Ctenogobius darienensis, Schwarzhans & Aguilera, 2024

Ctenogobius darienensis n. sp.

Figure 43d–e View Fig

Holotype NMB P15829 View Materials ( Fig. 43d View Fig ), Tortonian, Yaviza FM, Pacific Panama, Darien, PPP 1607 .

Paratypes 2 specimens Tortonian, Tuira FM , Pacific Panama, Darien , 1 specimen PPP 1554 ( NMB P15830 View Materials ) , 1 specimen PPP 1171 ( NMB P15831 View Materials ) .

Etymology Named after the province Darien of Panama where the otoliths of this species have been found.

Diagnosis Otolith size up to 1.95 mm in length. OL:OH = 0.95. Otolith ventrally box-shaped and dorsally with strongly expanded postdorsal region. Preventral and postventral angles orthogonal; postdorsal projection broad, protruding. Sulcus relatively short, with moderate ostial lobe, narrowed at ostial-caudal joint and rounded caudal tip; OL:SuL = 1.9–2.0; sulcus inclination angle 6–10°. Small subcaudal iugum located within ventral collum-like ingression. Ventral furrow distinct, regularly curved and relatively distant from ventral rim of otolith.

Description Otolith size up to 1.95 mm in length (holotype). OH:OT = 3.7. Otolith high-bodied with rectangular, box-shaped ventral part and high expanded postdorsal part; dorsal rim with relatively high, rounded predorsal angle, ascending to massive postdorsal region; postdorsal projection broad, high, distinctly protruding. Anterior rim slightly inclined towards dorsal, straight. Posterior rim slightly inclined towards ventral, with weak concavity below postdorsal projection. Ventral rim perfectly straight and horizontal, with orthogonal pre- and postventral angles. All rims smooth or slightly undulating.

Inner face distinctly bent in horizontal direction. Sulcus relatively short, relatively shallow, sole-shaped with moderate ostial lobe, its ostial tip tapering; sulcus margins at ostial-caudal joint broadly but not strongly ingressing, thereby narrowing sulcus; cauda slightly widened and with rounded tip; sulcus inclination angle 6–10°; OL:SuL = 1.9–2.0. Small subcaudal iugum in ventral ingression of sulcus margin at collum (ventral ingression of sulcus margin). Dorsal depression relatively indistinct; ventral furrow distinct, relatively distant from ventral rim of otolith, anteriorly approaching anterior rim of otolith, posteriorly curving behind cauda. Outer face slightly concave, smooth.

Discussion Ctenogobius darienensis closely resembles otoliths of the extant C. sagittula ( Fig. 43a–c View Fig ) in the specific development of the postdorsal region, the very specific shape of the sulcus and even the expression of the ventral furrow. Te main differences are the more compressed shape (OL:OH = 0.95 vs 1.05–1.15), the straight predorsal rim (vs middorsal concavity), the non-protruding rounded predorsal angle and the smaller subcaudal iugum. Ctenogobius darienensis looks like one might envisage the special features of C. sagittula have developed from more plesiomorphic otolith morphologies.