Oyster Blenny

Oviparous, distinct pairing (Ref. 205).

Common in shallow estuarine waters. Adults occur in pairs in dead oyster shells. 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).

Omobranchus anolius (Valenciennes)

Blennechis anolius Valenciennes in Cuvier and Valenciennes, 1836:288 [Port Jackson].

Petroscirtes altivelis Steindachner, 1863:1191 [Bombay; locality probably erroneous].

Blennius unicornis Castelnau, 1879:384 [enters oysters about Sydney].

Petroscirtes guttatus Macleay, 1881:9 [Port Jackson].

Petroscirtes cristiceps Macleay, 1881:9 [Port Jackson].

Petroscirtes wilsoni Macleay, 1884:171 [Port Jackson].

Salarius galeatus DeVis, 1884a: 147 [Moreton Bay]; 1886; 59 [St. Helena, Moreton Bay; twice described as new; impossible to determine if the same or different specimens formed basis of descriptions].

DESCRIPTION (see also Table 5).—Dorsal fin XI–XIII (XII in 79.2% of specimens), 17–19 = 29–31; anal fin II, 19–22 (20–21 in 94.3% of specimens); both anal-fin spines of males discernible externally; segmented caudal-fin rays 12–13 (13 in 94.3% of specimens); dorsal + ventral procurrent caudal-fin rays 11–14; vertebrae 10–11 (11 in only 1 of 42 specimens) + 26–28 (28 in only 1 of 41 specimens) = 36–38 (38 in only 2 of 41 specimens); epipleural ribs 11–13; prenasal pores present; interorbital pores 2–4 (3 in 87.5% of specimens); circumorbital pores 7–10 (8 in 87.5% of specimens); lateral-line tubes absent; gill opening varying from restricted to area dorsal to level of dorsalmost pectoral-fin ray (87.5% of specimens) to extending ventrally to opposite dorsalmost ray; lower-lip flap present; circumorbital bones 5; lower jaw teeth 20–27; upper jaw teeth 19–25 (Figure 36); males with fleshy bladelike crest on top of head (at least in specimens 34–60 mm SL), females with crest poorly developed or absent (at least in specimens 28–46 mm SL).

COLOR PATTERN.—Males: Head: Three dusky to dark dusky bands present. First band moderately wide, extending from anteroventral margin of orbit across mouth, just anterior to angle of jaws, to chin where it joins corresponding band of opposite side. Second band almost twice as broad as first, extending from ventral margin of orbit to ventral midline of head where it joins corresponding band of opposite side; band, interrupted by eye, continues from dorsoposterior margin of orbit across anterior nape to base of fleshy crest. Narrow, pale or pearly lines border anterior and posterior margins of both portions of second band. Third head band encircles head posterior to eye; band often obscured by dark background color of head. Narrow, pale or pearly line borders posterior margin of third band below level of ventral margin of orbit. Intensely dark, short line, blotch, or spot present on third band just above lateral midline of head. Narrow, pale or pearly line extends posteroventrally from preopercular head pores near dorsal end of operculum to anterior edge of fleshy pectoral-fin base. Another narrow, pale or pearly line occasionally extending from middle of nape and base of crest, along dorsoposterior edge of operculum and posteroventral edge of gill opening to upper end of fleshy pectoral-fin base; line broadens as it passes along edge of gill opening. Snout, interorbital, nape, and prepelvic areas dark dusky except where crossed by pale lines.

Trunk: Body crossed with about 17 to 19 evenly spaced, narrow, dusky, chevronlike bands flexed posteriorly; anterior and posterior bands indistinct; bands originating on dorsal body contour, becoming faint, then absent on ventral fifth of body; posterior 3 or 4 bands broken, forming 3 dusky stripes: 1 on lateral midline, 1 each midway between lateral midline and dorsal and ventral body contours; dorsal ends of bands occasionally expanded and intensified. Horizontal series of small, intensely dark spots present on lateral midline of body, each spot lying on body band at angle of flexion (not all bands with spot). Second horizontal series of small, dark spots present midway between lateral midline of body and dorsal body contour, each spot located on body band. Third horizontal series of small, dark spots usually present midway between lateral midline and ventral body contour, at least posteriorly; each spot located on body band. Area covered by appressed pectoral fin with posteroventrally directed, diagonal row of intensely dark marks or spots, more or less connected by dark dusky line on body midlaterally; second parallel line of dark marks occasionally present just posteriorly on dorsal half of body.

Pectoral Fin: Pale to transparent with fine dark specks of pigment scattered over fin; pigment heavy proximally and distally. Fleshy pectoral-fin base with large, intensely dark spot, occasionally broken into several intensely dark marks anteroventrally. Vertical, narrow, pale line present between large dark spot and base of pectoral fin; line confluent dorsally with narrow, pale line on head.

Pelvic Fin: Distal half pale, proximal half dark dusky, line of demarcation between contrastingly pigmented areas angled so inner rays darkly pigmented more distally than outer rays.

Dorsal Fin: Pale dusky with dark markings. Membranes between first 5 dorsal-fin spines with 2 or 3 evenly spaced, narrow, horizontal, dark lines; lines becoming dorsoposteriorly angled on more posterior spines; parallel series of similar dorsoposteriorly oriented, narrow, dark lines along rest of fin; lines becoming faint to absent all but proximally on posterior half of fin (particularly in large specimens).

Anal Fin: Dark dusky proximally, tips of rays abruptly pale. Several, often interrupted, posteroventrally directed, narrow, pale lines on proximal two-thirds of fin; lines faint posteriorly.

Caudal Fin: Proximal end of fin with pale membranes; rays outlined with dark dusky pigment, occasionally extending posteriorly at midlevel of fin; some specimens with vertical, narrow, dark dusky margin on fin at posterior end of fleshy caudal base.

Females: Similar to males except: head background usually not as dark; dark bands and markings on head more apparent; pale spaces between dark bands slightly broader; body background paler; body bands less distinct; usually 4th and occasionally 5th horizontal series of intense, dark spots present on body; spots in somewhat less distinctly arranged rows; fins less distinctly pigmented; dorsal fin often only with dark dusky blotches along base above dorsal ends of body bands.

McCulloch (1917, pl. 10:fig.2) presented a useful illustration of O. anolius, which is reproduced in Scott (1962:247).

GEOGRAPHIC DISTRIBUTION (Figure 4).—Spencer Gulf, South Australia, to the Queensland coast of the Gulf of Carpentaria. Scott (1962) reported that O. anolius occurs in Victoria, but we have seen no specimens from that state. See “Nomenclatural Discussion” for erroneous locality records.

HABITAT.—Shallow, usually estuarine waters in and around oyster and other mollusc beds on tidal mud flats (Thomson and Bennett, 1953).

COMPARISONS.—Omobranchus anolius is unique in Omobranchus in having the posterior segmented dorsal-fin rays of larger males long and filamentous. The 15th ray, for instance, may attain a length of up to 31.9% SL, more than in any other species of Omobranchus. In O. ferox and aurosplendidus the 15th ray may attain a length of 22–24% SL, but none of the rays become filamentous or much exserted beyond the margin of the interradial membrane (the dorsal-fin spines of male aurosplendidus do, however, become long and filamentous). In O. anolius there are several series of small, dark spots that appear to be superimposed on the color pattern of the body. Omobranchus elegans, aurosplendidus and, to a much lesser extent, meniscus also have a similar spotting, but the spots are smaller, more numerous, and more randomly distributed in these three species. Some specimens of O. fasciolatus appear to have a similar spotting, but the spots are not so intensely dark and do not appear to overlie other features of the color pattern.

Omobranchus anolius can be differentiated externally from the Australian populations of those species of Omobranchus with which it appears to be broadly sympatric (O. lineolatus, germaini, punctatus, r. rotundiceps, verticalis) most readily by its lack of lateral-line tubes. The majority of the specimens of O. r. rotundiceps from New South Wales also lack lateral-line tubes, but these specimens have 33–35 total dorsal-fin elements (versus 29–31 for anolius). O. anolius is also the only Australian species that may have a fleshy crest on the head.

MATERIAL EXAMINED.—AUSTRALIA: NEW SOUTH WALES: Sydney, USNM 197621 (26: 17.2–46.0, including 2 cleared and stained), MNHN A.2160 (ca. 48), BMNH 1862.8.1.16 (52.8); Port Jackson, MNHN A.1832 (ca. 46, holotype of Blennechis anolius), AMS 1.16409–001 (2: ca. 44–45, syntypes of Petroscirtes guttatus), I 16410–001 (ca. 49, holotype of Petroscirtes wilsoni), 1.16411–001 (4: 31.5–52.8, “cotypes” of Petroscirtes cristiceps); Shoalhaven River, BMNH 1929.12.3.31.2 (60.6); Clarence River, BMNH 1914.8.20.238 (53.4). SOUTH AUSTRALIA: Backy Point (Spencer Gulf), AMS IB.5142 (ca. 47). QUEENSLAND: Moreton Bay, AMS IA.4596 (41.8), 1.470 (47.0, “cotype” of Salarias galeatus), 1.383 (ca. 28, originally among syntypes of Salarias furtivus = O. r. rotundiceps); Manly, QM 1.7828 (52.2); Caloundra, AMS 1.6206 (2: 30.5–33.5); Norman River, QM 1.2200 (ca. 47), 1.2210 (45.2), 1.2211 (47.6), 1.2213 (40.7). INDIA: Bombay (probably erroneous), NMV 71774 (3: 43.9–50.3, syntypes of Petroscirtes altivelis). NEW ZEALAND (probably erroneous): BMNH 1864.1.17.4 (56.0).

Omobranchus anolius, the oyster blenny, is a species of combtooth blenny found in coral reefs in the western Pacific ocean. It can reach a maximum length of 7.5 centimetres (3.0 in) TL.