Smooth Fin Blenny

Dorsal fin X-XIII (typically XII), 18-21 (rarely 21), spinous and segmented-ray portions continuous. Anal fin II,17-22 (typically 19-21). Pectoral fin 14-16 (typically 15). Segmented caudal-fin rays 13 or 14 (rarely 14). Vertebrae 10 or 11 (rarely 10) + 23-26 (rarely 23) = 34 to 37 (rarely 34). Dentary incisor teeth which includes anterior canines very similar in appearance with incisors, 40-53 (rarely < 44); posterior canines 0 or 1(usually 1) on each side. Lateral line lacking vertical pairs of pores, extending posteriorly to point between verticals from 8th and 12th from anterior most dorsal-fin spine (usually past vertical from 8th). With cirrus on posterior rim of anterior nostril; absent on anterior rim. Body coloration of 3 basic color patterns: uniformly brown, dark-brown or black but pigmentless posterior of dark caudal fin base, or generally brownish with darker stripe along dorsal area.

Oviparous, distinct pairing (Ref. 205).

Dorsal spines (total): 10 - 13; Dorsal soft rays (total): 18 - 21; Analspines: 2; Analsoft rays: 17 - 22; Vertebrae: 34 - 37

Found among corals (Ref. 9710).

Adults are found among corals (Ref. 9710). Oviparous. Eggs are demersal and adhesive (Ref. 205), and are attached to the substrate via a filamentous, adhesive pad or pedestal (Ref. 94114). Larvae are planktonic, often found in shallow, coastal waters (Ref. 94114).

aquarium: commercial

Ecsenius (Ecsenius) frontalis Ehrenberg

Salarias frontalis Ehrenberg in Cuvier and Valenciennes, 1836, p. 328 [Massawa, Red Sea].

Salarias nigrovittatus Rüppell, 1838, p. 136 [Massawa, Red Sea].

Ecsenius albicaudatus Lotan, 1969, p. 372 [Marsa Murach, Gulf of Aqaba].

DESCRIPTION.—Dorsal spines 10–13 (rarely 10, 11, or 13); dorsal rays 17–21 (rarely 17 or 21); segmented anal rays 17–22 (rarely 17, 18, or 22); pectoral rays 14–16 (usually 15); segmented caudal rays 13 (rarely 14); dorsal procurrent caudal rays 6–8; ventral procurrent caudal rays 6–9 (rarely 9); total caudal elements 25–30 (rarely 25 or 30); gill-rakers 11–17 (rarely 11, 12, or 17); pseudobranchial filaments 5–7 (usually 6); lower incisor teeth 40–53; lower jaw posterior canines 0–1; total lower jaw posterior canines 0–2 (usually 2); upper incisor teeth 124–130 (4 counts); precaudal vertebrae 10–12 (rarely 10 or 12); caudal vertebrae 23–26 (rarely 23); total vertebrae 34–37 (rarely 34); epipleural ribs 11–16 (usually 12–14). Lateral line without paired pores, extending to below level of 8th-12th dorsal element (usually 9th–11th). Dorsal fin without notch (one of several hundred specimens had dorsal fin notched two-ninths length of first dorsal ray). Third (innermost) pelvic ray varying from obvious to not obvious (usually not obvious). One cirrus on each anterior nostril, each cirrus occasionally forked.

Color pattern: There are three basic color patterns found in E. frontalis. See discussion following, concerning the systematic status of these patterns. The smallest specimen examined was a postlarva, 15.0 mm SL, from the Gulf of Aqaba. It was not possible to assign this specimen to one of the three color pattern types. The specimen was pale with several irregular vertical bands composed of spots. A few small bright yellow individuals of E. frontalis were also seen in the Gulf of Aqaba. It may be that the banded and yellow forms represent the preadult color of the two color pattern forms found in the Gulf of Aqaba (more below).

The Problem of Ecsenius frontalis, E. albicandatus, and E. nigrovittatus

Although I have placed E. albicaudatus and E. nigrovittatus in the synonymy of E. frontalis, I am uncertain that my action is correct. In the discussion that follows I treat the three nominal species as color pattern forms of a single species, E. frontalis, and present the evidence on which my action is based.

Ecsenius frontalis and E. nigrovittatus were described from Massawa, Ethiopia, and E. albicaudatus was described from the Gulf of Aqaba, each from a single specimen. While the types of E. frontalis and E. nigrovittatus are in poor condition, data from these types, together with the distinctive color patterns given in the original descriptions, make it possible to identify recently collected specimens from Massawa with both these nominal species. The holotype of E. albicaudatus is in excellent condition. Its distinctive color pattern has been found in numerous recently collected specimens from near the type locality.

The morphology and meristics of the three nominal species are very similar, but the species differ consistently in color pattern. (In Figures 13–15 the apparent morphological differences exhibited in these illustrations are individual variations; when series of each color form are examined complete morphological overlap is encountered.) I have observed all three color pattern forms alive in their natural habitat. The frontalis form is generally brown, darkest anteriorly, grading into yellow-orange posteriorly, with a bright yellow-orange caudal fin. The head and body of the albicaudatus form are black with a narrow area of variable width at the caudal peduncle completely unmarked and pale (sometimes the pale area extends onto the dorsal fin); the caudal fin is immaculate except for a faint pink tinge observable only in freshly preserved specimens. The nigrovittatus form is usually brown with a black stripe on the body bordered by pale dorsal and ventral margins; the caudal fin is slightly tinged with orange. Occasional individuals of the nigrovittatus form have yellow-orange heads.

Two individuals, I believed at the time of capture to be the frontalis form, were brought to the laboratory alive. When the individuals were placed in an aquarium there appeared one frontalis form and one albicaudatus form, which was dark brown with a yellow-orange caudal—the only albicaudatus form I have collected with these colors. These and other individuals of both color pattern forms held in the aquarium paled considerably after several days, and it was not possible to tell one form from the other.

The geographical distributions of the albicaudatus and frontalis forms are nearly identical (Figure 5). The frontalis form has been taken widely in the Gulf of Aqaba, in the southern Gulf of Suez, widely in the Red Sea and in the Bay of Tadjoura (Gulf of Aden, just outside the southern entrance to the Red Sea). The albicaudatus form has a similar distribution to that of the frontalis form, but it has not been taken outside of the Red Sea or in the Gulf of Suez. It was observed by me in the Gulf of Suez, however. The nigrovittatus form has been taken only in the southern Red Sea, on and off the coast of Ethiopia.

I obtained all three forms in the same collection (poison) from a coral rock outcrop estimated to be about 3 meters in height and 8–10 meters in circumference; water depth was about 4 meters. The specimens in this collection included 55 frontalis forms, 25 nigrovittatus forms, and 6 albicaudatus forms. My six collections (all made at depths of 7 meters or less) in Ethiopian waters, where the frontalis and nigrovittatus forms were always taken together, yielded three times as many frontalis forms as nigrovittatus forms, and the frontalis forms were always more abundant. The six albicaudatus forms mentioned are the only ones known from Ethiopian waters.

In the Gulf of Aqaba and Gulf of Suez collections, where only the frontalis and albicaudatus forms were seen or taken, the frontalis form was generally dominant in the shallower waters and the albicaudatus form was generally dominant in the deeper waters. The depth of each collection and the number of specimens of each form taken in the poison collections that I made in Israeli waters are listed below. Because the poison spread, it was not possible to limit collections to a particular depth. The collections were all made during the day, July-September 1969.

Approximate depth (meters)

Albicaudatus form

Frontalis form

0–3

10

37

0–18

11

3

0–15

5

9

0–16

14

2

0–7.5

3

0

0–10.5

4

1

0–10

1

31

0–3.5

1

8

9–12

18

1

21–27

3

0

0–9

one seen

9 (seen commonly)

I observed both the frontalis and albicaudatus forms together and common at depths of about 3–12 meters on the coral reef preserve at Eilat, Israel. I cannot say whether one form was much more dominant than the other; my impressions varied from day to day.

The frontalis and albicaudatus forms were commonly observed together in the Gulf of Aqaba, and the frontalis and nigrovittatus forms were commonly observed together at Massawa, Ethiopia. I have not seen all three forms together, although as noted above, I have collected all three from the same rock. The three forms inhabit live and dead coral and are not found over the sandy bottom. They are frequently out from under cover, on top of the coral. They dart, but only rarely swim freely, and then for only a few centimeters. Their movements are only moderately jerky. They feed by nipping at the rocky substrate. Gut contents consist of unidentifiable calcareous granules less than 0.3 mm in diameter, particulate organic matter, ostracods, and foraminifera. I noted no differences in behavior of the three forms, which appeared to be identical and different from the behavior of the other species of Ecsenius that occur together with them in the same general area. For instance, E. gravieri spends much of its time swimming freely over sandy bottom, where it feeds by nipping into the sand; E. nalolo was never seen out from under cover or swimming freely, and its movements are very jerky; E. aroni is somewhat similar in behavior (but not morphology or color pattern) to E. frontalis, but it usually occurs at greater depths and spends more time under cover; E. midas, which was not seen alive, was reported by Starck (1969) to swim with other fishes and to feed on plankton.

Certain morphological and meristic characters are given with frequency distributions in Tables 11 and 12 for each of the three forms for the different localities where they occur. Examination of the data indicates the possibility of sexual dimorphism and also that Israeli specimens of the color forms have higher numbers of certain meristic characters than Ethiopian specimens of the same forms. To determine if the differences noted are statistically significant it is, therefore, necessary to test the data for the same forms, sexes separated, from the two areas, and for different forms from the same area, sexes separated.

Data for specimens of the frontalis form from Sanganib Reef (Sudan) and the Gulf of Aden and for specimens of the albicaudatus form from Ethiopian waters were not included in the tests because the numbers of specimens were small and the localities were well removed from Israel or Ethiopia.

The following significant differences were found:

Israeli frontalis form males and females have higher average numbers of teeth, segmented dorsal rays, segmented anal rays, and caudal vertebrae than Ethiopian frontalis form males and females.

Ethiopian frontalis form males have higher average numbers of segmented anal rays than Ethiopian frontalis form females.

Ethiopian frontalis form males have a close to significantly (p = between .02 and .01) higher average number of caudal vertebrae than Ethiopian frontalis form females.

Grouped data (Tables 13 and 14) of proportional characters also indicate differences among the three forms. These data were also graphed and the following differences noted:

Israeli frontalis form males have a relatively longer caudal fin than Israeli frontalis form females (Figure 10).

Israeli albicaudatus form males have a relatively longer caudal fin than Israeli albicaudatus form females (Figure 10).

Israeli frontalis form males have a relatively longer caudal fin than Ethiopian frontalis form males (Figure 10).

Ethiopian nigrovittatus form males have a relatively longer caudal fin than Ethiopian nigrovittatus form females (Figure 9).

Ethiopian nigrovittatus form males have a relatively longer caudal fin than Ethiopian frontalis form males or females (Figure 9).

Specimens of less than 30 mm SL of the Israeli frontalis and albicaudatus forms have relatively longer nasal cirri than specimens of any of the three Ethiopian forms (Figures 7 and 8).

Specimens of the Israeli frontalis and albicaudatus forms have a relatively longer last dorsal spine than any of the three Ethiopian forms (Figure 6). The same relationship exists between the relative lengths of the third dorsal spine and fifth dorsal ray of the Israeli frontalis and albicaudatus forms compared with the lengths of these elements for the three Ethiopian forms (study graphs).

There is some indication that Israeli frontalis form males have a relatively longer caudal fin than Israeli albicaudatus males (Figure 10).

Aside from the fact that there are differences between the Israeli and Ethiopian populations of the frontalis form, the above data provide only limited support for the concept that the three color pattern forms are different species: The nigrovittatus form exhibits sexual dimorphism in the length of the caudal fin, which the sympatric frontalis form does not (but the allopatric Israeli frontalis form does); nigrovittatus form males have a longer caudal fin than sympatric males of the Ethiopian frontalis form (but not longer than the allopatric Israeli frontalis and albicaudatus form males), and possibly the Israeli frontalis form males have longer caudal fins than Israeli albicaudatus form males. (This does not seem to be true of Ethiopian frontalis form males versus Ethiopian albicaudatus form males even though there are only a few specimens of the latter.)

The fact that the Gulf of Aqaba populations of the frontalis and albicaudatus color pattern forms have higher average numbers of each meristic character than their Ethiopian counterparts is probably due to the cooler water temperatures of the Gulf of Aqaba relative to those of the Ethiopian coast (Oren, 1962). The same type variation has been reported for other Gulf of Aqaba-Red Sea blenniids (Smith-Vaniz and Springer, in press).

There is, then, no consistent basis other than color pattern on which to recognize E. frontalis and E. albicaudatus as separate species. One might recognize E. nigrovittatus as a separate species, based on the small differences noted and the fact that it does not occur at the northern end of the Red Sea (Gulf of Aqaba).

There are other data that influence the recognition of the three forms as one species. There are no other species of Ecsenius that appear to be closely related to the three forms and speciation, if such occurred, would seem of necessity to have taken place in the Red Sea. The Red Sea is a relatively small body of water with a limited amount of coral reef habitat. It is difficult to postulate how three species so similar as the three color pattern forms could have evolved sympatrically, especially when there does not appear to be a difference in feeding habits or microhabitat preference.

There are other species of Ecsenius that have apparently evolved different color pattern forms that occur sympatrically. These forms are, however, more obviously derivative of the same basic form than are the Red Sea color pattern forms of E. frontalis. Ecsenius pulcher has a solid color form and one in which the melanophores have been suppressed in portions of the posterior region of the body, thus forming vertical dark and pale stripes (Figure 16). This form is somewhat similar to the albicaudatus form in which the melanophores on the caudal peduncle have been suppressed. Ecsenius bicolor has three basic color pattern forms: one that is completely dark, one that is paler (either gradually or abruptly, Figures 20 and 21), and one that has a diffuse, dark stripe on its side. Although these three forms duplicate the forms found in Ecsenius frontalis, they generally are not so strikingly different from each other, and the striped form is very rare. The life colors of the three E. bicolor forms are very much the same as opposed to the differences noted in the frontalis forms. It seems, therefore, that the tendency for species of Ecsenius to exhibit different color pattern forms is a trait of the genus.

Information on breeding behavior and the color patterns of the offspring are necessary for reaching a final solution to the problem of the taxonomic level that should be accorded the three color pattern forms of E. frontalis.

I know of no situation involving fishes that is exactly comparable with that reported here for E. frontalis. Although only slightly similar, the circumstances Stephens (1963) reported for Acanthemblemaria crockeri Beebe and Tee-Van (Chaenopsidae) is of interest. A. crockeri is represented by two color pattern forms in the Gulf of California, the only area where the species occurs. Only one form was found in the northern end of the Gulf, and its relative abundance gradually decreased toward the south until it was not found to occur in the southern end of the Gulf. The other form was the only one at the southern end of the Gulf and it decreased in relative abundance toward the northern end of the Gulf. The two forms occurred together in the midportion of the Gulf. Stephens was unable to explain the basis for these circumstances. The situation is somewhat paralleled by two of the E. frontalis color forms. The albicaudatus form is abundant at the northern end of the Red Sea (Gulf of Aqaba) and rare at the southern end. The nigrovittatus form is common at the southern end of the Red Sea but absent from the northern end. I hesitate to place much emphasis on these similarities.

MATERIAL (localities abbreviated).—Gulf of Aqaba: USNM 204535 (3 albicaudatus, 25.4–30.5), USNM 204536 (3 albicaudatus, 19.8–24.2; 1 post larva, 15.5), USNM 204685 (1 albicaudatus, 51.6; 8 frontalis, 29.2–44.8), USNM 204684 (9 albicaudatus, 18.0–44.4; 37 frontalis, 16.8–43.7), USNM 204534 (18 albicaudatus, 16.6–36.1; 1 frontalis, 36.7), USNM 204650 (11 albicaudatus, 18.0–37.7; 3 frontalis, 18.7–48.4), USNM 204533 (14 albicaudatus, 19.5–37.5; 2 frontalis, 19.5–21.7), HUI HUJ–F–3540 (holotype of E. albicaudatus, 43.0), HUI E–60/96.16 (albicaudatus, 46.9), HUI HUJ–F–4375 (2 albicaudatus, 19.1–21.4), HUI HUJ–F–3544 (2 frontalis, 40.2–42.1), HUI E–64/34 (4 frontalis, 32.0–41.0), HUI E–64/3013 (frontalis, 40.0), UTAI NS–3582 (albicaudatus, 43.8); Gulf of Suez, Et Tor: USNM 204651 (9 frontalis, 29.5–44.7); Egypt, Strait of Jubal: USNM 200613 (1 albicaudatus, 50.5; 6 frontalis, including one cleared and stained, 23.9–58.6); Egypt, Al Ghardaqa: NFIS 5118 (frontalis, 43.9); Sudan, Sanganeb Reef: NFIS 8236 (3 frontalis, 40.6–47.4); Ethiopia, Massawa: ISZZ 1947 (5 damaged syntypes of Salarias frontalis), NFIS 1680 (holotype of Salarias nigrovittatus, 29.0), USNM 204517 (4 nigrovittatus, 24.2–36.0; 8 frontalis, 21.2–34.6); Ethiopia, Harat Island: USNM 204490 (6 albicaudatus, 29.2–46.5; 25 nigrovittatus, 20.4–48.3; 55 frontalis, 21.9–61.4); Ethiopia, Dahlak Islands: HUI E–62/424A (21 frontalis, 16.3–47.3), HUI E–62/1280 (2 nigrovittatus, 32.5–34.2), HUI E–62/428 (2 nigrovittatus, 18.9–40.2), HUI E62/604 (nigrovittatus, 39.2), HUI E–62/3678A (nigrovittatus, 39.5), HUI E–62/1280A (8 frontalis, 30.8–48.3), HUI E–62/417H (18 nigrovittatus, 16.7–38.5), NFIS 8757 (7 nigrovittatus, 23.8–44.0); Ethiopia, Zubair Island: HUI HUJ–F–4628 (4 frontalis 29.4–35.0); Gulf of Aden, Bay of Djibouti, French Somaliland: MNHN 04–318 (3 frontalis, 37.8–47.3).

Numerous other uncataloged specimens from the Gulf of Aqaba and Ethiopia in the USNM collections were examined in order to obtain data on frequencies of occurrence of the color pattern forms. In Ethiopian waters, the following localities for this material are as follows: Isola Delemme (35°54´E, 15°30.5´N), Sciumma Island (40° 00´00" E; 15°32´ 31"N); Melita Bay (39°49´E; 15°15´N); Difnein Island (39°20´E, 16°36´N). The frontalis and nigrovittatus forms were present in all these collections.

Ecsenius frontalis (Ehrenberg)

Salarias frontalis Ehrenberg in Cuvier and Valenciennes, 1836:328 [Massawa, Red Sea; 5 syntypes in poor condition, ZMB 1947].

Salarias nigrovittatus Rüppell, 1838:136 [Massawa, Red Sea; holotype, SMF 1680].

Ecsenius albicaudatus Lotan, 1969:372 [Marsa Murach, Gulf of Aqaba; holotype, HUJ F-3540].

Ecsenius (Ecsenius) frontalis.—Springer, 1971:14.

DESCRIPTION.—Dorsal fin X–XIII (XII in 95% of specimens), 18–21 (rarely 21), not incised between spinous and segmented-ray portions. Anal fin II,17–22 (19–21 in 96% of specimens). Pectoral fin 14–16 (15 in over 80% of specimens of any population). Segmented caudal-fin rays 13 or 14 (rarely 14). Vertebrae 10 or 11 (rarely 10) + 23–26 (rarely 23) = 34 to 37 (rarely 34). Dentary incisor teeth (includes anterior canines, which differ little, if at all, in appearance from incisors) 40–53 (rarely less than 44); posterior canines 0 or 1 (usually 1) on each side. Lateral line without vertical pairs of pores, extending posteriorly to point between verticals from 8th and 12th from anteriormost dorsal-fin spine (usually past vertical from 8th). Cirrus present on posterior rim of anterior nostril; none on anterior rim.

Color Pattern: There are three basic color patterns found in E. frontalis: (1) more-or-less uniformly brown, except body paling slightly and gradually in area slightly anterior to caudal peduncle posteriorly (frontalis form); (2) more-or-less uniformely dark brown or black, except most intensely dark slightly anterior to caudal-fin base and abruptly pigmentless from this darkest area posteriorly (albicaudatus, or bicolor, form); (3) generally brownish with darker stripe dorsally on body extending from anterior portion of body onto anterior portion of caudal fin; narrow paler areas margining dark stripe dorsally and/or ventrally (nigrovittatus form). In life the frontalis form is generally brown anteriorly, changing gradually posteriorly into yellow orange, with a bright yellow-orange caudal fin. One color slide of a frontalis form showed the fish as generally faint dusky-olive with the caudal peduncle, caudal fin, and a narrow distal edging of the dorsal fin faintly yellow orange. The albicaudatus form is generally black or brown with the narrow, pale area on the caudal peduncle white and the caudal fin immaculate or tinged with pink. The nigrovittatus form is generally gray brown with the dark body stripe almost black and the caudal fin tinged with orange; the head is occasionally yellow orange anterior to the orbits, changing to orange brown posterolaterally. All three forms have a horizontally parallel pair of slender, yellow or white stripes, which sandwich the pupil and extend from the anterior to the posterior orbital margin. A 15 mm postlarva had a preserved pattern of irregular vertical bands composed of dark spots. Small, bright-yellow specimens identified by Springer (1971) as E. frontalis were more probably the young of Atrosalarias fuscus, which superficially resembles E. frontalis, occurs with it in the same habitat, and has bright yellow juveniles.


SEXUAL DIMORPHISM.—Springer (1971) erroneously reported that Ethiopian frontalis-form males have a statistically significant higher average number of segmented dorsal-fin rays than females; however, these males do have a significantly higher average number of caudal vertebrae than females (Springer, 1971, table 11; two-tailed t = 2.38; 0.02 > p > 0.01; df = 86). No other meristic character exhibits sexual dimorphism when tested by color pattern and geographic location, and it seems possible that the significant difference in caudal vertebrae is, nevertheless, the result of chance. Tests for differences in meristics among color-pattern forms from the same locality are also not significant. I have, therefore lumped the sexes and color patterns in tabulating the data for Table 10.

GEOGRAPHIC VARIATION.—Specimens from the northern end of the distribution have significantly higher average numbers of dorsal-, anal-, and pectoral-fin rays, caudal vertebrae, and dentary incisor teeth (p = < 0.001) than do specimens from the southern Red Sea. Specimens from the middle part of the Red Sea have averages for these counts that tend to be intermediate between those of the other two areas, and averages of specimens from the Gulf of Aden tend to be slightly higher than those for the middle Red Sea (Table 10).

DISTRIBUTION.—Known only from Red Sea (including Gulfs of Aqaba and Suez) and the westernmost portion (Bay of Tadjourah) of the Gulf of Aden.

MATERIAL (* = new material).—Gulf of Aqaba: USNM 204534 (19 specimens: 17–37 mm SL), 204535 (3:25–30), 204536 (4:16–24), 204650 (14:18–48), 204685 (9:29–52), 204684 (46:17–44), HUJ F-3540 (1:43, holotype of Ecsenius albicaudatus), E-60/90.16 (1:47), F-4375 (2:19, 21), F-3544 (2:40, 42), E-64/34 (4:32–41), E-64/3013 (1:40), TAU NS-3582 (1:44). Gulf of Suez, Et Tor: USNM 204651 (9:30–45). Egypt: Strait of Jubal, USNM 200613 (7:24–50, including one cleared and stained); A1 Ghardaqa, SMF 5118 (1:44). Saudi Arabia: Jeddah, USNM 217727* (10:42–73); Yanbu, BPBM 30380* (1:41). Sudan: Sanganeb Reef, SMF 8236 (3:41–47). Ethiopia: Massawa, ZMB 1947 (5: damaged syntypes of Salarias frontalis), SMF 1680 (1:29, holotype of Salarias nigrovittatus), USNM 204517 (12:21–36); Harat Island, USNM 204490 (86:20–61); Dahlak Islands, HUJ E-62/424A (21:16–47), E-62/1280 (2:32, 34), E-62/428 (2:19, 40), E-62/604 (1:39), E-62/3678A 1:40), E 62/1280A (8:31–43), E-62/417H (18:17–38), SMF 8757 (7:24–44); Zubair Island, HUJ F4628 (4:29–35). Gulf of Aden: Bay of Djibouti, MNHN 04-318 (3:38–47), USNM 223713* (10:20–44). Additional USNM material, some uncataloged, from Delemme, Sciumma, and Difnein islands, and Melita Bay, Ethiopia, were used by Springer (1971) to obtain data on frequencies of occurrence of the color pattern forms.

BICOLOR GROUP

The Bicolor Group comprises E. bicolor and E. namiyei. These two species are distinguished from all other species of Ecsenius in having cirri on both the anterior and posterior rims of the anterior nostril (versus on the posterior rim only) and in commonly having more than one (up to 10) vertical pairs of pores in the lateral line (many specimens of E. namiyei lack vertical pairs of pores, which I propose is a secondary loss). I consider these two characters to be synapomorphies. Furthermore, E. bicolor and E. namiyei exhibit sexual dimorphism in average numbers of caudal vertebrae and segmented dorsal-and anal-fin rays. Such sexual dimorphism is known otherwise in Ecsenius only for two other species: E. pulcher (Pulcher Group), in which the dimorphism affects only the number of segmented dorsal-fin rays, and the Ethiopian population of the frontalis form of E. frontalis (Frontalis Group), in which the dimorphism affects only the number of caudal vertebrae (see section on sexual dimorphism under Ecsenius frontalis species account, where this dimorphism is considered as possibly due to chance).

Ecsenius bicolor and E. namiyei specimens almost always have 14 segmented caudal-fin rays, a number that occurs modally in Ecsenius otherwise, only in the four species of the Stigmatura Group. No other blenniids have as high a modal number of segmented caudal-fin rays as these species, and it is possible that 14 segmented caudal-fin rays is a synapomorphy of the Bicolor and Stigmatura groups. For further discussion of relationships, see discussion in accounts of the Pulcher and Stigmatura groups.

Because the distribution of E. bicolor, which is one of the most broadly distributed species of Ecsenius, essentially envelops that of E. namiyei, it is not possible to hypothesize the vicariant scenario that split the ancestral population that gave rise to the two species.

Ecsenius frontalis, known commonly as the smooth-fin blenny in Micronesia, is a species of combtooth blenny in the genus Ecsenius. It is found in coral reefs in the western Indian ocean, in several gulfs in the Red Sea. It can reach a maximum length of 8 centimetres. Blennies in this species primarily feed off of plants, including benthic algae and weeds, and are commercial aquarium fish.