Diaphus maghrebensis, Schwarzhans, 2023

Diaphus maghrebensis n. sp.

Figure 13d–j View Fig

2022 Diaphus taaningi Norman, 1930 —van Hinsbergh & Hoedemakers: pl. 8, Figs. 1–5 View Fig View Fig View Fig View Fig View Fig .

Holotype SMF PO 101.201 ( Fig. 13f View Fig ), Dar bel Hamri, coquina at river level of Oued Beth, Zanclean.

Paratype 7 specimens, 4 specimens SMF PO 101.202 , Dar bel Hamri, Zanclean , 1 specimen SMF PO 101.203 , Kef Nsour, Messinian , 2 specimens SMF PO. 101.204, Sidi Mohamed ech Cleuch, Zanclean .

Further material 291 specimens, 23 Kef Nsour and Chaba Kaudiat el Mogen, Messinian , 213 specimens Dar bel Hamri, Zanclean , 38 specimens Sidi Mohamed ech Chleuh, Zanclean , 17 specimens Jebel Zebbouj, Zanclean.

Etymology After Maghreb, the name of the northwestern region of Africa.

Diagnosis OL:OH = 1.1–1.2; OH:OT = 3.25–3.35. Ventral rim regularly and deeply curved, with 6–9 denticles. OCL:CCL = 1.95–2.7. Inner face convex; outer face with distinct postcentral umbo.

Description Relatively small otoliths reaching sizes of 2.5 mm in length (holotype 2.3 mm). Dorsal rim high, regularly curved or anteriorly expanded; posteriorly rounded or with mild, short depression. Ventral rim deep, regularly curved, with 6–9 denticles (mostly 7–8). Rostrum slightly longer than antirostrum, 8–15% of OL, ratio rostrum to antirostrum about 2:1. Posterior rim broadly rounded, blunt.

Inner face distinctly convex in horizontal direction, less bent in vertical direction. Sulcus long, slightly supramedian, shallow, straight, OL:SuL = 1.25–1.35. Ostium slightly wider than cauda and twice to 2.5 times the length of the cauda (OCL:CCL = 1.95–2.7). Upper margin of ostium straight. Cauda short, with equally long caudal pseudocolliculum. Dorsal depression wide; ventral furrow mostly distinct, relatively close to ventral rim of otolith. Outer face relatively smooth, with distinct, broad postcentral umbo.

Discussion Many small and somewhat inconspicuous otoliths from the Miocene and Pliocene from the Mediterranean and Paratethys have been placed in the extant Diaphus taaningi Norman, 1930 , by Brzobohatý and Nolf (2000). Diaphus taaningi is a pseudoceanic species occurring in the tropical West and East Atlantic ( Froese & Pauly, 2022). In dredge samples from the Gulf of Guinea and in a comparative morphological study of extant otoliths of the genera Diaphus , Idiolychnus , and Lobianchia, Schwarzhans (2013a , 2013b) figured several extant otoliths of D. taaningi from both areas of its distribution and found slight but consistent differences between the West and East Atlantic populations. Schwarzhans & Aguilera (2013) concluded on this basis that none of the fossil otoliths figured as D. taaningi until then actually pertains to this species and also figured presumably valid D. taaningi otoliths from the Gelasian of Atlantic Panama. More recently, van Hinsbergh and Hoedemakers (2022) figured, without description or explanation, Diaphus taaningi otoliths from the Zanclean and Piacenzian of Estepona near Málaga, Spain.

In the late Tortonian/early Messinian and Zanclean of the locations in the Rharb Basin of Morocco studied here, the otoliths of Diaphus maghrebensis represent the most common myctophid species. Tey clearly represent the same species as the otoliths figured by van Hinsbergh & Hoedemakers as D. taaningi from Estepona near Málaga, but reach larger sizes (2.5 mm in length vs. <2 mm). Terefore, I assume that these otoliths from Morocco represent true adult forms of the species in question. In many aspects, they resemble extant D. taaningi otoliths ( Fig. 13k–m View Fig ), which reach nearly 3 mm in length, but they also differ in some consistent aspects as follows ( D. maghrebensis first, D. taaningi second): OH:OT = 3.25–3.35 vs. 4.3–4.5, OCL:CCL = 1.95–2.7 vs. 1.1–1.4, outer face with distinct postcentral umbo vs. flat or with shallow umbo.

Te relatively significant difference of the ratio of the ostium to the cauda length in the two species may even indicate that they are not closely related. In fact, I do not know of any the extant species that may be related. Diaphus maghrebensis is known from the Messinian and Zanclean of Morocco and from the Zanclean and Piacenzian of the Mediterranean. Earlier records of so-called Diaphus taaningi otoliths from the Tortonian of the Mediterranean require specific review; referenced records from the Badenian of the Paratethys have recently been re-identified as Diaphus cassidiformis (Frost, 1933) (see Schwarzhans & Radwańska, 2022).