Brachyrhamdia thayeria, Slobodian, Veronica & Bockmann, Flávio Alicino, 2013

Slobodian, Veronica & Bockmann, Flávio Alicino, 2013, A new Brachyrhamdia (Siluriformes: Heptapteridae) from Rio Japurá basin, Brazil, with comments on its phylogenetic affinities, biogeography and mimicry in the genus, Zootaxa 3717 (1), pp. 1-22 : 3-11

Brachyrhamdia thayeria , n. sp.

Figures 1–5 ; Table 1

Brachyrhamdia n. sp. ‘Amanã’.—Slobodian & Bockmann, 2013 [phylogenetic relationships: 462].

Brachyrhamdia sp. 1.—Queiroz & Hercos, 2009 [abundance in igarapés of Amanã Lake, sampled October, 2006: 63, unnumb. table]; Hercos, Queiroz & Almeida, 2009 [fishes of the Amanã Reservation: 51, tab. 1; photograph of live specimen in aquarium: 156; brief description: 156; considered rare: 156; observed in shoals of Corydoras : 156; data on habitat and natural history: 156–157; distribution in Lago Amanã basin: 157, map].

[Nova espécie de] Brachyrhamdia .—Slobodian, Bockmann & Sousa [Rio Japurá basin: 192; similar to B. rambarrani : 192; possible syntopy with Corydoras arcuatus Elwin (1939) (Callichthyidae) : 192].

Holotype. INPA 39534, 50.7 mm SL (xr), Brazil, Amazonas, Maraã, Lago Amanã, Rio Japurá basin, 02°32’06”S, 65°43’02”W, 44 m a.s.l., 14 Mar 2003, M. Catarino, J. Zuanon, L. M. Sousa et al.

Paratypes. ANSP 194110, 1, xy, 35.9 mm SL, Brazil, Amazonas, Amanã, Igarapé Baré, tributary to Rio Japurá, 02°17’15”S, 64°41’16”W, 44 m a.s.l., 6 Nov 2002, M. Catarino, L. M. Sousa et al.; INPA 25306, 2, xy, 37.9–41.0 mm SL, collected with the holotype; LIRP 10237, 1 xr, 44.5 mm SL, 1 c&s, 55.2 mm SL, collected with the holotype; INPA 25740, 1, xy, 31.3 mm SL, collected with ANSP 194110; INPA 25741, 2, xy, 36.8–37.1 mm SL, Brazil, Amazonas, Amanã, Igarapé Baré, tributary to Rio Japurá, 02°20’10”S, 64°42’43”W, 44 m a.s.l., 6 Nov 2002, coll. M. Catarino, L. M. Sousa et al.; MZUSP 114011, 1, xr, 34.1 mm SL, collected with INPA 25741.

Diagnosis. Brachyrhamdia thayeria is distinguished from all its congeners by a unique coloration pattern represented by a dark brown stripe at caudal region extending transversely from region immediately below middle of adipose-fin base to the base of the ventral caudal-fin lobe. It shares exclusively with B. rambarrani the presence of a dark brown band on dorsolateral region of body. In B. thayeria , however, the band originates just posterior to the eye and finishes on caudal peduncle just posterior to adipose-fin base, whereas in B. rambarrani the band begins just below the dorsal-fin origin. It further differs from B. rambarrani by the having the supraoccipital process roughly triangular (vs. roughly rectangular). Brachyrhamdia thayeria is distinguished from B. heteropleura , B. marthae , and B. meesi by having a lower vertebral count, usually 35–36 vertebrae (vs. 37–39 vertebrae) and absence of dark lateral stripe along the trunk (vs. distinct stripe in B. marthae and B. meesi and faint stripe in B. heteropleura ). It differs from B. heteropleura , B. imitator , and B. rambarrani in possessing the pharyngobranchial 1, which is otherwise missing in those species. Brachyrhamdia thayeria is promptly separated from B. marthae and B. meesi by having large, pointed, retrorse dentations along the basal portion of medial edge of pectoral spine (vs. dentations on medial edge of pectoral spine distinctly smaller, antrorse or perpendicularly oriented, and some with bifid apices).

Description. Morphometric data presented in Table 1 . Body ( Figure 1 ) stout, progressively more compressed caudally from cleithrum. Dorsal profile of body arched from snout tip to caudal peduncle. Ventral profile of body slightly convex from mandible to ventral-fin origin and approximately straight from this region to caudal peduncle. Greatest body depth at dorsal-fin origin. Pseudotympanum large, triangular, above posterior process of cleithrum ( Figure 1 ). Posterior cleithral process slender, sharply pointed. Axillary pore as slit immediately above the posterior portion of pectoral-fin base, below posterior cleithral process. Urogenital papilla tubular, triangular, short. Anus and urogenital papilla adjacent. Anus between verticals through end of first third of pelvic fin and anterior portion of second third of pelvic fin; urogenital papilla between verticals through end of second third of pelvic fin and anterior portion of the last third of pelvic fin.

Head ( Figure 1 ) long and deep; snout terminal. Eyes elliptical, large, with greatest length in horizontal axis, placed dorsolaterally. Limits of eye well defined by marked invagination, especially pronounced around anterior and dorsal rim. Anterior naris tubular; posterior naris completely surrounded by shallow skin flap except for narrow posterolateral region. Premaxilla without backward projecting angle. Premaxilla and dentary each with 5–6 rows of small viliform teeth. Anteriormost tooth row of each premaxilla with 29–31 teeth; anteriormost tooth row of each dentary with 37–42 teeth. Palate and vomer edentulous. Barbels relatively long, thin, and elliptical in crosssection ( Figure 1 ). Tip of maxillary barbel extending to posterior margin of anal fin or sometimes beyond, reaching base of caudal-fin rays. Mental barbel, when parallel to main body axis, with distal tip finishing in region between anterior and mid-third of dorsal-fin base. Inner mental barbel, when lying parallel to main body axis, with distal tip finishing in region between middle and outer border of branchiostegal membrane. Outer mental barbel longer than inner barbel. Insertion of inner mental barbel anterior to origin of outer mental barbel. Supraoccipital process roughly triangular, with broad base and lateral edges converging posteriorly towards tip ( Figure 2 ).

Branchiostegal membranes well developed, free, united to isthmus only at medial apex, and not connected to each other anteriorly. Branchiostegal rays 6 (9*)–7 (1). Branchial rakers short, 7 (4), 8 (5*), 9 (1) on first ceratobranchial (including one on angle formed with epibranchial), and 1 (1), 2 (6*), 3 (3) on first epibranchial. Pharyngobranchial 1 present ( Figure 3 ).

Dorsal fin triangular, distally concave ( Figure 1 ), reaching adipose fin when adpressed. Dorsal fin with i, 5 (1), i, 6 (8*), plus anteriormost spinelet. Cleared and stained specimen with abnormal extra posterior ray. Distance between dorsal and adipose fins short, about 60–80% of dorsal-fin base. Dorsal-fin rays supported by seven bladelike pterygiophores. Proximal tip of anteriormost pterygiophore of dorsal fin located between bifid neural spine of vertebra 4–5 (10*); proximal tip of posteriormost pterygiophore of dorsal fin located between space of neural (or pseudoneural) spine of vertebra 9 (1), 9–10 (7*), and 10 (2). Spinelet large, with wide base and rounded distal extremity. Supraneural triangular dorsally, with anterior point fitted into distal margin of supraoccipital process, and with long ventral process abutting anterior edge of first pterygiophore. Distal extremity of first pterygiophore expanded, forming typical median, anteriormost nuchal plate 1. Distal extremity of second pterygiophore expanded laterally, forming typically paired nuchal plates 2. Dorsal-fin pterygiophores 1 and 2 proximate to each other, distally sutured.

As percentage of Standard Length ......continued on the next page

Pectoral fin triangular with concave distal border, I, 7 (10*). First pectoral-fin ray long, roughly straight, with proximal part rigid, forming a spine, and short distal tip flexible and distinctly segmented. Lateral margin of spiny portion of first pectoral-fin ray with 26 (3), 27 (1), 30 (3), 31 (2), 32 (1*) tiny, perpendicular to slightly antrorse dentations from basal portion to or slightly short of midpoint of spine, and with 4–5 smooth serrae along its distal third. Medial margin of spiny portion of first pectoral-fin ray with 7 (2), 8 (7), 10 (1*) retrorse dentations, from region just beyond base of spine to or slightly short of midpoint of spine, plus 1–2 unossified distalmost dentations ( Figure 4 ).

Pelvic fin triangular with straight distal border, i,5 rays (10*). Anterior portion of pelvic-fin base at vertical through region just posterior of dorsal-fin base ( Figure 1 ). Inner margins of pelvic-fin bases remote from each other. Tip of adpressed pelvic fin falling short of vertical through anal-fin origin. First ray unbranched, completely flexible, segmented, and distinctly shorter than second and third rays (first and second branched rays, respectively). Site of insertion of first pelvic-fin ray on basipterygium below vertebral centra 12 to 14, with variation as follows: between centra 12–13 (2), centrum 13 (3), and centra 13–14 (5*).

Anal fin with short base and convex distal border, supported by 12 (5), 13 (3*), and 14 (2) rays, including 7 (5) and 8 (5*) branched rays. Anal-fin rays with following branching pattern: v,7 (4), vi,7 (1), iv,8 (1), v,8 (2*), and vi,8 (2). Two or three anteriormost anal-fin rays vestigial, unsegmented, embedded in thick anterior fold. Origin of anal-fin base posterior to adipose-fin origin. End of anal-fin base at vertical through the anterior portion of last fourth of adipose-fin base. Tip of anteriormost pterygiophore of anal fin between hemal spines of vertebrae 19–20 (8*) and 20–21 (2). Tip of posteriormost pterygiophore of anal fin between hemal spines of vertebrae 24–25 (9*) and 25–26 (1).

Adipose fin long, forming ascending elevated curve in lateral profile, with highest point approximately at middle third. Adipose fin merging gradually with back anteriorly, its origin difficult to pinpoint. Origin of adiposefin base above vertebral centra 17 to 19, with variation as follows: centrum 17 (1), 18 (7*), and 19 (2). Posterior limit of adipose fin well defined, ending in rounded free lobe. End of adipose-fin base above vertebral centra 29 to 31, with variation as follows: between centra 29–30 (2), centrum 30 (4), between centra 30–31 (3*), and centrum 31 (1).

Caudal fin ( Figures 1 and 5 ) deeply forked, with dorsal lobe usually slightly longer than ventral lobe. Branched caudal-fin rays divided two or three times. Central rays of caudal fin also branched, curved, and devoid of marginal expansions. Total caudal fin-rays 49 (2), 51 (5), 52 (2), and 53 (1*); with 24 (2), 25 (5), and 26 (3*) rays in dorsal lobe, and 24 (1), 25 (2), 26 (4), and 27 (3*) rays in ventral lobe. Dorsal lobe with 7 (10*) branched rays; ventral lobe with 8 (10*) branched rays. Parhypural not fused to hypural 1. Hypurals 1 and 2 completely co-ossified into single ventral caudal plate, without any vestige of suture. Hypurals 3 and 4 completely fused to each other. Hypural 5 completely free, not fused to hypural 4. Epural single, rod-like, autogenous. Hypurapophysis and secondary hypurapophysis fused, forming a continuous horizontal shelf (complex hypurapophysis) to base of hypural 2 (hypurapophysis “ type C” of Lundberg & Baskin, 1969). Dorsal hypural plate with 8 (10*) rays. Dorsal caudal rays arranged as follows on dorsal hypural plate: 6 rays on hypurals 3+4 and 2 rays on hypural 5 (10*). Caudal rays on dorsal plate with following branching pattern: i,7 (10*). Ventral caudal plate (parhypural plus hypurals 1+2) with 9 (10*) rays. Ventral caudal rays arranged as follows on ventral caudal plate: 2 rays on parhypural and 7 rays on hypurals 1+2 (10*). Caudal rays on ventral plate with following branching pattern: i,8 (10*) rays. Base of central caudal-fin rays (lowermost ray of dorsal caudal-fin lobe and uppermost ray of ventral caudal-fin lobe) not articulating directly to caudal plates, floating near diastema.

Total vertebrae 35 (3)–36 (7*). Ribs 7 (6)–8 (4*) pairs. Distal extremities of ribs tapered. First complete (i.e., not bifid distally) hemal spine on vertebrae 14 (7)–15 (3*).

Laterosensory system ( Figure 2 ). Head sensory canals with simple (unbranched) tubes ending in single pores. Supraorbital sensory canal continuous and connected to otic and infraorbital sensory canals posteriorly and, usually, to infraorbital anteriorly. Supraorbital sensory canal at least with five branches: s1, s2, s3, s6 (epiphyseal branch), and s8 (parietal branch). Left and right epiphyseal branches (s6) never fused to each other medially. Presence of s4 branch and pore variable: present on both head sides in 3 specimens, present on one head side only in 3 (*) specimens, and absent on both head sides in 1 specimen. Presence of s7 branch and pore (postorbital) variable: present on both head sides in 2 specimens, present on one head side only in 3 specimens, and absent on both head sides in 2 (*) specimens. S5 branch and pore absent. Supraorbital and infraorbital sensory canals anteriorly connected to each other through s2 and i2 branches (forming complex s2+ i2 pore), except in one c&s specimen. Otic sensory canal short, without pores, and continuous with posterior limits of supra- and infraorbital sensory canals, anteriorly, and with anterior limit of postotic sensory canal, posteriorly. Postotic (or temporal) sensory canal extends from posterior limit of otic sensory canal to anterior limit of lateral line, with 3 branches (po1, po2, and po3). First postotic branch (po1) fused to posteriormost branch preoperculomandibular sensory (pm11), forming po1+pm11 complex pore. Infraorbital sensory canal with six branches, with second branch (i2) usually fused to second supraorbital branch (s2) (see above). Preoperculomandibular sensory canal with 11 branches and pores; anteriormost preoperculomandibular sensory branch (pm1) not fused to its antimeric branch. Lateral-line sensory canal continuous with postotic sensory canal anteriorly and extending to base of caudal-fin rays. First lateral-line pore below level of adjacent pores of lateral line.

Color in alcohol. Background body coloration ( Figure 1 ) yellowish dorsally; dorsal and lateral regions of body with sparsely distributed dark melanophores, slightly more concentrated along limits between myomeres; a large area of trunk above the pectoral fin (covering the pseudotympanum) with dense concentration of melanophores. Each side of body with a broad, dark brown dorsolateral stripe extending from just behind the eye to region immediately posterior to adipose-fin base. Paired dorsolateral stripes separated anteriorly by supraoccipital process, converging anteriorly along midline of the dorsum from the dorsal-fin origin, although the region lateral to dorsal-fin base is sometimes unpigmented.

Top of head with heavy concentration of dark melanophores. Head with broad tranverse dark stripe from its posterodorsal part to region below eye (forming conspicuous subocular blotch). Ventral region of body lacking pigmentation except for region between gape and insertion of mental barbels; pectoral-fin base and region immediately posterior to pelvic fins with few melanophores. Maxillary barbel with brown pigment along its dorsal surface; mental barbels weakly pigmented, with scattered brown pigment along their dorsal surfaces. Sparse dark melanophores along all barbels.

Dorsal-fin spine and distal portion of first branched dorsal-fin ray heavily pigmented; remaining rays with scattered melanophores; interradial membranes hyaline. First ray of pectoral fin darkly pigmented, remaining rays with few scattered melanophores along basal portion. Rays of pelvic fin with few scattered melanophores along basal portion. Adipose fin has brown pigmentation on its basal half. Anal fin almost hyaline, with sparse pigment on bases of rays. Caudal fin with brown pigment along rays.

Geographic distribution. Brachyrhamdia thayeria is known to occur in the Rio Japurá basin, a left margin tributary of the Rio Solimões, in Brazil, especially in the Lago Amanã system ( Figure 6 ).

Ecological notes. Brachyrhamdia thayeria inhabits the upper and middle courses of both white and blackwater streams (“igarapés”) affluent to Lago Amanã. Specimens were captured in the water column associated with marginal vegetation or along sandy beaches in shallow streams (about 1 m depth) with 0.20 mg /l of dissolved oxygen and conductivity 27.6–57.1 µS/cm3 (Hercos et al., 2009).

Etymology. The specific epithet thayeria refers to Thayeria Eigenmann (1908), a genus of South American characin that has a similar diagonal dark stripe on the caudal peduncle, and also in honor of the North American businessman and philanthropist Nathaniel Thayer, Jr. (1808–1883), who sponsored the expedition to Brazil led by Swiss zoologist Louis Agassiz from 1865 to 1866 (then known as Thayer Expedition), which was responsible for important discoveries of the Amazon fish fauna.

Figures

FIGURE 1. Brachyrhamdia thayeria, INPA 39534, 50.7 mm SL, holotype, Brazil, Amazonas, Maraã, Lago Amanã, Rio Japurá basin.

FIGURE 2. Cranium of Brachyrhamdia thayeria, dorsal view, LIRP 10237, 55.2 mm SL, paratype. Abbreviations: afanterior fontanel; an—antorbital; ap—autopalatine; at—antorbital tubule; ec, ethmoidean cartilage; ep—epioccipital; esextrascapula; ex—exoccipital; fr—frontal; i 1 – 6 — infraorbital sensory branches 1 to 6; le—lateral ethmoid; me—mesethmoid; mx—maxilla; na—nasal; pf—posterior fontanel; pre—premaxilla; po 1 + pm 11 — postotic – preoperculomandibular complex sensory branch (postotic sensory branch 1 + preoperculomandibular sensory branch 11); po 2 — postotic sensory branch 2; ptpterotic; s 1 – 4 — supraorbital sensory branches 1 to 4; s 6 — supraorbital sensory branch 6 (epiphyseal branch); s 7 — supraorbital sensory branch 7 (postorbital branch); s 8 — supraorbital sensory branch 8 (parietal branch); sp—sphenotic; st 1 – 4 — suborbital tubules 1 to 4; soc—supraoccipital; socp—supraoccipital process. Scale bar— 2 mm.

FIGURE 3. Branchial arches of Brachyrhamdia thayeria, dorsal view, LIRP 10237, 55.2 mm SL, paratype. Gill rakers and dorsal elements of left gill arches not shown. Abbreviations: ac 4 — accessory element of ceratobranchial 4; cn—cartilaginous nodule; bb 2 – 4 — basibranchials 2 to 4; cb 1 – 5 — ceratobranchials 1 to 5; eb 1 – 4 — epibranchials 1 to 4; hb 1 – 3 — hypobranchials 1 to 3; pb 1 — pharyngobranchial 1; pb 3 – 4 — pharyngobranchials 3 and 4; tp—tooth plate; and up—uncinate process. Scale bar— 1 mm.

FIGURE 4. Right pectoral spine of Brachyrhamdia thayeria, dorsal view, LIRP 10237, 55.2 mm SL, paratype. Scale bar— 1 mm.

FIGURE 5. Caudal skeleton of Brachyrhamdia thayeria, LIRP 10237, 55.2 mm SL, paratype. Abbreviations: cf—caudal artery foramen; ep—epural; ha + has—complex hypurapophysis composed of hypurapophysis and secondary hypurapophysis; hu 1 + hu 2 — complex ventral plate formed by co-ossification of hypurals 1 and 2; hu 3 + hu 4 — complex dorsal plate formed by coossification of hypurals 3 and 4; hu 5 — hypural 5; ph—parhypural; pu 1 + u 1 — complex centrum composed of preural centrum 1 and ural centrum 1; pu 2 — preural centrum 2; and ur—uroneural. Scale bar— 1 mm.

FIGURE 6. Map of northern South America, showing distribution of Brachyrhamdia thayeria.

Tables

TABLE 1. Morphometric data of Brachyrhamdia thayeria. n. sp., based on holotype (INPA 39534) and 9 paratypes (ANSP 194110, INPA 25306, INPA 25740, INPA 25741, LIRP 10237, and MZUSP 114011). Abbreviation: Hholotype; Max—maximum; Min—minimum; n—number of specimens; SD—standard deviation; x — average.

	H	Min	Max	x	SD	n
Total length (mm)	65.5	40.6	65.5	-	-	10
Standard length (mm)	50.7	30.3	54.2	-	-	10
As percentage of Standard Length
Body depth (dorsal)	25.3	22.6	28.4	24.7	1.77	10
Body width (dorsal)	17.1	15.8	20.4	18.1	1.39	10
Cleithral width	21.3	21.3	23.7	22.1	0.68	10
Head length	34.6	27.3	41.8	35.2	5.18	10
As percentage of Head Length
Head depth	63.6	54.6	79.0	65.1	9.43	10
Head width	60.9	53.3	78.3	63.7	9.71	10
Eye diameter (left)	22.7	18.6	28.2	22.9	3.16	10
Eye diameter (right)	22.9	19.9	28.7	23.5	3.11	10
Fleshy interorbital	29.6	28.0	38.3	32.4	3.72	10
Bony interorbital	24.5	21.5	30.0	25.6	2.90	10
Mouth gape	32.9	28.0	40.5	33.1	5.15	10
Snout length (left)	27.4	25.2	36.6	30.8	3.62	10
Snout length (right)	28.0	23.0	37.6	30.3	4.11	10
Distance between snout tip and posterior nare (left side)	20.1	13.8	24.4	18.8	3.10	10
Distance between snout tip and posterior nare (right side)	19.8	15.2	20.5	17.9	1.85	10
Anterior internarial width	13.3	11.8	17.3	14.0	1.93	10
Posterior internarial width	17.1	14.9	22.4	17.9	2.55	10
Intranarial length (left side)	12.0	8.5	16.0	12.0	2.72	10
Intranarial length (right side)	12.5	8.1	17.6	11.5	3.21	10