Bathycongrus, Ogilby, 1898

Van Hinsbergh, Victor W. M. & Helwerda, Renate A., 2019, Fish Otoliths from the Cabarruyan Piacenzian-Gelasian fauna found in the Philippines, Zootaxa 4563 (3), pp. 401-443 : 403

Bathycongrus sp.

(Figures 2–4)

Material: 3 specimens in total. Anda2 (2) RGM 962094, RGM 962095 ; Anda3 (1) RGM 962096 .

Three small pentagonal to oval otoliths are available (OL=1.72–2.25; OH=1.27–1.47; OL:OH=1.26–1.46). The dorsal rim has a rounded predorsal part, a rather straight middorsal part and a steep postdorsal part separated from the former by a clear postdorsal angle. The ventral rim is rounded with a blunt ventral angle at its anterior side. The inner surface is convex and somewhat flattened in one of the smallest specimens. The otoliths are characterized by a median-localized homosulcoid sulcus, which is covered by one oval to rectangular colliculum, with a pointed extension at its dorso-anterior side directly connected to an excisural furrow. One of the small specimens lacks the excisural furrow (Figure 4b). A slightly depressed dorsal field is visible. The outer surface is strongly convex in all directions with no ornamentation in the larger specimen and small furrows running from the dorsal and ventral rims in the smaller ones.

Interestingly, the light microscopic picture (Figure 4b) shows a complex Clionid sponge borings (ichnotaxon Entobia ) (identification by courtesy of Steve Donovan), which causes decalcification (and color changes) around the boring channel. The presence of the sponge can be recognized in the SEM picture (Figure 5a) only by small holes, which are the entrances of the channels.

Comparison: The typical shape of the sulcus is also observed in the fossil species Bathycongrus nagymarosyi ( Nolf & Brzobohatý, 1994) from the Aquitanian in France ( Nolf and Brzobohaty, 1994, Bassanago (Pseudoxenomystax) whangaimoanaensis, Schwarzhans, 1980 from the lower Pliocene of New Zealand described by Schwarzhans (1980) and Congridarum mysticus described from the New Zealand Miocene ( Frost, 1933; Schwarzhans, 1980). However, the rostral parts of the first two species are more strongly developed than that of Congridarum mysticus . In B. whangaimoanaensis , the posterior end is also bluntly pointed. Furthermore, the Pliocene otoliths have a larger OL/OH ratio.

Figure 5 displays a small (OL: 1.60 mm, OH: 1.17 mm; OL:OH=1.36) otolith from Tiep2 (RGM962093), which is convex in all directions and has a median sulcus. SEM pictures show an oval shape, which has a blunt angle at 1/3 of the ventral rim and several shallow undulations at its dorsal rim. The central sulcus is covered by one colliculum that ends centrally in an excisural furrow, while its anterior margin bends sharply to the dorsal side. The otolith displays a larger posterior area between the sulcus and the posterior rim than the other small congrid otoliths described below. The inner surface is convex except for the excisural furrow; the outer one is smooth and strongly convex in all directions with a feeble depression at both the pre- and postdorsal rim. It may be a very juvenile specimen of Bathycongrus sp., but due to the juvenile nature identification remains uncertain.