Epigonus exodon Okamoto & Motomura, 2012

Okamoto, Makoto, Chen, Wei-Jen & Motomura, Hiroyuki, 2020, New distributional records of three deepwater cardinalfishes Epigonus angustifrons, E. denticulatus, and E. exodon (Perciformes: Epigonidae) in the South Indian Ocean, Cybium 44 (2), pp. 165-168 : 167

Epigonus exodon Okamoto & Motomura, 2012

( Fig. 4 ; Tab. I)

Material examined

One specimen: NTUM 13370 , 131.0 mm SL, female, 13°03’S, 45°01’E, south of Mayotte, western South Indian Ocean , 504 m depth, St. CP 4829, French beam trawl, 27 Jan. 2017, RV Antéa, BIOMAGLO Expedition .

Diagnosis

Dorsal-fin rays VII-I, 10; pectoral-fin rays 16-17; total gill rakers 26-28; vertebrae 10 + 15; pyloric caeca 7-10; pored lateral-line scales 35-40 + 3-5; opercular spine absent; ribs absent on last abdominal vertebra; anteriorly projecting teeth present on each side of symphysis of lower jaw (> 60 mm SL); tongue narrow; shallow V-shaped tooth patch present on rear two-thirds of tongue (<100 mm SL, reduced with growth), maxillary mustache-like process absent.

Distribution

Réunion and the Comoros Archipelago (south of Mayotte), western South Indian Ocean, at 450-504 m depths ( Okamoto and Motomura, 2012; present study: Fig. 2 ).

Remarks

The diagnosis of E. exodon given here is based on the present specimen and the original description. Epigonus exodon was originally described on the basis of two specimens collected from Réunion, Southwest Indian Ocean ( Okamoto and Motomura, 2012). Although a large number of specimens of Epigonus from the western Indian Ocean were examined in museum collections worldwide by Okamoto and Gon (2018); no additional specimens of this species were found. In the present study, we report this specimen as the third specimen and the first record of the species from the Comoro Archipelago with a colour photograph of the species when fresh. Epigonus exodon has been recognized as a member of the E. oligolepis group by lacking a pungent opercular spine and the absence of ribs on the last abdominal vertebra, and in having dorsal-fin rays VII-I, 10 and 35-40 pored lateral-line scales to the end of the hypural ( Okamoto and Motomura, 2011, 2012; present study). Among the species of this group, only E. exodon and E. glossodontus Gon 1985 (Hawaiian Islands) have anteriorly projecting teeth on the symphysis of lower jaw ( Gon, 1985); however, the former can be distinguished from the latter in having a narrower tongue with a smaller tooth patch ( Okamoto and Motomura, 2012).

According to the original description of E. exodon ( Okamoto and Motomura, 2012) , the holotype and paratype had tooth patch on the tongue, which was regarded as an important diagnostic character. However, the present specimen has only a few teeth on the tongue, not forming a tooth patch. Since the standard length of the present specimen (131.0 mm SL) is larger than those of the type specimens (60.2-97.0 mm SL), the difference is regarded here as change with growth. A similar reduction of the teeth on the tongue with growth has been confirmed in E. oligolepis Mayer, 1974 (M. Okamoto, unpubl. data).

Okamoto and Motomura (2012) reported that the sexes of the holotype and paratype of E. exodon were male and unknown, respectively. The present specimen was a female with a large number of developed eggs (ca. 0.4 mm in diameter).

Acknowledgments. – The BIOMAGLO was conducted jointly by French National Museum of Natural History (MNHN) as part of the Tropical DeepSea Benthos program, the French Research Institute for Exploitation of the Sea (IFREMER), the “ Terres Australes et Antarctiques Françaises ” ( TAAF), the Departmental Council of Mayotte and the French Development Agency (AFD), with the financial support of the European Union (Xe FED). The expedition was operated under permits delivered by the prefecture of Reunion Island (5000044/CZM REUNION /AEM) and TAAF (arrêté 2017-01). We are grateful to the crew of RV Antéa, the PIs of BIOMAGLO (Laure Corbari; Karine Olu, and Sarah Samadi), crews of the RV Austral Leader for organizing the surveys and the capture of the samples. We are most grateful to the following persons and institutions for specimen loans and assistance: A. Graham (CSIRO); M.-Y. Lee, H.-S. Lin, and J.-N. Chen (NTUM).

Figures

Figure 2. – Collection localities of Epigonus angustifrons (present study: Z; Okamoto and Gon, 2018: „), E. denticulatus (present study: Δ; Okamoto and Gon, 2018: A), and E. exodon (present study: C; Okamoto and Motomura, 2012: l) in the central and western South Indian Ocean.

Figure 4. – Epigonus exodon, NTUM 13370, south of Mayotte, western South Indian Ocean.A: Fresh specimen; B: After fixation.