Platydoras brachylecis , a new species of thorny catfish ( Siluriformes : Doradidae ) from northeastern Brazil

Platydoras brachylecis, new species, is described from coastal drainages of northeastern Brazil (Pindaré to Parnaíba rivers), and diagnosed from congeners by the unique combination of: pale yellow to white stripe beginning above orbits, continuing midlaterally on body and onto middle rays of caudal fin; skin in axil of each midlateral thorn without concentration of pigment forming small dark spot, midlateral scutes shallow (depth of 10 scute 8.8-11.9% of SL), and midlateral scutes on caudal peduncle distinctly separated by strip of skin from middorsal and midventral caudal-peduncle plates. Three additional species of Platydoras are recognized as valid: P. armatulus (lower Orinoco, Amazon and Paraguay-Paraná drainages), P. costatus (coastal drainages of Suriname and French Guiana), and P. hancockii (upper Orinoco, Negro, Essequibo and Demerara drainages). The nominal species P. dentatus and P. helicophilus are tentatively treated as junior synonyms of P. costatus. A key to species of Platydoras is provided.

Examination of extant types and ongoing studies by the two junior authors (MAH, MHSP) confirm the distinctiveness of three nominal species of Platydoras: P. armatulus (Paraguay-Paraná and portions of Amazon and Orinoco basins), P. costatus (Corantijn and Maroni basins), and P. hancockii (Negro, Essequibo, Demerara, and upper Orinoco basins).Doras dentatus Kner, 1855 and Doras helicophilus Günther, 1868b, both described from Suriname, the latter from the Maroni River, are tentatively considered junior synonyms of P. costatus based on: comparisons of their extant types and other Suriname specimens to Gronow's (Gronovius, 1756) description and illustrations of the Linnaean P. costatus, and the likelihood that the missing type(s) of P. costatus originated from Suriname.Independent work on Platydoras by the senior author (Piorski, 1997(Piorski, , 1999) ) uncovered a distinct, undescribed form from northeastern Brazil.The purpose of this study is to diagnose and describe this form as a new species of Platydoras.

Material and Methods
Measurements were made to the nearest 0.1 mm using dial or digital calipers (<180 mm) or a beam compass (>180 mm).This paper combines two studies conducted independently by two groups of authors using different methodologies for compiling and comparing morphometric data.As a result of this collaborative effort two sets of measurements were recorded separately: one for comparing the new species to Platydoras armatulus and nearby populations of Platydoras in the Tocantins and Xingu basins (Platydoras sp.) using a canonical variate analysis, and the second for presentation of standard morphometric data and broader comparisons among a larger set of specimens from throughout the range of Platydoras.
The second set of measurements (MAH, MHSP) represents point-to-point straight-line distances used in the species description with the following reported as percentages of standard length (SL), snout tip to posterior-most margin of hypural plate (midlateral point above and below which faint oblique creases follow bases of caudal-fin rays when caudal fin is gently flexed): head length (HL) = snout tip to posteriormost extremity of fleshy opercular flap (also expressed as percentage of PdD); predorsal distance (PdD) = snout tip to posterior margin of middle nuchal plate coinciding with medial sagittal plane; snout-postcleithral process (SPcPD) = snout tip to distal-most tip of postcleithral (humeral) process; dorsal origin-posterior adipose distance (DOAD) = from groove between medial posterior margin of middle nuchal plate (anterior to base of dorsal-locking spine) to posterior base of adipose fin; adipose-caudal distance (AdCD) = posterior base of adipose fin to flexion point of hypural plate coinciding with posterior terminus of SL; prepectoral distance (PpD) = snout tip to point between notch formed by margin of cleithrum and anterior base of erected (30-45 degrees) pectoral-fin spine; pectoral-pelvic distance (PPD) = from anterior base of pectoral-fin spine (terminus of PpD) to base of first (anterior-most) pelvic-fin ray (best measured by abducting pelvic fin); pelvic-anal distance (PAD) = from an-  terior base of first pelvic-fin ray to anterior base of first analfin ray; anal-caudal distance (AnCD) = from posterior base of posterior-most anal-fin ray to flexion point of hypural plate coinciding with posterior terminus of SL; dorsal-fin spine length (DSL) = from groove between medial posterior margin of middle nuchal plate and base of dorsal locking spine to bony tip of erected (30-45 degrees) dorsal-fin spine excluding soft break-away tip if present; pectoral-fin spine length (PSL) = from anterior base of erected (30-45 degrees) pectoral-fin spine to bony tip, excluding soft break-away tip if present; pelvic fin length (PFL) = from anterior-most base of first ray to distal-most tip of fin (not the measurement of an individual ray); anal-fin base (AnFB) = distance between anterior-most and posterior-most bases of anal-fin insertion; head width (HW) = greatest transverse distance between lateral contours of opercula (opercula compressed to normal position if flared) anterior to cleithra (also expressed as percentage of PdD); cleithral width (CW) = greatest transverse distance between lateral contours of cleithra (also expressed as percentage of PdD); head depth (HD) = vertical depth in medial sagittal plane at middle pitline (transverse groove) across center of supraoccipital (also expressed as percentage of PdD); body depth (BD) = vertical depth in medial sagittal plane between shallow crest of posterior margin of middle nuchal plate and midventral contour of body (also expressed as percentage of PdD); caudal peduncle depth (CPD) = least depth of caudal peduncle.
The following measurements are reported as percentages of predorsal distance: adipose eyelid diameter (AED) = horizontal diameter of eye including thin adipose eyelid; orbital diameter (OD), diameter of bony concavity dorsally enclosing eye from posterior lateral corner of lateral ethmoid to point formed usually by anterior-most lateral corner of sphenotic or rarely by posterior lateral corner of frontal (line of measurement at slight angle to that of AED); snout-anterior nares distance (SAND) = snout tip to center of opening of anterior nares; snout-posterior nares distance (SPND) = snout tip to center of opening of posterior nares; snout-posterior orbit distance (SPOD) = snout tip to posterior-most bony corner of orbital concavity (posterior terminus of OD); anterior naresposterior orbit distance (ANPOD) = from center of opening of anterior nares to posterior-most bony corner of orbital concavity (posterior terminus of OD); posterior nares-posterior orbit distance (PNPOD) = from center of opening of posterior nares to posterior-most bony corner of orbital concavity (posterior terminus of OD); internares distance (ID) = between centers of openings of anterior and posterior nares; postorbital length (PL) = from posterior-most bony corner of orbital concavity (posterior terminus of OD) to posterior margin of middle nuchal plate in medial sagittal plane; postcleithral (humeral) process length (PcPL) = from posterior-most tip to point along dorsal margin of exposed surface of process that is vertically aligned with posterior-most margin of fleshy opercle (exposed surface of postcleithral process appears slightly elevated and textured compared to smooth face of medially deflected portion of cleithrum lying beneath opercle); postcleithral (humeral) process depth (PcPD) = greatest depth orthogonal to straight line formed by long axis of process (also expressed as percentage of PcPL); interorbital width (IW) = shortest transverse distance between bony orbital margins of frontals.
Finally, two measurements are reported separately as percentages of SL and body depth taken in same transverse plane (adapted from Böhlke, 1970): depth of fifth (SD5) and tenth midlateral scutes (SD10) = vertical depth orthogonal to horizontal line formed by medial thorns of scutes, from dorsal-most exposed margin of fifth (or tenth) plate to ventralmost margin of corresponding plate.The ratio of scute depth to SL is more consistent and reliable for comparisons between species because ratios of scute depth to body depth are strongly influenced by the contents of the gut (i.e., full vs. empty; compare standard deviations for ratios of scute depths in Table 2).
Counts of dorsal-, anal-, and paired-fin elements are separated into anterior spine (capital roman numeral) or unbranched soft ray (lower-case roman numeral) and posterior branched soft rays (arabic numerals).The small locking spine (spinelet) anterior to the dorsal-fin spine is counted.The last (posterior-most) pectoral-fin ray may appear unbranched, particularly in juveniles); it was counted if clearly segmented with its base separated from the penultimate ray.In rare instances the last pectoral-fin ray may be followed by a much smaller and rather inconspicuous sliver-like element that is clearly unsegmented; this bony element was not included in the count.The anterior-most anal-fin ray counted may be extremely small and closely adhered to the second ray.The last anal ray may be simple or composed of two branches with bases joined or in very close proximity (counted as one).Counts of midlateral scutes begin with the vertically expanded infranuchal scute that dorsally contacts the posterior nuchal plate, ventrally contacts or approaches the distal tip of the postcleithral process, and medially contacts the first rib, borne on the 6 th vertebra.Though conspicuous and sometimes bearing a medial thorn, the third scute in the tympanal region (immediately anterior to the infranuchal scute) was not included in counts of midlateral scutes.
Museum abbreviations follow Ferraris (2007) with the addition of LISDEBE for Laboratório de Ictiologia Sistemática do Departamento de Ecologia e Biologia Evolutiva da Universidade Federal de São Carlos, Brazil.
Platydoras brachylecis was distinguished from both P. armatulus and Platydoras sp. on CV1, and Platydoras sp. was distinguished from both P. brachylecis and P. armatulus on CV2.Measurement variables distinguishing P. brachylecis by loading most heavily on CV1 (Table 1) are for the lateral trussnet (Fig. 1a), in decreasing magnitude: posteriormost base of dorsal fin to posteriormost base of anal fin (A19; longer in P. brachylecis), distance between the posteriormost bases of dorsal and adipose fins (A20; longer in P. brachylecis), and anteriormost base of dorsal-fin locking spine to origin of anal fin (A14; longer in P. brachylecis).Measurement variables loading most heavily on CV1 for the dorsal trussnet (Fig. 1b) are, in decreasing magnitude: diagonal between right anteriormost limit of middle nuchal plate and left intersection of opercle and posttemporal-supracleithrum (B8; shorter in B. brachylecis), transverse distance between anteriormost limits of paired orbits (B16; shorter in B. brachylecis), and diagonal between right posterior and left anteriormost limits of paired orbits (B14; shorter in B. brachylecis).
Measurement variables distinguishing Platydoras sp. by loading most heavily on CV2 (Table 1) are for the lateral trussnet, in decreasing magnitude: posteriormost base of adipose fin to posterior margin of last lateral line scute (A23; shorter in Platydoras sp.), origin of anal fin to posteriormost base of adipose fin (A18; longer in Platydoras sp.), posteriormost base of anal fin to posterior margin of last lateral line scute (A22; shorter in Platydoras sp.).Measurement variables loading most heavily on CV2 for the dorsal trussnet are, in decreasing magnitude: largest orbital diameter (B15; larger in Platydoras sp.), diagonal between right intersection of opercle and posttemporal-supracleithrum and left posteriormost limit of orbit (B11; shorter in Platydoras sp.), transverse distance between anterior nares (B22; shorter in Platydoras sp.) lateral distance between left posteriormost limit of orbit and left intersection of opercle and posttemporalsupracleithrum (B12; shorter in Platydoras sp.).

Diagnosis. Platydoras brachylecis is diagnosed among
Platydoras by the following unique combination of characters: pale yellow to white stripe beginning above orbits, con- tinuing midlaterally on body and onto middle rays of caudal fin; skin in axil of each midlateral thorn without concentration of pigment forming small dark spot; midlateral scutes shallow (depth of 10 th scute 8.8-11.9% of SL, n = 15); and midlateral scutes on caudal peduncle distinctly separated by strip of skin from middorsal and midventral caudal-peduncle plates (i.e., modified procurrent caudal-fin rays).
Platydoras costatus lacks the pale yellow to white midlateral stripe and has a small dark spot in the axil of each midlateral thorn.Platydoras armatulus has deeper scutes (depth of 10 th scute 12.0-16.6% of SL, n = 59), and midlateral scutes on caudal peduncle usually contacting, and often interdigitating with, middorsal and midventral caudal-peduncle plates.Platydoras hancockii has deeper scutes (depth of 10 th scute 12.0-17.8% of SL, n = 37), and pale yellow to white midlateral stripe usually punctuated with small dark spots in axils of few to many midlateral thorns.
Description.Morphometric data presented for 15 specimens (111.2-190.0mm SL) in Table 2. Head moderately depressed, body more evenly rounded anteriorly, gradually becoming slightly compressed beyond dorsal fin origin to caudal peduncle; ventral surface moderately flattened from mouth to vent (Fig. 3).Dorsal profile gradually ascending and very gently rounded, convex to nearly straight, oblique from between anterior nares to middle pitline of supraoccipital, then straight and slightly less oblique from middle pitline to dorsal-fin origin; from dorsal-fin origin to caudal peduncle more gradually descending, very gently rounded, convex to nearly straight, oblique.Ventral profile gently rounded, convex to nearly straight from mouth to anal-fin origin; then rounded, convex, ascending more steeply along anal fin insertion to caudal peduncle.Caudal peduncle moderately long and relatively narrow (minimum depth 7.5-8.4%SL), profile gently concave dorsally and ventrally.Nuchal region subtriangular in cross-section; body depth greatest at dorsal-fin origin (19.3-26.6% of SL).Body width greatest across cleithral bulges (width 28.1-32.1% of SL), tapering gradually to caudal fin.
Head moderately long (26.4-29.0%SL, 66.4-73.8%predorsal distance); in dorsal view weakly triangular with moderately short, rounded snout.Eyes subcircular, relatively small, without well-developed adipose eyelid (horizontal adipose eyelid diameter 10.3-13.4% predorsal distance), and placed dorsolaterally on head with center slightly less than one-third distance from snout tip to dorsal-fin origin.Bony orbits well separated (interorbital width 20.5-24.5% of predorsal distance); dorsal margin distinctly concave in dorsal view with arch not elevated above dorsal profile of head; enclosed largely by frontal dorsally with anteriormost quarter bordered by lateral ethmoid and posteriormost corner usually formed by anteriormost lateral corner of sphenotic or rarely by posterior lateral corner of frontal.Four infraorbitals (including lacrimal as infraorbital one), well ossified, superficially exposed; second one smallest, excluded from orbit; third one large, horizontal, forming ventral rim of orbit; fourth one narrower, vertical, completing posterior rim of orbit.Anterior and posterior nares well separated (internares distance 9.8-12.1% of predorsal distance).Anterior naris near anterior margin of snout, opening surrounded by distinct tube of skin.Posterior naris closer to eye than to anterior one, opening surrounded by tube of skin with anterior wall enlarged to form flap. Anterior cranial fontanel with elongate teardrop to wedge shape (tapered anteriorly); rounded posterior rim extending slightly beyond transverse line through centers of orbital concavities; opening enclosed by mesethmoid anteriorly and frontals posteriorly and laterally.Posterior cranial fontanel absent.
Mouth subterminal with moderately fleshy lips weakly expanded posteriorly as rounded flaps at corners of mouth.Lip surfaces rugose, weakly scalloped with low, rounded, closely-space papillae (particularly on lower lip).One pair of simple (non-fimbriate), slender maxillary barbels with tips extending well beyond pectoral-spine insertion, usually to near midlength (before tip) of postcleithral process; weakly compressed anteriorly; surfaces relatively smooth, studded with small papillae.Two pairs of simple, slender mandibular barbels; origin of inner pair slightly more anterior than outer pair, both origins near lower lip; outer pair longer with tips finishing near transverse line through anteriormost origin of pectoral-fin spines; inner pair usually finishing just shy of transverse line through ventralmost extent of gill openings; both pairs of barbels studded with small papillae.Branchiostegal membranes broadly united to isthmus.
Both jaws with many small, conical teeth confined to premaxillae and dentaries.Upper jaw teeth in single rectangular patch relatively continuous across premaxillae; teeth gradually decreasing in size from outermost to innermost rows.Lower jaw teeth in two subrectangular patches; each patch tapered laterally and weakly separated by narrow hiatus at symphysis; teeth relatively uniform in size.Outermost gill arch with 3 upper and 8-10 lower rakers (n = 4); rakers stiffened, moderately spaced and moderately long (length up to about 4 times width).
Nuchal shield well developed, moderately arched in transverse plane; medial furrow generally absent, sometimes evident but shallow from middle pitline of supraoccipital to suture between anterior and middle nuchal plates.Nuchal foramina absent.Anterior nuchal plate moderately wide (length about equal to width), pentagonal with posteriorly directed apex sutured to middle nuchal plate; also sharing transverse anterior suture with supraoccipital and lateral sutures with epioccipitals.Middle nuchal plate broad with shallowly concave lateral margins; anterior lateral tips of anterior wings sharing short, weak suture with posttemporal-supracleithrum (excluding epioccipital from bony margin of shield enclosing tympanal region).Posterior nuchal plate with paired limbs, each L-to widely V-shaped superficially with anterolaterally directed wing contacting third tympanal scute and posteriorly directed wing contacting infranuchal and first postinfranuchal scutes.Dorsal surfaces of nuchal shield and neurocranial bones moderately rugose, ornamented with complex network of low fine ridges and granulations.
Pectoral girdle covered with skin ventrally.Postcleithral process long and narrow, lanceolate with acute tip; dorsal margin rises obliquely from base to moderately defined apex just distal to posterior margin of posttemporal-supracleithrum, then descends gradually, more or less linearly to posterior tip; ventral margin more or less straight, shallowly oblique; both margins largely entire or with minute dentitions.Postcleithral process with surface ornamentation separable into two longitudinal fields from base to posterior tip; dorsal field much wider, dominated by fine granulations and short irregular ridges; ventral field narrow, slightly elevated with more elongate longitudinal ridges and often separated posteriorly from dorsal field by low thin carina that continues to and often ventrally defines posteriormost tip of process.
Tympanal region with three separate ossifications (tympanal scutes); anterior two relatively small, weakly exposed, without well-defined dorsal and ventral wings; third tympanal scute large, well exposed with distinct dorsal and ventral wings spanning distance between posterior nuchal plate and postcleithral process, largely resembling subsequent midlateral scutes except with low medial carina instead of distinct thorn.
Sum of midlateral scutes including infranuchal: 56 (1), 57 (2), 58 (3), 59 (3 including holotype), or 60 (8).Midlateral scutes per left and right sides in 17 specimens: 28 (4), 29 (11), or 30 (19).Each midlateral scute with well-developed dorsal and ventral wings above and below sturdy thorn curved posteriorly (thorn sometimes indistinct on infranuchal scute, replaced by carina).Dorsal and ventral wings further separated by deep V-shaped notch along posterior margin in axil of thorn (location of lateral-line pores).Wings tall, subrectangular, subequal anteriorly (dorsal wing about a third taller) becoming equal near anal-fin origin; surfaces weakly ornamented with low, fine, longitudinal, roughly parallel ridges in vertical column along posterior half of scute; posterior margins nearly entire or with minute dentations imparted by ridges.Infranuchal scute contacts posterior nuchal plate dorsally, and ventrally slips beneath postcleithral process (but does not appear to contact internal surface of process).Scutes weakly overlapping (anterior margin embedded in skin), deepest anteriorly, becoming gradually shallower posteriorly; last scute usually on base of caudal fin beyond hypural flexure.Midlateral scutes on caudal peduncle not contacting middorsal and midventral caudal-peduncle plates (modified procurrent fin rays), distinctly separated from same plates by thin strip of skin.
Dorsal fin II,6 (includes spinelet); pectoral fin I,7 (very rarely I,8); pelvic fin i,6; anal fin iii-iv,8-9; caudal fin i,7/8,i with 10-14 dorsal and ventral procurrent elements (rays and plates).Dorsal fin triangular with relatively short base.Dorsal-fin spine sturdy, gently curved posteriorly over entire length, laterally compressed and relatively smooth sided except for long, fine, nearly parallel striations running the length of the spine from base to tip; anterior margin (except distal-most tip) with 16-29 antrorse serrations; posterior margin (except basal third and distal-most tip) with 5-14 straight to weakly antrorse serrations.Serrations surrounded by thick, porous skin, obscuring their presence; anterior serrations small and crowded basally, becoming gradually larger and more spaced distally; penultimate usually largest; posterior dorsal-spine serrations weaker (thinner), more spaced; largest near midlength.Pectoral fin triangular with folded spine extending more or less to vertical through pelvic-fin origin.Pectoral-fin spines sturdy, gently curved, dorsoventrally compressed, and with surface striations similar to those on dorsal-fin spine; anterior (leading) margin with 26-37 antrorse serrations to tip; posterior (trailing) margin with 18-27 retrorse serrations to tip.Serrations similarly surrounded by thick, extremely porous skin; anterior and posterior serrations similarly developed (smaller and more crowded basally, largest subterminal), except posterior serrations slightly larger, more broadly triangular.Pelvic fins relatively short with broadly rounded distal margin when extended.Anal fin also with broadly rounded distal margin, middle rays longest (length more or less equal to anal-fin base).Caudal fin distinctly forked with moderately pointed lobes; lower lobe slightly broader and more rounded than upper.Upper and lower procurrent caudal-fin rays grading into series of three to five flat, laterally expanded and weakly overlapping plates.Procurrent plates extend to or near bases of adipose and anal fins, thereby framing caudal peduncle dorsally and ventrally.Adipose fin prominent, main portion elongate and tear-drop shaped (tapered anteriorly) with origin vertically aligned to that of the anal fin.Adipose fin continues anteriorly as a low, narrow, fleshy ridge that begins approximately at the midpoint between verticals through last dorsal-fin ray and anal-fin origin.
Gas bladder two part with anterior (main) bladder and much smaller posterior (terminal) bladder (Fig. 4); bladder walls moderately thick and smooth.Main bladder cordiform with internal T-shaped septum that partially isolates single anterior chamber and completely divides paired posterior chambers.Posterior bladder elliptical, without internal septum.Lumen enclosed by terminal bladder apparently continuous with that of only one of the two posterior chambers of main bladder through a narrow opening at point of constriction between two bladders.
Coloration.Ground color of dorsal and lateral surfaces of head and body dusky, dark gray-brown; undersurfaces largely pale white to yellow.Midlateral sides with distinct light stripe along central portions of scutes and thorns (small dark spots in axils of thorns absent); stripe continues anteriorly through tympanal region, becoming less distinct as it converges dorsally with its pair in interorbital region.Thin faint light middorsal stripe usually evident from dorsal to adipose fin and sometimes evident in posterior nuchal region.Barbels dusky gray-brown with mandibular barbels somewhat lighter than maxillary barbels.Dorsal fin with dusky gray-brown spine and dusky spot in distal half of anterior three to four rays and intervening membranes; remaining portions relatively pale with few scattered pigment.Adipose fin largely dusky graybrown, becoming somewhat lighter towards distal margin.Pectoral fin with light to dusky spine; anterior three rays and intervening membranes usually darker, gray-brown; remaining portions relatively pale.Pelvic fins with anterior three to four rays and intervening membranes dusky, becoming lighter, pale posteriorly.Anal fin with large dusky blotch on central rays and membranes, relatively lighter, pale anteriorly and posteriorly.Caudal fin with wide dark gray-brown streaks on central portions of upper and lower lobes (streaks continuous with gray-brown ground color on sides); remaining portions relatively pale.
Distribution.Platydoras brachylecis is known from basins of rio Mearim, rio Pindaré, rio Itapecuru and rio Parnaíba, northeastern Brazil (Fig. 5).Fowler (1941:139) reported three specimens (ANSP 81733) from "Fortaleza, Ceará [State]", Brazil, collected by Rodolpho von Ihering in 1937.There are no major rivers emptying into the Atlantic Ocean at the coastal city of Fortaleza, and Ihering's specimens, with bellies slit from pectoral girdle to vent, may have been obtained from a local market.Their precise origin remains uncertain.
Ecological notes.Menezes & Menezes (1948) studied diet and relative gut length among 26 specimens (78-129 mm SL) from lagoa de Nazaré, Floriano municipality, Piauí State, Brazil.Gut contents were dominated by larva and adult insects (found in 17 specimens) with lesser amounts of fishes, shrimp and other crustaceans, plant remains and small stones.
Etymology.The specific name brachylecis is derived from the Greek brachy (short), and lekis (plate or dish), in reference to the relatively shallow midlateral scutes.
Remarks.Species commonly known as "graviola" in the Parnaíba River, "grangiola" in the Itapecuru River, and "corró" in the Mearim river.

Discussion
Platydoras costatus has long been misunderstood despite the early illustrations of Gronow's type specimen (Pl.5, figs. 1 and 2 in Gronovius, 1756) upon which Linnaeus (1758) based this name.Gronow's (Gronovius, 1756) illustration depicts a Platydoras with dorsal head and midlateral scutes uniformly colored.Platydoras costatus, however, is often applied to specimens with a distinct, continuous light midlateral stripe (white to yellow in life) that converges dorsoanteriorly with its pair in the interorbital region.Based on our examination of Platydoras from throughout its wide range, only specimens from coastal drainages of Suriname and French Guiana (i.e., Corantijn, Suriname, Maroni) lack a distinct light stripe on the head and sides, evidence that the types of P. costatus originated from this region.The distinctiveness and width of the light stripe on the head and sides vary both ontogenetically and geographically in other Platydoras (i.e., P. armatulus, P. hancockii and P. brachylecis), and the taxonomic utility of this character remains unclear for these species.Another variable pigmentation feature is the occurrence of small black spots in the axils of the medial thorns of the midlateral scutes.In P. costatus these black spots are usually evident in the axils of all medial thorns (though sometimes poorly contrasted with the dark plates), and Kner (1855) noted their occurrence in his de-scription of D. dentatus (tentatively a junior synonym of P. costatus).In P. hancockii the black spots are usually present and more distinct against the light midlateral stripe (particularly in juveniles), but may not occur in the axils of all thorns.Dark axillary spots are always absent in P. armatulus and P. brachylecis.
Pigmentation aside, Platydoras from throughout its distribution exhibits variation in the shape of the head and postcleithral process, relative eye size, scute depth, and the number of midlateral scutes.All of this variation (coloration, morphometric and meristic), however, is subtle, complex and usually characterized by overlapping ranges among the four valid species recognized herein: P. armatulus, P. brachylecis, P. costatus, and P. hancockii.

Fig. 1 .
Fig. 1.Sets of anatomical landmarks (numbered) and distance measurements among them for trussnets of lateral head and body (A) and dorsal head and nuchal shield (B).

Fig. 2 .
Fig. 2. Scatter plot of individual scores for three groups of Platydoras resulting from SFCVA of both lateral and dorsal trussnets.Canonical variate axes 1 and 2 explain 52.48% and 22.8% of the variance, respectively.