Monotocheirodon kontos, A.Menezes & Weitzman & Quagio-Grassiotto, 2013

A. Menezes, Naércio, Weitzman, Stanley H. & Quagio-Grassiotto, Irani, 2013, Two New Species And A Review Of The Inseminating Freshwater Fish Genus Monotocheirodon (Characiformes: Characidae) From Peru And Bolivia, Papéis Avulsos de Zoologia 53 (10), pp. 129-144 : 139-143

Monotocheirodon kontos , new species

Figs. 12-15 , Table 3

Monotocheirodon sp. – Burns & Weitzman, 2006: 529-530 ( MUSM 6756 and 11250).

Monotocheirodon personi [sic] – Ferreira et al. 2011 (misidentification; MUSM 11416, listed in comparative material).

Specimens examined: All specimens from Peru.

Holotype: MUSM 41542 , male, SL 33.5 mm, Río Inambari , Sandia, Muspaypampa, 14°14’41”S, 69°25’51”W, 6 July 1994, Fonchii Chang.

Paratypes: MUSM 6756 (4, SL 22-37.1 mm) collected with holotype . MUSM 11644 (2, SL 30.7 and 31.3 mm), Ouno, Sandia, Zona Reservada Tambopata-Candamo , cuenca Ebebahuaeji, 13°24’ 52”S, 70°00’48”W . MUSM 11250 (4, SL 24.5-31.3 mm) , USNM 405297 (2, SL 26.8 and 28.5 mm), Río Malinowski (empties into Rio Madre de Dios), Zona Reservada Tambopata-Candamo, 13°08’00”S, 70°17’00”W .

Diagnosis: M. kontos has a urogenital papilla in sexually active males and females which is absent in M. pearsoni . The urogenital papilla in M. kontos is about equal length of anal-fin base versus half length of anal-fin base in M. drilos . Females and juveniles of M. kontos and M. drilos can be distinguished in the height of dorsal fin (13.4-15.8% of SL in the former versus 16.1-17.8 in the latter). The number of premaxillary tooth cusps (7 in M. kontos versus 5 in M. drilos ) differentiate adult males and females of both species.

Description: Morphometrics of holotype and paratype presented in Table 3. Stevardiin characid reaching at least 37.1 mm SL. Body cylindrical in cross section; greatest body depth situated between verticals through tip of pectoral fin and dorsal-fin origin. Dorsal profile of head anterior to nape strongly convex in males, slightly convex in females to snout region dorsal to nostril. Snout bluntly convex; tip of snout situated along horizontal through approximate mid-point of orbit. Lower jaw convex in ventral profile and somewhat included below upper jaw. Ventral profile of head gently convex, continuous with gently convex in males and strongly convex abdominal region in females extending to anal-fin origin. Body profile along anal-fin base approximately straight to slightly convex to posterior termination of anal fin. Ventral profile of caudal peduncle almost straight in males, slightly convex in females. Dorsal profile of body between nape and dorsal-fin origin gently convex. Base of dorsal fin straight and somewhat inclined posteroventrally. Body profile between basal of last dorsal-fin ray and caudal-fin rays almost straight in males, slightly concave posterodorsally in females

Unbranched dorsal-fin rays 2 in all specimens, branched rays 7-8, 7.7, (8), n = 13, SD = 0.5; posterior ray not split to its base. Dorsal-fin height sexually dimorphic (see discussion under Sexual dimorphism). Adipose fin absent. Unbranched anal-fin rays ii or iii, most usually ii; branched rays 10-11, 10.1, (10), n = 13, SD = 0.4; posterior ray split to its base and counted as one ray. No hooks present on anal fin of mature males. Pectoral-fin rays i, 8-9, 8.5, (8) n = 13, SD = 0.5. Tip of pectoral fin falling short of pelvic-fin origin. Pectoral-fin rays lacking hooks. Pelvic-fin rays i, 5, i, n = 13. Sexually active males lacking pelvic-fin hooks. Pelvic-fin length of sexually mature males sexually dimorphic (see under Sexual dimorphism). Principal caudal-fin rays 10/ 9 in all specimens.

Scales cycloid: Lateral line complete, perforated scales 36-38, 37.1, (37) n = 12, SD = 0.6. Predorsal scales 13-15, 14.2, (15), n = 12, SD = 0.7. Scale rows between dorsal-fin origin and lateral line 4-5, 4.6, (4), n = 12, SD = 0.5. Scale rows from pelvic-fin origin to lateral line 2-3, 2.7, (2), n = 12, SD = 0.4. Scale rows around caudal peduncle 10 in all specimens, n = 12. Row of enlarged scales along anal-fin base.

Premaxilla with single row of 4 multicuspid teeth ( Fig. 14 ) in all 13 specimens. All teeth compressed and pedunculate with distal parts spatulate with 7 cusps in adult males and females; 3 middle cusps largest, and marginal cusps smaller. Maxillary teeth ( Fig. 14 ) identical in form to premaxillary teeth; most teeth with 6-7 cusps, 5-8, 7.1, (7), n = 13, SD = 1. Dentary dentition identical in form to that on premaxilla and maxilla; with 3 middle cusps slightly larger than marginal cusps. Total number of dentary teeth 7-11, 8.6, 9 (13), n = 13, SD = 1.2.

Vertebrae 37-39, 37.8, (38), n = 14, SD = 0.5. Dorsal limb gill rakers 8-9, 8.4, (8), n = 13, SD = 0.5; ventral limb gill rakers 12-14, 12,7, (13), n = 13, SD = 0.7. Branchiostegal rays 4 in one cleared and stained specimen; 3 rays originating on anterior and one on posterior ceratohyal.

Color in alcohol: Identical to that of M. drilos , except that the head is dark overall with the central portions of maxilla, infraorbitals, preopercle, dorsal and ventral parts of opercle, subopercle and branchiostegal rays and basal portion of pectoral fin lighter with scattered dark chromatophores. Longitudinal dark stripe on body identical to that of M. pearsoni , but dark chromatophores are more densely concentrated along its dorsal and posterior portions.

Sexual dimorphism: The p values in Table 3 indicate that pelvic-fin length, dorsal-fin height and anal-fin lobe length are sexually dimorphic, but testing these differences through regression analysis is inappropriate in light of using the limited number of available males and females.

Reproductive mode and gonad anatomy: Males and females of this species ( MUSM 6756 and 11250), identified as Monotocheirodon sp. were also used by Burns & Weitzman (2006) for histological analysis of the urogenital papilla and the ovary of mature females. The results revealed that the intromittent organ of Monotocheirodon kontos , which is larger than that of M. drilos is also used to inseminate females and that the more elongate nuclei of the spermatic cells are 4.1 µm in length.

As in Monotocheirodon drilos , the sperm nucleus contains highly condensed granular chromatin, but it is more elongate toward the flagellar axis being approximately 3.95 µm in length (SD ± 0.4µm) ( Fig. 15 , A-F). The flagellum originates along the first quarter of the nuclear length ( Fig. 15 , A-B). In cross section the flagellum shows an irregular outline with depressions ( Fig. 15 , C-F) and in the centriolar complex the centrioles are oblique to one another ( Fig. 15 B-inset). Other distinctive sperm nucleus features of M. kontos are: the mitochondria are elongate, display a longitudinal position relative to the flagellar axis ( Fig. 15 B ) and are mainly accumulated in the depressions on the nuclear outline ( Fig. 15 E-F); the vesicular system is formed by a large number of small interconnected vesicles positioned very close to one another giving the system an alveolar appearance ( Fig. 15 , F-L); due to the superposition of the membrane, the points where the vesicles are connected are seen as electron dense dots ( Fig. 15 J ); the vesicles are intermingled with the mitochondria and are mainly external to them; this vesicular system and also the mitochondria are found in the midpiece at the base of the nucleus ( Figs. 15 , H-L). The midpiece, identical to that of M. drilos ( Fig. 15 B ) is about 0.7 µm in length (SD ± 0.1 µm), and as in that species a single flagellum also emerges from the midpiece ( Fig. 15 G ).

Etymology: The name kontos is Greek masculine meaning a long pole. The word is used here in reference to the prominent male inseminating organ. A noun in apposition.

Distribution: Monotocheirodon kontos was collected in tributaries of the Río Madre de Dios basin, Peru ( Fig. 7 ) between 350 and 3,200 m of altitude. It is sympatric with M. drilos in the Río Ebebahuaeji basin.

Figures

FIGURE 7: Map of western South America showing collecting sites and type localities (black symbols) of species of Monotocheirodon. Squares: Monotocheirodon kontos; circles: M. drilos; triangle: M. pearsoni. Some symbols may represent more than one locality.

FIGURE 12: Monotocheirodon kontos, MUSM 6756, adult male above, 36.7 mm SL and adult females, 33.7 mm SL.

FIGURE 13: Monotocheirodon kontos, MUSM 11250, female, 37.1 mm SL; gill rakers on first gill arch, lateral view, left side.

FIGURE 14: Monotocheirodon kontos, MUSM11250, C&S, female, 37.1 mm SL; jaws and dentition, lateral view, left side, anterior at left.

FIGURE 15: Spermatozoa of Monotocheirodon kontos, MUSM 6756, 38.1 mm SL. A, B: Longitudinal section of spermatozoa. Note lateral position of nucleus (n) relative to flagellar axis. Short midpiece containing mitochondria (m), several vesicles (v) and cytoplasmic canal (*) into which initial segment of flagellum fits (f). Proximal (p) and distal (d) centrioles located at very shallow nuclear fossa (B-inset) located near tip of nucleus. C-F: Cross section at different levels of nucleus showing strongly irregular nuclear outline, proximal centriole inside nuclear fossa (arrow), beginning of cytoplasmic canal (*) that houses initial segment of flagellum, elongate mitochondria between cytoplasmic canal and nuclear outline (E and F). Also note vesicles (v) visible along nuclear outline. G: Cross view at different levels of midpiece showing mitochondria accumulated especially at base of nucleus and decreasing progressively along midpiece. Cytoplasm of midpiece filled by vesicular system.