Description and variation

This is a medium-sized goby measuring up to 9. 5 cm.

Body design

This can take several forms, which is why this is also known as the Varied Shrimpgoby. In the barred form the body markings are pale brown with 4 irregular brown bars. In Australia, some have blue iridescence in the dorsal fin. The saddled form is uniformly dark brown with several whitish saddles along the dorsum. Both forms have indistinct iridescent blue spots on the head and along the body. There is also a mottled form which has four diffuse brown bars on the side and operculum, and strong mottling on the back. It looks like a pale version of the barred form.

These forms are described in Allen and Erdmann 2012. There is also a yellow form which may be pale or dark, barred or saddled. Reflective blue spots are prominent in all the yellow forms. These spots are circular and, although most dense on the head and gill cover, usually extend along the body to the tail.

The head is uniformly coloured grey, brown, black or yellow, the cheeks being covered by a random sprinkling of white or iridescent blue circular spots The top of the head and eyes either continue the colour of the cheeks or may be white with white tops to the eyes. Not surprisingly given the variability of this species there are intermediate patterns ranging from an off-white transverse bar to a continuous white back as far as the first dorsal fin.

Fin design

The first dorsal fin is usually unmarked, apart from the dark accentuation of the fin rays, an occasional extension of body pattern into the base and sometimes a dark patch in the interspace between the first two rays. There is a pattern of spots or broken brown lines on the second dorsal fin is colourless with three brown stripes and an iridescent blue edge in the mottled, brown and saddled forms but not in the blue-finned and yellow forms, where this decoration is less apparent. The brown stripes may be extensive enough to look like broken white stripes on brown. In black fish, the lower half of the fin is black with the outer margin contrasting white.

The pectoral fin is transparent.

The pelvic fin has blue spots., a pattern that is continued on the lower portion of the caudal fin. is brown with scattered white speckles.

The anal fin is dark brown with one or two longitudinal blue lines

The caudal fin is translucent, often suffused with the base body colour and darker in the lower segment.

Diagnostic features

The dorsal fin pattern is distinctive in having no spots and usually displaying a dark patch at the leading edge and dark accentuation of the dorsal rays.

All colour forms have a dark anal fin with blue stripes

Variation

As the common name suggests there are fairly well-defined variant forms. There are yellow and dark forms. Among the dark forms are saddled, barred, mottled and blue-finned. Among the yellow are pale and dark, barred and saddled forms.

Fishes of Australia calls this the Y-bar shrimpgoby but gives no information. Three photos. 

Similar species

Cryptocentrus cinctus, which has spots on the first dorsal fin.

Cryptocentrus sericus, which has bright bars on the pelvic fin.

Cryptocentrus cyanotaenia, which has a grey and yellow anal fin.

Cryptocentrus bulbiceps may be the same species but differs in the following respects: larger, inhabits silt substrate, lives away from the reef, associates with different shrimps and has a more tapered profile. There are differences in the fins, for example, the parallel broken lines seen in the second dorsal fin in some C fasciatus have not been seen in C bulbiceps.