Parancistrus nudiventris, Rapp Py-Daniel & Zuanon, 2005

Rapp Py-Daniel, Lúcia H. & Zuanon, Jansen, 2005, Description of a new species of Parancistrus (Siluriformes: Loricariidae) from the rio Xingu, Brazil, Neotropical Ichthyology 3 (4), pp. 571-577 : 573-576

Parancistrus nudiventris , new species

Figs. 1 , 2

Holotype. INPA 15037 (152 mm SL); Brazil; Pará State; rio Xingu, bedrock at ilha do Bacabal , 3º23’19"S, 51º43’24"W; J. Zuanon, 8 Sep 1997.

Paratypes. (25 specimens) All localities in Brazil, Pará State, rio Xingu : INPA 3941 (5, 102- 131 mm SL), Furo do Tucum Seco near Arroz Cru , 3º25’6"S, 51º55’8"W; L. Rapp Py-Daniel and J. Zuanon, Oct 1990 . INPA 3962 (5, 60- 114 mm SL), cachoeira do Kaituká , cast-net, 3º33’47"S, 51º51’20"W; L. Rapp Py-Daniel and J. Zuanon, Oct 1990 . INPA 4095 (1, 117 mm SL), bedrock at ilha de Babaquara , collected manually, 3º25’44"S, 52º14’25"W; J. Zuanon, Sep 1997 . INPA 15038 (1, 149 mm SL), bedrock at ilha do Bacabal , collected manually, 3º23’19"S, 51º43’24"W; J. Zuanon, Sep 1997 . INPA 15042 (1, 130 mm SL), ilha da Bela Vista , cast-net, 3º24’22"S, 51º43’3"W; J. Zuanon, Sep 1997 . INPA 15043 (1, 151 mm SL), corredeiras do Jutaizão , cast-net, 3º16’42"S, 52º2’20"W; J. Zuanon, Sep 1997 . INPA 15044 (1, 175 mm SL), bedrock at ilha do Sr. Izaltino , gill-net, 3º16’21"S, 52º12’7"W; J. Zuanon, Sep 1997 . INPA 15045 (1, 153 mm SL), bedrock at ilha do Sr. Izaltino , collected manually, 3º16’21"S, 52º12’7"W; J. Zuanon, Sep 1997 . INPA 15046 (1,140 mm SL), igarapé Bacajá , cachoeiraAlpercata, castnet, 3º29’53"S, 51º43’00"W; J. Zuanon, Sep 1996 . INPA 15047 (2, 96- 135 mm SL), bedrock at ilha do Sr. Izaltino , gillnet, 3º16’21"S, 52º12’7"W . INPA 17961 (2, 53- 150 mm SL), Costa Júnior , collected manually, 3º29’28"S, 52º19’7"W; J. Zuanon, Sep 1996 . INPA 17960 (3, 1 c&s: 58-81 mm SL), Altamira , specimens from aquarium trade, approx. 3º12’S, 52º24’W; A. Uchoa, Apr-Sep 1997 . ZUEC 4538 (1, 100 mm SL), Furo do Ramiro , 03º15’21"S, 52º05’06"W; J. Zuanon, Sep 1997 .

Diagnosis. Parancistrus nudiventris is distinguished from P. aurantiacus (the only other valid species of Parancistrus ) by the lack of abdominal plates, larger interbranchial distance (39-56% in HL vs. 24.9-39.5% in P. aurantiacus ), narrower interorbital distance (26.8-38% in HL vs. 38.5-43.1% in P. aurantiacus ), buccal teeth more conspicuous, and shorter posterior dentary processes. Skeletal differences include the presence of a strong condyle on the lateral ethmoid for articulation with the metapterygoid in P. nudiventris (not seen in P. aurantiacus ); anguloarticular processes short in P. nudiventris (long in P. aurantiacus ); opercle with odontodes, partly exposed in P. nudiventris (completely embedded in skin in P. aurantiacus ). Parancistrus nudiventris also has a different pattern of coloration from P. aurantiacus : alive, the fish is covered by small bluish white spots; in preserved specimens, these spots become yellowish. Parancistrus aurantiacus can be uniformly darkly colored or covered by large pale blotches or even marbled.

Description. Body proportions and meristics in Table 1. Head and body short, broad and flat, tapering both anteriorly and posteriorly. Maximum body width at pectoral girdle. Cleithrum covered by strong odontodes. Body plates hispid, not carinate. Predorsal plates organized in series of pairs in some specimens, or without any organization. Head without keels or ridges. Snout triangular, completely covered by small plates. Interorbital area flat. Orbit large and round. Supraoccipital conspicuously distinct from pterotic-supracleithrum.

Evertible cheek plates with associated hypertrophied odontodes and disposed as unique block ligamentously connected to opercle. Opercular movements causes expansion of opercular block, thereby everting odontodes. Opercle with small area exposed with short odontodes. Subpreopercle not reaching border of head.

Mouth wide, lips papillate. Upper lip smooth externally, but densely papillated internally. Maxillary barbels very short. Premaxillae round, reduced and ligamentously attached to each other. Dentaries short and spaced widely apart. Buccal teeth villiform, well developed, not numerous and weakly cuspidate. Gill opening wide, branchial chamber large. From mouth to anus, ventral surface completely naked, except for some scattered platelets disposed close to pectoral-fin insertion.

Dorsal fin long and low, connected to adipose fin by thick membrane. Pectoral and pelvic fins well developed. Pectoral spine stiff and strong, covered by long piercing odontodes on large specimens. Anal fin extremely reduced. Caudal fin truncate to slightly emarginate. Caudal peduncle flat ventrally.

Metapterygoid channel complete, ending on articulation with lateral ethmoid. Quadrate abutted to metapterygoid. Opercle elongate, almost straight, with small area with odontodes. Preopercle with exposed area with odontodes. Basipterygia anterior processes curved. Basipterygia connected by three sutures (additional suture between mesial anterior basipterygia processes). Lateral line complete, not entering supracaudal plates.

Color in alcohol. Body and fins evenly dark brown covered by minute yellowish spots. Spots more concentrated and conspicuous on dorsal and caudal fins. Head and abdomen poorly spotted.

Color in life. Overall body color dark grey to olive, with scattered small bluish white dots ( Fig. 2 ).

Sex dimorphism. Sexual dimorphism in Parancistrus nudiventris is expressed by the presence of strong spines on the pectoral fin spine, the cheek area and body plates of sexually mature males. Fleshy folds were not observed in the examined material despite the presence of large mature males in the type series.

Geographic distribution. All specimens examined of Parancistrus nudiventris are from the rio Xingu ( Fig. 3 ).

Ecological notes. Parancistrus nudiventris is a rheophilic species, found in rocky-bottom areas subjected to moderate to strong current (40 to 190 cm /sec). Specimens were found individually or in pairs in shelters under boulders or in narrow cracks on submerged rocks up to 2 m deep. Young specimens (up to 5 cm SL) were observed under flat rocks over the bottom, usually sharing the shelter with specimens of Baryancistrus spp. , Oligancistrus sp. , O. punctatissimus , Hopliancistrus tricornis , Ancistrus sp. , A. ranunculus , Peckoltia vittata and Pseudancistrus aff. barbatus .

Parancistrus nudiventris is a nocturnal fish that feeds by grazing over rock surface, browsing algae and other food items off the periphyton. Analysis of the stomach contents revealed the presence of algae as the most frequent food ingested, and included mainly diatoms. Other food items were cyanobacteria, plant remains, bryozoans, larvae of aquatic insects (most chironomids), microcrustaceans, and few small molluscs; sand grains and silt were also recorded. Dissected specimens had long digestive tracts, approximately 20 times the SL, characteristic of algae-feeding fishes. The consumption by P. nudiventris of food items found loosely attached to the rocks characterize this species as a comber, following the feeding-strategy classification proposed for African Rift Lake cichlids (cf. Konings, 1989; Yamaoka, 1997).

Etymology. The name nudiventris is derived from the Latin nudus, naked, and ventris, belly.

Morphological and skeletal remarks. There are clear differences in body format between P. nudiventris and P. aurantiacus . Parancistrus nudiventris is slender, has larger eyes, and has a shorter caudal peduncle, whereas P. aurantiacus has a shorter and wider head and wider branchial openings.

Metapterygoid channel ( Howes, 1983; Schaefer, 1987) is not completely closed, with tall wall only on the anterior half of the channel in P. aurantiacus . In P. nudiventris the channel is complete and it ends on the articulation site with the lateral ethmoid ( Fig. 4 ). Quadrate loosely sutured to metapterygoid in P. aurantiacus and just abutted in P. nudiventris . The opercle in P. aurantiacus is elongate and almost straight, embedded in skin and without any odontode. In P. nudiventris , however, the opercle is similar in shape but shows a small area with odontodes. Preopercle with larger exposed area with odontodes in P. aurantiacus than in P. nudiventris . Anterior process of basipterygium straight in P. aurantiacus and curved in P. nudiventris ( Fig. 5 ). Basipterygia connected by two sutures in P. aurantiacus (the anterior and posterior sutures to the cartilage plug) and by three in P. nudiventris (additional suture between the mesial anterior basipterygia processes).

Lateral line complete, not entering the supracaudal plates on both P. aurantiacus and P. nudiventris . Table 2 summarizes the main differences described for both species.

Figures

Fig. 1. Parancistrus nudiventris. Lateral, dorsal, and ventral view of the holotype (INPA 15037, 152 mm SL).

Fig. 2. Parancistrus nudiventris. Living color and detail of mouth of the holotype (INPA 15037, 152 mm SL).

Fig. 3. Distribution of Parancistrus nudiventris.

Fig. 4. Suspensorium, dorsal view. a. Parancistrus aurantiacus; b. Parancistrus nudiventris. aa = angulo-articular, dt = dentary, hyo = hyomandibular, mpt = metapterygoid, mpt.c.= metapterygoid channel, op = opercle; pop = preopercle, q = quadrate.

Fig. 5. Basipterygia (bspt), anterior processes (ant. proc.) and lateropterygium (ltpt), dorsal view. a. Parancistrus aurantiacus; b. Parancistrus nudiventris.