Introduction

Zameus squamulosus was first described as Centrophorus squamulosus in 1877 by Günther from a female specimen collected in Japan. Barbosa du Bocage & de Brito Capello 1864 reassigned this species to the genus Scymnodon. Later Jordan & Fowler in 1903 designated this species as the type for their newly described genus Zameus, but Bigelow & Schroeder (1957) concluded that Zameus was a junior synonym of Scymnodon. After morphological studies Taniuchi & Garrick (1986) resurrected the genus Zameus and redefined Scymnodon as a monotypical genus from the North Atlantic. White et al. (2014) placed Zameus as a monotypical genus excluding the species Zameus ichiharai (Yano & Tanaka 1984), now assigned to Scymnodon.

Zameus differs from Scymnodon, among other characters, in the presence of a medial tooth in the lower jaw (Fig. 1) and of dermal denticles with transverse ridges (Fig. 2). Recent molecular studies have confirmed the distinctiveness of the genus Zameus from Scymnodon, and place it closer to the genus Centroselachus (Naylor et al. 2012).

Fig. 1
figure 1

Front view of teeth of Zameus squamulosus CNPE-IBUNAM 14608 (a) and Scymnodon ichiharai (b)

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Fig. 2
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Dermal denticles of Zameus squamulosus CNPE-IBUNAM 14608 (a) and Scymnodon ichiharai (b)

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Zameus squamulosus is a poorly known somniosid shark that has a patchy world-wide distribution and has been reported throughout the Atlantic, Indian, western, north, central and south-eastern Pacific Oceans (Compagno et al. 2005; Akhilesh et al. 2013 and Ebert et al. 2014). This shark is epipelagic and bathypelagic, and is usually found off continental and insular slopes, on or near the bottom at depths of 550 to 1,450 m, but also found well off the bottom at depths between 0 and 580 m in waters up to 2,000–6,000 m deep (Ebert et al. 2014).

In the Northern Gulf of Mexico Zameus squamulosus is occasionally captured by longlines in deep waters off the coast of Florida (Castro 2011), but until now there were no records of the species in the Southern Gulf of Mexico.

Four female specimens of Zameus squamulosus were captured during two separate collecting trips, conducted by the Research Vessel (RV) ‘Justo Sierra’ in the continental slope of Campeche and Veracruz. These records represent evidence of the presence of Zameus squamulosus in the Southern Gulf of Mexico.

Materials and methods

The identification of the specimens was based on McEachran & Fechhelm (1998), Castro (2011) and Ebert et al. (2013). Measurements (Table 1), were presented as a percentage of the total length (TL), were taken after Ebert & Stehmann (2013) and were made in preserved specimens. Specimens were fixed in 10 % formalin and subsequently preserved in 70 % ethanol. All of the specimens were deposited in the Colección Nacional de Peces of the Instituto de Biología, Universidad Nacional Autónoma de México (CNPE-IBUNAM).

Table 1 Morphometric and meristic data for the specimens of Zameus squamulosus deposited at the Colección Nacional de Peces of the Instituto de Biología, Universidad Nacional Autónoma de México (CNPE-IBUNAM). Measurements are expressed as a percentage of total length (% TL)
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Systematics

Order SQUALIFORMES

Family SOMNIOSIDAE

Genus Zameus Jordan & Fowler 1903

Zameus squamulosus (Günther 1877)

(Fig. 3)

Fig. 3
figure 3

Lateral view of Zameus squamulosus CNPE-IBUNAM 14608 (a) and Scymnodon ichiharai (b)

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Results

Two specimens (CNPE-IBUNAM 14608) were captured on 2004–07–27 at a depth of 689 m, using a 12 m long, 9 m wide and 1.5 m tall semi-balloon otter trawl with a 6.35 cm mesh, during the Sigsbee VII project (22.41722 – 96.61110). The other two specimens (CNPE-IBUNAM 16547) were captured on 2009–08-23 at a depth of 701 m, using a 12 m long, 9 m wide and 1.5 m tall semi-balloon otter trawl with a 6.35 cm mesh, during the COBERPES III project (18.97537–94.12077). Both campaigns were conducted over the continental slope in the Gulf of Mexico (Fig. 4.).

Fig. 4
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Locations of the reported specimens of Zameus squamulosus (Square, CNPEIBUNAM 14608; Triangle, CNPE-IBUNAM 16547)

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Specimens were identified as Zameus squamulosus in laboratory. All of them show the distinctive transverse ridges on their dermal denticles (Yano & Tanaka 1984; Taniuchi & Garrick 1986) (Fig. 2). Specimens are also dark colored and low-flat headed (Head height 5.1–7.6 % TL) with a short-narrow snout (Preoral length 8.2–9.6 % TL). Their mouths are nearly transverse and narrow (Mouth wide 6.8–7.7 % TL) with well-developed labial furrows (length of upper labial furrow 3–3.6 %TL and length of lower labial furrow 2–2.4 %TL). Teeth in the lower jaw are large, broad and with knife-shaped cusplets. Teeth in the upper jaw are small and lanceolate, without cusplets (Fig. 1). Both dorsal fins are preceded by a very minute spine. First dorsal fin is long (7.6–9.2 % TL), narrow at its base (4.4–5.5 %TL) and inserted posteriorly to the pectoral fin. Second dorsal fin is small (7.6–9.1 %TL) with a wide base (6.8–7.7 % TL). Rear tips of the pectoral fins are short and broadly rounded. Anal fin is absent and caudal fin lacks subterminal notch (see Table 1 for complete meristics of the four specimens).

Conclusion

These are the first confirmed records of Zameus squamulosus in the Southern Gulf of Mexico and therefore increase the number of known shark species in Mexico. Zameus squamulosus has been recorded in catches at midwater trawls (Cadenat & Blache 1981), on pelagic longlines (Taniuchi 1990; Last & Stevens 2009) and very close to the surface (Wetherbee & Crow 1996), but although the specimens reported here were captured in the depth range of the species already described (550–1,450 m), they were collected in a trawl associated to the bottom, which supports the idea of Last & Stevens (2009) and Wetherbee & Crow (1996) that this species is more commonly found at the bottom.

Abbreviations

CNPE-IBUNAM, colección nacional de peces, Instituto Biología, Universidad Nacional Autónoma de México; RV, research vessel; TL, total lenght.