Creagrutus cracentis Vari & Harold 2001

Creagrutus cracentis

DIAGNOSIS.—The presence of two distinct rows of premaxillary teeth, the very elongate, moderately sloping maxilla compared with the condition in most congeners, and the five median scales between the posterior margin of the anus and the anal-fin origin distinguish Creagrutus cracentis from all congeners with the exception of C. maxillaris, a species known from the upper portions of the Rio Negro and Río Orinoco of northern Brazil and southern Venezuela and the upper Rio Madeira basin along the Bolivian-Brazilian border. These two species can be differentiated by the postorbital head-length (36.8%–38.0% of HL in C. cracentis versus 40.6%–46.8% of HL in C. maxillaris), the orbital width (37.0%–40.0% of HL in C. cracentis versus 28.7%–34.6% of HL in C. maxillaris), and to a lesser degree on the pectoral-fin length (17.9%–20.0% of SL in C. cracentis versus 15.1%–18.2% of SL in C. maxillaris).

DESCRIPTION.—Morphometric and meristic data for Creagrutus cracentis in Table 15. Overall appearance of head and body distinctly elongate compared to most congeners; elongation particularly pronounced in smaller paratypes. Greatest body depth at vertical through dorsal-fin origin. Dorsal profile of head smoothly rounded from margin of upper jaw approximately to vertical through posterior nostril in specimens of all examined sizes; nearly straight from that point to rear of supraoccipital spine. Interorbital region slightly convex or flat. Dorsal profile of body straight to slightly convex from tip of supraoccipital spine to dorsal-fin origin, barely angled at dorsal-fin base. Ventral profile of head and body gently convex from isthmus to anal-fin origin.

Characters A B

Morphometrics

Standard length 38.3 21.5–33.3

1. Snout to anal-fin origin 66.5 63.7–67.3

2. Snout to pelvic-fin insertion 46.2 46.3–48.3

3. Snout to pectoral-fin insertion 23.2 23.4–25.1

4. Snout to dorsal-fin origin 46.2 46.4–47.0

5. Dorsal-fin origin to hypural joint 54.0 51.2–54.1

6. Dorsal-fin origin to anal-fin origin 28.7 26.6–28.2

7. Dorsal-fin origin to pelvic-fin insertion 19.1 16.5–20.1

8. Dorsal-fin origin to pectoral-fin insertion 28.1 25.6–27.8

9. Caudal peduncle depth 9.2 9.2–9.9

10. Pectoral-fin length 19.3 17.9–20.0

11. Pelvic-fin length 13.8 13.5–15.0

12. Dorsal-fin length 19.5 18.0–19.5

13. Anal-fin length 15.7 14.6–16.2

14. Head length 26.1 25.9–26.8

15. Postorbital head length 38.0 36.8–38.0

16. Snout length 26.0 25.7–28.1

17. Bony orbital diameter 37.0 38.0–40.0

18. Interorbital width 25.0 25.2–27.1

Meristics

Lateral line scales 39 39–40

Scale rows between dorsal-fin origin and lateral line 4 4

Scale rows between anal-fin origin and lateral line 3 3

Predorsal median scales 9 9

Branched dorsal-fin rays 8 8

Branched anal-fin rays 10 9–10

Branched pelvic-fin rays 7 6–7

Pectoral-fin rays 14 13–14

Vertebrae 37 38–39

Head pointed anteriorly in lateral view and more so in dorsal view. Upper jaw slightly longer than, and slightly overhanging, lower jaw. Anterior portion of mouth nearly horizontal. Ventral margin of upper jaw gently curved and relatively longer than in all congeners with exception of Creagrutus maxillaris. Anterior surface of snout not as fleshy as in all congeners other than C. maxillaris; with numerous minute papillae over anterior surface. Papillae also along ventral margin of upper lip, dorsal margin of lower lip, and anterior and anterolateral surfaces of lower jaw. Plicae and fleshy flaps extending between outer and medial premaxillary teeth of most Creagrutus species absent. Lower lip not as fleshy anteriorly as in other Creagrutus species.

Infraorbital series well developed. Third infraorbital well developed, with ventral margin nearly in contact with horizontal limb of preopercle. Posterior margins of third through fifth infraorbitals nearly in contact with vertical limb of preopercle.

Premaxillary dentition unusual for Creagrutus species, with only two distinct rows of teeth. Outer row consisting of 3 teeth arranged in slightly irregular series. First and third teeth of outer row unicuspidate, middle tooth with very weak lateral cusps. Inner tooth row on premaxilla consisting of 4 teeth, all with middle cusp distinctly more developed; medial and two lateral teeth tricuspidate, second tooth in series penticuspidate with very small lateral cusps. Elongate maxilla with 8 or 9 tricuspidate teeth with central cusp longer and typically somewhat posteroventrally curved. Dentary teeth 10 to 12; anterior 3 teeth largest and following teeth progressively smaller. Two anterior dentary teeth quadricuspidate, with second cusp distinctly larger than others; third through ninth teeth tricuspidate, with central cusp stronger and varyingly posteriorly recurved; tenth through twelfth teeth conical (when 11 or 12 teeth present).

Dorsal-fin rays ii,8. Dorsal-fin origin anterior to vertical through pelvic fin-insertion. Profile of distal margin of dorsal fin slightly concave. Anal-fin rays ii,9–10. Profile of distal margin of anal fin concave. Mature males with hooks on anal- fin rays limited to posterior margin of basal and middle segments of the first and second branched rays. Pectoral-fin rays i, 12–13. Tip of pectoral fin reaching posteriorly approximately one-half of distance to pelvic-fin insertion. Pelvic-fin rays i,6,i or i,7. Larger mature males with hooks on all branched rays other than medialmost ray. Tip of pelvic fin extending posteriorly approximately two-thirds of distance to anus.

Gill rakers 6–7 +10–11.

COLORATION IN ALCOHOL.—Overall coloration light tan. Dorsal surface of head with superficial small dark chromatophores. Surface of brain covered with larger, deep-lying, stellate, dark chromatophores, latter pigmentation masked by thicker bones and adipose deposits in larger individuals. Snout and upper jaw with scattering of small, dark chromatophores slightly more concentrated anterior to nares. Scattered chromatophores on lower jaw and on dorsal portions of opercle and infraorbital series. Distinct concentration of chromatophores anterior to nares and along ventral and posterior margins of orbit present in other Creagrutus species not apparent in C. cracentis. Lateral and dorsolateral portion of body with scattered chromatophores. Faint band formed by small dark chromatophores on midlateral surface of body of smaller specimens; distinction between midlateral band and dorsolateral pigmentation on body becoming increasingly obscure anteriorly with increasing size such that midlateral band is only discrete on posterior one-third of body in specimens of greater than approximately 25 mm SL. Humeral mark vertically elongate, very slightly anteriorly concave, extending from slightly above horizontal through pectoral-fin insertion to approximately one scale width from dorsal midline. Pigmentation of humeral mark most intense in region centered along lateral line, variably less intense in its dorsal and ventral portions.

Dorsal-fin ray margins and membranes with small dark chromatophores. Basal portions of anterior branched anal-fin rays outlined by chromatophores. Caudal fin with dark horizontal stripe formed by superficial chromatophores over middle caudal-fin rays; stripe more intense basally. Stripe on middle caudal-fin rays flanked dorsally and ventrally by 2 or 3 relatively unpigmented rays. Remaining caudal-fin rays with few scattered, dark chromatophores; chromatophores somewhat more concentrated along ray margins. Pectoral and pelvic fins with only few scattered, small, dark chromatophores.

ETYMOLOGY.—The specific name, cracentis, from the Latin for slender or graceful, refers to the slender body form of the species.

ECOLOGY.—The type series was collected on a sandy beach in slow water current with no bottom or floating vegetation and limited vegetation along the shoreline.

DISTRIBUTION.—Creagrutus cracentis is known only from the type locality in the lower portions of the Rio Tapajós (Figure 33, star).

COMPARISONS.—The only other Creagrutus species known from the Rio Tapajós basin is C. ignotus, which has been collected in the upper portions of that drainage basin. Creagrutus cracentis and C. ignotus differ in numerous features, most obviously in their dentition (see “Key to the Species of Creagrutus in the Amazon Basin”).

MATERIAL EXAMINED.—6 specimens (5, 21.5–38.3).

HOLOTYPE.—BRAZIL. Pará: Rio Tapajós, sandy beaches on an island located 5 km S of Itaituba (latter locality at 4°17′S, 55°59′W), collected by C.A.S. Lucena et al., 8 Dec 1991, MCP 15213, 1 (38.3).

PARATYPES.—5 specimens (4, 21.5–33.3).

BRAZIL. Pará: Rio Tapajós, sandy beaches on an island located 5 km S of Itaituba (latter locality at 4°17′S, 55°59′W), collected with holotype, MCP 22018, 3 (2, 21.5–26.3; other specimen with damaged snout), USNM 353862, 2 (26.1–33.3; 1 specimen cleared and counterstained for cartilage and bone).

Creagrutus cracentis és una espècie de peix de la família dels caràcids i de l'ordre dels caraciformes.

Creagrutus cracentis es una especie de peces de la familia Characidae en el orden de los Characiformes.

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Creagrutus cracentis Creagrutus generoko animalia da. Arrainen barruko Actinopterygii klasean sailkatzen da, Characidae familian.

纖細鈎齒脂鯉，為輻鰭魚綱脂鯉目脂鯉亞目脂鯉科的其中一個種，分布於南美洲Tapajós河下游流域，體長可達3.8公分，棲息在底中層水域，生活習性不明。