Diaphus angulatus Ohe & Araki, 1973

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 angulatus Ohe & Araki, 1973

Fig. 8A-F

Diaphus angulatus 1973 Diaphus angulatus - Ohe & Araki: pl. 49, figs 1-2, 20-21.

Material.

2 specimens; 1 specimen (SMF PO 101.130) Nagano River at Inabacho, Tsu City, Mie Prefecture, Katada FM, level I 2, late Burdigalian, lower part of planktonic foraminifera biozone N8; 1 small, tentatively assigned specimen (SMF PO 101.131), Osedani, Toyama City, Toyama Prefecture, Higashibessho FM, level H 20, late Burdigalian to early Langhian, diatom zone 3A-4A .

Remarks.

Diaphus angulatus was described based on a single incomplete specimen from the Yakuoji Formation, a partial lateral equivalent of the Katada Formation (see Oshida et al. 2018). Due to the incomplete preservation, D. angulatus was considered a doubtful species by Nolf (2013). Now, we have found a second specimen from the Katada FM which perfectly resembles the holotype but again lacks a rostrum (size 4.3+ mm; Fig. 8A-C ). A complete smaller specimen of 2.6 mm in length from the Higashibessho FM (Fig. 8D-F ) somewhat deviates from the larger specimens in the shape of the posterior rim and is therefore only tentatively assigned to the species. This difference is here considered to reflect an ontogenetic effect. These new finds are here used to revalidate and redefine the species.

Diagnosis

(emended). OL:OH = 1.2-1.3. Ventral rim regularly curved with 6 denticles of variable strength. Rostrum long, massive; antirostrum and excisura small. Dorsal rim with prominent postdorsal angle; predorsal portion depressed. Inner face flat. Caudal colliculum shorter and much narrower than ostial colliculum (OCL:CCL = 1.5-1.8; OCH:CCH = 1.6-1.8).

Description

(emended). Large, thin otoliths reaching at least 5.5 mm in length (holotype recorded by Ohe and Araki 1973); OH:OT = 4.0 (4.5 in tentatively assigned specimen). Rostrum long, pointed, 20% of OL in tentatively assigned small specimen with completely preserved rostrum (Fig. 8D ). Antirostrum distinct, but very short; excisura small. Ventral rim relatively shallow and regularly curved, with 6 denticles of varying strength. Dorsal rim smooth, anteriorly depressed, posteriorly with prominent postdorsal angle positioned above termination of cauda. Posterior rim obliquely cut in large specimens (holotype figured by Ohe and Araki 1973, and Fig. 8A ), rounded and without postventral angle in tentatively assigned small specimen of Fig. 8D .

Inner face flat with distinctly supramedian sulcus. Ostial colliculum about twice as long and wide as caudal colliculum; caudal pseudocolliculum long and distinct. Dorsal margin of ostium straight; cauda slightly bent upwards. Ventral furrow distinct, moderately close to ventral rim of otolith; dorsal depression large, rather deep but with indistinct margins except for crista superior towards sulcus. Outer face slightly convex with shallow postcentral umbo, smooth.

Discussion.

A typical and rather large otolith-based species of the Diaphus theta Otolith Group that resembles the coeval D. haereticus (Brzobohatý & Schultz, 1978) but differs in the far more backward positioned postdorsal angle and the much narrower caudal colliculum. In the latter aspect, it resembles D. audax Schwarzhans, 2019 from the early Miocene of New Zealand and Chile but again differs in the distinctly further backward positioned postdorsal angle and the complete lack of a postdorsal concavity.

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.