Mueller'S Rockskipper

Istiblennius muelleri (Klunzinger)

Salarias muelleri Klunzinger, 1880:388 [Australian, Hobsons Bay (Victoria; erroneus locality); holotype SMNS 1519].

DESCRIPTION.—Dorsal fin. XII to XIV,19 to 21 = 32 to 34 (XIII in 44 of 47 specimens examined for character; 34 total elements only in males, which have statistically significant higher mean number of total elements than females); membrane between spinous and segmented-ray portions notched deeper than half length of first segmented ray; membrane from posteriormost ray attaching to point ranging from on dorsal edge of caudal peduncle at caudal-fin base (rarely) to point out on dorsal edge of caudal fin up to 18% caudal-fin length in specimens ≥30 mm SL.

Anal fin. II,21 to 23 (23 only in males; Shen et al., 1986:40, reported II,20 and 21 for 2 specimens from Taiwan); posterior element usually not split to base (split in <33% of specimens); posteriormore element of split ray variably well developed or vestigial and visible only on radiographs; fin usually not bound by membrane to caudal peduncle; when bound, membranous attachment almost unnoticeable, extending along basal portion of posteriormost ray no more than 10% length of ray. Skin covering anal-fin spines and distal half of rays not modified in any of 21 males available (32 to 59 mm SL).

Pectoral-fin rays 13 or 14 (14 bilaterally in 34 of 36 specimens examined for character).

Pelvic-fin rays I,3.

Caudal fin. Dorsal procurrent rays 6 or 7, ventral procurrent rays 5 to 7, total procurrent rays 11 to 14, segmented rays 12 or 13 (13 in 40 of 41 specimens examined for character).

Vertebrae. 10+27 to 30 = 37 to 40 (40 in only one specimen, male); posteriormost pleural rib on 11th from anteriormost centrum; posteriormost epineural on 15th to 19th from anteriormost centrum.

Cirri. Nape cirrus absent. Orbital cirrus simple, rarely a single branch or a few short, fine filaments at tip, shorter than orbital diameter in females, usually shorter than orbital diameter in males. Nasal cirrus simple, relatively long (usually about half orbital diameter).

Lateral line. Continuous canal anterodorsally with simple pores (no vertical pairs of pores), extending posteriorly to point between verticals from bases of 6th and 9th dorsal-fin spines (usually to between verticals from 7th and 8th spines), then continuing posteriorly and posteroventrally as series of 1 to 6 (rarely 1 or 6) short, disconnected, horizontally bi-pored canals (tubes) in skin; posteriormost tube in area below and between verticals from bases of 7th spine and second segmented dorsal-fin ray (rarely posterior to vertical from 12th spine).

Mandibular pores 3 to 5 (always 5 pores, at least unilaterally; 5 bilaterally in 22 of 41 specimens examined for character).

Five to 7 sensory pore positions between 1 o'clock and 5 o'clock on postorbital margin (usually 6 pores); no more than 1 position occupied by a pair of pores (all positions with single pores in 40 of 41 specimens examined for character).

Posterior canines absent.

Ventral margin of upper lip and dorsal margin of lower lip entire.

Well-developed, fleshy, blade-like crest dorsally on head of both males and females (at least at sizes ≥ 30 mm SL); crest of female relatively smaller than that of males of comparable size.

COLOR PATTERN (in preservative; Figure 50).—Males and females basically similar, but male color pattern more strongly delineated. Head more or less uniformly dusky, except crest darkest posterodorsally and with central, diffuse pale area separating dusky anterior and posterior regions. Body with up to about 10 pairs of slender, almost vertical, dusky bands; dusky band pairs separated by slender, pale interspaces, each of which may appear as pair of pale bands separated by interrupted, slender, dusky band; dusky band pairs least distinct anteriorly on body, breaking up into fine, dusky specks or reticulation of small pale spots with dusky margins on caudal peduncle. Dorsal fin: spinous portion dusky, crossed by several diagonal, paler-dusky stripes with dark margins; segmented-ray portion faint dusky with numerous dark pinstripes coursing length of fin, stripes coalescing into reticular pattern posteriorly. Anal fin: more or less uniformly dusky, or dusky with very faint, small, pale spots basally. Caudal fin dusky, with dusky reticular pattern of small, pale spots (especially males). Pelvic and pectoral fins unmarked.

Chapman (1951:323) provides a reasonable illustration of a male specimen.

Size. Largest male, approximately 70 mm SL; largest female, approximately 55 mm; smallest specimen, ~30 mm (female).

COMPARISONS AND RELATIONSHIPS.—We have no subjective impression as to what the sister group of I. muelleri might be, although it falls into a weakly supported polytomous clade that also includes I. bellus and I. zebra in our phylogenetic analysis (Figure 60, see Phylogenetic Analysis section). Istiblennius muelleri differs from all other Istiblennius species in its color pattern, and all except I. rivulatus, in having a simple nasal cirrus at all sizes. It differs most conspicuously from I. rivulatus in having 14 (as opposed to 12) pectoral-fin rays, in lacking nape cirri (as opposed to having nape cirri), and in having the orbital cirrus length equal to (usually) or shorter than the orbital diameter, whereas it usually exceeds the orbital diameter in I rivulatus. I. muelleri differs from I. bellus in that I. muelleri females have a blade-like crest on the head and a color pattern similar to that of males. It shares the latter 2 characters with I. zebra in the clade, but differs from I. zebra in having, among other characters, the dorsal margin of the lower lip entire, as opposed to crenulate. Although the ventral margin of the upper lip is entire in both I. muelleri and I. zebra, I. zebra often exhibits indications of fine lip crenulae laterally or as crenulae-like pads on the buccal surface of the lip.

DISTRIBUTION (Figure 69).—Known definitely only from Hsiao-liu-chiu Island, off southwest Taiwan, south to Kur Island, Indonesia. Occurs in tidepools, also close to edge of rocky shores at low tide. The type locality of Istiblennius muelleri, Hobson's Bay, Victoria, Australia, is clearly an error. As Whitley (1943:186) noted, no species of Istiblennius is found so far south as Victoria, in fact, no further south than Sydney, New South Wales (~33°51′S) on the east Australian coast. Müller, the collector of the holotype of I. muelleri, made collections at various localities between Port Darwin and southern Queensland along the warm coast of Australia, and possibly (although improbably) obtained the specimen in that area. Whitley remarked that the specimen may have come from Port Darwin, probably because that is the Australian locality most proximate to localities (in Indonesia) from whence I. muelleri is definitely recorded. The only problem with such an assumption is that there is no well-documented record of I. muelleri from Australia.

The record of Istiblennius muelleri from Taiwan, plotted on the distribution map, is based on the well-documented record in Shen et al. (1986:40 and fig. 54i).

MATERIAL.—Australia, Hobson's Bay [probably erroneous; see previous discussion]: SMNS (holotype of Salarias muelleri). Indonesia: Nusa Laut, USNM 210953 (5, including 2 cleared and stained); Ambon, ZMA 120.378 (1); Haruku, RMNH 20338 (2), 20763 (7); Kur Id, ZMA 120.379 (1); Karakelang Id, ZMA 120.375 (3); Sula Besi Id, ZMA 120.377 (1); Salebabu Id, ZMA 120.376 (3); Sorong, Irian Jaya, ANSP 168866 (1). Philippines: Homonhon Id, USNM 123361 (1); Simaluc Id, USNM 122435 (7); Negros: Dumaguete, CAS 46498 (2), Ciagba Bay, CAS 66856 (2); Mindoro, Calapan, CAS-SU 32304 (1); Iba Id, CAS-SU 32305 (1); Tataan, Tawi Tawi Group, USNM 122436 (2). No locality [Bleeker specimens, probably Indonesia), RMNH 30339 (6).