Melanorivulus interruptus, Volcan, Matheus V., Severo-Neto, Francisco & Lanes, Luis Esteban K., 2018

Volcan, Matheus V., Severo-Neto, Francisco & Lanes, Luis Esteban K., 2018, Unrecognized biodiversity in a world's hotspot: three new species of Melanorivulus (Cyprinodontiformes: Rivulidae) from tributaries of the right bank of the Rio Parana basin, Brazilian Cerrado, Zoosystematics and Evolution 94 (2), pp. 263-280 : 263-266

Melanorivulus interruptus sp. n.

Holotype.

MCP 53145, male, 32.3 mm SL, Brazil, Mato Grosso do Sul State, municipality of Campo Grande, first order stream, in the headwaters of Rio Pardo, 20°28 ’11” S, 54°29 ’25” W, altitude 589 m a.s.l.; M.V. Volcan & L.E.K Lanés, 13 Dec 2016.

Paratypes.

MCP 53146, 4 males, 21.6-31.0 mm SL (1 C&S), 3 females, 22.5-29.0 mm SL, 1 juvenile, sex undetermined, 16.9 mm, all collected with the holotype. ZUFMS 5409, 7 females, 20.2-26.0 mm SL (3 C&S), same locality as holotype; F. Severo-Neto, T.R.F. Sinani & S. Ichikawa, 5 Aug 2017.

Diagnosis.

Melanorivulus interruptus is distinguished from all species of the M. pictus group, except M. nigromarginatus , by the presence of oblique chevron-like bars interrupted, mainly on the midline of the flank in males (vs. bars continuous, vestigial, irregular or presence of longitudinal rows of red dots on the side of the body; never bars interrupted on the midline of the body). It is distinguished from all other species in the M. pictus species group, except M. planaltinus , M. leali and M. pictus , by the presence of a rounded dorsal fin (vs. slight pointed or pointed dorsal fin). In addition, M. interruptus differs from M. amambaiensis , M. apiamici , M. egens , M. faucireticulatus , M. ivinhemensis and M. leali by a higher caudal fin ray count (32-33 vs. 28-31); from M. egens , M. faucireticulatus , M. leali , M. litteratus , M. rutilicaudus and M. formosensis by the position of the anal-fin origin between the pleural ribs of 15th and 16th vertebrae (vs. 13th and 15th vertebrae); from M. apiamici , M. egens , M. faucireticulatus , M. pictus , M. polychromus and M. proximus by the dorsal-fin origin at a vertical through the base of the 8th anal-fin ray (vs. vertical through base of 7th or 9th-10th anal-fin ray); from M. amambaiensis , M. egens , M. faucireticulatus , M. ivinhemensis , M. planaltinus , M. polychromus , M. nigropunctatus , M. ofaie and M. formosensis by the dorsal-fin origin between neural spines of 18th and 19th vertebrae (vs. 19th and 22th); from M. egens , M. faucireticulatus , M. leali , M. litteratus , M. scalaris , M. vittatus , M. linearis and M. proximus by the tip of pelvic fin reaching the urogenital papilla in males (vs. tip of pelvic fin reaching 1st to 4th anal fin ray). Another interesting diagnostic character is the presence of 8 rays in the pelvic fin in about 35% of the analysed specimens (vs. 5-7 rays, never 8 rays present in the pelvic fin).

Description.

Morphometric data are presented in Table 1. Males larger than females. Largest male examined 32.3 mm SL, largest female 29.0 mm SL. Dorsal profile slightly convex from snout to end of dorsal-fin base. Ventral profile convex from lower jaw to origin of anal-fin. Dorsal and ventral profiles of caudal peduncle nearly straight. Body slender, approximately cylindrical and compressed. Greatest body depth at pelvic-fin base. Snout weakly pointed in lateral view. Jaws short.

Short dorsal and anal fins. Dorsal-fin rays 9-10. Dorsal fin rounded in males and females. Dorsal-fin origin on vertical through base of 8th anal-fin ray, and between neural spines of 18th and 19th vertebrae. Anal-fin rays 12-13. Anal fin slightly pointed in males and females. Origin of anal fin at vertical through pleural ribs of 15th-16th vertebrae. Caudal fin rounded 32-33 rays. Pectoral fin rays 14. Pectoral fins rounded, with posterior margin reaching vertical at about 60-90% of length between pectoral-fin and pelvic-fin bases. Pelvic-fin rays 7-8. Pelvic-fin posterior tip reaching vertical at anus to 3rd anal-fin ray. Pelvic-fin bases in close proximity.

Scales cycloid. Body and head entirely scaled, except anterior ventral surface of head. Body squamation extending over anterior 15-25% of caudal-fin base. No scales on dorsal and anal-fin bases. Frontal squamation E-patterned; E-scales not overlapping medially; scales arranged in regular circular pattern around A-scale without exposed margins; transverse row of scales anterior to H-scale. Longitudinal series of scales 30-32; transverse series of scales 8-9; scale rows around caudal peduncle 16. No contact organs on flank and fins.

Cephalic neuromasts: supraorbital 3+3, parietal 1, anterior rostral 1, posterior rostral 1, infraorbital 1+9-11+1, preorbital 2, otic 1, postotic 1-2, supratemporal 1, median opercular 1, ventral opercular 1, preopercular 2+4, mandibular 2-3+1, lateral mandibular 1-2, paramandibular 1. Two neuromasts on caudal-fin base.

Six branchiostegal rays. Gill rakers on first branchial arch 1+7. First epibranchial slightly curved. Total number of vertebrae 29-30, 13-14 precaudal vertebrae, 16-17 caudal vertebrae. Ventral process of angulo-articular short, pointed. Vomerine teeth 1-3. Dermosphenotic present. Basihyal sub-triangular, greatest width 45-50% of length; basihyal cartilage 20-25% of total basihyal length. Second pharyngobranchial teeth absent.

Colouration in life.

Males (Figs 1 and 2). Flank light grey or light metallic blue; sometimes purple-blue close to anal fin; 7-9 oblique narrow red bars anteriorly directed, often forming chevron-like marks irregularly arranged and usually interrupted in the midline of the body; commonly, the chevron-like bars are vestigial in the anterior region and begin at the end of the pectoral fin; well-defined, but interrupted, bars begin behind insertion of the pelvic fins. Inconspicuous dark pigmentation between postorbital region and area above midlength of pectoral fin, forming an irregular mid-lateral dark stripe; vertical rows of reddish dots on antero-ventral part of flank, between pectoral and pelvic fins. Dorsum yellowish-grey, venter whitish-grey. Dorsal portion of the head yellowish-grey; ventral portion yellowish-grey or pale golden without dots, marks or any pigmentation pattern; pale golden-greenish iridescence on opercular region. Jaws dark grey or brown. Iris pale yellow to pale brown, sometimes with dark brown bars on anterior and posterior portions. Dorsal fin yellow with four or five narrow red bars. Anal fin yellow, basal portion light blue-whitish, posterior portion pale blue with two or three faint red marks; distal region becoming gradually dark red-brown. Caudal fin yellow with five to seven red oblique parallel bars, covered generally 1/3-1/2 of caudal fin on mid-dorsal portion, sometimes red bars inconspicuous; ventral portion light yellow without bars, distal ventral region becoming gradually dark red-brown with a not well delineated margin of orange-brown colour. Pectoral fin yellowish-hyaline. Pelvic fin yellow with posterior margin orange-brown.

Females (Fig. 2). Generally flank similar to males, but with paler colours. Venter white. Dorsum and dorsal portion of head yellowish-grey; ventral portion of head yellowish-grey without spots and without any colouration pattern. Jaws yellowish-grey or brown; opercular region pale greenish-gold. Dorsal fin yellow, with three or four faint grey bars on posterior region forming a reticulated pattern. Anal fin yellow; basal portion light blue; distal region becoming dark red-brown gradually; distal margin with high concentration of melanophores. Caudal fin pale yellow, with four or six grey bars usually interrupted in the inferior region (lower third of fin); a small irregularly shaped black spot on dorso-basal portion of fin, sometimes overlapping the first bar; faint grey margin. Pectoral fin hyaline or yellowish hyaline. Pelvic fin yellowish hyaline.

Distribution.

Melanorivulus interruptus is only known so far from a small stream, in the headwaters of the Rio Pardo, a tributary of the right margin of Rio Paraná, state of Mato Grosso do Sul, Brazil (Fig. 3).

Etymology.

The name interruptus , from the Latin adjective interrupted, referring to the presence of conspicuous oblique red bars forming chevron-like marks usually disrupted in the midline of the body in males.

Habitat.

The species was recorded in a typical Cerrado area, inserted into the urban area of Campo Grande town at an altitude of 594 m a.s.l.. It was recorded in a small first order creek, but was only captured in border areas with dense aquatic vegetation, mainly grasses (Fig. 4). The biotope, which is locally called “veredas”, a freshwater ecosystem comprising streams bordered by the buriti-palm, typically found in the Cerrado Biome, has moderate current speed. But, the place where the species was recorded is formed by small backwaters, with a clayey substrate and with a maximum depth of 10 cm. The species is encountered in areas exposed to the sun as well as in areas shaded by trees, mainly buritis-palm ( Mauritia flexuosa ). The region has a slightly undulating terrain and according to the classification of Koppen-Geiger has rainy summers and dry winters.

Conservation.

There are imminent threats to the population of M. interruptus : the stream is located in the Campo Grande urban area, which is developing rapidly around the area of the new species; there is a large real estate development alongside the stream that can cause significant impacts on the environment quality; the stream is crossed by a high traffic road and it is subject to accidents with potentially dangerous loads; besides, there are agricultural activities over its complete extension. Although larger collection efforts are likely to be undertaken in the area to better understand the species distribution pattern, M. interruptus appears to have a very restricted distribution. In the adjacent watersheds distinct species occur (e.g. M. apiamici in the mouth of the Rio Pardo, M. egens in the upper Rio São Domingos and M. nigropunctatus and M. ofaie in the Rio Verde - see Figure 4 with the distribution map of the M. pictus species group). Thus, according to the previously mentioned threats, a high degree of endemism and the observations made in the field, M. interruptus was considered “Vulnerable”, following the criteria of IUCN (2012). The species has an area of occupation of less than 2000 km², it occurs in only one locality and it suffers from a reduction in its occupation area and in its habitat quality (VU B2abii,iii).