Akko brevis ( Guenther 1864)

James L. Van Tassell & Carole C. Baldwin, 2004, A review of the gobiid genus Akko (Teleostei: Gobiidae) with description of a new species., Zootaxa 462, pp. 1-15 : 6-10

Akko brevis ( Guenther 1864)

Fig. 3

Amblyopus brevis Guenther 1864 : 151, type locality Panama, Pacific coast. Holotype: BMNH 1864.1.26.416 .

Gobioides brevis -Palmer 1952:55

Tyntlastes brevis Jordan and Eigenmann 1887: 511

Material examined: El Salvador - USNM 371781, 11 specimens, Gulf of Fonseca, shrimp trawler Amancer, Captain Francisco Antonio Lopez, 13°06.95’N, 87°52.15’W to 13°08.79’N, 87°47.79’W, 20.0 m . USNM 371782, 28 specimens, same as above except 13°09.54’N, 87°48.30’W to 13°08.42’N, 87°48.00’W . USNM 371782, 13 specimens, Gulf of Fonseca, trawl, 13°09.14’N, 87°51.89’W to 13°09.87’N, 87°50.91’W, 14.5-17.0 m, mud . USNM 371784, 20 specimens, same as above . USNM 371785, 4 specimens, Gulf of Fonseca, trawl, 13°09.99’N, 87°50.75’W to 13°11.01’N, 87°49.56’W, 14.0-12.0 m, mud . USNM 371786, 7 specimens, Gulf of Fonseca, trawl, 13°11.97’N, 87°48.30’W to 13°10.44’N, 87°47.79’W, 10.4-13.3 m, mud . USNM 371787, 94 specimens, off Las Tunas, Departmento La Union, trawl, 13°04.74’N, 88°02.82’W to 13°05.02’N, 88°01.27’W, 21.0-25.0 m, mud . EL-01-017 ( JVT collection), 2 specimens cleared and stained, shrimp trawler, 13°09.54‘N, 087°48.30‘W to 13°08.42‘N, 087°48.00‘N, 20.0 m, mud . Panama - URC 2554.011; 7 specimens, Panama, Darien; 23 Jan 2000 San Miguel, midway between Pta. Garachine and Pta. San Lorenzo, 18 km W Pta. Patiño . BMNH 1864.1.26.416 holotype Amblyopus brevis , Pacific coast of Panama, radiograph . USNM 339614; 1 specimen, 1954, field number W54-326 station 47, Pacific Panama . USNM 43428; 2 specimens, Panama: U.S. Colombia (Equador to Panama) Albatross Expedition, F.C. 5577, 15 Mar 1888 . Peru - USNM 77581; 1 specimen, Paita, Peru, 13 Apr 1907 . USNM 128187; 1 specimen, Sechura Bay near Sechura 16 May 1941 .

Description: Morphometric data are given in Table 1. Frequency distributions of numbers of pectoral- and caudal-fin rays are given in Table 2.

Median fins: Each count is followed parenthetically by the number of specimens recorded with that count; an * indicates value for holotype. The first dorsal fin has seven spines (145*) or six (1) [specimen missing the posteriormost spine], 15 second dorsal-fin elements (146*), and 15 anal-fin elements (143*). The caudal fin is lanceolate, with 17 (133*) segmented rays, 3-5 procurrent rays in the upper lobe, and 2-5 in the lower lobe (Table 2). Rays of the median fins are serially branched three to four times.

Caudal skeleton: Hypurals 1-2 are fused to one another, and hypurals 3, 4, and the terminal half centrum are fused into a single unit. The parhypural supports the lower segmented element, hypural 5 is free, and the single epural supports the uppermost segmented element.

Paired fins: The pectoral fins are relatively short, falling just short of the posterior extreme of the pelvic fin when depressed. There are 19-21 pectoral-fin rays, all dichotomously branched except for the uppermost and lowermost rays. The pelvic fins are united, forming a disk with a well-developed anterior frenum. The pelvic base is a muscular pedicel with strong muscle bundles extending from the vicinity of the pelvic process to the vicinity of the pelvic spine, with some of the fibers inserting on the spines. All pelvic-fin rays are branched dichotomously four to five times. The pelvic fin extends posteriorly to a point that is short of the anus by a distance equal to 2-3 eye diameters.

Pectoral and pelvic girdle: The osteology is the same as that described by Birdsong & Robins (1995) for A. dionaea .

Head: The mouth is large, capable of expanding to a complete circle equal to the body diameter in live specimens. When the mouth is closed, the opening is oriented at an angle of 50° to the horizontal. The upper jaw is slightly protrusible, and there is no rostral firenum. An oral velum is present with dorsal and ventral projections. Upper and lower lips possess 10-15 fleshy papillae along the lateral upper edges. The anterior nostril is composed internally of a thickened, U-shaped, fleshy tube (the anterior section of which forms the external nostril, the remainder is visible under the overlying skin). A histological examination of this structure shows it to possess some smooth muscle fibers. The posterior nostril consists of a short tube or raised rim with no muscular development. The gill opening extends from the fourth pectoral ray ventrally to just above the pelvic-fin base, terminating at a membrane supported by the second branchiostegal ray and extending to the ventral-most pectoral ray. No pseudobranch present. The eye is small, covered with skin, slightly recessed, and has a large lens. Head canal pores B’ and G’ are present. No preopercle pores are present.

Sensory papillae: The sensory papillae pattern is shown in Fig 2. Horizontal row b has an elongate anterior extension ending under the eye; row d is complete, not divided into two sections, and row ot extends ventrally onto the branchiostegals, ending just past the second branchiostegal ray. The first vertical papillae row is complete, extending from the eye to near row d. Additional vertical rows are divided by row b, with two rows above and four rows below row b. Only the last vertical row below row b extends below the level of row d. Dorsal rows x1 and x2 are continuous, or nearly so, as is row n.

Jaws: The upper jaw has a single row of enlarged teeth, 10-11 on each premaxilla in males and 16-18 in females. The lower jaw consists of two rows of teeth, an outer row of 6-8 enlarged teeth in males (7-10 in females), and an inner row of 13-15 small teeth in males (18-20 in females). There is an unossified extension of the ventromedial process of the dentary and the ventral margin of the anguloarticular. The lacrimal is large and ossified.

Myology: The superficial adductor mandibulae is subdivided into the A1 beta, A1 alpha, and A2 bundles (Fig. 4). The A1 beta passes under the large lacrimal and inserts directly by a broad non-ligamentous connection onto the posterodorsal margin of the maxilla. Both the A1 alpha and A2 combine via a strong tendon, which inserts on the coronoid process of the dentary. The ramus mandibularis V passes between the A1 and A2. The origin of the A1 alpha is along the anterior margin of the dorsal half of the preopercle. Adductor mandibulae 2 originates along the anterior margin of the ventral half of the preopercle and along the quadrate, but the area of origin does not reach the condyle of the quadrate.

Braincase: The osteology of the cranial region of Akko brevis and A. dionaea is essentially the same. The primary difference is the lateral expansion of the frontals and parasphenoid in A. dionaea , which is absent in A. brevis .

Vertebral column: There are 11 precaudal and 16 caudal vertebrae (144*). Pleural ribs of vertebrae 3-11 articulate with their respective parapophyses. Epineural bones are found on vertebrae 1-21. Epineurals 1 and 2 articulate with the parapophyses, 3-10 with the pleural ribs, 11 articulates with the parapophysis dorsal to its articulation with the pleural rib, and the remaining epineurals articulate with the centrum of each vertebra. The posterior process of the neural spine present in A. dionaea on each of vertebrae 1-6 is variably present or absent from most of the neural spines in A. brevis . When present it ranges in size from very small to large, and size is not consistent between specimens. The haemal spines of caudal vertebrae 13 and 14 are broad but not bifurcated. There are 2 anal-fin pterygiophores preceding the first haemal spine.

Scales: Scales are cycloid, small, embedded, and non-overlapping anteriorly, becoming larger and overlapping on the caudal peduncle. There are 53-60 in the lateral series. Predorsal scales extend forward to the region above the anterior portion of the opercle. The pectoral-fin base, operculum, and breast are naked. No modified basicaudal scales are present.

Viscera: A small gas bladder is located in the posterior 1/3 of the body cavity and is characterized by a thick tunica interna. The intestine is coiled twice, and its total length is about equal to ¾ body length. A single gravid female contained about 700 eggs in one of the ovaries, each about 0.5 mm in diameter.

Genitalia: In males the genital papilla is short, thin, and pointed. Gravid females possess a short, rounded, bulbous papilla with a rounded opening and a narrow slit along the dorsal margin. Non-gravid females do not have a bulbous papilla.

Pigment: The general body color is whitish with a light pink overtone in live specimens. The upper body has numerous densely packed melanophores, the pigment becoming less dense ventrally and ending at the lateral midline. The belly is whitish from the ventral surface to the lateral midline. The head and upper lip have densely packed small melanophores dorsally that become less concentrated ventrally and terminate at the ventral midline. The pectoral, pelvic, and anal fins are transparent. The caudal fin is black except for the midbasal area, which is whitish with a few scattered melanophores. The dorsal fins have scattered melanophores restricted to the membranes between the fin elements that become more concentrated towards the margin of the fin. Neither males nor females possess any genital pigmentation.