Diaphus watatsumi, Schwarzhans & Ohe & Tsuchiya & Ujihara, 2022

Schwarzhans, Werner, Ohe, Fumio, Tsuchiya, Yuki & Ujihara, Atsushi, 2022, Lanternfish otoliths (Myctophidae, Teleostei) from the Miocene of Japan, Zitteliana 96, pp. 103-134 : 103

Diaphus watatsumi sp. nov.

Fig. 8U

Etymology.

Named after Watatsumi, a Shinto spirit of the sea in Japanese.

Holotype.

SMF PO 101.136 (Fig. 8U-X ), Miya River at Numa, Tsuyama City, Okayama Prefecture, Takakura FM, level MS 52, late Burdigalian, diatom zone 3A-3B.

Paratypes.

3 specimens (SMF PO 101.137), same data as holotype, levels gh, h, j.

Additional material.

7 specimens, same data as holotype, levels MS 15, MS 22, MS 27, MS 36, MS 70, f9, j .

Diagnosis.

OL:OH = 1.35-1.45; OH:OT = 3.8-4.5. Dorsal rim with distinct postdorsal angle above central position of cauda, slightly concave postdorsal section and depressed predorsal section. Rostrum moderately long, 16-18% of OL. Ventral rim with 13-15 feeble denticles. Sulcus long, relatively narrow, slightly bent; OCL:CCL = 2.0.

Description.

Slender, thin and relatively large otoliths reaching about 4.1 mm in length (holotype 3.8 mm). Rostrum moderately long and pointed; excisura mostly shallow and narrow, antirostrum much shorter than rostrum. Dorsal rim anteriorly depressed, ascending to distinct postdorsal angle positioned relatively forward above center of cauda; postdorsal section inclined, slightly concave. Ventral rim rather shallow and very regularly bent, with 13-15 feeble denticles which erode easily and are rarely completely preserved like in holotype. Posterior rim gently and regularly curved, slightly crenulated.

Inner face slightly bent in horizontal direction, relatively smooth, with long, slightly supramedian and slightly bent, shallow sulcus. Ostium about as wide as cauda but twice as long. Ostial colliculum only slightly wider than caudal colliculum (OCH:CCH = 1.1-1.3). Caudal pseudocolliculum distinct, long, fine. Dorsal margin of ostium slightly oscillating. Ventral furrow very indistinct; dorsal depression large, well marked towards crista superior. Outer face nearly flat except slightly thickened central and postcentral region, with numerous rapidly fading radial furrows on dorsal and ventral fields.

Discussion.

Diaphus watatsumi is superficially an inconspicuous Diaphus otolith but can be relatively easily identified by its proportions and the shape and number of delicate denticles along the ventral rim. It resembles D. marwicki (Frost, 1933), a common species in the early and middle Miocene of the southern Pacific in New Zealand and Chile (see Schwarzhans 2019 and Schwarzhans and Nielsen 2021), but differs in the more elongate shape (OL:OH = 1.35-1.45 vs. 1.25-1.35), the thin appearance (OH:OT = 3.8-4.5 vs. 3.5-3.6), the larger number of denticles on the ventral rim (13-15 vs. 10-13), and the anteriorly depressed dorsal rim. Diaphus watatsumi resembles even more closely D. sulcatus (Bassoli, 1906) from the middle and late Miocene of Europe and the extant D. splendidus (Brauer, 1904), which is known since at least the early Pliocene, and is therefore associated with the Diaphus splendidus Otolith Group. Diaphus watatsumi differs from D. sulcatus in the rostrum being much longer than the antirostrum (vs. slightly longer to equal length) and the more depressed and longer predorsal region. It differs from D. splendidus in the relatively higher ratio OCL:CCL (2.0 vs. 1.6-1.8) and the higher number of denticles on the ventral rim (13-15 vs. 9-13). Diaphus watatsumi also resembles otoliths of the extant Lobianchia gemellarii (Cocco, 1838) (see Schwarzhans and Ohe 2019 for figures) but differs in the higher number of denticles along the ventral rim (13-15 vs. 5-9), the more regularly rounded posterior rim and the many radial furrows on the outer face.

Figures

Figure 8. A-F: Diaphus angulatus Ohe & Araki, 1973; A-C: SMF PO 101.130, Inabacho, Tsu City, Katada Formation, level ML 2305; D-E: SMF PO 101.131, Fuchu machi, Toyama City, Higashibessho Formation, level H 20; G-N: Diaphus epipedus sp. nov.; G-I: holotype, SMF PO 101.132, Tsuyama City, Takakura Formation, level MS 15; K-J: paratype, SMF PO 101.133, Tsuyama City, Takakura Formation, level MS 15; L-N: paratype, SMF PO 101.134, Yatsuo, Toyama City, Higashibessho Formation, level H 21; O-T: Diaphus metopoclampoides Steurbaut, 1983, SMF PO 101.135, Tsuyama City, Takakura Formation level MS 06, f; U-AB: Diaphus watatsumi sp. nov., Tsuyama City, Takakura Formation; U-X: holotype, SMF PO 101.136, level MS 52; Y-AB: paratypes, SMF PO 101.137, levels gh, j; AC-AE: Diaphus sp. 1, col. Tsuchiya, Ichishi Group.