Akko, Birdsong & Robins, 1995

Akko View in CoL clade

Discussion Te genus Akko was reviewed by Van Tassell and Baldwin (2004) and was deemed to contain three species: Akko dionaea Birdsong & Robbins, 1995 , from the Atlantic off northern Brazil; A brevis (Günther, 1896) in the Pacific from El Salvador to Peru; and A. rossi Van Tassell & Baldwin, 2004 , based on a single specimen from off El Salvador. Akko is characterized by a number of autapomorphic characters and its relationships have long been enigmatic. Van Tassell and Baldwin (2004) placed Akko in the Microgobius group of the Gobiosomatini and compared it to Bollmannia and Parrella . Tis placement is apparently supported by molecular phylogenetic analysis shown by Tornabene and Van Tassell (2014) and Tornabene et al. (2016). In the latter article and Tornabene et al. (2022), Akko is shown in a clade further containing Parrella and Microgobius . Based on otoliths we consider Akko and Parrella to constitute a separate clade, closely related, however, to a clade combining all Microgobius species.

Fishes of the genus Akko have a secretive lifestyle in burrows or covered in mud in the substrate at depth down to about 20 m ( Froese & Pauly, 2023). Te reduced eye size may be indicative of living in muddy environments or being hidden in the substrate ( Birdsong & Robins, 1995) Teir large, caninoid teeth suggest that they could be ambush hunters.

Otoliths are available from two of the three extant species of Akko , namely A. dionaea ( Fig. 22b–c View Fig ) and A. brevis ( Fig. 22a View Fig ), and of two of the five species of Parrrella, namely P. ginsburgi Wade, 1946 ( Fig. 22h View Fig ) and P. lucretiae (Eigenmann & Eigenmann, 1888) ( Fig. 22n–o View Fig ) both from the East Pacific. In addition, we place two new fossil otolith-based genera in this clade, namely Cubaguanichthys n. gen. and Proparrella n. gen. Te otoliths of these genera are characterized by being slightly longer than or equally long as high, showing a recessed preventral angle (except in Cubaguanichthys , where it is projecting), lack or weak indentation of the posterior rim which is nearly vertical, a sole-shaped sulcus with low ostial lobe, and a distinct subcaudal iugum (sulcus reduced in size in

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Fig. 22 a View Fig Akko brevis (GÜnther, 1864), extant, USNM 368666, 13°41’N 90°00’W, 13 m. b–c Akko dionaea Birdsong & Robins,1995 , extant, paratypes, USNM 329525, Brazil, 02°32’N 49°57’W, SL 80 and 83 mm. d–e Akko canoa n. sp.; d holotype, NMB P15556, Canoa FM, Ecuador,PPP 3363; e paratype, Canoa FM, Ecuador, NMB 19146, NMB P15557. f Akko lobata n. sp., holotype, NMB P15558,Yaviza FM, Darien, Panama,PPP 1566. g Cubaguanichthys lanceolatus n. gen., n. sp., holotype, NMB P15559,Cubagua FM, Venezuela,PPP 2568. h–i Parrella ginsburgi Wade, 1946 ; h extant, CAS ex SU 46827, Costa Rica, Gulf of Nicoya; i Armuelles FM, Pacific Panama,PPP 3236,NMB P 15560. j Parrella sp. , Swan Cay FM,Swan Cay,Atlantic Panama, PPP 2221, NMB P15561. k–m Parrella lucida n. sp.; k holotype, NMB P690, Manzanilla FM, Trinidad,K 9833; l–m paratypes, l Shark Hole FM,Valiente Peninsula, Panama, PPP 2217,NMB P15562, m Cubagua FM, Venezuela, PPP 2653, NMB P15563. n–o Parrella lucretiae (Eigenmann & Eigenmann, 1888) , extant, USNM 322734, 08°06’N 80°31’W

Akko ). Otoliths of the proposed Antilligobius and Microgobius clades are higher than long.