Achirus mucuri, Ramos, Robson T. C., Ramos, Telton P. A. & Lopes, Paulo R. D., 2009

Ramos, Robson T. C., Ramos, Telton P. A. & Lopes, Paulo R. D., 2009, New species of Achirus (Pleuronectiformes: Achiridae) from Northeastern Brazil, Zootaxa 2113, pp. 55-62 : 56-58

Achirus mucuri n. sp.

Figs. 1 , 2 a,c, and 3a–b, d–e, j, l

Holotype: UFPB 6101, 90.3 mm SL. Brazil, Bahia, Mucuri , estuary of the Mucuri River; approximate geographic coordinates: 18º 05’ 15’’ S, 39º 33’ 53’’ W, 20 August 2001, collected by Cláudio L. S. Sampaio and Frederico D. Fernandes with beach seine.

Paratypes: From the Mucuri River estuary, Mucuri , Bahia state, Brazil: LIUEFS 4456 (1), 76.7 mm SL; LIUEFS 4457 (1), 78.9 mm SL; September, 1999, collected by F. D. Fernandes with beach seine. UFPB 6102, (2), 74.5 – 76.8 mm SL; collected with holotype. UFPB 6130 (3, 1 C & S, 2 alcohol; both alcohol-preserved specimens have connection between branchiostegal membrane and isthmus damaged), 70.2 – 79.6 mm SL; UFPB 6515 (1, C & S, partially disarticulated), 69.4 mm SL; Jun 2000, collected by F. D. Fernandes with beach seine. MZUSP 93253, (1) 73,0 mm SL; collected with holotype. MZUSP 93254 (1) 72.7 mm SL; September 1999, collected by F. D. Fernandes. USNM 389553 (1), 82,0 mm SL; collected with holotype. USNM 389554 (1), 75.1 SL (connection between branchiostegal membrane and isthmus damaged); 20 June 2000, collected by F. D. Fernandes with beach seine. From Porto Alegre ( Mucuri and environs), Bahia state, Brazil: MCZ 11440 (1), 72.8 mm SL; 18º 5’ S and 39º36’ W; 1866, collected by C. F. Hart & E. Copeland.

Nontypes: From the Mucuri River estuary, Mucuri , Bahia state, Brazil: LIUEFS 4454, (1), 76.7 mm SL; September 1999, collected by C. L. S. Sampaio and F. D. Fernandes. LIUEFS 5076 (2), 70.7–72.9 mm SL; September 2000, collected by C. L. S. Sampaio and F. D. Fernandes.

Diagnosis: Achirus mucuri n. sp. ( Fig. 1 ) is distinguished from all its congeners, except A. novoae , by possessing a connection on both the blind and ocular sides between the branchiostegal membrane and the isthmus ( Fig. 2 a), with the connection being slightly stronger on the blind side (vs. complete absence of connections between branchiostegal membranes and isthmus – Fig. 2 b). Additionally, the new species is distinguished from its congeners by having a light-brown body color, with regularly-scattered, minute, darkbrown blotches that are sometimes concentrated to form larger spots. Five specimens differed from the typical light-brown body color in having a brownish-gray background, and one specimen showed brownish-white body pigmentation. The new species differs from A. novoae by the presence of a large, ramified labial fimbriae ( Fig. 3 a–b) (vs. simple, non-ramified, minute labial fimbriae in A. novoae , Fig. 3 c) and by the shape of the infraorbital canal (extending around ventral margin of fixed eye, Fig. 2 c) (vs. infraorbital canal that stops dorsal to fixed eye in A. novoae , Fig. 2 d).

Description: Body ovate. Eye comparatively large, its diameter approximately twice the interorbital space. Eyed-side anterior nostril short, its length equal to its diameter, with a small notch on its anterior wall, and very short fimbriae on its margin. Blind-side posterior nostril with thin skin, wide opening, its diameter equal or nearly equal to greatest width of nostril tube ( Fig. 3 d–e); two specimens (including holotype) with slightly narrower nostril opening than remaining specimens. Length of labial fimbriae not exceeding that of anterior nostril, and forming stalk supporting two to five ramifications of similar size ( Fig. 3 a); some fimbriae with additional ramifications emerging from base of stalk ( Fig. 3 b). One to five non-ramified fimbriae close to mouth corner, and one or two close to mandibular symphysis. Lower lip and its fimbriae cover upper lip when mouth closed. Cirri ( Fig. 3 f) present on upper lip, and scattered on nasal area. Ventral margin of nasal area also with cirri, and with one or more small fringes ( Fig. 3 g–h) on this margin, close to anterior end of nasal area. Branchiostegal membrane slightly connected to isthmus, very weakly on eyed-side of head. Supratemporal canal and epiphyseal branch of latero-sensory cephalic canal system conspicuous. Supratemporal canal arched posteriorly, extending dorsally ( Fig. 2 c); epiphyseal branch extending anteriorly and dorsally, its proximal part close and parallel to migrated eye, its distal end almost reaching dorsal-fin base ( Fig. 2 c); orientation of both canals can be slightly displaced dorsally or ventrally relative to position represented in Figure 2 c. Other canals with a typical pattern of other achirid species (except A. novoae for infraorbital canal), as stated and illustrated ( Fig. 1 ) by Ramos (2003b); holotype with uncommon external connection between distal end of infraorbital canal (at ventral margin of fixed eye) and ventral portion of preopercular canal.

Dorsal-fin rays 48–57; anal-fin rays 38–42; eyed-side pectoral-fin rays 3–6, blind-side pectoral-fin rays absent; eyed-side pelvic-fin rays 5, blind-side pelvic-fin rays 4–5; caudal-fin rays 13–16. Total vertebrae 27: precaudal vertebrae 9, caudal vertebrae 18. Supracranial proximal radials 6. Longitudinal series of scales 57–62. Morphometric data shown in Table 1.

Eyed side. All scales ctenoid, absent from nasal area, lips, margin of preopercle, margin of gill opening, and inter-radial membranes. Dorsal-, anal- and pelvic-fin rays with series of larger scales along their posterior margins. Larger scales preceded by two series of irregularly ordered, smaller scales that extend only on proximal half of each ray; posteriormost rays support only one or two incomplete series of scales. Dark brown cirri present on lateral surfaces of dorsal-, pelvic-, and anal-fin rays, and scattered on trunk, more evident on darkly-pigmented areas. Lateral-line on trunk with simple (non-ramified) tubes.

Blind side. All scales ctenoid, absent from nasal area, lips, margin of preopercle, margin of gill opening, central region of opercular area, and inter-radial membranes. Fringes with a large, rounded basal flap ( Fig. 3 i) and cirri in relatively small numbers, present only on head, more numerous on anterior margin of supracranial and infracranial areas, nasal area, and around mouth. Cirri rare or absent on trunk, except for regularly-spaced cirri along anterior third of lateral-line; cirri replaced by paired or unpaired small fringes on meddle and posterior third of lateral line. Fringes and cirri present on posterior margin of each dorsal-fin ray; more numerous on those in anterior one-third of fin. Fringes and cirri reduced in number posteriorly, and absent on posteriormost rays. Cirri present on all pelvic-fin rays, and on rays of anterior one-third of anal fin. Lateral line dermal tubes on trunk, when present, minute.

Coloration: General body coloration usually light brown to light gray, occasionally (one specimen) brownish-white. Regularly-scattered, minute, dark-brown blotches present on head, trunk and fins and sometimes concentrated to form larger spots. Seven specimens (including holotype) with dark-brown irregular blotches on blind-side caudal-fin base. Vertical lines of chromatophores (achirine lines) faint, sometimes not visible. Coloration on fins more pronounced on rays than interradial membranes, but fins generally of a uniformly pale pigmentation similar to that of body.

Distribution: Achirus mucuri n. sp is known only from the Mucuri River estuary, a small system situated between the Jequitinhonha and Doce rivers, south of Bahia state coast drainage, northeastern Brazil.

Habitat: No data exist regarding its habitat preferences within the estuarine environment.

Figures

FIGURE 1. Holotype of Achirus mucuri, UFPB 6101, 90.3 mm SL from the Mucury River estuary, Bahia, Brazil.

FIGURE 2. Schematic drawing of eyed-side lateral view of head showing internal features of branchial chamber in A. mucuri (a) and A. lineatus (b), and external latero-sensory cephalic canal pattern related to main external features of head, plus anterior part of trunk lateral line in A. mucuri (c) and A. novoae (d). Canal names: 1, pterotic + preopercular + mandibular; 2, extrascapular; 3, trunk lateral line; 4, supratemporal; 5, supraorbital; 6, epiphyseal branch of supraorbital; nasal not represented; arrows indicate distal end of infraorbital canal. For more details see Ramos (2003, Fig. 1).

FIGURE 3. Schematic drawing of: individual eyed-side lower-lip fimbriae of A. mucuri (individualized: a, b) and A. novoae (a set: c); blind-side posterior nostril A. mucuri (d, e); achirids’ typical cirri (f) and fringes (g – i); blind-side lateral view of neurocranium of A. mucuri (j) and A. lineatus (k); blind-side lateral view of caudal skeleton of A. mucuri (l) and A. lineatus (m).