Enneapterygius nanus ( Schultz, 1960 )

Dewa, Yuna, Tashiro, Satokuni & Motomura, Hiroyuki, 2023, A new species of the genus Enneapterygius (Perciformes: Tripterygiidae) from Japan and the Philippines, with a synopsis and synonymy of related species, Zootaxa 5374 (3), pp. 333-360 : 352-354

Enneapterygius nanus ( Schultz, 1960)

[English name: Pygmy Triplefin]

Figures 4–6 , 12 ; Tables 4 , 6 , 7

Tripterygion nanus Schultz, 1960: 288 , fig. 112 (original description; type locality: Rujoru Island , Eniwetok Atoll, Marshall Islands).

Enneapterygius nanus : Myers, 1991: 204, unnumbered fig. [Enewetak, Marshall Islands (based on Schultz, 1960)].

Holotype. USNM 142233 , male, 15.8 mm SL, lagoon reef at Rujoru island , Eniwetok Atoll, Marshall Islands, 2 June 1946, L. Schultz.

Paratypes. 4 specimens (16.4–17.9 mm SL). USNM 142234 *, 2 males, 16.4–17.6 mm SL, same data as holotype; USNM 142238 , 2 males, 17.5–17.9 mm SL, tidepool at Enybarbar island , Rongelap Atoll, Marshall Islands, 18 June 1946, L. Schultz .

Non-type specimen. NSMT-P 54443 , male, 14.3 mm SL, Eroj island , Majuro Atoll, Marshall Islands, 0.5 m, 6 Aug. 1982, K. Matsuura .

Diagnosis. A species of Enneapterygius ( Fig. 12 ) with the following combination of characters: 12 or 13 (modally 12) second dorsal-fin spines; 9 or 10 (9) third dorsal-fin rays; I, 16 or 17 (16) anal-fin rays; ii–iv (ii) + 4–6 (6) + vii = 15 pectoral-fin rays (ii + 6 + vii = 15 in holotype, iii + 5 + vii = 15 in 2 specimens, iv + 4 + vii = 15 in single specimen); 12 or 13 pored lateral-line scales; 19–21 (20 or 21) notched lateral-line scales; 31–33 (33) scale rows in longitudinal series; 1 or 2 (1½ or 2) scales above 1st pored lateral-line scale; 2 or 2½ (2) scales below 1st notched lateral-line scale; 8 circumpeduncular scales; mandibular pore formula 3 + 1 +3; head relatively short, its length 28.3–30.1% (mean 29.5%) of SL; upper jaw relatively long, its length 9.8–11.2% (10.4%) of SL; 1st spine of first dorsal fin shorter than that of 2nd dorsal fin, its length 8.2–10.5% (9.8%) of SL; anterior nostril tentacle unbranched; orbital tentacle small, leaf-shaped, the edge slightly rounded, its length less than or subequal to half of pupil diameter; body translucent, lower half and ventral surface of head, including pelvic-fin base, black in nuptial males; no black pigmentation on pectoral-fin base; caudal fin transparent, sometimes with faint brownish bars; body plain and pale in females; pectoral-fin rays with no pigmentation.

Distribution. Enneapterygius nanus is currently known only from the Marshall Islands ( Schultz, 1960; Myers, 1991; this study) ( Fig. 4 ).

Remarks. Enneapterygius nanus was originally described as Tripterygion nanus based on 41 specimens from the Marshall Islands (Bikini, Eniwetok, Rongerik, Rongelap, and Kwajalein atolls). Subsequently, Myers (1989) transferred the species to Enneapterygius , adding a record from the Mariana Islands. However, Myers (1989) ’s description and a sketch were based entirely on Schultz (1960). Although Myers (1989, 1991) included an underwater photograph of E. nanus taken in Guam, that individual was identified here as Enneapterygius sp. 3 sensu Motomura et al. (2010). In addition, Fricke (1994, 1997) recorded E. nanus from widespread western Pacific localities, ranging from Taiwan and Thailand, south to New Caledonia, and east to American Samoa. However, meristics and measurements of E. nanus given by Fricke (1994, 1997) matched poorly those of the E. nanus type specimens examined in the present study. Examination of the specimens identified as E. nanus in this study revealed that those from the Marshall Islands tended to have fewer anal-fin rays (16 or 17 rays) [vs. 17–19 (modally 19) rays in specimens from other areas] and mandibular pores (7 pores in total; mandibular pore formula 3 + 1 + 3) (vs. 7–9 pores; mandibular pore formula 3 + 1 + 3, 3 + 2 + 3, and 4 + 1 + 4). Fricke’s (1994, 1997) description of the mandibular pore formula of E. nanus as 3 + 2 + 3, contradicts that of the Marshall Islands’ specimens, suggesting that the former was based on a different, misidentified species. In fact, it is likely that E. nanus is endemic to the Marshall Islands, as no reliable distributional records of the species from other localities exist.

Enneapterygius nanus is similar to E. olivaceus n. sp. in having 12 or 13 (modally 12) second dorsal-fin spines, 12 or (13) pored lateral-line scales; 19–21 (19 or 20) notched lateral-line scales, 1–2 (2) scales above 1st pored lateral-line scale, 2 or 2.5 (2) scales below 1st notched lateral-line scale, mandibular pore formula 3 + 1 + 3, long upper jaw, its length 9.5–13.1%, and leaf-shaped orbital tentacle with rounded edge ( Fig. 5A, C ; Tables 1 , 4 , 6 , 7 ). However, E. nanus differs from E. olivaceus n. sp. in shorter lengths of head length and 1st spine of the first dorsal fin, orbital tentacle shape, and the pigmentation of pectoral-fin (See E. olivaceus n. sp. Remarks.).

Figures

FIGURE 4. Distributional map of five species of Enneapterygius examined in this study.

FIGURE 5. Orbital tentacle shape of A Enneapterygius olivaceus n. sp., KAUM–I. 101347, holotype, male, 19.3 mm SL, Yoron-jima Island, Japan; B E. gracilis, AMS I. 25500-005, male, 19.5 mm SL, Western Australia; C E. nanus, NSMT-P 54443, male, 14.3 mm SL, Eroj Island, Marshall Islands; D E. minutus, lectotype, BMNH 1961.10.20.1, female, 20.4 mm SL, Apia, Western Samoa. Bars represent 1 mm

FIGURE 6. Lengths of A head, B upper jaw, and c 1st spine length of first dorsal-fin (% standard length) relative to standard length in five species of Enneapterygius. Yellow triangles, orange circles, red diamonds, blue squares, and a green star indicate E. gracilis, E. minutus, E. nanus, E. olivaceus n. sp., and E. philippinus, respectively

FIGURE 12. Photograph of the holotype of Enneapterygius nanus (USNM 142233, male, 15.8 mm SL, Rujoru Island, Eniwetok Atoll, Marshall Islands)

Tables

TABLE 4. Counts and morphometric measurements (as % of SL) of specimens of Enneapterygius nanus

	Holotype	Paratypes	Non-type
	USNM 142233	n = 4	NSMT-P. 54443
	Marshall Islands	Marshall Islands	Marshall Islands
	Male	Males	Male
Standard length (SL; mm)	15.8	16.4–17.9	14.3
Counts
Dorsal-fin rays	III, XII, 9	III, XII–XIII, 9–10	III, XII, 9
Anal-fin rays	I, 16	I, 16–17	I, 16
Pectoral-fin rays	ii + 6 + vii = 15	iii + 5 + vii = 15	iv + 4 + vii = 15
Scale rows in longitudinal series	31	33	damaged
Pored lateral-line scales	12	12–13	13
Notched lateral-line scales	19–21	20–21	damaged
Scales above of 1st PLL	2	1–2	2
Scales below 2nd dorsal fin	2½	2–3	2
Scales below of 1st NLL	2½	2	2
Circumpeduncular scales	8	8
Mandibular pore formula	3 + 1 + 3	3 + 1 + 3	3 + 1 + 3
Measurements (% SL)
Body depth	18.6	18.5–20.4	18.9
Body width	16.4	15.0–17.7	18.2
Head length	29.5	28.3–30.0	30.1
Snout length	8.4	7.5–7.8	9.1
Orbit diameter	9.4	10.8–10.9	9.8
Interorbital width	2.4	2.7–3.0	1.4
Upper-jaw length	10	10.6–11.2	9.8
Postorbital length	12.5	13.1–13.2	11.9
Pre-1st-dorsal-fin length	26.3	23.4–25.1	25.9
Pre-2nd-dorsal-fin length	36.2	35.4–36.1	34.3
Pre-3rd-dorsal-fin length	70.4	70.1–72.0	64.3
Pre-anal-fin length	49.8	48.4–49.1	51.0
Anal-fin base length	37.7	41.6–45.0	38.5
Pre-pectoral-fin length	31.0	29.6–30.4	32.9
Pre-pelvic-fin length	23.0	24.1–25.1	23.8
Caudal peduncle length	12.7	9.8–13.6	11.9
Caudal peduncle depth	8.3	8.2–10.6	7.7
1st spine length of 1st dorsal fin	10.0	8.2–10.5	10.5
2nd spine length of 1st dorsal fin	8.2	7.9	9.8
3rd spine length of 1st dorsal fin	8.0	damaged	7.0
1st dorsal-fin base length	5.5	5.1–6.9	5.6
1st spine length of 2nd dorsal fin	damaged	14.4	12.6
2nd spine length of 2nd dorsal fin	damaged	13.0	15.4
3rd spine length of 2nd dorsal fin	15.6	14.9	14.0
2nd dorsal-fin base length	29.2	32.7–32.9	26.6
1st ray length of 3rd dorsal fin	damaged	16.1	15.4
2nd ray length of 3rd dorsal fin	damaged	13.0	14.0
3rd dorsal fin base length	15.7	15.2	damaged
Pectoral-fin length	31.0	31.8–32.8	14.7
1st ray length of pelvic fin	17.6	15.6–19.3	27.3
2nd ray length of pelvic fin	25.8	25.0–25.4	damaged