Overview

Comprehensive Description

Akko Birdsong and Robins ZBK

Diagnosis: Body elongate; vertebrae 11 + 16-17 = 27-28; first dorsal fin with seven spines; dorsal-pterygiophore formula 3-221110; second dorsal and anal fins with equal numbers of elements, 15 or 16 present in each; dorsal, caudal, and anal fins continuous, connected by a membrane; upper and lower jaws with enlarged widely spaced teeth which overlap the lips of both jaws; head with very small eyes (2-8% of head length); mouth large, the opening at an angle of 50° to the horizontal; a cephalic lateral-line canal with two pores (B’,G’). Pores very reduced in size and occasionally absent. Sensory papillae pattern in a transverse pattern; horizontal row b elongate, extending to vertical through middle of eye; dorsal rows n elongate, approaching or meeting at midline; rows x1 and x2 continuous.

  • 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, 1-15: 3-3, URL:http://www.zoobank.org/urn:lsid:zoobank.org:pub:73EC2E7B-E100-4C34-9485-3BBC53531905
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[[ Akko Birdsong and Robins ZBK ]]

Introduction

Amblyopus brevis ZBK was described by Günther (1864) from a single specimen collected along the Pacific coast of Panama. Two additional specimens were later obtained from stomach contents of a Centropomus ZBK and added to the collection at the British Museum. Günther (1869) placed A. brevis ZBK in the subgenus Tyntlastes ZBK based on its dentition (teeth in a single series). Jordan and Eigenmann (1886[1887]) elevated Tyntlastes ZBK to a genus and assigned to it the same species that comprised Günther ’s subgenus ( A. brevis ZBK and A. sagitta ZBK ). When Palmer (1952) reviewed the genus Gobioides ZBK , he created two subgenera: Gobioides ZBK , with 25-26 vertebrae and 14-16 anal-fin rays, and Tyntlastes ZBK , with 31 vertebrae and 19 anal-fin rays. He placed A. brevis ZBK in Gobioides ZBK based on its vertebral count of 26 (an incorrect count) and anal-fin count of 15.

Murdy (1998) reviewed Gobioides ZBK and noted that Amblyopus brevis Guenther ZBK does not belong in Gobioides ZBK based on its dorsal pterygiophore pattern of 3-221110 and a vertebral count of 11+16 (not 26 as given by Palmer [1952]). Those characters would place it in the “ Gobiosoma ” or “ Microgobius ZBK ” groups of the Gobiosomatini and thus part of the Gobiinae (sensu Pezold, 1993).

Birdsong and Robins (1995) erected Akko ZBK for a new species, A. dionaea [1] ZBK , from off Brazil. Akko dionaea ZBK has a dorsal pterygiophore pattern of 3-221110, 11+16 vertebrae, and a distinctive sensory papillae pattern in which horizontal row b is elongate, extending anteriorly to a vertical through the middle of the eye; dorsal row n is elongate, the left and right elements approaching or meeting at the dorsal midline; and rows x1 and x2 are continuous. Birdsong and Robins (1995) placed the genus in the Gobiosomatini but did not comment further on its relationships within the tribe because of the large number of osteological autapomorphies it possesses.

Fish collections made during a Smithsonian Institution cruise aboard the R/V Uracca to the Darien province of Panama in 2000 resulted in several specimens initially identified as Gobioides brevis . A Smithsonian expedition to El Salvador in 2002 resulted in 144 additional specimens. This species has a dorsal pterygiophore pattern of 3-221110, 11 precaudal and 16 caudal vertebrae, and the distinct papillae pattern of and most of the osteological autapomorphies present in Akko dionaea ZBK . Several specimens were sent to the British Museum where Anthony Gill confirmed that our specimens match those of the holotype of Amblyopus brevis ZBK . We therefore take the opportunity to redescribe Amblyopus brevis ZBK based on the new material and place it in the genus Akko ZBK , thus extending the range of Akko ZBK from the Atlantic to the eastern Pacific Ocean.

In addition, a previously undescribed gobiid species obtained during the El Salvador expedition appears to represent a new species of Akko ZBK . This species, which is larger than A. brevis ZBK , found in shallower waters (7-9 meters as opposed to 15-25 meters for A. brevis ZBK ), and separable from A. brevis ZBK on the basis of numbers of lateral-line scales, vertebrae, dorsal- and anal-fin rays, and pigment pattern, is described herein.

[1] Birdsong and Robins (1995) spelled the name of their new species “dionea” in the abstract but “dionaea ” in all other places in the paper. The species was named after the plant genus Dionaea. We conclude that “dionea” is a misspelling.

  • 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, 1-15: 1-2, URL:http://www.zoobank.org/urn:lsid:zoobank.org:pub:73EC2E7B-E100-4C34-9485-3BBC53531905
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[[ Akko Birdsong and Robins ZBK ]]

Discussion

All species of Akko ZBK are easily recognized by their large teeth, elongate body, small eyes, anterior nostril located within a fleshy tube, and by having the dorsal, caudal, and anal fins connected by membrane. The species can be differentiated by numbers of lateral scales, vertebrae, and fin rays, and by color. In A. dionaea ZBK the lateral scales do not overlap on the caudal peduncle, and there are approximately 76 in the series; A. brevis and A. rossi ZBK both have overlapping scales on the caudal peduncle, with 53-60 and 155 scales, respectively, in the lateral series. Color patterns are distinctive, even in preserved specimens. Akko dionaea ZBK has no trunk or head melanophores, and only the distal two-thirds of the caudal fin and posterior portion of the anal fin have some melanophores; A. brevis possesses melanophores on the upper portion of the trunk, on the interradial membranes of the dorsal fin, and on the caudal fin; A. rossi ZBK has a heavily pigmented dorsal trunk, and all fins are dark brown. Vertebral counts in A. dionaea ZBK and A. brevis are 11 precaudal and 16 caudal, 11+17 in A. rossi ZBK ; additional specimens of A. rossi ZBK are needed to determine if this vertebral count is characteristic for the species. Akko dionaea ZBK can be separated from the Pacific species by having fewer pectoral-fin rays: 17 in A. dionaea ZBK , 19-21 in A. brevis , and 19 in A. rossi ZBK . The second dorsal and anal fins both have 15 elements in A. dionaea ZBK and A. brevis but 16 in A. rossi ZBK . The pelvic-fin rays are branched in the three species, with A. dionaea ZBK and A. brevis having all rays dichotomously branched. In A. rossi ZBK , rays 1,2,3 are serially branched, and rays 4,5 are dichotomously branched. Differences that readily separate the three species are given in Table 3.

The head pores in all species of Akko ZBK are very small and difficult to observe. All species of Akko ZBK have a short cephalic head canal with two pores, B’ and G’. Pore G’ was reported as absent by Birdsong and Robins (1995) in A. dionaea ZBK , and, although it is absent in the holotype, we have observed it in several of the paratypes. The three species also possess small fleshy flaps on the posterior dorsal edges of the upper and lower lips, a character not mentioned in the original description of A. dionaea ZBK . Birdsong and Robins (1995) stated that row ot in A. dionaea ZBK has a disjunct extension on the branchiostegals. Our examination of the types of A. dionaea ZBK with 0.5mm fiber optic lighting shows this row to be complete, not disjunct, and similar to our Figure 2 of A. brevis . A large ossified lacrimal is present in all species of Akko ZBK . In all other Gobiosomatini and most members of the Gobiinae the lacrimal is small. Akko brevis has the ability to open its mouth in a complete circle equal to the body diameter. The large lacrimal, which is attached to the maxilla by a broad tendinous sheath, may play a role in this movement.

Akko ZBK belongs within the tribe Gobiosomatini based on the presence of seven spines in the first dorsal fin, a dorsal-pterygiophore formula of 3-221110, and a vertebral count of 11 precaudal and 16 caudal vertebrae (17 in rossi ZBK ). Although Birdsong and Robins (1995) placed Akko ZBK within the tribe, they did not comment further on its relationships within the group because of the large number of autapomorphies possessed by A. dionaea ZBK . Additional information now available from mtDNA places Akko ZBK within the “ Microgobius ZBK ” group of the Gobiosomatini (Birdsong et al. 1988) and provides support for a sister-group relationship with Microgobius ZBK (Ruber et al. 2003).

Further supporting the placement of Akko ZBK within the “ Microgobius ZBK ” group are patterns of sensory papillae. There are two general categories of sensory papillae patterns within the Gobiosomatini: In the “ Gobiosoma ” group, row n on the dorsal surface of the head is short, the right and left elements never joining at the dorsal midline, and rows x1 and x2 are not connected to form a continuous row (Fig. 5A); in the “ Microgobius ZBK ” group row n is generally elongate, the left and right elements frequently joining at the dorsal midline, and rows x1 and x2 are united to form a single row (Fig. 5B). This arrangement of sensory papillae has been observed in most species of Microgobius ZBK , Bollmannia ZBK , and Parrella ZBK of the “ Microgobius ZBK ” group by one of us (JVT). All species of Akko ZBK possess a papillae pattern similar to that of the “ Microgobius ZBK ” group.

Myological features, particularly origin and insertion patterns within the adductor mandibulae complex, also support the proposed relationship between Akko ZBK and other species of the “ Microgobius ZBK ” group. In the “ Gobiosoma ” group (Fig. 6A) the adductor mandibulae1 complex (A1) originates along the dorsal half of the preopercle and along the lateral edges of the pterotic and sphenotic. The A1 complex separates into A1 beta and A1 alpha sections. An additional separation of the A1, the A1 gamma, occurs in all genera of the “ Gobiosoma ” group except Aruma ZBK , Barbulifer ZBK , Gymneleotris ZBK , Chriolepis ZBK , Eleotrica ZBK , Pycnomma ZBK , Gobulus ZBK , Nes ZBK (Van Tassell, 1998). The A1 gamma inserts on the maxilla and on the A2 gamma, the A1 beta inserts on the maxilla, and the A1 alpha inserts on the coronoid process of the dentary. The adductor mandibulae 2 (A2) originates on the ventral half of the preopercle and on the quadrate. The A2 separates into two sections, one inserting along with the A1 alpha on the coronoid process and the other inserting on the maxilla and A1 gamma, near or at the insertion of the primordial ligament.

In the “ Microgobius ZBK ” group the A1 complex does not originate along the sphenotic, and the A1 gamma is absent. In Bollmannia ZBK (Fig. 6B) the A1 originates along the dorsal half of the preopercle and on the pterotic; it inserts via two heads, one on the maxilla, in conjunction with the A1 beta, and the second via a tendon on the coronoid process of the dentary. An A1 beta is present medial to the large A1 alpha, originating on the hyomandibular and inserting with the A1 alpha on the maxilla. In Microgobius ZBK there is a partial separation of an A1 beta from A1 alpha anteriorly, just prior to the insertion on the maxilla; otherwise, the A1 remains a single muscle mass. The adductor mandibulae 2 is a single mass originating along the ventral half of the preopercle and on the quadrate. It inserts, along with the A1 alpha, via a tendon onto the dentary. The cheek myology pattern of Akko ZBK is most similar to that of the “ Microgobius ZBK ” group (Fig. 4). Cheek myology of Parrella ZBK and Palatogobius ZBK in the “ Microgobius ZBK ” group has not been examined.

  • 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, 1-15: 10-14, URL:http://www.zoobank.org/urn:lsid:zoobank.org:pub:73EC2E7B-E100-4C34-9485-3BBC53531905
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Ecology

Habitat

Depth range based on 11 specimens in 3 taxa.
Water temperature and chemistry ranges based on 1 sample.

Environmental ranges
  Depth range (m): 8.25 - 23
  Temperature range (°C): 27.145 - 27.145
  Nitrate (umol/L): 0.628 - 0.628
  Salinity (PPS): 35.964 - 35.964
  Oxygen (ml/l): 4.523 - 4.523
  Phosphate (umol/l): 0.321 - 0.321
  Silicate (umol/l): 2.608 - 2.608

Graphical representation

Depth range (m): 8.25 - 23
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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Wikipedia

Akko (genus)

Akko is a genus of gobies native to the Atlantic and Pacific coasts of the Americas.

Species[edit source | edit]

There are currently three recognized species in this genus:[1]

References[edit source | edit]

  1. ^ Froese, Rainer, and Daniel Pauly, eds. (2013). Species of Akko in FishBase. April 2013 version.
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