Benthosema aff. fibulatum

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 : 411-413

Benthosema aff. fibulatum

(Figures 28–35)

Material: 55 specimens in total. Anda1 (12) RGM962340 ; Anda2 (15) RGM 962156 , RGM 962173 ; Anda3 (8) RGM 962174 ; Anda4 (2) RGM 962175 AndaDeVos (4) RGM 962158 , RGM 962159 , RGM 962160 ; Roxas (10) RGM 962161 , RGM 962162 , RGM 962163 , RGM 962164 , RGM 962165 , RGM 962166 , RGM 962167 , RGM 962168 , RGM 962169 , RGM 962170 ; AndaCliff1 (3) RGM 962197 ; AndaCliff3 (1) RGM962199 .

Five adult specimens of a rather round otoliths (OL:OH=1.15–1.20) with a length of 3.1–3.5 mm are available together with a large number of juvenile specimens. A brief rostrum slightly exceeds the antirostrum. The slightly convex inner surface harbors a Myctophid sulcus with an ostium that is larger than the cauda (OCL:CCL ratio = 1.50–1.81). There is a distinct but short excisural notch. The ventral rim has a flattened massive denticle at its posterior end and 4–6 poorly developed rounded denticles that are restricted to the anterior part of the ventral rim. The mid-ventral rim is more strongly bent than the other parts, by which the ventral rim gets a deepened, bluntly pointed shape. The dorsal rim displays rounded pre- and postdorsal angles; its middle part runs parallel to the sulcus usually with some undulations. In some of the specimens a feeble depression is present behind the postdorsal angle. In particular the ventral part of the inner surface is convex, while its dorsal area is more flattened. The outer side shows the strongest convexity at the rims, while its central part is rather fat. From the dorsal and ventral rims several ridges and furrows run to the center of the otolith, which vanish in the rather smooth central part. In several of the adult specimens a broad depression runs from the mid-dorsal rim towards the ventral rim; this depression is connected to the undulation of the dorsal rim. The posterior part of the outside is thicker than the anterior part.

The otoliths belong clearly to Benthosema . The round Diaphus metopoclampus (Cocco, 1829) markedly differs from by the specific regular denticulation or crenulation of the ventral rim, an ostium that narrows toward the anterior side, and a pronounced blunted rostrum. The outline of the specimens differs from other round Benthosema specimens B. panamense Táning, 1932 and B. pterotum (Alcock, 1890) . Bethosema fibulatum otoliths display a considerable variation in length:height ratio. Our specimens have the typical Benthosema - type ventral rim denticulation, but are shorter than that those of Benthosema fibulatum depicted in Figure 27 and reported by

PLATE 3

Rivaton & Bourret (1999). Variation in length was reported by Smale et al. (1995) from South African and Mozambique waters, but these specimens had a lower ostium:cauda length ratio, and a less prominent ventral part with a regularly rounded ventral rim than our specimens. In addition, the flattened or even slightly depressed middorsal rim discriminates our specimens from these B. fibulatum otoliths. Our specimens mostly resemble B. fibulatum specimens depicted by Schwarzhans (1980), which were collected in Hawaii waters (photographs depicted in figures 36–38; courtesy of Dr. W. Schwarzhans), but small differences in the middorsal and midventral rims remain. Our specimens may represent a new species or a unknown variation, given the variation in B. fibulatum . Therefore we have reported on this variant separately as Benthosema aff. fibulatum .