Chromis abyssus, Pyle, R. L., Earle, J. L. & Greene, B. D., 2008

Pyle, R. L., Earle, J. L. & Greene, B. D., 2008, Five new species of the damselfish genus Chromis (Perciformes: Labroidei: Pomacentridae) from deep coral reefs in the tropical western Pacific., Zootaxa 1671, pp. 3-31 : 6-9

Chromis abyssus , new species

urn:lsid:zoobank.org:act:8BDC0735-FEA4-4298-83FA-D04F67C3FBEC

Deep Blue Chromis

(Figs. 1a -1c; Table 1; Morphbank59; DigiMorph60; GenBank61; Barcode62)

Holotype. BPBM 4086163 (81.6 mm SL), Belau ( Palau) Islands ; off Ngemelis Island ; below and slightly N of Blue Holes caverns (7°8'16.49"N, 134°13'18.5"E): above large rock outcrop, 110 m, hand net, R.L. Pyle, 27 April 2007 [ PCMB 311364 ] .

Holotype Paratypes

BPBM BMNH BPBM BPBM BPBM CAS MNHN USNM USNM W A M 40861 2007.10.31.1 40855 40855 40855 225755 2007-1922 391136 391136 P.32898

Paratypes. BMNH 2007.10.31.165 (50.2 mm SL) [ PCMB 310366 ] . BPBM 4085567 (3; 37.6-98.0 mm SL) [ PCMB 310068 , 310269 ] . CAS 22575570 (64.1 mm SL) [ PCMB 310571 ] . MNHN 2007.192272 (63.7 mm SL) [ PCMB 310473 ] . USNM 39113674 (2; 44.4-90.2 mm SL) [ PCMB 310175 ] . WAM P.32898-00176 (64.5 mm SL) [ PCMB 310677 ] . All from same locality as holotype: sand and rubble slope with scattered rock outcroppings, 107-116 m, quinaldine and hand net, R.L. Pyle and B.D. Greene, 25 April 2007 .

Diagnosis. Dorsal rays XIV,12-13 (usually 13); anal rays II,12-14 (usually 13); pectoral rays 18-19 (usually19); spiniform caudal rays 3; tubed lateral-line scales 14-16; gill rakers 6-7+17-18 (usually 7+18; total 24-25, usually 25); body depth 1.58-1.83 in SL; color when fresh dark gray with a large iridescent dark blue spot at center of each scale; membranes on median fins and pelvic fins opaque charcoal gray, with an iridescent dark blue margin on the spinous portion of the dorsal and anal fins; caudal fin mottled iridescent dark blue and black; pectoral fins with a black ovoid spot covering the basal portion and pectoral-fin axil.

Description. Dorsal rays XIV,13 (two paratypes with XIV,12); anal rays II,13 (II,12-14); all dorsal and anal rays branched, the last to base in some specimens; pectoral rays 19 (one paratype with 18), the upper 2 and lowermost unbranched; pelvic rays I,5; principal caudal rays 8+7=15; upper and lower procurrent caudal rays 5, the anterior 3 spiniform, the posterior 2 segmented and unbranched; tubed lateral-line scales 16|14 (14-16 except for one paratype with 11|15); posterior midlateral scales with a pore or deep pit 7|6 (5-8); scales above dorsal fin to origin of dorsal fin 3.5 (3-3.5); scales below lateral line to origin of anal fin 9 (9-10); gill rakers 7+18=25 (6-7+17-18=24-25), 6 gill rakers on upper limb of gill arch in one paratype, 17 gill rakers on lower limb of gill arch in one paratype); surpaneural (predorsal) bones 3; vertebrae 12+13.

Body moderately deep, depth 1.73 (1.58-1.83) in SL, and compressed, the width 3.23 (2.65-3.56) in body depth; head length 3.01 (2.79-3.05) in SL; dorsal profile of head with slight convexity anterior to eye, slight concavity dorsal to eye, and slight convexity on nape; snout shorter than orbit diameter, its length 4.11 (4.00-5.74) in head length; orbit diameter 2.66 (2.28-2.90) in head length; interorbital space convex, its width 2.79 (2.59-2.92) in head length; caudal-peduncle depth 2.17 (2.15-2.59) in head; caudal-peduncle length 3.01 (3.34-4.39) in head.

Mouth terminal, small, oblique, the upper jaw forming an angle of about 40º to horizontal axis of head and body; posterior edge of maxilla reaching slightly beyond a vertical at anterior edge of pupil, the upper jaw length 3.57 (3.39-4.11) in head; an outer row of conical teeth in each jaw, largest anteriorly; about 27 upper and about 20 lower teeth on each side of jaw; a narrow band of villiform teeth lingual to outer row, in 2-3 irregular rows anteriorly, narrowing to a single row on side of jaws; tongue triangular with rounded tip; gill rakers long and slender, the longest on lower limb near angle about four-fifths length of longest gill filaments; nostril with a fleshy rim, more elevated on posterior edge and located at level of middle of pupil, slightly less than one-third distance from front of snout to base of upper lip.

Opercle ending posteriorly in a flat spine, the tip relatively obtuse and obscured by a large scale; margin of preopercle smooth, the posterior margin extending dorsally to level of upper edge of pupil; suborbital with free lower margin extending nearly to a vertical at posterior edge of pupil.

Scales finely ctenoid; anterior lateral line ending beneath rear portion of spinous dorsal fin (between 11th and 12th dorsal-fin spines); head scaled except lips, tip of snout, and a narrow zone from orbit to edge of snout containing nostrils; a scaly sheath at base of dorsal and anal fins, about two-thirds pupil diameter at base of middle of spinous portion of dorsal fin, progressively narrower on soft portion; a column of scales on each membrane of dorsal fin, narrowing distally, those on spinous portion of dorsal progressively longer, reaching about two-thirds distance to spine tips on posterior membranes; scales on anal-fin membrane in two columns, progressively smaller distally; small scales on caudal fin extending slightly more than two-thirds distance to posterior margin; small scales on basal one-fifth of pectoral fins; a median scaly process extending posteriorly from between base of pelvic fins, its length about half that of pelvic spine; axillary scale above base of pelvic spine about one-half length of spine. Origin of dorsal fin over second lateral-line scale, the pre-dorsal length 2.29 (2.24-2.54) in SL; base of spinous portion of dorsal fin contained 2.24 (2.02-2.39) in SL; base of soft portion of dorsal fin contained 5.75 (5.65-6.48) in SL; first dorsal spine 10.85 (7.78-11.01) in SL; second dorsal spine 6.64 (5.22-7.14) in SL; third dorsal spine 5.41 (4.53-5.42) in SL; fourth dorsal spine 5.00 (4.44-5.08) in SL; fifth dorsal spine 4.88 (4.39-5.05) in SL; sixth dorsal spine 4.90 (4.45-4.99) in SL; last dorsal spine 6.19 (6.11-7.40) in SL; membranes of spinous portion of dorsal fin moderately incised; fourth dorsal soft ray longest, sometimes with a filamentous extension, its length 4.39 (4.21-5.06) in SL; first anal spine 10.92 (8.76-11.13) in SL; second anal spine 4.03 (3.66-4.24) in SL; first anal soft ray the longest, its length 4.41 (4.15-4.62) in SL; caudal fin forked, without significant filamentous extensions, its length 2.89 (2.87-3.64) in SL, the caudal concavity 5.83 (4.54-8.00) in SL; fourth pectoral-fin ray longest, 2.77 (2.65-3.08) in SL; pelvic spine 5.20 (4.95-5.67) in SL; first soft ray of pelvic fin filamentous, usually reaching to first through third anal-fin ray (when not broken or damaged), its length 2.86 (2.54-4.03) in SL.

Color of adults and juveniles when fresh predominantly charcoal gray, a large iridescent dark blue spot at center of each scale (including scales on head and median fins), blue spots occupying about half of visible area of each scale on body, decreasing in size slightly towards abdomen and ventral portion of body, blue spots forming a near-continuous line along base of dorsal and anal fins, a vertical column of scales with iridescent dark blue spots extending dorsally on each interspinous membrane of dorsal fin, blue spots on scales covering soft portions of dorsal and anal fins varying in size, forming a mottled pattern of blue and black; membranes on median fins and pelvic fins opaque charcoal gray, with an iridescent dark blue margin on spinous portion of the dorsal fin, and a broad iridescent dark blue margin on the anal fin; caudal fin mottled iridescent dark blue and black; pelvic-fin spine entirely iridescent dark blue, an iridescent dark blue streak on the pelvic-fin soft rays, the filamentous extension on the pelvic fin white; pectoral fins translucent charcoal gray with a ovoid black spot on base and axil; iris charcoal gray to black; iridescent blue fleshy orbit margin.

Color in alcohol similar to general color pattern when fresh, except charcoal gray pigment sometimes fades to brownish gray, and iridescent dark blue is either faded to pale gray blue, or has disappeared altogether (leaving the specimen uniform brownish gray, or sometimes charcoal gray overall).

Distribution. Only collected from the type locality; also observed at similar depths at Augulpelu Reef in Palau . An individual of what appears to be this species was observed and photographed by Mr. Forrest Young at 120-150 m near Manado, Sulawesi, Indonesia .

Etymology. Named abyssus , a Latinized form of the Greek noun abyssos (meaning "abyss"), to honor the documentary film Pacific Abyss, produced by the British Broadcasting Corporation (BBC), which funded the expedition on which the type specimens were collected. The vernacular name "Deep Blue Chromis ", a reference to both the life color of this species and the relatively (within the context of the genus) deep-dwelling habits, is suggested instead of the more literally translated "Abyss Chromis ", so as not to imply that the species inhabits depths commonly defined as "abyssal".

Remarks. This species was first observed by the senior author on May 10, 1997, during a mixed-gas rebreather dive to 120 m on the east side of Augulpelu Reef; Palau (07º 16.41' N, 134º 31.44' E). It was later observed at the same reef at depths of 117-139 m from a submersible by Patrick L. Colin and Lori J. Bell in February -March, 2001. In April 2005, Mr. Forrest Young and colleagues observed several individuals of this (or a very similar) species during mixed-gas rebreather dives at depths of 120-150 m at Manado, Sulawesi, Indonesia. The type specimens included herein are the first of this species to be collected.

From these observations, C. abyssus appears to prefer depths in excess of 115 m, staying close to the substratum among boulders and rock outcroppings, where it takes refuge in small caves and holes. Juveniles and some subadults were also observed around limestone talus. Adults were usually observed singly or in pairs, while subadults and juveniles were seen in small groups. All type specimens were collected in the same general area, where the species is not uncommon. Other Chromis observed in the vicinity include three of the new species described herein ( C. brevirostris, C. degruyi , and C. earina ).

Chromis abyssus is not obviously allied with any other known species of the genus. It shares some similarities with a group of seven Indo-Pacific deep-dwelling Chromis species, characterized by a similar stout body shape, a large eye, and usually XIV dorsal spines. In their 1985 description of C. abyssicola, Allen and Randall noted a complex of deep-dwelling Chromis species distinguished by, among other characters, 19 or 20 pectoral rays, and 28-34 gill rakers. In addition to C. abyssicola , their complex included C. megalopsis 78 Allen 1976 (now regarded as a junior synonym of C. mirationis Tanaka 1917), C. mirationis Tanaka 1917 and C. struhsakeri Randall and Swerdloff 1973, to which we would add the subsequently named C. planesi 79 Lecchini and Williams 2004. C. abyssus has fewer pectoral rays (18 or 19) and fewer gill rakers (24-28) than members of this species complex, and may comprise a second grouping of deep-dwelling Chromis species, along with C. okamuri Yamakawa and Randall 1989 from Japan, the East African C. woodsi 80 Bruner and Arnam 1979 (both easily distinguished from C. abyssus on the basis of color and certain morphological characters such as number of gill rakers and tubed lateral-line scales), as well as the two new species C. circumaurea and C. degruyi , both described herein. Of the remaining two deep-dwelling Indo-Pacific stout-bodied Chromis species with XIV spines, C. onumai Senou and Kudo 2007 has the high pectoral-ray count of the first complex (19-20) and the gill-raker count of the second (25-27). C. axillaris 81 (Bennett 1831) has a wide gillraker range (26-30) and cannot easily be placed in either complex by this character. Of the three new Chromis with XIV dorsal-fin spines described herein (C. abyssus, C. circumaurea, and C. degruyi ), each has a unique and distinctive color pattern, and is readily distinguished from the others. Among the three, the former two ( C. abyssus and C. circumaurea ) share the most similarities both in terms of morphology and in Barcode DNA sequence data.