Pseudancistrus corantijniensis, Chambrier, Sophie De & Montoya-Burgos, Juan I., 2008

Chambrier, Sophie De & Montoya-Burgos, Juan I., 2008, Pseudancistrus corantijniensis, a new species from the Guyana Shield (Siluriformes: Loricariidae) with a molecular and morphological description of the Pseudancistrus barbatus group, Zootaxa 1918, pp. 45-58 : 47-53

Pseudancistrus corantijniensis new species

Fig. 1

Holotype: SURINAME: Sipaliwini District, Corantijn River Dr., MHNG 2672.092 (field number SU05-296). 167.16 mm SL. Corantijn River at Kaw Falls, 4°59'48.3'' N, 57°37'49.5'' W, J. I. Montoya-Burgos, R. Covain and P. Hollanda Carvalho, 5 October 2005.

Paratypes. All localities SURINAME, Sipaliwini District, Corantijn River Dr., Corantijn River, and same collectors as holotype: MHNG 2672.092, 7, 56.6-160.6 (field numbers SU05-282; SU05-292; SU05-293; SU05-297 - SU05-299); MNHN 2007-1931 (SU05-294); MNHN 2007-1932 (SU05-295); NZCS F7064 - F7065; same data as holotype. MHNG 2672.090, 1, 134.94 (SU05-309), Temery area, 4°41'10.2'' N, 57°50'03.2'' W, 5 October 2005. MHNG 2672.074, 10, 62.52-178.76 (SU05-321 - SU05-330), Wonotobo Falls, 4°22'35.3'' N, 57°57'25.1'' W, 6 October 2005. MHNG 2672.066, 1, 108.12 (SU05-355), Wonotobo Falls, 300m upstream of previous locality, 6 October 2005. MHNG 2672.056, 1, 86.0 (SU05-391), Wonotobo Falls, 4°22'35.3'' N, 57°57'25.1'' W, 7 October 2005. MHNG 2672.081, 1, 132.0 (SU05-516), Kaw Falls, 5°00'45.6'' N, 57°18'23.5'' W, 8 October 2005.

Diagnosis: Pseudancistrus corantijniensis is distinguished from non-derived Pseudancistrus and other Ancistrini by the presence of hypertrophied odontodes along the snout in males as well as in females and quite early in ontogeny. Pseudancistrus corantijniensis is diagnosed from derived Pseudancistrus on the basis of coloration: whitish spots very small, crowded and faint (especially in preserved specimens) on the snout to the posterior border of the eyes and the anterior border of the cleithrum, becoming abruptly larger (at least 1 mm in diameter even in young specimens), more spaced and more visible on the posterior part of the head ( Figs. 1 and 2 ). Large whitish spots continue along the body with a slight and gradual increase in size posteriorly. A single large whitish spot is generally present on each dorso-lateral plate posterior to the pelvic-fins. Pseudancistrus barbatus and P. depressus have smaller whitish spots covering the body and the spots increase slightly and gradually in size from snout to caudal peduncle rather than displaying an abrupt spot size reduction posterior to the eyes as in P. corantijniensis . In P. nigrescens , the whitish spots increase gradually in size from the snout to caudal peduncle, yet they become bigger and hazier than in the other derived Pseudancistrus . In the latter species, larger spots are often not round and can cover more than one plate.

Pseudancistrus corantijniensis can be further distinguished from other derived Guyanese Pseudancistrus by having a trapezoidal cross section in the region posterior to the head and anterior to the dorsal-fin spine versus a more round, almost semicircular cross section in other derived Pseudancistrus species. In addition, P. corantijniensis can be distinguished from P. barbatus and P. d e p re s s u s by the color and length of snout odontodes. In the new species, the odontodes are whitish and homogenous in length, with the exception of shorter ones on the tip of

Photos by S. Chraiti.

the snout, and slightly longer ones finishing on the cheek. In P. barbatus and P. depressus , the odontodes are reddish-brown (in young specimens, this color is more visible on the posterior snout odontodes) and their length increases gradually from tip of the snout to cheeks. A comparison of snout odontodes and spotting pattern on the head of the four derived Guyanese Pseudancistrus is given in Figure 3 . Moreover, in P. corantijniensis the head is more depressed (height 7–8 times in SL; mean = 7.47, N= 23) than in P. nigrescens (height 5.3 - 6.4 times in SL; mean = 5.89, N= 12).

Description. Selected morphometrics are given in Table 1 . Pseudancistrus corantijniensis is a quite large species, largest specimen 178.8 mm in SL. Head gently sloped from snout tip to posterior part of orbit, then dorsal profile almost flat and straight to insertion of adipose-fin spine. Supraoccipital flat with slight posterior point medially. Dorsal margin of orbit higher than mesial portion of head. Iris with small dorsal flap, sometimes reaching the center of pupil. Body widest at the cleithrum with a marked and linear narrowing from cleithrum to the caudal-fin. Body dorsoventrally flattened. Dorsal profile of caudal peduncle slightly concave. Ventral surface flat. Caudal peduncle trapezoidal in cross section with ventral and dorsal surface flat, ventral surface larger.

Upper lip wide with thin papillae. Lower lip wide with thin papillae slightly larger in the central portion, posterior margin almost devoid of papillae. Only maxillary barbel present, short, sometimes bifurcated. Number of lateral plates in median series: 24. Dorsal plate series bent, flattened dorsally, forming a marked ridge from base of the dorsal-fin spine to base of caudal fin. The ridge is less marked posterior to the base of adipose-fine spine. Inframedian plate series bent in middle from the cleithrum to the insertion of pelvic-fin creating a marked keel. Ventral plates of caudal peduncle also bent, ventrally flat and forming almost a right angle on lower sides. Five rows of plates on caudal peduncle. Abdomen naked.

Numerous whitish hypertrophied odontodes along the head margin, homogenous in length excepting the anterior portion of the snout where odontodes are smaller. The few longest odontodes are on the posterior most portion of the nonevertible cheek plates. Body plates and cleithrum bear minute odontodes, which become modestly hypertrophied on the posterior margin of plates. All fin spines and rays suppor odontodes, which are moderately hypertrophied on the pectoral-fin spines, gradually larger towards the tip, in males, females and young specimens.

Dorsal-fin (I + 7) reaching adipose-fin when adpressed (mainly in young specimens). Dorsal-fin margin straight, oblique. Dorsal-fin spinlet with a concave posterior margin. Dorsal-fin lock functional. Adipose-fin with single median preadipose plate and slightly curved spine. Caudal-fin (I+14+I) margin slightly concave. Pectoral-fin (I+6) spine usually reaching the middle portion of the pelvic-fin when adpressed ventral to pelvic-fin. Pelvic-fin (I+5) spine usually reaching insertion of anal-fin spine or slightly beyond. Anal-fin (I+4) spine three fourths the length of first branched ray.

Long bicuspid teeth with a longer median lobe. 57 - 93 dentary teeth per ramus (median = 72, N = 23). 48 - 78 premaxillary teeth per ramus (median = 62, N = 23). Wide jaws, dentaries forming an oblique angle, premaxillaries almost co-linear.

Color. Ground color dark greenish-brown laterally and dorsally, becoming lighter ventrally on ventral plate series. Belly light yellow, sometimes with pinkish areas. Anterior part of head to posterior margin of orbits with many small, crowded, whitish spots; spots becoming abruptly larger and more spaced on posterior part of head and continuing onto body becoming slightly and gradually larger towards caudal peduncle. Median and supra median plate series usually with 2-3 large spots per plate anterior to pelvic-fins and one large spot per plate posterior to the pelvic-fins. Dorsal plate series with three, sometimes four spots per plate anterior to the dorsal-fin and generally two large spots per plate posterior to dorsal-fin spine. Inframedian plate series with 4-6 spots per plate anterior to the insertion of the pelvic-fin spine, generally 2-3 spots along the pelvic-fin, and generally a single spot elongated dorsoventrally in posterior plates. Ventral surface of upper lip dark greenish-brown. Dorsal-fin membrane, spine and rays with whitish oval medium size spots. Adipose-fin with one or two large whitish spots on the membrane and spine. Caudal-fin with whitish round spots centered in rays, spots slightly smaller than on the caudal peduncle. Pectoral-fin spine with whitish spots in the proximal part, fading distally; round spots centered on pectoral-fin rays. Pelvic-fin spine with or without whitish spots; when present, round spots centered on pelvic-fin rays. Anal-fin with few whitish spots or lighter areas.

Range. Known from middle and lower Corantijn River in Suriname ( Fig. 4 )

Etymology. The name is derived from the Corantijn River, to which this species seems to be restricted.

A molecular phylogenetic approach was used to investigate species relationships among putatively derived Guyanese members of Pseudancistrus (i.e., species bearing hypertrophied odontodes along the snout). The mitochondrial D-loop sequences were obtained for 27 individuals collected in various localities and representing five species: P. barbatus (type species), P. depressus , P. nigrescens , P. n i g e r, and P. corantijniensis , n. sp. ( Table 2 ). Lasiancistrus was used as outgroup because it lacks hypertrophied odontodes along the snout and has evertible cheek plates. The sequence alignment comprised 574 positions, from which 214 where variable within the ingroup. Base composition was biased in favor of Thymine (34.8% of all bases) and Adenine (33.7% of all bases). The model of sequence evolution that fit the best our sequence data set is GTR + gamma, according to MODELTEST ( Posada and Crandall, 1998).

The maximum likelihood phylogenetic tree obtained is shown in Figure 5 . Based on the selected outgroup ( Lasiancistrus ), P. n i g e r is distantly related to the four other members of the putatively derived Guyanese Pseudancistrus , which in turn form a monophyletic group of closely related species. This group will be referred to as the Pseudancistrus barbatus group. The type species, P. barbatus , which occurs in the Oyapock and Maroni rivers, clusters with P. depressus , for which we have samples from the Suriname and Coppename Rivers in Suriname. The closest relative to P. corantijniensis , n. sp., is P. nigrescens , collected in the Rupununi River and in the middle part of the Essequibo River in Guyana. All the inter-specific relationships are strongly supported as indicated by high bootstrap values.

Figures

FIGURE 1. Pseudancistrus corantijniensis MHNG 2672.092 (SU 05 - 296), Holotype. Dorsal, lateral, and ventral views,

FIGURE 2. Pseudancistrus corantijniensis MHNG 2672.074 (SU 05 - 321), paratype, dorsal view showing the marked change in spots size in the posterior part of the head. Photo by R. Covain.

FIGURE 3. Comparison of snout odontodes and spotting pattern on the head of the four derived Guyanese Pseudancistrus. From left to right and up to down: Pseudancistrus depressus, Pseudancistrus barbatus, Pseudancistrus nigrescens and Pseudancistrus corantijniensis. Photographs by R. Covain, R. Kssas, S. Chraiti.

FIGURE 4. Map of the Guyana Shield coastal rivers showing the sampling localities. Rectangle = P. nigrescens, round = P. corantijniensis, triangle = P. depressus, star = P. barbatus and diamond = P. niger. One symbol may cover more than one locality. We also present the type localities for each species given by filled symbols. The type locality of P. barbatus (Valenciennes, 1840) is the Mana River, while for P. depressus (Günther, 1868) it is the Suriname River, without further indications.

FIGURE 5. Maximum Likelihood tree of the Guyanese derived Pseudancistus (- lnL = 3218.93185; gamma shape parameter = 0.613; number of categories = 6). Number above branches indicates bootstrap support. Cop. = Coppename basin; Cor. = Corantijn basin; Es. = Essequibo basin; Ma. = Maroni basin; Oy. = Oyapock basin; Su. = Suriname basin.

Tables

TABLE 1. Selected morphometrics of Pseudancistrus corantijniensis. Measurements 2 to 24 are percentage of Standard Length while 25 to 36 are percentage of Head Length.

	Measurements	Holotype	Average (N=23)	S.D.	Minimum	Maximum
1	Standard Length	160.72	109.1	37.8	56.6	178.8
2	Predorsal Length	41.73	40.74	1.06	38.78	42.66
3	Head Length	33.78	32.97	0.80	31.63	34.98
4	Head-dorsal Length	7.96	7.94	0.80	6.59	9.37
5	Cleithral Width	31.32	29.81	4.02	11.66	32.50
6	Head-pectoral- Length	31.07	27.69	0.67	26.67	28.97
7	Thorax Length	21.76	23.35	1.84	19.99	26.83
8	Pectoral-spine Length	36.52	31.47	2.59	27.16	36.48
9	Abdominal Length	26.79	26.34	1.77	24.28	30.36
10	Pelvic-spine Length	22.95	23.22	1.74	18.15	26.29
11	Postanal Length	33.97	32.24	2.05	24.79	34.91
12	Anal-fin spine Length	10.93	10.06	8.94	4.85	50.62
13	Dorsal-pectoral Distance	25.37	25.50	1.13	23.82	29.27
14	Dorsal spine Length	25.12	27.18	1.75	22.54	31.24
15	Dorsal-pelvic Distance	19.79	17.66	0.98	16.67	21.11
16	Dorsal-fin base Length	28.79	28.36	1.43	25.61	31.44
17	Dorsal adipose Distance	19.86	17.75	1.76	15.03	22.11
18	Adipose-spine Length	7.82	10.17	10.52	6.09	58.32
19	Dorsal Adipose-cadal Distance	13.6	12.76	1.05	10.52	15.26
20	Caudal peduncle Depth	9.98	9.31	1.59	6.57	15.44
21	Ventral adipose-caudal Distance	20.54	19.47	0.73	17.93	21.00
22	Adipose-anal Distance	21.52	20.53	1.06	18.17	22.44
23	Dorsal-anal Distance	14.18	12.72	0.65	11.08	13.52
24	Pelvic-dorsal Distance	27.2	25.96	4.25	8.93	31.20
25	Head-eye Length	29.46	35.99	9.10	28.66	53.00
26	Orbit Diameter	18.21	21.23	2.31	17.19	24.33
27	Snout Length	69.63	65.73	3.94	58.84	71.63
28	Internares Width	18.43	20.36	3.16	17.99	33.76
29	Minimal interorbital Distance	31.45	29.88	1.49	27.34	32.20
30	Mouth Length	58.87	58.38	3.97	51.52	67.43
31	Mouth Width	68.87	68.34	3.82	60.66	75.23
32	Barbel Length	10.12	10.53	14.00	1.86	61.93
33	Dentary tooth cup Length	21.65	19.48	4.11	1.51	22.88
34	Premaxillary tooth cup Length	18.67	17.83	3.41	4.47	21.31
35	Head Depth	39.63	40.66	1.45	38.38	44.99

TABLE 2. List of specimens used for the molecular phylogeny, with GenBank accession numbers.

Species Field number	Catalog number Basin	GenBank
Lasiancistrus sp. GY04-310	MHNG 2651.68 Essequibo	EF688085
GY04-341	MHNG 2650.076 Essequibo	EF688086
P. n i g e r GF06-295	MHNG 2682.037 Oyapock	EF688087
P. barbatus GF06-028	MHNG 2680.093 Oyapock	EF688106
GF06-031	MHNG 2680.093 Oyapock	EF688107
GF06-146	MHNG 281.073 Oyapock	EF688108
GF06-148	MHNG 281.073 Oyapock	EF688109
GF06-291	MHNG 2682.039 Oyapock	EF688110
GF00-094	MHNG 2653.060 Maroni	EF688111
GF00-342	MHNG 2653.063 Maroni	EF688112
P. depressus SU05-020	MHNG 2674.26 Suriname	EF688101
SU05-084	MHNG 2674.013 Suriname	EF688102
SU05-138	MHNG 2673.075 Suriname	EF688103
SU05-154	MHNG 2673.064 Suriname	EF688104
SU05-275	MHNG 2673.015 Suriname	EF688105
SU01-439	MHNG 2690.14 Coppename	EF688099
SU01-441	MHNG 2690.14 Coppename	EF688100
P. nigrescens GY04-034	MHNG 2651.022 Essequibo	EF688089
GY04-036	MHNG 2651.022 Essequibo	EF688091
GY04-293	MHNG 2650.098 Essequibo	EF688090
GY04-294	MHNG 2650.098 Essequibo	EF688088
P. corantijniensis SU05-282	MHNG 2672.092 Corantijn	EF688094
SU05-292	MHNG 2672.092 Corantijn	EF688095
SU05-295	MNHN 2007-1932 Corantijn	EF688092
(Holotype) SU05-296	MHNG 2672.092 Corantijn	EF688113
SU05-297	MHNG 2672.092 Corantijn	EF688096
SU05-299	MHNG 2672.092 Corantijn	EF688093
SU05-321	MHNG 2672.074 Corantijn	EF688097
SU05-324	MHNG 2672.074 Corantijn	EF688098
Molecular Phylogeny