create a superficial iridescence especially evident on the middle and posterior portion of body. There is a large translucent area immediately posterior to head, corresponding to the pseudotympanus, forming a light collar seen in dorsal, lateral and ventral views in live specimens ( Fig. 1 ). The fins are hyaline. In preserved specimens, the body is uniformly white, with no trace of dark pigmentation. The only coloration differences are muscle limits and some internal structures seen superficially by transparency. Freshly-preserved specimens have a large greenish blotch in the abdominal region, probably corresponding to the liver. That structure gradually turns brownish and fades after approximately eight months of preservation. A specimen kept for five months in aquarium showed no change in pigmentation.

Distribution: Known from type-locality. Although specimens collected were all from a single well, individuals of Phreatobius , probably P. dracunculus , were observed (by JMC) swimming in two additional wells in the same area. Reports by locals indicate that the species probably occurs in at least another 12 of 20 wells in the region.

Etymology: The specific epithet, dracunculus , is from the Latin draco, meaning dragon, combined with a diminutive suffix -unculus. The name, a noun in apposition, is a reference to the color and general aspect of the body and fins of the fish.

Ecological notes

The type locality is located just outside of the eastern limit of a conservation unit called Floresta Nacional Bom Futuro, created in 1988 ( Olmos, 1998). The stream closest to the type locality is approximately 200 m apart in straight line from the well where specimens of P. dracunculus were collected. That stream joins the Rio Branco approximately 10 km downstream from the type locality. The annual mean pluviosity and temperature are 2.262 mm and 26.7°C respectively, according to the pluviometric station of Porto Velho, period of 1954 to 1993 ( Bezerra, 1996).

Specimens of P. dracunculus were collected in a recently opened hand-dug well intended for domestic use. According to owners, the well was excavated sometime in September 2005, and fish began to appear approximately ten days later, accidentally trapped in buckets used to extract water. The well is one meter in diameter and approximately five meters in depth. Water fills it up to 2.5 m in the rainy season, but drops to ca. 1 m in the drought (fig 4a). The walls of the well have soft stones and gravel that release a red stain (fig. 4b). They are probably loose conglomerates of the canga type described by Muriel-Cunha & de Pinna (2005), which are composed of ferruginous lateritic rocks widespread in the Amazon region ( Costa, 1991). The well water is clear but turns milky when disturbed, which is an indication that the bottom probably has a fine white clay locally known as “tabatinga”. Locals reported that similar fish had been seen sporadically in other wells in the region for the past five years.

Two specimens were kept live in aquaria, furnished with rocks from the well and without artificial aeration. One specimen was preserved after one month in captivity and the second was kept alive for approximately three months. Fish stayed in apparent good health the entire period in captivity and showed a general behavior similar to that of P. cisternarum as described by Muriel-Cunha & de Pinna (2005). Compared to its sister species, however, P. dracunculus specimens seemed more active overall, and spent more time exploring the bottom and middle portions of the water column. The food items in captivity were live earthworms ( Fig. 3a ), dried blood-worms and fresh dead adult Artemia . As with P. cisternarum , stress conditions temporarily induced a vertical body position in specimens of P. dracunculus ( Fig. 3b ).

Figures

FIGURE 1: Phreatobius dracunculus, Holotype, 36.0 mm SL; lateral view; dorsal view of body; and ventral view of live sedated specimen. Photo: L.M. Sousa.

FIGURE 3: A. Phreatobius dracunculus, MZUSP 93955, Holotype 36.0 mm SL eating live earthworm; B. MZUSP 93958, Paratype 31.2 mm SL in vertical position. Photos: E. Baena and J.M. Cunha.

FIGURE 5: Phreatobius dracunculus, MZUSP 91680, paratype 38.1 mm SL. Radiograph of head and anterior portion of trunk, dorsoventral view.