Lined Rockskipper

Diagnosis: Dorsal fin XII-XIV, 19-22, notched between spinous and segmented-ray portions; anal fin II, 18-22; pectoral rays 13-15 (usually 14); pelvic fin I, 3; caudal fin, procurrent rays 10-14, segmented rays 11-13. Vertebrae 11-12 + 26-29. Orbital cirrus simple filamentous; nasal cirri short and palmate with 2-6 branches; nape without cirri. Lateral line, continuous anterodorsally with simple pores below dorsal spines from 6-7th to 9-10th, disconnected bi-pored series posteroventrally ending below 9th dorsal spine to 1st segmented ray. Mandibular pores 5-7 Lips margin entire. Occipital crest low (up to 2.6 mm) in males, most females only have faint indication of ridge-like crest precursor except greatest specimens which may have a developed ridge up to 0.6 mm (Ref. 559, 9962). Body depth at anal-fin origin 6.8-7.3 in SL. Male body with vertical bars olive brown separated by paler interspaces, and also with dark thin horizontal stripes; also with spots near the tail; preopercular spot dark; dorsal fin spots brown, forming bands. Female with vertical dark H-shaped bars; dorsal fin spotted, caudal fin with 4-5 dark bars (Ref. 48636, 90102). Exhibits geographical color pattern variation (Ref. 9962).

Distinct pairing (Ref. 205).

Dorsal spines (total): 12 - 14; Dorsal soft rays (total): 19 - 22; Analspines: 2; Analsoft rays: 18 - 22; Vertebrae: 37 - 41

Oceanic (Ref. 6110). Inhabits shallow, exposed shores and near-shore tidepools, 0-3 m deep (Ref. 9962, 90102). Occurs in intertidal zones in large rock pools or coastal bays. Sometimes numerous individuals can be seen clinging to rocks out of the water when the level drops on the low of the swell. When disturbed in rock pools during low tide, they may jump out of the water to get to other rock pools or safer deeper water nearby. Feeds on algae scraped from rubble or rock surfaces (Ref. 48636).

Adults occur in intertidal zones in large rock pools or coastal bays (Ref. 48636). Found near-shore (Ref. 9962); common in tide pools (Ref. 559). They feed on algae scraped from rubble or rock surfaces. Sometimes numerous individuals can be seen clinging to rocks out of the water when the level drops on the low of the swell. When disturbed in rock pools during low tide, they may jump out of the water to get to other rock pools or safer deeper water nearby (Ref. 48636). 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).

fisheries: of no interest

Blenniella bilitonensis (Bleeker)

Salarias bilitonensis Bleeker, 1858a:231 [Biliton, occident.; lectotype, RMNH 4792, largest specimen, designated below, same specimens as neotype of Salarias hendriksii Bleeker].

Salarias hendriksii Bleeker, 1858a:233 [Biliton occidentalis; neotype, RMNH 4792, largest specimen, designated below, same specimen as lectotype of Salarias bilitonensis Bleeker].

Salarias deani Jordan and Seale, 1905:799 [Negros, Philippine Islands; holotype, USNM 51950].

Alticus novemmaculosus Snyder, 1908:109 [Naha, Okinawa; holotype, USNM 62244].

Salarias periophthalmus visayanus Herre, 1934:97 [Philippine Islands, Oriental Negros, Dumaguete; neotype, CAS-SU 28435, designated below].

Salarias brevoorti Fowler, 1946:177 [Aguni Shima, Riu Kiu Islands; holotype ANSP 72048].

DESCRIPTION.—Dorsal fin (Table 10). XII to XIV, 19 to 22 = 32 to 35 (XIII in 94% of 226 specimens examined for character; 22 and 35 in only one male, of 35, from Okinawa); mean numbers of total elements tending to be higher for males from any locality than for females from the same locality (higher at 7 of 8 localities where means for both sexes are available, statistically significantly higher at 4 of the 7 localities); membrane between spinous and segmented-ray portions notched deeper than half length of first segmented ray (usually more than three-fourths length); membrane from posteriormost ray attaching to point ranging from well in advance of caudal-fin base to out on dorsal edge of caudal fin up to 15.4% length of fin in males (rarely more than 11%), up to 7.7% in females (rarely attached on fin in females).

Anal fin (Table 10). II,18 to 22 (18 only in 1 female); mean numbers of segmented rays higher for males from any locality than for females from same locality (higher at all 8 localities where means for both sexes are available, statistically significantly higher at 2 localities); posteriormost element split to base in only 4.5% of 223 specimens examined for character; posterior element of split ray usually visible externally; fin not bound by membrane to caudal peduncle in 98% of 293 specimens examined for character. Skin covering anal-fin spines and distal half of segmented rays of large or mature males rarely thickened or inflated, never rugose or crinkled along edges.

Pectoral-fin rays 13 to 15 (14 bilaterally in 91% of 174 specimens examined for character; 15 only unilaterally, in only 4 specimens).

Pelvic-fin rays I,3.

Caudal fin. Dorsal procurrent rays 4,6 or 7 (6 or 7 in 99% of specimens examined for character); ventral procurrent rays 6 or 7 (7 in 78% of specimens), total procurrent rays 10, or 12 to 15; (modally 14; 10 or 15 total procurrent rays in only 1 specimen each); segmented rays 11 to 13 (1 with 11, 2 with 12 of 185 specimens examined for character).

Vertebrae (Table 10). 11 or 12+26 to 29 = 37 to 40 (12 in only 7 of 198 specimens examined for character, 40 in only 1 specimen, female), mean numbers of total (and caudal) vertebrae tending to be higher for males from any locality than for females from same locality (higher at 6 of 8 localities where means for both sexes are available, statistically significantly higher at 1 of the 6 localities); posteriormost pleural rib on 12th or 13th from anteriormost centrum (on 13th in only 1 of 195 specimens examined for character); posteriormost epineural rib on 20th to 30th from anteriormost centrum (on 23rd-30th in 96% of 142 specimens).

Cirri. Nape cirrus absent in 307 of 314 specimens examined for character (present unilaterally in 2 specimens from Ambon). Orbital cirrus a simple filament in 197 of 203 specimens (with 2 or 3 short branches distally in 3 specimens); absent on 1 side in 1 specimen, almost always shorter than orbital diameter in females, ranging from shorter than to slightly longer than orbital diameter in males. Nasal cirri short, palmate, with 2 to 6 branches in specimens over 25 mm SL (usually 3 or 4 branches in specimens over 30 mm).

Lateral line. Continuous canal anterodorsally with simple pores (no vertical pairs of pores), extending posteriorly to point between vertical from between bases of 6th and 7th dorsal-fin spines and vertical between bases of 9th and 10th spines (posterior to vertical from 7th spine in 98% of 163 specimens examined for character), then continuing posteroventrally and posteriorly as series of 1 to 7 short, disconnected, horizontally bi-pored canals (tubes) in skin (2 to 5 tubes in 93% of specimens; 7 in only 1 specimen); posteriormost tube in area between verticals from 9th spine and 1st segmented dorsal-fin ray (posterior to 10th spine in 89% of specimens).

Mandibular pores 5 to 7 (6 bilaterally in 92%, and unilaterally in 5%, of 166 specimens examined for character).

Table 10.—Frequency distributions for certain characters of male and female specimens of Blenniella bilitonensis from various localties. Underlined means indicate significant differences between means of sexes from same locality (p ≤.05).

Five to 7 sensory pore positions between 1 and 5 o'clock on postorbital margin (6 in 92% of 165 specimens examined for character); 0 to 2 positions occupied by pair of pores (2 positions in 90% of specimens).

Posterior canines present in both sexes (visible in specimens as small as 28 mm SL, but usually not obvious in specimens less than 30 mm SL).

Margins of both lips entire.

Males >32 mm SL either with well-developed crest on head (highest crest 19.7% HL, but crest height usually <15% HL) or noticeable ridge-like crest precursor; males 27 to 31 mm SL with or without indications of ridge development, but shorter males exhibit no indication; highest male crest, 2.6 mm, crests ≥2.0 mm present only in males >60 mm SL. Well-developed crests absent in females, but females ≥40 mm SL may exhibit faint indications of ridge-like crest precursor, and few females >50 mm have well-developed ridge up to 0.6 mm high (up to 5% head length).

Color pattern (in preservative). Males (Figures 14a, 15a–c). Head: variably dusky, diffuse band between ventral margin of orbit and upper lip, occasionally discontinuous across ventral surface of head; ventral usually lacking distinct markings; similar band at corner of mouth, also occasionally continuing across ventral surface of head; dark, vertical pair of small slashes just posterior to orbit, dorsal slash extending dorsally above mid-level of orbit, ventral slash extending below mid-level, slashes sometimes connected, ventral slash sometimes forming tiny ocellus; small, faintly dusky mark sometimes present near pore at 2 o'clock on postorbital margin; large, dark spot dorsally on opercle (most consistent and prominent of all head markings), much smaller dark spot occasionally just dorsal to opercle; diffuse, dusky spot occasionally on preopercular area ventrally. Body: dusky band on side in area below anteriormost 4 dorsal-fin spines, another below posterior half of spinous portion, 4 or 5 bands in area below segemented-ray portion of fin (60% of specimens have 4 bands bilaterally, 13% have 5 bands bilaterally, 27% have 4 bands on one side, 5 on other), and 1 band on caudal peduncle (peduncular band faint or absent in many specimens); bands may fork at dorsal body contour (appear as series of small saddles) or be restricted to sides mid-laterally; vertical pair of small, dark-margined ocelli variably present in mid-portions of anteriormost 1 to 3 bands below segmented-ray portion of fin, dorsal or ventral ocellus of pair variably absent in as many as 4 bands (maximally 7 ocelli); variably, small, dark spot included in dorsal extension of any band; up to 9 diffuse to relatively well-marked pinstripes variably present on some portion of side below and between mid-spinous portion of dorsal fin and posterior third of segmented-ray portion, stripes becoming more diffuse posteriorly, changing into pattern of small, diffuse, pale spots that extend onto caudal fin. Dorsal fin spinous portion variably dusky or with numerous, diffuse, dusky spots in distal half; segmented-ray portion with up to 6 well-spaced, dark pinstripes in anterobasal half (pair of stripes radiating dorsoposteriorly from each of 3 anteriormost body bands below segmented-ray portion), remainder of fin with numerous dusky dashes more or less aligned in rows (number increasing with size). Anal fin uniformly dusky, gradually darkening distally. Caudal fin dusky with rows of diffuse, pale spots; dorsoposterior margin noticeably paler. Pectoral fin with up to 5 fine, dark spots on distal half of each ray in specimens over 25 mm SL (no more than 25, usually fewer than 15, spots on a fin); about 5% of specimens without spots (except 5 of 9 males from Northern Territory lacked pectoral-fin spots). Pelvic fins immaculate.

Females (Figures 14b, 15d). Head varying from lacking distinct marks to having short, dusky stripe at mid-tip of upper lip, dusky stripe extending ventrally from mid-orbit across upper lip, faintly dusky pair of small slashes posterior to orbit, dusky spot ventrally on preopercular area. Body with 1 to 3 dusky bands on midside below spinous dorsal fin, anterior band faintest, bands may fork at dorsal body contour, posteriormost band usually forks ventrally; 5 dark bands on midside below segmented-ray portion of dorsal fin, bands usually forking dorsally and ventrally, forked portions occasionally disjunct from central, darkest, portion of each band, dusky blotch in pale area between each pair of bands. Dorsal fin with diagonal rows of dark spots. Anal fin with sub-basal row of dusky spots and diffusely dusky interradial membranes distally. Caudal fin with up to 7 dark spots on each ray, spots forming irregular bands. Pectoral fin rays each with up to 5 tiny, dark spots (maximum spots per fin, 27, usually fewer than 15, spots rarely absent). Pelvic fins immaculate.

Fresh coloration (based on color photographs taken by J.E. Randall at Okinawa and Tioman Island, Malaysia). Male, 59 mm SL. Head: crest pale dusky with 2 brownish bands, anterior band extending ventrally to dorsal orbital margin, posterior band extending ventrally posterior to orbit to level opposite ventral orbital margin; dark slash-like mark with slender, bright-white margin bordering previous band posteriorly opposite level of orbit; short, dusky band with slender, bright-white margin posteriorly extending ventrally from ventral orbital margin; 2 white spots on upper lip posteriorly; iris with alternating pink and pale dusky spokes; blackish spot with narrow, orange posterior margin on opercle dorsally. Body: bands olive brown dorsally separated by paler olive-brown interspaces; bands dusky ventrally with bright-white interspaces; pair of ocelli in third from posteriormost band, dorsal ocellus of pair oblong, dark gray with pale-blue margin surrounded by diffuse, dull-orange halo; ventral ocellus smaller, more elongate, consisting of slender, dark, dorsal and slightly wider, white, ventral portions; dark olive-brown pinstripes anteriorly, widening and becoming paler brown posteriorly; pinstripes separated posteriorly by bright-white areas, stripes broaden and coalesce to form area punctuated with small, white spots, which extend onto and cover most of caudal fin. Dorsal-fin spines with tips and adjacent margins of interradial membranes bright white; 3 rows of dark-brown spots distally in posterior half of spinous dorsal; anterior 8 segmented dorsal-fin rays with white tips, margin of interradial membranes of succeeding rays pinkish orange; distal third of segmented-ray portion of dorsal with bright-white pinstripes separating brownish, subquadrate blotches; 7 dark pinstripes radiating obliquely from dark body bands into dark-brown basal half of fin. Caudal fin mostly dusky with small, pale spots, except for moderately wide, pinkish, distal margin. Pelvic fin white. Pectoral fin unmarked except for fine, dark spots on rays. Schultz and Chapman (1960, pl. 117: fig. D), as I. coronatus, present a useful black and white illustration of male.

Female, 45 mm SL (much faded): Most obvious features: 2 brownish orange stripes on head similar to those arising from crest in male, also similar spokes in iris; moderately large, diffuse, brownish orange spots with diffuse, dusky halos in spinous dorsal fin, spots arranged in more or less curving pattern, distal tips of spines bright white; distal tips of segmented anal-fin rays and adjacent interradial membranes bright white; bright-white spots on segmented-ray portion of dorsal fin and caudal fin more prominent than dark spots separating them (other dark or dusky markings on body and fins similar to those of preserved specimens).

SIZE.—Largest male slightly longer than largest female (90.8 mm SL vs 87.1 mm SL), males usually largest specimens in large samples from any locality. Ophioblennius-stage specimens unknown for B. bilitonensis. Several small specimens, 15.3 to 23.4 mm SL, from widely scattered localities, with relatively well-developed color patterns; males as small as 20 mm distinguishable from females by having a large, dusky blotch on opercle.

GEOGRAPHIC VARIATION.—Means for meristic characters (Table 10) tend to be highest for specimens from northernmost distributional areas of species (Okinawa and vicinity), and lowest for Gulf of Thailand. Southernmost specimens, from Northern Territory, exhibit very little color pattern on body, and 4 of 7 available males lack pectoral-fin spots; 2 other males have only a few poorly developed spots, but all females have well-developed pectoral-fin spots.

The pattern of conspecific populations in the Gulf of Thailand and Northern Territory varying from other populations resembles the situation discussed by Williams (1988:36) for Cirripectes filamentous. Cirripectes filamentosus is the only species of Cirripectes that occurs in both the northern Gulf of Thailand and Northern Territory, and specimens from these 2 areas are noticeably divergent from all others. Both areas are characterized by high river runoff and it is possible that environmental factors, such as low salinity, influence the expression of certain characters.

ECOLOGY.—Blenniella bilitonensis is a shallow, near-shore inhabitant, taken often in tidepools.

COMPARISONS AND RELATIONSHIPS.—Blenniella bilitonensis appears to be closely related to the 2 sister-species pairs, B. cyanostigma and B. caudolineata, and B. interrupta and B. leopardus, either as the sister group to both pairs of sister species, or as the sister group of the second pair of sister species (see Phylogenetic Analysis section). Although differing in several respects, the males of these species are superficially quite similar, and it is necessary to use a complex of characters (often their modal expression) in order to distinguish them (Table 5). Females, in contrast, are easily separated. Those of the 2 sister-species pairs are distinguished by having dark (almost black) spots, dashes, or pinstripes on the body, whereas such markings are absent from the body of female B. bilitonensis. Both sexes of B. bilitonensis are modally distinguishable from those of the other 4 species in having small, dark spots on the pectoral fins.

DISTRIBUTION (Figure 62).—Between 100°–135° E longitude, from Riu Kiu Islands south to McClure and New Year islands, Northern Territory, Australia.

NOMENCLATURAL VARIATION.—Meristic variation (Tables 11 and 12). Means for total numbers of dorsal-fin elements, segmented anal-fin rays, and vertebrae are lowest at localities from the Red Sea to Gulf of Oman (color-pattern Type Ic) and generally highest at the Cargados Carajos and Mauritius (color-pattern Type Ib) and in southern Oceania (color-pattern Type II). Otherwise, means are generally high at western Indian Ocean localities (color-pattern Type Ib) and intermediate at localities in the eastern Indian-western Pacific oceans (color-pattern Type Ia) and central Pacific Ocean (color-pattern Type II).

Means for serial number of vertebra bearing the terminal pleural rib (Tables 13 and 14) overlap considerably among the color-pattern types. The means range from 12.0 to 12.8 for color-pattern Types Ia to c, and 12.5 to 13.0 for Type II. There is a noticeable difference between the means of Types I and II, however, if only means based on 10 or more specimens are considered (Table 14). The 15 such means in the area comprising Types Ia to Ic vary from 12.0 to 12.6, whereas the 21 such means in the area comprising Type II vary from 12.7 to 13.0, with only the mean for Fiji (12.7) less than 12.8. To summarize, in specimens from areas with color-pattern Types Ia to c, the serial position of the terminal pleural rib is usually (27 of 35 means) on the 12th (posteriormost precaudal) vertebra, and in specimens from the area with color-pattern Type II, the terminal rib is almost always (42 of 44 means) on the 13th (first caudal) vertebra.

Table 13.—Frequency distributions for serial number of vertebra bearing terminal pleural rib in specimens of Istiblennius periophthalmus (Types Ia–c) and I. paula (Type II) from various localities.

Color-pattern variation (preserved). There are two main types (I, II) of color pattern exhibited by the various populations of the Periophthalmus complex. These color-pattern types are, for the most part, correlated with the position of the terminal pleural rib (thus, also correlated with geography). Although it is usually possible to assign a series of specimens comprising adults of both sexes from a single locality to 1 or the other of the 2 main color-pattern types, some specimens can be confusing. We also recognize 3 main, geographically differentiated color-pattern subtypes (Types a,b,c) within the Type I-color pattern, but there is overlap among the subtypes. We first give a brief, general summary of the color-pattern types, and then discuss the patterns in detail.

Table 14.—Frequency distributions for means reported in Table 13; upper half of table includes all means; lower half includes only means based on 10 or more specimens.

Summary description. Type-I color pattern (B. periophthalmus): body of adult females sprinkled with fine, dark spots; dark opercle spot, if present, located entirely, or almost entirely, dorsal to widest portion of opercle. Type-Ia pattern (Figures 20a,b): dark opercle spot often present, rarely extending ventrally onto widest portion of opercle; no dark spots on pectoral fin; body of males without sprinkling of fine, dark spots. Type-Ib pattern (Figures 19, 21): dark opercle spot usually lacking, usually faint when present, similar to that of Type Ia when most fully developed; few small pale spots on opercle when no dark spot present; no dark spots on pectoral fin; some portion of body of males often with sprinkling of fine, dark spots. Type-Ic pattern (Figures 20c,d, 22): dark opercle spot usually present, occasionally extending ventrally onto widest portion of opercle; dark spots usually present on pectoral fin; body of male usually sprinkled with fine, dark spots. Type-II color-pattern (B. paula; Figures 16 to 18): no sprinkling of fine, dark spots on body of either sex; dark opercle spot, if present, at least partially, if not completely, located at level of widest portion of opercle; no dark spots on pectoral fin.

Detailed description. Several color-pattern markings may occur only in specimens of one or the other of the color-pattern types, but the most consistent characteristic for separating Types I and II involves only females. In most adult Type-I females, there is a sprinkling of tiny dark spots that covers some to all of the body (but not the head, except for some specimens from the east African coast, which are like some Type-II specimens from Kwajelein, Marshall Islands (compare Figure 18d with head of specimen in Figure 21d). The spots appear to lie in a superficial layer of the skin, and overlie other dark markings on the body (e.g., the body bands). At some localities (e.g., Agalega, Type Ib), however, many females have these spots so reduced in number or so faintly expressed as to be almost unnoticeable, if not actually absent Figure 19a). Such Type-Ib females can be confused easily with Type-II females, which never exhibit fine spotting on the body. In small (size varies considerably) Type-II females, the developing body ocelli or developing posterior dark body bands are spot-like, and may superficially resemble the spots of Type-I females. The body spots of Type-Ic specimens are often slightly larger and more prominent than those of Types Ia and b.

At one locality, Gulf of Bone, southern Sulawesi, essentially within the Type-Ia area, females (only 3 available) lack body spots (Figure 18a,b) and, except for a unique pattern of large, dusky spots on the ventral surface of the head, are remarkably similar in color pattern to Type-II females (males from Gulf of Bone unavailable). With reservation, we have identified the Gulf of Bone specimens (Figure 61) as belonging to Type II.

Many Types Ib and c, but few Type-Ia, males also exhibit female-type body spotting, particularly males from the Red Sea (Type Ic), where the spots are often prominent and may cover almost the entire body, Figure 22d). In contrast to the Red Sea males, males from the Gulf of Oman and Strait of Hormuz (also Type Ic, Figure 20c) have few to no dark body spots. In Comores and Chagos islands and southern Madagascar males (Type Ib), the spots are not prominent and may be restricted to the body ventrally (Figure 21b). In the Type-Ia area, sparsely spotted males are known only from the main islands of the Philippines. At most of these localities there are males with few or no fine, dark body spots, and these males might be confused with Type-II males (see also following).

Type-Ia and Type-Ic specimens usually have a dusky-to-dark ovoid spot (often partially surrounded by a diffuse, unpigmented margin) that covers some to almost all of the dorsalmost area of the opercle (dorsal to the widest portion of the opercle, Figures 20, 22). In Type-Ic (but not Ia) specimens, the spot may extend ventrally onto the widest portion of the opercle and touch or surround a sensory pore of the preopercle canal (the ventral portion of the spot appears to be a homologue of one of the Type-II opercle spots). Type-Ib specimens at most localities have no recognizable dark spot on the opercle, but in exceptional specimens, a spot similar to that of Types Ia and Ic does occur (but does not extend onto the widest portion of the opercle). For instance, among more than 25 specimens of each sex available from Aldabra (see material examined), 4 males, but no females, have a dark opercle spot: 2 have a large, dark spot and 1 a moderately dark spot, and the fourth has only a faintly dusky spot.

A somewhat intermediate state for opercle spot occurs on specimens from the Chagos Islands, which are geographically intermediate between the Maldive Islands, where all specimens have a well-developed opercle spot, and the western Indian Ocean, where few specimens have a well-developed opercle spot. Among 39 adult specimens in a single collection from the Chagos Islands (ROM 43907), 4 males and 2 females have moderately well-developed opercle spots, 10 males and 8 females have faint, but noticeable spots, and 3 males and 12 females show no evidence of opercle spots. Among 18 small, sex-indeterminate specimens from the same collection, 9 have small or faint opercle spots and 9 show no evidence of spots. The Chagos Islands specimens are assigned to Type Ib, rather than Ia, because none exhibit as well-developed an opercle spot as occurs in Type Ia, and most of the adult males have some portion of the body sprinkled with fine, dark spots, which are present only in some Type-Ia males from the Philippines.


Based on the proportion of specimens with an opercle spot, the Type-Ia distribution can be divided into two sub-areas, which correspond to the Pacific Ocean and Indian Ocean portions of the distribution. With only the rarest of exceptions (e.g., none of 66 specimens from the Maldive Islands, in only 1 of 49 specimens from Cocos-Keeling Islands) is a well-developed opercle spot lacking on Type-Ia specimens from the Indian Ocean. None to about half the Type-Ia specimens from any Pacific Ocean locality lack opercle spots.

Type-II specimens may also have a dark or dusky opercle spot, but it is usually much smaller than the Type-I spot and all or part of the spot is located more ventrally—at the level of the widest portion of the opercle. The Type-II spot almost always touches or partially surrounds a pore of the preopercular sensory canal, and the spot, when restricted to the widest portion of the opercle, scarcely impinges on the opercle (this portion of the opercle spot appears to be a homologue of a portion of the Type-Ic opercle spot). The Type-II spot often appears as a small, black dot (Figures 16a, 17c); however, a pale spot may be in the position where a dark spot might be expected. A second small, dusky opercle spot also may be present just posterodorsal to the widest portion of the opercle, and the two spots may fuse and appear as a single, more or less vertically elongate spot. When vertically elongate, the marking may be more or less uniformly dark, or pale with a narrow, dark margin (Figure 17d). We believe that the pale variations of the dark opercle spots are artifacts of preservation and the result of light diffraction: in life these spots are whitish or bluish and may become dark only after preservation (the opercle spot of Type-I specimens also appears as a pale area in color photographs of living or freshly dead specimens).

The opercle spot of Type-II specimens is predominantly restricted in occurrence to males. Poorly developed opercle spots occasionally occur in Types Ia and Ic specimens, and these spots can closely resemble those of Type-II specimens, but they are positioned more dorsally. Some male specimens from the northeastern portion of the Type-Ia distribution area lack all indications of opercle spots and these males are virtually impossible to distinguish externally from Type-II males that lack opercle spots.

Klausewitz (1963, as Istiblennius periophthalmus) recognized two subspecies of Blenniella periophthalmus, based on the presence or absence of the opercle spot. He believed that the spot was present in his Indian Ocean subspecies (I. p. biseriatus) and absent in his Pacific Ocean subspecies (I. p. periophthalmus). He was only partially correct, because his conclusions were based on incomplete data and an erroneous interpretation of the identities of the holotypes of his two nominal subspecies (biseriatus is a synonym of periophthalmus). Additionally, his I. p. periophthalmus comprises both of the species that we recognize in the Periophthalmus complex. In Type-I males, the segmented-ray portion of the dorsal fin frequently bears slender, dark, posteriorly inclined pinstripes that course through, at least, the dusky basal half of the fin (Figures 20a, 21a,b, 22c; see also Smith, 1959, pl. 14: fig. B, Type-Ib male from Mozambique, or Springer, 1986, fig. 235.22, same illustration as Smith). In Type-II males, the dusky basal half of the segmented-ray portion of the dorsal fin rarely incorporates distinctive markings, although faint indications of inclined pinstripes are sometimes noticeable just dorsal to the basal dusky area similar to the pattern shown in the drawing of the male from Agalega (Type Ib, Figure 19c). Irregular, inclined dorsal extensions of the body bands may enter the segmented-ray portion of the dorsal fin of males from any locality.

Type-I females often have noticeable dusky spots and irregular markings in the segmented-ray portion of the dorsal fin, whereas, Type-II females rarely have such markings, the fin usually appearing to be almost immaculate.

Type-Ic specimens (both sexes) usually have the basal half of the pectoral fin covered with fine, dark spots (Figures 20c,d, 22). Similar, but much less numerous and less conspicuous spots occur in some Type-Ib females (Figure 21d) from the east African coast, and some specimens of both sexes of Type II from Kwajelein, Marshall Islands (Figure 18d).

Winterbottom et al. (1989, fig. 387) provide a halftone photograph of a female Type Ib from the Chagos Islands. The head and basal third of the pectoral fin of the specimen appears to bear numerous, fine, dark spots. The original photograph, however, was in color, and the spots were red; they have completely faded from the preserved specimen. Many of the dark spots on the head and body of preserved Type-I specimens were surrounded by red chromatophores in life. The red spots of live or fresh specimens of both Types I and II (especially, females of Type II) fade in preservation and leave no evidence unless they occurred in a dusky area, in which case they are replaced by pale spots (Figures 17a, 19a). Often, each red spot surrounds a fine, black spot on the body of females. When the red pigment fades the dark spot remains.

COMPARISONS AND RELATIONSHIPS.—Blenniella periophthalmus and B. paula form a sister group which is the sister group of the sister-species pair B. gibbifrons and B. chrysospilos (see section on Phylogenetic Analysis). The 4 species share a general similarity in morphology and, uniquely in Blenniella (and Istiblennius), predominantly 12 precaudal vertebrae. Less exclusively, they all lack a well-developed head crest in males and share a habitat preference for clear, subtidal, fully marine waters in the vicinity of rocky or coral reefs, although B. paula and B. periophthalmus are often collected in tidepools, whereas the other two species are not. Blenniella periophthalmus and B. paula can be readily distinguished from B. gibbifrons, and B. chrysospilos, with which they are extensively sympatric, in lacking paired dorsal and ventral branches extending from the lateral line.

DISTRIBUTION.—The distribution of the Periophthalmus species complex was discussed in the section on geographic variation, and is given in Figure 61.

Blenniella paula (Bryan and Herre), new combination

Salarias paulus Bryan and Herre, 1903:136 [Marcus Island; holotype BPBM 2455]. [Type II.]

Salarias tubuensis Seale, 1906:87 [Tubuai, Austral Ids.; holotype BPBM 784]. [Type II.]

NOMENCLATURAL

分布於西太平洋區，由日本、台灣至澳洲。台灣分布於南部、北部、東北部、東部、澎湖、小琉球、綠島及蘭嶼等海域。

小型魚類，僅具學術研究價值。

體延長，稍側扁，似圓柱狀；頭鈍短。雄魚頭頂具薄而圓的冠膜，雌魚只有一小肉質狀隆起。鼻鬚掌狀分支；眼上鬚單一不分支，等於或短於眼徑；無頸鬚。上下唇平滑。D. XIII-XIV, 18-21；A. II, 19-21； P. 14; V. I, 3。背鰭具缺刻，背鰭與尾柄相連，臀鰭不與尾柄相連。雄魚眼後緣有一中央斷裂的半月形紋， 鰓蓋上緣有一大黑斑，黑斑下方有一小黑點，體側中央有黑橫帶，橫帶上具短縱線，形成8條平行縱線；背鰭灰黑色而具黑、白線；臀鰭具寬暗色緣；尾柄與尾鰭有許多白點；胸鰭上半部有黑點。雌魚頭部的圖案和身體的色帶較不明顯且無橫紋；臀鰭灰黑色，鰭緣較深；胸鰭上半部有黑點；尾鰭有幾列黑點；背鰭具2-3列黑斑。

主要棲息於潮間帶礁石潮池區，受驚嚇時可見其用一前一後的方式跳躍於潮池與空氣間。以藻類為食。

Blenniella bilitonensis, also known as Biliton blenniella or the lined rockskipper, is a species of combtooth blenny found in the western Pacific ocean.