Body depth less than or equal to head length, depth contained 2.3 to 2.8 times in standard length (for fish 13 to 21 cm standard length); caudal-peduncle depth 10.6 to 12.0% of standard length. Eye diameter subequal to snout length, contained 4.1 to 5.5 times in head length; preopercle rounded, the posterior edge distinctly serrate, with a large spine (usually hidden by skin) directed downward and forward at the “angle.” Gill rakers 5 to 7 on upper limb, 14 to 16 on lower limb, 20 to 22 total. Dorsal fin with XI spines and 17 to 19 rays; anal fin with III spines and 9 rays; pectoral fins with 16 to 18 rays; caudal fin rounded. Scales smooth; lateral-line scales 55 to 63, lateral-scale series 71 to 75.
Colour: Head and body marbled reddish brown, with obscure bars and small dark spots; 7 or 8 irregular transverse series of small dark spots on pectoral fin; pale spots and blotches over all of head, body, and median fins.

Eastern tropical Pacific from the northern Gulf of California to Peru and the Galapagos Islands.

See "Ecology" under the genus Alphestes description.

Maximum total length about 30 cm.

As indicated in the account of A. afer, Heemstra and Randall (1993) regard A. immaculatus as a valid species. When Hildebrand described Alphestes fasciatus as a new species in 1946, he apparently was not aware of Fowler’s description of A. galapagensis, which was published in 1944. The original description of A. immaculatus Breder (1936) was based on a juvenile of 82 mm standard length with an “almost uniform” colour pattern. The dorsal-fin soft-ray count of 17 for this holotype is one ray less than any of the A. multiguttatus for which Heemstra and Randall (1993) have data (range 18 to 20, mean=19, n = 42) but it is within the range of counts for A. immaculatus (range 17 to 19, mean = 18, n =29, 5 fish with a count of 17 dorsal-fin rays). The holotype was collected at San Francisquito Bay in the northwestern Gulf of California, not the Galapagos, as listed by C.L. Smith (1971). According to Thomson et al. (1979), the pacific mutton hamlet (“Epinephelus afer") is much more common than the rivulated mutton hamlet (A. multiguttatus) in the Gulf of California. Although Thomson et al. (1979) correctly distinguish these two species on differences in colour pattern, their stated differences in fin-ray counts appear to be mean values for each species (no range in counts is given for either species). Johnson and Keener (1984) described and illustrated the dorsal- and pelvic-fin spine morphology of the larvae (as “Pacific E. afer”).