Chlorophthalmus imperator, Fujiwara & Wada & Motomura, 2019

Fujiwara, Kyoji, Wada, Hidetoshi & Motomura, Hiroyuki, 2019, A new species of the greeneye genus Chlorophthalmus (Teleostei: Chlorophthalmidae) from the central North Pacific, Zootaxa 4555 (3), pp. 396-406 : 397-404

Chlorophthalmus imperator sp. nov.

New English name: Emperor Greeneye

Figures 1–4 , 6 ; Table 1

Holotype. KAUM–I. 120091 (formerly SNFR 21135 ), 130.0 mm SL, Daikakuji Seamount , Emperor Seamount Chain , central North Pacific, 32°13′47″N, 172°50′48″E– 32°15′39″N, 172°53′17″E, midwater trawl, 596–605 m, RV Kaiyou-maru, 6 Aug. 2015.

Paratypes. 8 specimens, 98.1–174.8 mm SL, all from the Emperor Seamount Chain in the central North Pacific (formerly deposited at SNFR). KAUM–I. 120092, 147.7 mm SL, KAUM–I. 120093, 144.5 mm SL, Koukou Seamount, 35°39′00″N, 171°03′00″E– 35°38′42″N, 171°02′36″E, bottom trawl, 430 m, FV Hiroe-maru, 20 Sept. 2005 ; KAUM–I. 120094, 146.6 mm SL, Daikakuji Seamount , 32°12′00″N, 172°54′00″E– 32°17′00″N, 172°52′00″E, bottom trawl, 366 m, FV Tomi-maru, 8 Dec. 2008 ; KAUM–I. 120095, 122.1 mm SL, KAUM–I. 120096, 103.0 mm SL, KAUM–I. 120097, 98.1 mm SL, KAUM–I. 120098, 123.6 mm SL, Kammu Seamount , 32°01′28″N, 173°11′20″E– 32°00′02″N, 173°08′16″E, midwater trawl, 349–497 m, RV Kaiyou-maru, 4 Aug. 2015 ; KAUM–I. 120099, 174.8 mm SL, Kammu Seamount, 31 July 2015 .

Diagnosis. A relatively large species (standard length exceeding 170 mm: Fig. 1D ) of Chlorophthalmus , characterized by the following combination of characters: 49–51 lateral-line scales; 6 scale rows above lateral line; 3 + 19–22 = 22–25 (modally 22) gill rakers; outermost tooth patches on lower jaw with 6–14 large thorn-shaped teeth, its tips projecting in advance of lower-jaw profile ( Fig. 2 ); lower-jaw symphysis with two distinct moderately-sized projections ( Fig. 2 ); tongue without teeth; pelvic-fin origin vertically below 4th or 5th (usually 5th) dorsal-fin ray base; head length 26.7–28.9 (mean 27.7) % SL; snout length 6.9–7.7 (7.3) % SL; horizontal orbit diameter 11.9–12.9 (12.3) % SL; upper-jaw length 11.7–13.2 (12.6) % SL; maxillary depth 3.1–3.8 (3.4) % SL; pre-dorsal-fin length 34.2–36.6 (35.3) % SL; pre-pectoral-fin length 27.3–29.8 (27.9) % SL; anus to anal-fin origin length 27.3–29.9 (28.5) % SL; pectoral-fin length 21.0–24.9 (22.7) % SL.

Description. Data for the holotype are presented first, followed by data for paratypes in parentheses (if different). Characters included in the diagnosis are not repeated here. Counts and measurements (percentages of SL) are given in Table 1.

Body slender, cylindrical, compressed at caudal peduncle; maximum depth at dorsal-fin origin. Snout pointed in lateral view, semicircular in dorsal view, its profile straight (weakly concave). Dorsal surface of snout tip with two small bluntly pointed spines. Anterior and posterior nostrils slit-like and more-or-less triangular (circular), respectively, latter much larger; closely positioned just forward eye, slightly below horizontal level of snout tip. Eye very large with diameter greater than snout length, upper profile included in head profile in lateral view. Interorbital region slightly concave in midline; least interorbital very narrow, width less than pelvic-fin base length. Preopercle rounded. Upper portion of opercle bluntly pointed, lower portion rounded. Anus very close to pelvic-fin base, hidden by pelvic fin when depressed. Perianal light organ present.

Mouth terminal. Upper jaw long, posterior end of maxillary somewhat rounded, reaching to between vertical through anterior margin and center of eye; with ca. 1 to 3 rows of villiform teeth, tooth band and size, respectively, becoming wider and smaller posteriorly. Anterior tip of lower jaw extending beyond that of upper jaw, with two tooth patches including ca. 4 (5) irregular rows of thoron shaped teeth, its size becoming large anteriorly, its tips strongly curved posteriorly (4 of 9 specimens variously damaged, but teeth fragments confirmed: Fig. 2F ); posteriorly 1 or 2 rows more-or-less of relatively large (larger than upper-jaw teeth), slightly recurved pointed villiform teeth; jaw symphyses without villiform teeth. Vomer with 1 (1–4) teeth on anterior margin, thereafter margin (sides of vomer) with 6–17 (usually 6 or 8) sharp, moderately-sized teeth (some lost in holotype). Anterior half of palatine with minute pointed teeth in ca. 2–4 rows, tapering to single row posteriorly. Two pores just behind projections of lower-jaw symphysis. Gill rakers long, with pointed tips.

Dorsal fin triangular, positioned anteriorly, its origin anterior to vertical through pelvic-fin origin; 3rd (rarely 2nd) dorsal-fin ray longest; 1st and 2nd dorsal-fin rays unbranched, other rays with 2 or 3 branches. Pectoral fin base low, just behind pointed portion of opercle; uppermost pectoral-fin ray unbranched; tip of fin pointed, extending to between vertical through last dorsal-fin ray base and tip of depressed pelvic fin. Pelvic fin short, its tip pointed; 2nd and 3rd rays longest. Anal fin short, its base shorter than longest anal-fin ray length; 4th (3th) ray longest; 1st to 3rd (4th) rays unbranched, other rays with 2 or 3 branches. Adipose fin small, slightly behind vertical through anal-fin origin. Caudal fin forked, tips pointed. Body covered with deciduous cycloid scales, scale pockets distinct; scale margins weakly serrated. Anterior extent of pre-dorsal scales slightly forward of posterior margin of eyes. Head without scales, except for cheek; scales on isthmus and thorax smaller. Scales absent on all fins.

Fresh coloration ( Fig. 3 ): Body generally faint gray. Anterodorsal surface (between posterior margins of orbit and dorsal-fin base) black. Dorsal surface (upper lateral line) with black diagonal lines along scale margins. Tip of snout black. Branchial cavity and opercular margin black. Cheek and thorax with many black melanophores. Dorsal fin blackish-gray, anteriormost 3–4 rays somewhat darker. Anal and adipose fins translucent to light gray, bases black. Pectoral fin translucent to light gray, upper half part slightly darker pigmentation. Pelvic fin generally translucent to light gray, inner 4–5 rays black, fin tip blackish. Caudal fin gray, fin base black.

Preserved coloration: Similar to fresh coloration but body generally light yellow to brown. Oral cavity and tongue yellowish [upper and posterior surface of oral cavity with black pigmentation in largest specimen (174.8 mm SL)]. Anal region and light organ black.

Distribution. Currently known only from the Emperor Seamount Chain in the central North Pacific ( Fig. 4 ).

The specimens were collected in depths of 349– 605 m.

Etymology. The species name imperator , derived from Latin, means emperor in reference to the type locality of the species (Emperor Seamount Chain).

Remarks. The number and size of thorn-shaped teeth in the outermost tooth patches on the lower jaw probably tend to increase in number and become relatively smaller with growth ( Fig. 2 ). Similar changes have also been noted in C. proridens ( Fig. 5 A–E). However, additional specimens are required to understand such ontogenetic changes in detail.

Humphreys et al. (1984) recorded C. albatrossis Jordan & Starks 1904 from Kammu Seamount, the Emperor Seamount Chain. That record may have in fact been based on the new species, since the main distributional range of C. albatrossis is in the western Pacific Ocean ( Paxton 2000; Nakabo & Kai 2013), but must remain equivocal due to the lack of further details.

Comparisons. Chlorophthalmus imperator sp. nov. is very similar to C. proridens (in the Hawaiian Islands), C. ichthyandri (in the southeastern Pacific Ocean) and C. mascarensis (in the central western Indian Ocean) in having large thorn-shaped teeth in the outermost tooth patches on the lower jaw ( Figs. 2 , 5 A–E). However, C. imperator differs from the latter three species as follows: head length 26.7–28.9 (mean 27.7) % SL [vs. 30.8–32.2 (31.5) % SL in C. proridens , 29.8–32.7% SL in C. ichthyandri and 30.3–33.9% SL in C. mascarensis ]; pre-dorsalfin length 34.2–36.6 (35.3) % SL [vs. 36.3–37.9 (37.3) % SL, 35.9–39.1% SL and 37.6–41.7% SL]; and prepectoral-fin length 27.3–29.8 (27.9) % SL [vs. 30.0–32.0 (31.4) % SL, 28.7–31.1% SL and 31.5–33.1% SL] ( Fig. 6A, F ). Although the new species most closely resembles C. proridens ( Fig. 7 ), it also differs in having slightly smaller eyes with a horizontal diameter of 11.9–12.9 (12.3) % SL vs. 13.1–14.7 (14.1), a shorter snout, its length 6.9–7.7 (7.3) % SL vs. 8.0–8.8 (8.3), a shorter upper jaw with a length of 11.7–13.2 (12.6) % SL vs. 14.1–15.0 (14.5) and a narrower maxilla having a depth of 3.1–3.8 (3.4) % SL vs. 3.8–4.9 (4.2) ( Fig. 6 B–E). The new species is also of distinct from C. ichthyandri and C. mascarensis in having a greater anus to anal-fin origin length of 27.3– 29.9 (28.5) % SL vs. 23.2–28.2% SL in C. ichthyandri and 21.7–24.9% SL in C. mascarensis and lacking teeth on the tongue. Moreover, compared with C. mascarensis , the new species has a shorter pectoral fin with a length of 21.0–24.9 (22.7) % SL vs. 25.7–29.0% SL, a shorter snout with a length of 1.6–1.8 times in its horizontal orbit diameter vs. 1.1–1.2 times, a more anteriorly positioned pelvic-fin origin located vertically below the 4th or 5th dorsal-fin ray base vs. below the 7th or 8th ray and fewer lateral-line scales, 49–51 vs. 53–55. The maximum recorded length of the new species (174.8 mm SL) also exceeds that of C. ichthyandri recorded to 122 mm SL.

The outermost lower-jaw tooth patches in C. imperator extend beyond the lower-jaw profile, as they also do in C. albatrossis , C. borealis , C. punctatus and C. pectoralis . Counts of lateral-line scales and/or scale rows above the lateral line differ between the new species and the above four species [viz., 49–51 lateral-line scales and 6 scale rows above lateral line in C. imperator vs. 52–56 (given in error as 53– 16 in original description) and 7.5–8.5 in C. albatrossis , 56 and unknown in C. punctatus , 51–52 and 7.5 in C. pectoralis and 50–56 (modally 54) and unknown in C. borealis ]. Compared with C. albatrossis , C. pectoralis and C. borealis , the new species has larger thornshaped teeth in the outermost lower-jaw tooth patches vs. relatively small teeth ( Figs. 2 , 4H, I ) and a slightly higher gill raker count: 3 + 19–22 = 22–25 (22) vs. 3 + 18–19 = 21–22 in C. albatrossis , 2–3 + 18–19 = 20–22 in C. pectoralis and total 17–22 (19) in C. borealis . The new species also has larger eyes than C. borealis , the horizontal orbit diameter 11.9–12.9 (12.3) % SL vs. 8.7–10.4 (9.6) % SL.

Projections of the lower-jaw symphysis also distinguish C. imperator , which has two distinct moderately-sized projections from C. corniger with two very large spine-like projections, C. albatrossis without projections ( Fig. 5H, I ) and C. pectoralis , which has three distinct, moderately-sized projections.

Chlorophthalmus productus differs from the new species in lacking enlarge teeth on the periphery of the dentary (M. Gomon, personal communication) and in having 58 lateral-line scales and 2 + 15 gill rakers. The remaining nine species C. agassizi , C. chalybeius , C. mento , C acutifrons , C. atlanticus , C. nigromarginatus , C. brasiliensis , C. zvezdae and C. vityazi all have a smooth lower-jaw profile without tips of lower-jaw teeth extending in advance of the lower-jaw profile ( Fig. 5F, G ).

Figures

FIGURE 1. Preserved specimens of Chlorophthalmus imperator sp. nov. collected from the Emperor Seamount Chain in the central North Pacific. (A–C), KAUM–I. 120091, 130.0 mm SL, holotype; (D), KAUM–I. 120099, 174.8 mm SL, paratype; (E), KAUM–I. 120094, 146.6 mm SL, paratype; (F), KAUM–I. 120097, 98.1 mm SL, paratype. (A, D–F), lateral views; (B), dorsal view; (C), ventral view.

FIGURE 2. Lower-jaw tips of Chlorophthalmus imperator sp. nov. in dorsal view. (A), KAUM–I. 120097, paratype; (B), KAUM–I. 120098, paratype; (C), KAUM–I. 120091, holotype; (D), KAUM–I. 120093, paratype; (E), KAUM–I. 120099, paratype; (F), KAUM–I. 120096, paratype (damaged).

FIGURE 3. Fresh specimens of Chlorophthalmus imperator sp. nov. (A), KAUM–I. 120091, 130.0 mm SL, holotype; (B), KAUM–I. 120095, 122.1 mm SL, paratype; (C), KAUM–I. 120098, 123.6 mm SL, paratype; (D), KAUM–I. 120094, 146.6 mm SL, paratype. Photos by SNFR.

FIGURE 4. Distribution of Chlorophthalmus imperator sp. nov. (red squares), arrowhead indicates type locality.

FIGURE 5. Dorsal view of lower-jaw tips of (A–E) Chlorophthalmus proridens, (F) C. acutifrons, (G) C. nigromarginatus and (H, I) C. albatrossis. (A, C), USNM 47715 (paratypes); (B, D), CAS-SU 4916 (paratypes); (E), USNM 47715 (holotype); (F), KAUM–I. 151740; (G), KAUM–I. 111668; (H), KAUM–I. 151705; (I), KAUM–I. 151739.

FIGURE 6. Relationships of (A) head length, (B) snout length, (C) upper-jaw length, (D) maxillary depth, (E) horizontal orbit diamter, and (F) pre-pectoral-fin length (all as % of standard length) to standard length (mm) in Chlorophthalmus imperator sp. nov. (red squares) and C. proridens (blue circles). Arrowheads indicate holotype.

FIGURE 7. Preserved holotype of Chlorophthalmus proridens, USNM 47715, 149.9 mm SL. (A), lateral view; (B), dorsal view; (C), ventral view.