Comprehensive Description
provided by Smithsonian Contributions to Zoology
Ecsenius tigris
DESCRIPTION.—Dorsal fin XII,13 or 14 (14 in 77% of specimens), deeply notched between spinous and segmented-ray portions. Anal fin II,15 or 16 (16 in 89% of specimens). Pectoral fin 12–14 (usually 13). Caudal fin 13. Vertebrae 10 + 22. Dentary incisor teeth 42–48 (includes anterior canine teeth, which differ little, if at all, in appearance from incisors); posterior canines one on each side. Lateral line without vertical pairs of pores, terminating posteriorly at point between vertical from interspace between dorsal-fin spines 10 and 11 and vertical from spine 12. Short cirrus present on posterior rim of anterior nostril, none on anterior rim.
Preserved Color: Faintly to darkly dusky stripe (sometimes originating as dark spot) extending posteriorly from pore at about mid-postorbital margin to about origin of lateral line; dusky spot on postorbital margin sometimes present at pore just dorsal to origin of dusky stripe; two darkly dusky bars extend across anterior interorbital area; dorsal surface of sclera blackish; ventral surface of ventral lip darkly dusky. Body with 10 or 11 dark marks along dorsal body contour: anteriormost, which may be absent, spot-like, at posterior base of first dorsal-fin spine; next three spot-like, at bases of third and fifth spines and between bases of sixth and seventh spines; next six usually bar-like, between bases of ninth and tenth spines, at base of twelfth spine, between bases of second and third segmented rays, fifth and sixth rays, eighth and ninth rays, and eleventh and twelfth rays; dark spot near dorsal body contour posterior to last dorsal-fin ray; dark spot, in line with previous spot, just anterior to caudal-fin base, giving rise to dusky, ventroposterior extension on caudal fin; up to 7 small, pale-margined, faintly dusky spots in interspaces between dark marks on dorsal body contour (none apparent in most specimens); 3 or 4 dark spots on dorsal third of body below spinous dorsal fin, posteriormost spot occasionally coalescing with dark spot on dorsal body contour; deep, faintly dusky stripe extending body length, embodying dark marks on dorsal half of body; 7 or 8 dark spots on ventral third of body; anteriormost spot, when 8 are present, faintest, anterior to vertical from anus; next spot, occasionally with dorsal extension, below vertical from eleventh dorsal-fin spine; other spots, except posteriormost, below band-like spots on dorsal body contour; posteriormost spot slightly anterior to caudal-fin base, giving rise to dusky dorso-posterior extension on caudal fin; deep, faintly dusky stripe extending body length, embodying dark spots on ventral third of body; body immaculate to faintly dusky below stripe; up to 9 small, elongate, pale-margined, dusky spots along midline of body in interspaces between dark marks (none apparent in most specimens); fleshy pectoral-fin base slightly darker dorsally than ventrally.
Slender, dusky stripe extending basally along spinous dorsal fin and anteriorly along segmented-ray portion; dusky extensions from stripe extend along spines; distal margin of segmented-ray portion dusky. Anal fin with deep, darkly dusky subdistal stripe. Pectoral-fin rays lined with melanophores. Pelvic fins immaculate. Caudal-fin rays variably lined with melanophores; dusky stripe-like extensions, originating from dark body spots, meeting on fin, enclosing pale area basally.
Live Color (based on photographs taken in the wild at Osprey, Bougainville, and Holmes reefs): Iris and pupil black with fine, bright-white or pale-yellow stripes extending dorsal and ventral to pupil; three small, bright-white or pale-yellow dash-like spots on dorsal surface of eye; short stripe-like marks on head in line with and same color as eye stripes (marks border dark postorbital stripe dorsally and ventrally); fine, bright-white or pale-yellow stripe between eyes anteriorly; bright-white or pale-yellow spot dorsal to latter stripe; head dusky yellow to plain brown dorsal to midorbital level; cheeks pink. Dusky stripes on body pinkish-orange brown to brown; row of small, bright-white spots in interspaces between dorsal dark marks; another row of rectangular or dash-like bright-white spots along body midline. Fins untinted except for brownish orange stripe in anal fin.
COMPARISONS.—In preservation, if not in life, Ecsenius tigris appears to be most similar in color pattern to E. fijiensis and the banded form of E. axelrodi. Ecsenius tigris differs from E. fijiensis in having 5 or 6 dark spots (versus less than 3) along the dorsal body contour below the spinous dorsal-fin, in having a row of 4 (versus less than 3) dark spots on the dorsal third of the body below the previous row, and in having but 2 vertical pairs of dark spots on the caudal peduncle (versus 3 pairs), with at most only the dorsal member of the posteriormost pair noticeably encroaching on the caudal fin (versus both members clearly present on the caudal fin).
Ecsenius tigris differs most obviously from the banded form of E. axelrodi in having 4, approximately equally spaced dark spots anteriorly on the body that are in line and posterior to the dark postorbital head stripe, whereas the banded form of E. axelrodi has only 2 widely separated spots in this area, and the anterior spot is invariably at the posterior margin of the opercle, slightly anterior to the position of the anteriormost spot of E. tigris. Ecsenius tigris further differs from the banded form of E. axelrodi in having two vertical pairs of dark spots on the caudal peduncle, whereas E. axelrodi has but one dark band and indications of a pair of short, dark stripes that extend onto the caudal fin.
Similar to E. fijiensis, but not to E. axelrodi, E. tigris lacks a dark-striped color-pattern form, and the members of a vertical pair of body spots are either completely separate or, when linked, clearly recognizable as separate. In E. axelrodi individual members of the vertical pairs of dark spots are scarcely, if at all, distinguishable in the dark body bands.
Information on live coloration is unavailable for E. fijiensis, and available information on freshly dead specimens is inadequate for comparisons. In live banded forms of E. axelrodi, the body stripes appear to be more orange than in E. tigris. Although E. tigris is most similar to E. fijiensis and E. axelrodi in overall color pattern, I am uncertain of its phylogentic relationships within the Opsifrontalis Group. I believe that the presence of two distinct color pattern types is a synapomorphy of a clade comprising E. axelrodi, E. bathi, and E. dilemma. This might suggest that E. tigris is the sister group of E. fijiensis, but, certainly, there are other possibilities.
HOLOTYPE.—BPBM 31034, female, 28.9 mm SL, entrance to lagoon, Osprey Reef, Coral Sea, reef in 5 m, J.E. Randall, 25 January 1987.
PARATYPES (all Osprey Reef).—BPBM 31035 (1 specimen: 19.7 mm SL) and USNM 285461 (2:21.1 and 28.4), collected with the holotype; AMS I.25110-021 (17:15.6–35.7), W edge reef flat, 8 m, 6 November 1984; AMS I.25112-025 (15:15.2–34.4), W edge 0.75 km N Osprey reef, 1 m, 8 November 1984; AMS I.25113-020 (3:14.6–30.0), West Pass inside reef, 8 November 1984, all Australian Museum Sunbird Party.
ISOS GROUP
This group consists of three species, E. isos, E. lubbocki, and E. trilineatus, which share several features of a complex color pattern that are probably synapomorphic. One unique feature is the presence of two stripe-like markings on the fleshy pectoral-fin base. In E. trilineatus the stripes are distinct and dark, the upper positioned near the level of the interspace between the uppermost two pectoral-fin rays; the lower usually positioned at about the interspace between the sixth and seventh from dorsalmost rays. The upper stripe often bends ventrally anteriorly (bend frequently hidden by opercle); occasionally the anterior end of the lower stripe also bends ventrally. In the other two species these two stripes are usually represented by scarcely noticeable, diffuse, dusky stripes that occupy the same positions as in E. trilineatus.
Ecsenius trilineatus has a conspicuous ventroanteriorly curving dark line on the opercle well anterior to the posterior margin of the opercle. The line usually reaches dorsally to about the dorsal level of the opercle and ventrally extends to the ventral surface of the head, or is represented there by a disconnected dark spot. In E. lubbocki the line is variably well defined or diffuse. In E. isos the line appears to be absent, but is represented by a series of diffuse, dusky spots. Based on its position, the dark opercular line of the ISOS Group is most similar to that of the Yaeyamaensis Group species (see footnote in discussion under the account of the Yaeyamensis Group).
Ecsenius trilineatus has three dark, well-defined stripes on the body, the dorsalmost extends along the dorsal body contour to the end of the dorsal fin and is the least noticeable. The two more ventral stripes break up posteriorly into a series of dashes and dots, with faint indications of dusky extensions onto the caudal fin from the vertical pair of spots at the caudal-fin base. Ecsenius isos exhibits diffuse dusky markings anteriorly in the position of the three stripes of E. trilineatus, but posteriorly the two more ventral stripes are represented by dark spots, the posteriormost vertical pair of which also continue as dusky extensions onto the caudal fin. In E. lubbocki the stripes are diffuse, the two more ventral stripes are relatively deep and continue very faintly onto the caudal fin.
There is a dark spot on the axillary (internal) surface of the fleshy pectoral-fin base in E. trilineatus; occasionally the spot is diffuse. In the other two species, of which only poorly preserved material is available, the spot is represented by a diffuse concentration of melanophores. A discrete axillary spot is otherwise found only in the species of the Yaeyamaensis Group and E. alleni of the Opsifrontalis Group; the species of the Oculus Group have a diffuse axillary spot.
Males, at least, of Ecsenius trilineatus and E. lubbocki have dark pigment on the pelvic fins; the fins of E. isos are immaculate. Dark pelvic-fin pigment occurs commonly among the species of the Oculus and Yaeyamaensis groups, and E. fourmanoiri (Opsifrontalis Group).
I am unable to hypothesize unequivocally the sister group of the Isos Group, but based on color-pattern characters, my putative Oculus-Yaeyamaensis clade appears to be a good candidate (see discussions of relationships under accounts of Oculus and Yaeyamaensis groups).
The three species of the Isos Group have allopatric distributions, with the distributions of E. isos and E. trilineatus being almost parapatric. Ecsenius lubbocki is known only from Phuket, Indian Ocean coast of Thailand; E. trilineatus ranges from the Moluccas east and south to the Solomon Islands; and E. isos ranges through the New Hebrides south and slightly west to New Caledonia.
I cannot hypothesize a single, unequivocal cladistic pattern of relationships for the three species of the Isos Group that might be used as a basis for hypothesizing a vicariographic (Springer, 1982:5) scenario. Even without such information I propose that historically there was a single ancestral species that occupied essentially the entire range of the group. At least two vicariant events are necessary to have evolved the present three species from that ancestral species. I believe that the first event either isolated an Indian Ocean population or a New Hebrides-New Caledonian population from the remainder of the distribution (population) of the ancestral species. The resulting two populations subsequently diverged. The second vicariant event isolated either an Indian Ocean population from an Indian Ocean-to-Solomon Islands population (if the first event had isolated a New Hebrides population) or a New Hebrides-New Caledonian population from a Moluccan-New Hebrides-New Caledonian population (if the first event had isolated an Indian Ocean population). The resulting two populations subsequently diverged. The three populations formed during this scenario are represented today by three species. The presence of an extensive geographic gap between the distributions of E. trilineatus and E. lubbocki, and a much smaller gap between E. trilineatus and E. isos, may be the result of collecting artifacts and/or extinction in the gap areas.
Based on the timing of various geological and climatic events, it is possible to hypothesize the nature and order of the two vicariant events that gave rise to the three species. I believe that the first event occurred between the Solomon Islands and New Hebrides, where the distributions of E. trilineatus and E. isos come closest together. This event resulted in the formation of a barrier to dispersal between these two island groups. To hypothesize such a barrier it is necessary to note that the Santa Cruz Islands, although politically part of the Solomon Islands, geologically are part of the New Hebrides Islands (Kroenke, 1984) and form the northern extension of the New Hebrides. No collections of Ecsenius are known from the Santa Cruz Islands, but the presence of E. isos in those islands would corroborate the vicariance scenario I will propose. The presence of only E. trilineatus in the Santa Cruz Islands would falsify the scenario, and the presence of both species in those islands would neither corroborate nor falsify the scenario.
The vicariance scenario assumes the former existence of a common ancestral species occurring in both the Solomons and New Hebrides (and possibly as far west as the Moluccas and as far south as New Caledonia). These two island arcs were once part of a more-or-less east-west linearly continuous ridge that existed at least as recently as about 10 m.y.a.. (Packam and Andrews, 1975; Kroenke, 1984:117). During that time I hypothesize that the islands on the ridge were spaced closely enough (much less than 350 km between an island and its nearest neighbor) to have allowed the ancestral species to colonize ridge segments representing both of today's island arcs. A complex tectonic history has resulted in the present-day location and configuration of the island arcs on the original ridge. During approximately the past 6 million years, the Santa Cruz-New Hebrides portion of the originally continuous ridge rotated about 30° clockwise (Kroenke, 1984), and broke the continuous ridge between the Solomon and Santa Cruz-Solomon islands. Independent movement of the resulting ridges created what is presently an islandless gap of about 350 km between the closest Solomon and Santa Cruz islands. The length of this gap was sufficient to isolate portions of the parental population on either side and permit their subsequent divergence. The New Hebrides are currently on the verge of colliding with the Loyalty Islands, which are adjacent to New Caledonia. Dispersal from the New Hebrides to the Loyalties and then to New Caledonia could account for the occurrence of E. isos in New Caledonia (and it probably will be found in the Loyalties; the gaps separating the New Hebrides from the Loyalties and the Loyalties from New Caledonia are both less than the gap between the Santa Cruz and Solomon islands).
As I have shown in the discussion of the distributions of the Opsifrontalis Group species, gaps of as little as 85 km are adequate to isolate populations of different species from each other.
If this scenario explains the distribution of E. isos (and I believe it does), then E. isos must be the sister group of the other two species. It is possible to propose reasonably a vicariant event that would have isolated the Indian Ocean portion of an ancestral population that had a distribution extending from the west (Indian Ocean) coast of the Malay Peninsula to the Solomon Islands.
Present-day marine connections between the Indian and western Pacific oceans are through the very shallow Straits of Malacca or along the outer coast of the southern chain of Indonesian islands, an area in which no species of the Isos group is known to occur today. Any of the drops in sea level that have occurred during the many glacial periods of the recent Cenozoic (last occurred about 18,000 years ago) would have been sufficient to close the Strait of Malacca and dry up most of the inland seas of western Indonesia (Potts, 1983, 1984; Woodland, 1983; McManus, 1986), thus isolating the Indian Ocean from the western Pacific. Conspecific populations on either side of the barrier could then have begun to diverge.
The distribution of Ecsenius lubbocki is widely separated from the nearest known population of E. trilineatus. If this large distributional void is real, rather than apparent, it might be the result of extinction, resulting from elimination of much of the coastal area during the last glaciation, and subsequent non-recolonization by dispersal since sea level last rose.
Ecsenius lubbocki is one of the few species endemic to the eastern Indian Ocean. Another is E. oculatus (Oculus Group), which, however, is not sympatric with E. lubbocki. My hypothesized sister group of E. oculatus, E. paroculus, however, is sympatric over part of its range with E. lubbocki.
Jeffrey T. Williams (pers. comm.) suggested the possibility that a period of glaciation as early as Miocene could have been responsible for the isolation of E. lubbocki. Depending on the timing of this isolation, then, E. lubbocki, could be the sister group of the other two species.
Ecsenius isos McKinney and Springer
Ecsenius (Ecsenius) yaeyamaensis.—Springer, 1971:32–33 [misidentification in part, New Hebrides].
Ecsenius (Ecsenius) trilineatus Springer, 1972:2 [in part: nonparatypic “additional material”].
Ecsenius isos McKinney and Springer, 1976:5 [New Hebrides, Efate; holotype, BPBM 12122].
DESCRIPTION.—Dorsal fin XII,14 or 15, deeply notched between spinous and segmented-ray portions. Anal fin II,16 or 17. Pectoral fin 13 or 14 (14 unilaterally only in one of seven specimens available). Segmented caudal-fin rays 13. Vertebrae 10 + 22 or 23. Dentary incisor teeth (includes anterior canine teeth, which differ little, if at all, in appearance from incisors) 43–51; posterior dentary canines 1 on each side. Lateral line without pairs of pores, terminating posteriorly at point between verticals from dorsal-fin spines 8 and 11. Cirrus present on posterior rim of anterior nostril; none on anterior rim.
Color Pattern: Head diffusely dusky, darker dorsally, with series of up to 4 small spots extending ventroanteriorly from opercular area; when four spots are present, dorsalmost is on opercle dorsally, and is diffusely or darkly dusky; next spot is also on opercle, mid-laterally, and is dark or diffusely dusky; next spot is on opercle just posterior to ventralmost preopercular pores, and is dark or diffusely dusky; last spot is on mid-lateral ventral surface of head, always present, dark, and most prominent of series; another, small dark or dusky spot occasionally present on cheek anterior to first from dorsalmost spot of opercular series; ventral margin of lower lip dusky anteriorly. Side of body with two longitudinal series of markings, dorsal series beginning below spinous dorsal anteriorly as diffuse, relatively deep stripe of somewhat connected blotches, gradually intensifying as dark spots in area below mid-section of segmented-ray portion of fin; terminal spot of dorsal series positioned no further posteriorly than very end of body; ventral longitudinal series of markings similar to, and paired with, dorsal series (no more than 3 or 4 pairs of dark spots). Pectoral-fin axil with noticeable dark spot or marking in well-preserved specimens, diffusely represented in poorly preserved specimens. Fleshy pectoral-fin base with dark or dusky spot dorsally and another at about level of seventh from dorsalmost ray; another spot just posterior (distal) to that at seventh ray extending from base a short distance onto fin rays. Spinous-dorsal fin with a diffusely dusky stripe suprabasally, usually continuous on segmented-ray portion, which has a diffusely dusky stripe distally. Anal fin with a deep, subdistal dusky stripe. Diffuse dusky extensions from terminal pair of spots on body extend a short distance on caudal fin. Pelvic fins unmarked.
A fresh specimen, not in a good state of preservation, photographed in color (Plate 13: figure 1) exhibits little remarkable color, except for two rows of large pinkish spots on the anterior half of the body. These spots, of which there is no trace in preservation, are in the position of the two faintly dusky stripes present in preserved specimens of E. lubbocki.
COMPARISONS.—The color pattern of Ecsenius isos appears to be similar to that of E. trilineatus. The same basic pattern is present in both species but the markings on the body anteriorly, and on the fleshy pectoral-fin base, of E. trilineatus are much more intense, continuous, and discrete. The dark, curving stripe in the opercular area of E. trilineatus is represented by four diffuse or dusky spots in E. isos, and the two dark stripes on the fleshy pectoral-fin base of E. trilineatus are represented by the dusky spots in the same area on E. isos. In some specimens of E. trilineatus the curving opercular stripe is interrupted near its ventroanterior end, and the “end piece” is comparable in position to the spot on the ventral side of the head in E. isos. include pinkish tints, as are present in E. isos.
Because of the bilateral pair of dark spots on the ventrolateral surface of the head, E. isos superficially appears to belong to the Prooculis Group, but the dark spots in the latter group of species occur only in males, whereas both males and females of E. isos have the dark spots. Ecsenius isos and E. trilineatus are further distinguished from the Prooculis Group in having a dark spot in the pectoral-fin axil (spot diffuse in available material of E. isos) and in a tendency for the lateral line to extend slightly further posteriorly.
DISTRIBUTION.—New Hebrides and New Caledonia.
MATERIAL (* = new material).—New Hebrides: Efate, BPBM 12122 (holotype: 26 mm SL); Espiritu Santo Harbor, USNM 195787 (3 specimens: 21–26). New Caledonia: Solitaire Island, BPBM 22524* (1:32); Kinde Reef, MNHN 1980–807* (1:32); Baie de Prosny [= Prony?], MNHN 1980–920* (1:32).
- bibliographic citation
- Springer, Victor G. 1988. "The Indo-Pacific blenniid fish genus Ecsenius." Smithsonian Contributions to Zoology. 1-134. https://doi.org/10.5479/si.00810282.465
