Spintherobolus leptoura,, 1999

Weitzman, Stanley H. & Malabarba, Luiz R., 1999, Systematics of Spintherobolus (Teleostei: Characidae: Cheirodontinae) from eastern Brazil, Ichthyol. Explor. Freshwaters 10 (1), pp. 1-43 : 35-39

Spintherobolus leptoura, new species

( Figs. 36-37 )

Holotype. MZUSP 41854 , male, 19.1 mm SL; rio Quilombo , fazenda Dalila , Registro, São Paulo, Brazil; 16 Feb 1990, M. Damato & O. Oyakawa .

Paratypes. MZUSP 51023 , 2 males, 17.2-19.6 mm SL, 7 immature - females, 16.2-27.2 mm SL, 1 male, c&s, 19.9 mm SL, 1 female, c&s, 25.2 mm SL ; USNM 346386 , 1 male, 21.8 mm SL, 2 immature - females, 16.2-25.0 mm SL ; MCP 19254 , 1 male, 18.9 mm SL; 2 immature - females, 16.6- 25.4 mm SL; collected with holotype .

Diagnosis. Most elongate and slender species, adult males differing from other small species by caudal peduncle depth and body depth ( Figs. 24 , 25 , 38 ). Body depth in S. leptoura 26.6-29.7, x = 28.3 % SL, versus 29.3-37.9, x = 34.2 in S. ankoseion ( Fig. 24 ), and 29.2-32.8, x = 30.5 in S. broccae. Caudal peduncle depth in S. leptoura 11.0-13.1, x = 12.3 % SL, versus 12.8-15.6, x = 14.8 in S. ankoseion , and 12.6-15.1, x = 13.8 in S. broccae. Although these ratios overlap in juveniles, they do not in adult males and females as demonstrated by Figures 24 and 25 .

Description. Morphometric data are summarized in Table 5 . Body compressed and relatively elongate. Predorsal body profile slightly convex with a slight concavity at nape. Body profile along dorsal-fin base posteroventrally inclined becoming straight or slightly concave between dorsal and caudal fins in females and nearly straight to slightly convex in males. Ventral profile from tip of mandible to pelvic-fin origin convex and slightly concave between pelvic- and anal-fin origins. Entire body profile along anal-fin base concave in females. This same profile convex in anterior anal-fin lobe of males. Remaining posterior anal-fin body profile nearly straight and continuous with straight or nearly straight caudal peduncle profile. Ventral profile of caudal peduncle somewhat concave in females, but straight and slightly serrated in males because of prominent ventral procurrent caudal-fin rays.

Snout short, shorter than eye diameter. Mouth terminal, angled posteroventrally; maxilla reaching line drawn vertically through anterior mar ­ gin of eye.

Dorsal-fin rays, ii, 9 in all specimens. Dorsal-fin origin slightly posterior to midbody. Adipose fin absent.

Anal-fin rays iii, 14 (anterior unbranched rays iii-iv, x = 3.1, n = 16; branched anal-fin rays 12-14, x = 12.6, n = 16). Anterior lobe of anal fin of males strongly developed, rounded profile. Distal tip of longest (and largest) rays reaching posteriorly beyond distal tip of most posterior anal-fin rays. Distal profile of posterior anal-fin lobe concave. Distal profile of entire anal fin in females concave, with length of first 6 branched rays decreasing in size and posterior rays smaller, near ­ ly of equal size. Branched anal-fin rays 1 -5 of males very large, and rays 2 to 4 most enlarged and best developed, becoming more than 5 times wider than following posterior rays. Rays 2-4 with a process on anteroproximal face of each lepidotrich. Processes inserted between lepidotrichia of next anterior ray. Each bony ray segment of posterior branch of branched rays 2 to 4, and sometimes also first and fifth branched rays, not rectangular as other branches of same ray, but all with a posteroventral acute and elongate angle extending towards distal tip of that fin ray. Segments of branched fin rays 2 to 4 progressively fused to each other. Holotype only specimen with hooks. These on two segments of first branched ray. Hooks extremely reduced, with 2 or 3 hooks on posterior face of both segments.

Pectoral-fin rays i,9 (branched rays 8-11, x = 8.9, n = 14). Posterior tip of longest pectoral-fin ray extended beyond pelvic-fin origin in both males and females. Pelvic-fin rays, i, 5 in all counted specimens (n = 18). Tip of longest ray reaching to or beyond anal-fin origin in both sexes. Pelvic fin of males with short, wide-based hooks on ventromedial face of unbranched ray and first two branched rays (one male had them on first to third branched rays) along almost their total length.

Principal caudal-fin ray count 10/ 9. Dorsal procurrent caudal-fin rays 9 (7- 10, x = 8.8, n = 9). Ventral procurrent caudal-fin rays, 15 (13-15, x = 14.1, n = 10). Ventral procurrent caudal-fin rays of males strongly-developed, with their proximal tips fused, slab shaped, and expanded in a sagittal plane. Four or five posteriormost caudal (preural) vertebrae (including posterior half centrum) supporting caudal fin and procurrent rays and bearing large, modified hemal spines. Those elements anterior to hemal spine of antepenultimate vertebra fused to each other and having lateral bony processes between muscles and skin. Proximal tips of anterior ventral procurrent rays undeveloped.

Scales cycloid. Lateral line with 4 perforated scales (n = 10). Scales in longitudinal series 33 (n = 3). Scale rows between dorsal-fin origin and lateral-line series 5 (n = 6), and between lateralline series and pelvic-fin origin 5 (4-5, x = 4.5, n = 6). Scale rows around caudal peduncle 14 in all countable specimens (n = 2). No modified scales on caudal fin. Scale sheath along anal-fin base absent.

Teeth. All jaw teeth with basal pedicle and somewhat laterally expanded distal conical cusp. Anterior dentary teeth tricuspid but each with single cusp laterally and posteriorly. Premaxillary and maxillary teeth all conical. Premaxillary teeth 7-8, maxillary teeth 5-6 and dentary teeth 10-11 in 2 c&s specimens.

Vertebrae 33 (range = 32-34, x = 32.9, n = 16). Branchiostegal rays 4 in two cleared and stained specimens, arranged as in other species.

Color in alcohol. See Figures 36-37 for the approximate preserved and similar color patterns of adult males and females. A discrete lateral body stripe extends from just dorsal to the dorsalmost part of the gill opening to the caudal peduncle where it continues onto the caudal fin as a very solid dark wedge with its apex covering the two middle caudal-fin rays. The dark stripe consists of a dusting of dark chromatophores anterior to the pseudotympanum area and this continues posterior to this, merging with the dark lateral stripe that becomes dense with dark chromatophores external to the dorsal region of the abdomen. This stripe increases in width, and density posteriorly to the base of the caudal fin. In the photographs of a male and female ( Fig. 36- 37 ), there appears to be a dark humeral spot just posterior to the more dorsal region of the opercular flap. This is the area of the anterior and posterior pseudotympanums and the black pigment coating the swimbladder can be seen through the skin, appearing black in the print.

The scale borders above the lateral dark stripe are covered by a single row of dark chromatophores, giving the dorsal part of the body a retic ­ ulate pattern. Just ventral to the stripe the scale borders continue to be dark for about one to one half the width of a scale row. The belly and sides ventral to the lateral stripe are pale cream color or yellowish (the color of preserved muscle tissue) and the ventrolateral surface of the abdomen may be covered with dark chromatophores of varying density. The posterior termination of the caudal peduncle, both dorsal and ventral to the lateral stripe, is white, without dark pigment of any kind, except for the procurrent caudal-fin rays in this region which are covered with dark chromatophores.

The pectoral and pelvic fins of both sexes are hyaline with scattered dark chromatophores, especially on the anterior undivided ray of both fins. The dorsal fin is more or less hyaline except for its anterior dorsal border where the anterior undivided rays and the first and second branched rays have numerous dark chromatophores. The rays posterior to these dark rays progressively have fewer dark chromatophores distally. The caudal fin is hyaline, especially for the proximal one third of its length. There is a thin scattering of small dark chromatophores over the rays and membranes, especially along their distal length. A second longitudinal dark, but relatively broad stripe covers the muscular anterior base of the fin and extends posteriorly to almost completely cover the short anal-fin rays that follow the large, elongate, anterior anal-fin lobe. The anterior lobe of the anal fin, distal to its muscular base is hyaline except for the basal one third the distal tips of the anterior unbranched and the first two branched rays. These are covered with dark chromatophores.

The head is pale brown around the mouth with a scattering of dark chromatophores over the ventral surface of the snout, jaws, and oper ­ cular region. The snout region, especially the jaws possess a scattering of dark chromatophores. The dorsal surface of the snout and the area between the eyes are pale brown, while the dorsum of the cranium and the nape are dark brown. The head area posterior to the eye and extending ventrally from the parietal region to the preopercle and branchiostegal rays is white except for some dark chromatophores in the dorsal region of the oper ­ cle. The circumorbital region ventral to the eye is dark, with a series of dark chromatophores, giving the impression of a spot ventral to the eye when these chromatophores are expanded. The opercular region is dark dorsally and pale brown to white below in both sexes.

Color in life. Life colors have not been recorded, but we expect that life colors are very much like those in preservative except that the dark stripes are usually black, the abdominal region white and the two white areas at the posterior termination of the caudal peduncle are intense white.

Sexual dimorphism. The sexes are easily identified externally by the shape of anal fins ( Figs. 36- 37 ). The distal border of the anal fin of females is concave and the anterior lobe has an acute distal tip. When this lobe is depressed it does not reach the posterior termination of the fin. The anterior lobe of the anal fin of males is largely rounded, with the tip of largest rays reaching beyond the tip of last anal-fin rays. The shape of first to fifth branched anal-fin rays, the modified ventral procurrent caudal-fin rays and the presence of hooks in the pelvic fins are also characteristic for males.

Etymology. The word leptoura is from the Greek leptos meaning small, thin or delicate and oura, Greek for tail. The name is given in reference to the relatively slender caudal peduncle of this species. A noun in apposition.

Ecological notes. We have no ecological infor ­ mation about this species.

Figures

Fig. 36. Spintherobolus leptoura, MZUSP 41854, holotype, adult male 19.1 mm SL, Brazil, São Paulo, fazenda Dalila, Registro.

Fig. 37. Spintherobolus leptoura, MZUSP 41854, paratype, adult female 25.0 mm SL, Brazil, São Paulo, fazenda Dalila, Registro.

Fig. 24. Graph of body depth as a function of standard length for Spintherobolus leptoura (black symbols) and S. ankoseion (empty symbols). Axes are logarithmic. Note that the 95 % confidence intervals in lengths of about 21 to 28 mm SL do not overlap with the means of the of the compared species indicating a significant difference in these size ranges. These growth pattern differences are used to separate these species in the key and text.

Fig. 25. Graph of caudal peduncle depth as a function of standard length for Spintherobolus leptoura (black symbols) and S. ankoseion (empty symbols). Axes are logarithmic. Note that the 95 % confidence intervals in lengths of about 21 to 27 mm SL do not overlap with the means of the compared species indicating a significant difference in these size ranges. These growth pattern differences are used to separate these species in the key and text.

Fig. 38. Graph of caudal peduncle depth as a function of standard length of Spintherobolus leptoura (black symbols) and S. broccae (empty symbols). Axes are logarithmic. Note that the 95 % confidence intervals in lengths of about 18 to 24 mm SL do not overlap with the means of these of the compared species indicating a significant difference in these size ranges. Comparison of these growth patterns are discussed under the diagnosis of S. leptoura.

Tables

Table 5. Morphometries of Spintherobolus leptoura. Table includes measurements of all type specimens. Values for the holotype are given separately.

	holotype	males				females
		n	low	high	mean	n	low	high	mean
Standard length [mm]	21.8	6	17.3	21.8	19.5	12	16.2	27.2	20.9
Percentage of standard length
Snout to anal-fin origin	58.7	6	57.3	61.9	58.9	12	58.6	62.2	60.5
Snout to dorsal-fin origin	56.0	6	53.8	56.0	55.3	12	53.5	57.0	55.5
Snout to pelvic-fin origin	44.5	6	42.2	44.5	43.4	12	37.4	45.1	41.6
Dorsal-fin base length	11.3	6	11.3	12.5	11.7	12	9.6	12.9	11.5
Anal-fin base length	21.1	6	21.1	22.9	21.9	12	21.0	24.0	22.8
Caudal peduncle length	18.4	6	16.7	21.5	18.8	12	15.2	18.1	163
Caudal peduncle depth	12.4	6	11.0	13.1	12.3	12	9.5	13.5	11.8
Depth at dorsal-fin origin	27.5	6	26.6	29.7	28.3	12	26.6	33.7	29.9
Dorsal-fin length	25.7	6	22.5	28.6	26.4	12	23.0	29.4	26.2
Pelvic-fin length	20.2	6	17.8	20.2	18.8	12	14.2	19.0	17.0
Pectoral-fin length	17.9	5	15.6	17.9	16.9	10	14.6	19.0	16.3
Bony head length	28.9	6	28.9	30.4	29.3	12	26.1	30.2	28.2
Percentage of head length
Snout length	19.5	6	19.0	22.4	19.9	12	18.9	23.2	20.9
Upper jaw length	19.5	6	19.0	21.4	19.9	12	18.4	22.9	21.0
Horizontal eye diameter	27.0	6	25.9	28.1	26.9	12	23.2	30.3	27.4
Least interorbital width	27.0	6	26.3	29.3	27.5	12	25.5	30.3	27.9