Chromis abyssus
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Genus: Chromis
Name
Chromis abyssus Pyle, R. L., 2007 – Wikispecies link – Pensoft Profile
- Chromis abyssus Pyle, R. L., 2007, Zootaxa 1671: 6-9.
Distribution
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.
Diagnosis
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
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
Discussion
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.
Materials Examined
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.
Etymology
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".
Taxon Treatment
- Pyle, R. L.; Earle, J. L.; Greene, B. D.; 2007: Five new species of the damselfish genus Chromis (Perciformes: Labroidei: Pomacentridae) from deep coral reefs in the tropical western Pacific. Zootaxa 1671: 6-9. doi
