Apareiodon agmatos, Taphorn, Donald C., López-Fernández, Hernán & Bernard, Calvin R., 2008

Taphorn, Donald C., López-Fernández, Hernán & Bernard, Calvin R., 2008, Apareiodon agmatos, a new species from the upper Mazaruni river, Guyana (Teleostei: Characiformes: Parodontidae), Zootaxa 1925, pp. 31-38 : 33-36

Apareiodon agmatos , new species

( Figs. 1–2 , Table 1 )

Holotype. CSBD F 1650, 66.3 mm SL; Guyana: Mazaruni River: sandy beach on right bank, downstream from village of Kamarang (5º56’10.1” N, 60º36’53.8” W); H. López-Fernández, D. C. Taphorn, E. Liverpool, K. Kramer, C. Thierens; 24 Apr 2008.

Paratypes. All specimens from Guyana, Mazaruni River drainage: ROM 83874, 2, 24.7–46.0 mm SL; collected with holotype. ROM 83755, 236, 21.4–63.2 mm SL; sandy beach and embayment on right bank, upstream from village of Jawalla (5º41’35.4” N, 60º28’11.8” W); H. López-Fernández, D. C. Taphorn, E. Liverpool, K. Kramer, C. Thierens; 18 Apr 2008. ROM 83765, 1, 42.0 mm SL; Kukui River approximately 1.5 km from confluence with Mazaruni (5º39’11.5” N, 60º28’12.3” W); H. López-Fernández, D. C. Taphorn, E. Liverpool; 19 Apr 2008. ROM 83750, 3, 61.2–80.4 mm SL; Ata Creek near its confluence with Mazaruni (5º41’23” N 60º28’14.4” W); D. C. Taphorn, H. López-Fernández, E. Liverpool; 18 Apr 2008. ROM 83736, 4, 38.8–46.8 mm SL; sandy beach opposite to the mouth of Kukui River at village of Jawalla (5º40’21.2” N, 60º28’58.6” W); H. López-Fernández, E. Liverpool, D. C. Taphorn, C. Thierens; 17 Apr 2008. AUM 47714 (ex ROM 83755), 5, 40.6–57.7 mm SL. ANSP 187448 (ex ROM 83755), 5, 42.8–51.7 mm SL. FMNH 117790 (ex ROM 83755), 5, 43.7–49.4 mm SL. MBUCV-V-35375 (ex ROM 83755), 5, 43.2–52.5 mm SL. CSBD F1651 (ex ROM 83755), 5, 39.3–45.5 mm SL. MCNG 56000 (ex ROM 83755), 5, 39.2–50.1 mm SL. MNRJ 32486 (ex ROM 83755), 5, 44.0–48.9 mm SL. NUP 5950 (ex ROM 83755), 5, 41.6–49.1 mm SL. NCSM 48264 (ex ROM 83755), 5, 38.1–45.2 mm SL.

Additional material examined: Radiographs of Apareiodon gransabana USNM 267917. Apareiodon gransabana AUM 36502, 1; Apareiodon itapicuruensis AUM 20598, 14; Apareiodon orinocensis AUM 43479, 4; 43479, 3; 43629, 3; Parodon apolinari AUM 36536, 3; 22766, 1; 35433, 1; Parodon bifasciatus AUM 36813, 15; 36814, 1; 36815, 1; 38265, 1; Parodon pongoense AUM 46665, 3; Parodon guyanensis AUM 38766, 50; 38981, 19; 39007, 9; 38159, 50; Parodon suborbitalis MCNG 4624, 20; 7802, 27; 8681, 22; Saccodon caucae MCNG 47833, 3; Saccodon wagneri AUM 4229, 2; 21558, 1.

Diagnosis: Apareiodon agmatos is distinguished from all other known parodontid species by having an incomplete lateral line with only the anterior five to 14 scales perforated by the lateral line canal. The species is also distinguished by having more numerous scales than all congeners: 19–25 predorsal scales vs. 16 or fewer and 16–17 transverse scales vs. nine to 11. The new species can be further distinguished from all its congeners (except A. gransabana ) by its color pattern, consisting of a dark stripe along the dorsal midline (present in most Apareiodon species) combined with four additional narrow lateral stripes on the sides. The second stripe on the midlateral surface includes the perforated lateral series of scales and is the widest and darkest. It continues anteriorly through the eye onto the snout and posteriorly onto the middle caudal-fin rays. Each premaxilla has five teeth, a character it shares only with Apareiodon gransabana and Parodon guyanensis . The premaxillary teeth usually have one large central spatulate cusp bordered on each side by one (two in one individual examined) minute lateral cusp on either side vs. more than 9 cusps in all other species of the family.

Description: Morphometric data are presented in Table 1 . Aspects of body shape in lateral profile are evident in Figure 1 . Dorsal profile convex from tip of snout to dorsal-fin origin and straight to gently concave from posterior limit of dorsal-fin base to adipose fin, concave from adipose fin to upper margin of caudal fin. Ventral profile convex from snout to pelvic fin, concave at pelvic-fin insertion then convex from this point to anal fin, strongly concave from anal fin to caudal fin. Body rounded dorsally in cross section, ventral profile generally rounded. Caudal peduncle slightly compressed. Snout broad and rounded. Eyes on lateral surface of head, edge of orbit with slight development of adipose eyelid, strongest along antero-dorsal margin. Mouth sub-terminal. Upper lip indistinct from and continuous with snout skin (sometimes described as “absent”). Nostrils adjacent, the anterior opening horizontally oval and encircled by skin fold which projects slightly over round to oval larger posterior opening which lacks skin fold. Breeding tubercles not observed. Gill membranes joined together but not connected to isthmus; isthmus scaled. Gill rakers very thin, lamellar, very close together. Epibranchial gill rakers 64–85, ceratobranchial gill rakers 66–74 (counted in paratypes only to avoid damage to holotype). Total vertebrae: 39(1), 40(4), 41(1), holotype not radiographed.

Premaxilla with 5*(20) teeth, maxillary with 2*(19), 3(1) teeth. Premaxillary teeth spatulate, peduncle not much exposed, one or two minute lateral cusps present on either side of large central cusp. Teeth flattened in cross-section, with cutting edge flat. In a few individuals, one tooth bilobed. Maxillary teeth aligned in straight line, similar to premaxillary teeth and aligned with them in smaller specimens, rarely with cutting margin divided into two unequal shallow lobes ( Fig. 2 ). In most adult parodontids the premaxillary teeth have an unusual orientation, lying flat along the horizontal axis of the body with the tips pointing back (caudad). In A. agmatos the teeth are in a more typical position for fish, that is in a vertical position perpendicular to the horizontal axis of the body with the tips pointing down (ventrally). Lower jaw edentulous and with straight anterior border.

Dorsal-fin rays ii,9(20); anal ii,5(1), ii,6(2), ii,7(15)*, ii,8(1); pectoral i,8(1), i,9(11)*, i,10(7), i,11(1); pelvic i,6(1), ii,7(19)*; caudal-fin rays 10 upper lobe, 9 lower (20). Dorsal-fin origin anterior to vertical through pelvic-fin insertion and slightly nearer to snout than to base of caudal fin; tip of depressed dorsal-fin rays reaching slightly posterior of vertical line through tips of depressed pelvic-fin rays, but not reaching adipose fin. Pectoral fin short and pointed, neither its rays nor the membranes are thickened or enlarged as in some species of Parodon . Tip of longest pectoral-fin ray reaching posteriorly more than half distance to vertical through dorsal-fin origin. Anal-fin base short, distal margin slightly rounded or straight. Adipose fin well developed, inserted just behind vertical through posterior margin of anal-fin base. Caudal fin with broad, equal lobes, not strongly forked, middle rays more than half length of longest ray.

Body scales cycloid, regularly distributed on predorsal region, less regular on ventrum between isthmus and anus. Lateral scales 46(1), 47(1), 48(3), 49(6)*, 50(4), 51(1), 52(2), 53(1), 54(1); predorsal 19(1), 21(3), 22(5), 23(8)*, 24(1), 25(1); tube-bearing lateral scales 5(1), 8(4), 9(3), 10(2)*, 11(2), 12(2), 13(4), 14(2). Scales between lateral line and dorsal-fin origin 8(20). Scales between lateral line and pelvic-fin origin 8(20). Circumpeduncular scales 20(2), 22(12)*, 24(5). Scales from rear limit of dorsal-fin base to adipose fin 12(1), 14(1), 15(6), 16(5), 17(6)*, 19(1). Scales from adipose to caudal fin 7(6), 8(6), 9(4)*, 10(4). Scales from isthmus to anterior margin of anus 36(1), 37(2), 38(2), 39(2), 40(4)*, 41(4), 42(1), 43(2), 44(1), 45(1). Scales between anus and anal-fin origin 0(9)*, 1(11). Small axillary scale present, its tip extending about three scales posteriorly. Base of caudal fin covered by two to four rows of scales. Anal-fin rays anteriorly covered by a row of three or four scales forming narrow sheath.

Color in alcohol ( Fig. 1 ): Ground color of body white, tan or light yellow. Head dark dorsally, white ventrally. Dorsal region darker along midline, with scales outlined in black ventrally to first lateral stripe. Dorsal most of four dark lateral stripes originates on head, one scale row dorsal to edge of operculum and extends to upper caudal-fin base, sometimes continuing onto fin. Second lateral stripe darkest and widest, covering lateral line series and ¼ of series above and below that series, originating on snout, passing through eye across opercle and continuous along midlateral surface to middle caudal-fin rays. Pored lateral-line scales run through middle of stripe. Third stripe very narrow, originating behind middle posterior margin of opercle, located two scale rows below pored lateral line scales, forming a zigzag along scale margins and continuing caudally to vertical through adipose fin origin. Fourth stripe originates behind pectoral-fin base, five or six scales below pored lateral line scales. Stripe narrow, often forming zigzag along scale margins; often faint, extending caudally to above anal-fin base which it parallels, then curving along postero-lateral edge of caudal peduncle to terminate at base of lower most caudal-fin rays, sometimes continuing onto rays. Dorsal, pectoral, pelvic and anal fins hyaline to whitish. Caudal-fin lobes dusky with pigment concentrated along rays. Concentration of pigment forming irregular blotch at bases of upper most and lower most caudal-fin lobes (an extension of the dark lateral stripes). Five to seven broad, faint transverse bars between first and second lateral stripes sometimes visible.

Distribution: Figure 3 . Apareiodon agmatos is known from the upper Mazaruni River basin in Guyana.

Etymology: Agmatos is a Greek noun meaning “fragment”, derived from agmos, meaning break or fracture, in reference to the incomplete lateral line that distinguishes Apareiodon agmatos from all other parodontids. To be regarded as an adjective in masculine form.

Ecological notes. Contrary to most other species of Apareiodon and most Parodontidae , Apareiodon agmatos appears to inhabit backwaters or streams with little or no current. Substrate was generally a mixture of sand and mud, frequently with abundant flocculent sediments and leaf litter. Finer sediments were dominant in a quiet side embayment of the Mazaruni River where the fish were collected from large schools. Radiographs revealed an extremely long intestinal tract, which along with the unusually high gill-raker counts and the habitat preferences, suggest a detritivorous diet (e.g. Kramer & Bryant, 1995). This is in contrast with other taxa in the family which are generally thought to be periphyton scrapers (e.g. Flecker 1992).

Figures

FIGURE 1. Holotype of Apareiodon agmatos CSBD F 1650 66.3 mm SL; Guyana: Mazaruni River: sandy beach on right bank, downstream from village of Kamarang (5 º 56 ’ 10.1 ” N, 60 º 36 ’ 53.8 ” W).

FIGURE 2. Apareiodon agmatos n. sp. Teeth in ventral view. ROM 83755, 49.0 mm SL.

FIGURE 3. Known distribution of Apareiodon agmatos in the upper Mazaruni river basin (black triangles). Records of A. gransabana represented by specimens deposited at MCNG (circles) are provided for comparison. Notice the proximity of the upper Mazaruni river and upper Río Caroní drainages. One symbol may represent more than one collection locality.

Tables

TABLE 1. Selected morphometrics of Apareiodon agmatos (n = 20). Measurements are percentages of Standard length (SL) or Head length (HL) as indicated.

	Holotype	n Mean	Minimum	Maximum
SL	66.3	19 52.6	40.0	81.0
Percent SL
Head length	21.9	19 23.1	21.6	25.3
Predorsal length	48.9	19 50.0	48.5	52.5
Caudal peduncle length	16.6	19 18.0	15.2	20.9
Least caudal peduncle depth	9.7	19 8.7	7.8	9.8
Body depth at dorsal-fin origin	20.8	19 21.0	18.1	22.2
Dorsal-fin length	18.4	19 19.1	17.7	20.6
Anal-fin length	11.8	18 12.9	11.7	15.7
Pectoral-fin length	15.4	19 16.1	13.4	17.6
Pelvic-fin length	11.9	19 13.3	11.6	16.4
Pre-anal length	76.2	19 76.0	74.7	79.0
Percent HL
Snout length	29.7	19 29.7	26.1	33.0
Orbital diameter	32.4	19 32.1	29.2	35.7
Interorbital diameter	34.5	19 31.5	26.0	35.4
Head width	48.3	19 47.6	43.5	50.9
Lower jaw width	23.4	19 18.8	17.6	23.2
Head depth	66.9	19 64.1	58.7	68.2