Eviota nigriventris Giltay

Greenfield, David W. & Randall, John E., 2011, Two new Indo-Pacific species in the Eviota nigriventris complex (Teleostei: Gobiidae), Zootaxa 2997, pp. 54-66 : 60-65

Eviota nigriventris Giltay

Redbelly dwarfgoby

( Figs. 1 , 10 , 13 , 19 , 20 )

Material examined. Syntypes: IRSNB 42A, 12.5 mm male, IRSNB 42B, 11.8 mm female, Entre Banda Neira et Goenoeng Api, 24 Feb. 1929, S.A.R. le Prince Leopold de Belgique. Others: BPBM 36216, 3 specimens 14.2–20.5 mm, Papua New Guinea, east end Milne Bay, north side of outer bay, “Sullivan’s Patches”, 10.3600ºS, 150.7250ºE, 26 m, from live coral on rubble-sand slope, rotenone, J.E. Randall, 8 Dec. 1993; BPBM 33614, 2 specimens 15.8– 18.3 mm, Chesterfield Islands, lagoon, S.E. corner, small patch reef, 19.8917ºS, 158.4683ºE, 14–15 m, rotenone, J.E. Randall, M.L. Kulbicki, P.J. Doherty, et al., 22 August 1988; BPBM 37686, 1 specimen 16.4 mm, Palau, Uchelbeluu Reef (Short Drop-off) west side, 7.2781ºN, 134.6956ºE, dropoff on branching coral, quinaldine, J.E. Randall, 10 May 1997.

Diagnosis. The following combination of characters distinguish E. nigriventris from congeners: A red band on entire lower body from head back to caudal-fin base where it grades into black ending in an asymmetrical spot that angles down sharply towards the ventral portion of the caudal fin ( Fig. 19 ); pectoral-fin base peppered with small black dots, more intense dorsally; cephalic sensory pore system lacking the PITO and IT pores and the AITO pore enlarged; dorsal/anal fin-ray formula 9/8. Pectoral-fin rays simple; spinous dorsal elongate or filamentous in both sexes. Genital papilla nonfimbriate. In life the ventral red band is bordered dorsally by a bright white band that runs from the top of the head back to the caudal fin where it curves down following the angled black spot.

Description. Dorsal-fin rays VI+I,9–10; anal-fin rays I,8–9; unbranched pectoral-fin rays 16, lateral scale rows 23–24. The six specimens for which we have live color records are in poor condition and counts were not possible for several of them. Therefore, the range of counts given here will not represent the true range of variation and pelvic-fin information was not possible. The ranges given by Lachner and Karnella (1980), although based on at least two species, are probably closer to the range of variation for this species.

Measurements (based on five specimens). Standard length 14.2 –20.9 mm; head length (31.7–36.5, 33.3); origin of first dorsal fin (31.0–39.3, 35.0); origin of second dorsal fin (53.4–63.8, 58.5); origin of anal fin (58.5–66.7, 62.2); caudal-peduncle length (21.5–21.7, 21.6); caudal-peduncle depth (13.4–15.5, 14.4); body depth (22.5–29.6, 26.3); eye diameter (10.7–13.0, 11.8); snout length (5.2–7.0, 6.3).

Color in preservative (from BPBM 33614). Background color of head and body pale yellowish. A light brown band overlaid with a peppering of tiny brown dots on lower body, slightly above midline, from behind eye posterior to caudal-fin base. Ventral band progressively darker posteriorly, ending in an asymmetrical curve angling down sharply towards the ventral part of the caudal fin. Side of head and pectoral-fin base with a scattering of small brown dots as on the snout and tips of jaws. Underside of head and belly pale yellowish. Anal, distal margin of second dorsal, and lower half of caudal fin dusky. Pectoral and pelvic fins clear. Pupil of eye yellowish, iris black.

Color in life ( Fig. 1 ). A red to reddish orange band on entire lower body, slightly above midline from behind eye back to caudal-fin base where it grades into black. The black area at end of the band angles down sharply towards the ventral part of the caudal fin. The ventral band bordered dorsally by a brilliant white line that also angles down at the caudal-fin base. The white line extends forward onto the head, through the interorbital area onto the snout. Back above white line translucent to cream colored. End of snout and jaws black, the black extending back under the eye and onto the preoprecular area. Undersurface of head and ventral surface across belly and back to anal-fin base cream colored. Fin spines and rays with a reddish tinge. Membranes of anal fin dusky. Pupil of eye black. Iris from top of pupil down reddish, sprinkled with some black pigment. Iris above pupil light cream to a brilliant white line that extends back a short distance behind eye.

Distribution. Known from the Yaeyama Islands, Japan; Philippine Islands; Palau; Ceram; Bali; Flores; Kimbe Bay, New Britain; Papua New Guinea; and Chesterfield Islands ( Fig. 13 ).

Comparisons. All three species in the E. nigriventris complex fit the description of the Group IV species group of Lachner and Karnella (1980): Cephalic sensory pore system lacking the PITO and the IT pores, the AITO pore is enlarged or paired; pectoral-fin rays never branched; genital papilla of male nonfimbriate; pelvic membrane well developed; spinous dorsal fin elongate or filamentous; fifth ray of pelvic fin more than one-half length of fourth ray; upper and lower subcutaneous bars and ventral midline spots on body posterior to origin of anal fin absent. There are only four other species in that group, plus E. shimadi Greenfield and Randall (2010) which fits except for having a shorter fifth pelvic-fin ray: E. bifasciata Lachner and Karnella 1980 , E. lachdeberei Giltay 1933 , E. partimacula Randall 2008 , and E. raja Allen 2001 . Eviota raja and sometimes Eviota bifasciata have two dark stripes, one along the ventral surface and the other along the dorsal surface of the sides, whereas the species in the E. nigriventris complex have only a ventral stripe. Eviota bifasciata may only have the ventral stripe, but the ventral band above the anal-fin base is narrow, less than the eye diameter, whereas it is wider in the E. nigriventris complex, equal to or greater than the eye diameter. Both E. lachdeberei and E. partimacula have a dark mark at the center of the caudal-fin base that is lacking in the E. nigriventris complex. Eviota shimadai lacks all of the above mentioned dark markings.

Because of the major color differences, the recognition of the three species discussed in this paper is obvious when looking at live or fresh individuals, but when dealing with preserved specimens the task is more difficult. Of the three species, E. nigriventris is the easiest to recognize because the sloped angle on the dorsal side of the black caudal spot is retained in preserved specimens. The caudal spot of E. dorsogilva and E. dorsopurpurea is a semicircle. The pattern of dark chromatophores on the pectoral-fin base is helpful in recognizing larger (14.2 mm and greater) individuals of E. dorsopurpurea , because they form a reversed L-shaped pattern ( Fig. 18 ). Some smaller individuals from the same lot with larger individuals have scattered dark chromatophores on the pectoral-fin base as do E. dorsogilva individuals of all sizes. The anal-fin soft rays are almost always 8 in E. dorsogilva , whereas they are usually 9 in E. dorsopurpurea . One other helpful character used in separating preserved specimens of E. dorsogilva and E. dorsopurpurea is eye size, which shows strong allometric growth ( Fig. 20 ), so specimens of similar size must be compared. Eviota dorsopurpurea appears to have a larger eye than similar sized E. dorsogilva .

In order to determine which of the three species was E. nigriventris , we borrowed the two syntypes of E. nigriventris (IRSNB 42A and B). The black caudal spots of the syntypes have the asymmetrical sloped dorsal surface. When eye size was plotted on the graph containing other specimens ( Fig. 20 ), their values fell along the line of points of other specimens with a similar caudal spot. In addition, neither E. dorsogilva nor E. dorsopurpurea have been collected to the west of Papua New Guinea where the type locality is located. We feel confident that E. nigriventris is the red species with the asymmetrical caudal spot.

Lachner & Karnella (1980: Fig. 66) illustrated three male individuals from different collections in Papua New Guinea. The specimens in 66a & 66b have the caudal spot pattern of E. nigriventris and also the ventral band is darkest posteriorly, typical of individuals with a red ventral band. The specimen in 66c has a semi-circular caudal spot and a complete dark ventral band as do E. dorsopurpurea and E. dorsogilva . The drawing of a specimen (USNM 209680) from Ceram has a semi-circular caudal spot and the reversed L-shaped pectoral-base pigment pattern typical of E. dorsopurpurea . Assuming that the artist carefully measured the specimen, the 13.2 mm-specimen has an eye size of 13.7% SL which would be close to that of the 14.2 mm-specimen of E. dorsopurpurea on the plot ( Fig. 20 ); however, this would be a new record, being found outside the eastern Papua New Guinea area.

We do not have genetic information on the three differently colored species discussed here to test their taxonomic status. We do, however, have differences in eye size between them. The second author has collected both E. dorsopurpurea and E. nigriventris from the same area at Milne Bay, each in a separate aggregation above a different coral species. We have made over three hundred rotenone collections in Fiji and have only collected or seen E. dorsogilva there. It also has been collected at the geographically adjacent Tonga Islands, Wallis Island, and New Caledonia as well as more distant localities north to Japan.

Figures

FIGURE 1. Eviota nigriventris. Kimbe Bay, New Britain. Photograph by J. E. Randall.

FIGURE 10. Eviota nigriventris, Kimbe Bay, New Britain. Photograph by J. E. Randall.

FIGURE 13. Distribution of species in the Eviota nigriventris complex. E. dorsogilva = star; E. dorsopurpurea = circle; E. nigriventris = square.

FIGURE 18. Eviota dorsopurpurea, pectoral-fin base. Paratype USNM 400921, 20.5 mm-female. Photograph by D. W. Greenfield.

FIGURE 19. Eviota nigriventris, caudal-base coloration, Milne Bay, Papua New Guinea. Photograph by J. E. Randall.

FIGURE 20. Eye diameter as percentage of standard length versus standard length. Eviota nigriventris = blue diamond, E. dorsogilva = yellow triangle, E. dorsopurpurea = purple square, E. nigriventris syntypes blue X.