Platyberyx rhyton Stevenson and Kenaley, 2013

[Japanese name: Sanriku-yaegisu] (Fig. 1B)

Platyberyx rhyton Stevenson and Kenaley, 2013: 424 (type locality: off Iwate Prefecture, northeastern Japan); Okamoto et al. 2014: 26 (off northeastern Japan).

Caristius macropus (not Bellotti, 1903): Tatsuta et al. 2014: 52 (Ogasawara Islands, Japan, in part).

Material examined. 1 specimen: HUMZ 211061, 145 mm SL, off the Ogasawara Islands, Japan, western North Pacific, 27°37.5′N, 141°35.1′E– 27°10.0′N, 141°57.3′E, 300– 2000 m depth, beam trawl, 14–15 December 2010, T/S Oshoro-maru.

Diagnosis. A species of Platyberyx with the following combination of characters: dorsal-fin rays 30–31; analfin rays 18–19; pectoral-fin rays 17–18; vertebrae 33–34; ventral caudal spur absent; prepectoral length 31.4–34.0% SL; dorsal-fin base 76.0–79.0% SL; upper jaw extending approximately to posterior margin of orbit; gill rakers narrow, bladelike, with few bristles concentrated near tip; jaw teeth arranged in single row; dorsal pharyngeal papillae saclike, multifid papillae absent inside mouth; body color brown.

Remarks. Platyberyx rhyton was described based on a single specimen from northeastern Japan off Iwate Prefecture at 650–677 m depth (Stevenson and Kenaley 2013). Subsequently, a second specimen was collected near the type locality at 0–750 m (Okamoto et al. 2014). The present specimen represents the third known specimen of the species and the first record from southern Japan (Fig. 2).

The present specimen matches the morphological descriptions given by Stevenson and Kenaley (2013) and Okamoto et al. (2014), and its meristics and morphometrics are similar to those of the previous specimens (Table 1). Counts of anal-fin rays (19 in the present study vs 18 in Stevenson and Kenaley 2013 and Okamoto et al. 2014) and pectoralfin rays (17 vs 18) are slightly different, but well within the typical range of meristic variation in caristiids (see Stevenson and Kenaley 2013: table 1). Vomerine and palatine tooth counts are slightly higher than those previously reported, but the present specimen is in relatively good condition, so unlike previously reported specimens (Okamoto et al. 2014), it is unlikely to have lost any teeth in preservation. The morphometrics of the present specimen do not differ notably from those of previous specimens.

Numbers separated by “/” indicate left-side and right-side counts. * These counts and measurements based on two specimens due to damage to the caudal region of HUMZ 211062.

Comparative material. Caristius macropus: 2 specimens (KAUM–I. 59000, 192 mm SL; UW 153100, 163 mm SL), 39°58.47′N, 146°06.52′E, off Iwate Prefecture, northeastern Japan, 0–950 m depth, MOHT trawl, 8 March 2005. Paracaristius maderensis: KAUM–I. 59002, 215 mm SL, Kinmei Seamount, Emperor Seamount chain, 720 m depth, 23 August 2013. Paracaristius nudarcus: KAUM–I. 59001, 62 mm SL, 38°03.12′N, 147°18.14′E, off Miyagi Prefecture, northeastern Japan, 0–300 m depth, MOCNESS, 11 February 2004; UW 153101, 85 mm SL, 39°57.60′N, 146°04.76′E, off Iwate Prefecture, northeastern Japan, 0–750 m depth, mid-water trawl, 15 March 2005. Platyberyx andriashevi, KAUM–I. 59003, 205 mm SL, Kinmei Seamount, Emperor Seamount chain, 720 m depth, 23 August 2013. Platyberyx rhyton: KAUM–I. 59004, 88 mm SL, 39°57.60′N, 146°04.76′E, off Iwate Prefecture, northeastern Japan, 0–750 m depth, mid-water trawl, 15 March 2005.