Description
Dorsal spines (total): 6-7; Dorsal soft rays (total): 9-10 (usually: 10); Anal spines: 1; Anal soft rays: 9; Pectoral fin rays: 15-17 (usually: 16); Longitudinal scale count: anterior cycloid = 13-26 (usually: 18); Posterior ctenoid = 28-41; Total longitudinal scale count: 47-59; Transverse scale count: (TRB) 17-25; Gill rakers on outer face of first arch: 2-3 + 1 + 9-11; Gill rakers on outer face of second arch:  2-3 + 0-1 + 10-13; Segmented caudal fin rays: 9/7 or 9/8; Branched caudal fin rays: 7/6 - 8/8; Vertebrae: 10 + 15-16, anterior zygapopheses prominent on vertebrae 1 to 8-9. Head strongly compressed, head length: 28.3–34.5% SL, head width at preopercular margin: 16.1–19.9% SL. Snout rounded in dorsal view, steeply oblique (slightly convex) in side view, 6.5–9.8% SL. Eye relatively small and elevated, no groove behind eye, eye slightly less than snout length, 5.8–8.1% SL. Anterior nostril at end of short tube, just above upper margin of upper lip (by less than a nostril diameter). Posterior nostril a large pore anterior to lower part of eye, about one nostril diameter from eye and about three nostril diameters from anterior nostril. Preoperculum short, horizontal distance from end of eye to upper posterior preopercular margin 10.0–13.9% SL, subequal to distance from snout to posterior half of pupil. Postorbital long, 17.7–20.8% SL, slightly shorter than distance from tip of snout to posterior preopercular margin. Body moderately robust, depth at anal-fin origin: 16.7–21.1% SL. Upper jaw relatively short, 12.2–14.4% SL, reaching to below a point between posterior margin of pupil and just in front of posterior margin of eye. Teeth conical and curved; upper jaw with outer row of teeth curved, enlarged, and wide-set, teeth larger near angle of jaw, three to 4 rows of smaller depressible teeth anteriorly, tapering to two to three rows posteriorly, teeth in rows pointing inward into mouth, an innermost row of enlarged backwardly directed teeth anteriorly on each side of jaw; Lower jaw with teeth in outer row curved, conical, wide-set, covering anterior end of dentary only, three to four inner rows of smaller conical teeth anteriorly and two to three rows posteriorly, innermost row enlarged and larger than teeth in outer row, largest just behind bend in dentary. Tongue tip slightly rounded to slightly emarginate. Gill rakers on outer face of first arch slender, denticulate on posterior margin, rakers shorter than filament length, longest raker near angle of arch about three-quarters filament length; rakers on inner face of first arch and other arches short and denticulate at distal tip. Body covered with cycloid scales anteriorly and with ctenoid scales posteriorly, ctenoid in wedge to below a point between fifth first-dorsal-fin spine and second dorsal-fin origin, extending dorsally and posteriorly to below or near end of second dorsal fin and ventrally to below posterior end of anal fin or on to anterior part of caudal peduncle posteriorly on body, becoming cycloid anteriorly on midside below sixth dorsal-fin spine to second dorsal-fin origin, except a thin line of cycloid scales at base of anal fin. Head naked, including cheeks and operculum, midline of predorsal area naked, anterior extent of body scales reaching forward to a curved line from first dorsal-fin origin to between upper pectoral-fin insertion and middle of operculum. Pectoral fin base naked or with a few minute embedded scales; Midline of prepelvic area naked with scales ending on side of breast along margin of gill cover; Belly usually covered with cycloid scales, anteriormost scales minute and embedded, rarely with a small naked patch behind pelvic fin insertion. First dorsal fin low, with rounded margin, in both sexes, third spine usually longest, but only slightly longer than fourth spine, 17.6–30.0% SL in males and 16.3–20.3% SL in females; Adpressed length of first dorsal fin reaching to just before second dorsal-fin origin up to base of second segmented dorsal-fin ray, 21.0–33.9% SL in males and 20.3–26.0% SL in females. First dorsal-fin origin just behind a vertical line from pelvic fin insertion. Pectoral fin with rounded margin, reaching to above or slightly behind pelvic-fin tip, to or just before anus, length: 24.7–32.9% SL. Pelvic disc large, reaching to anus or slightly beyond in males and females below 30 mm SL, but reaching well short of anus in larger females; pelvic-fin length 22.2–27.2% SL. Caudal fin with rounded posterior margin, central rays longest, length 26.4–32.9% SL. Max. length: 10.0 cm SL. Depth range: 0 - 6 m.

Color
Head and body mostly olivaceous and brownish with overlay of blue spots and dorsal and anal fins with distinctive patterns of brownish spots, stripes, and bars.

Etymology
Cryptocentrus: from Greek, kryptos = hidden + from Greek, kentron = sting. Referring to a concealed point or projection on preopercle.
caeruleomaculatus: from Latin, caeruleus = dark blue, dark green, cerulean, azure + from Latin, macula, -ae = stain, spot. Referring to small “pearl blue” spots scattered over body.
Original description: Mars caeruleomaculatus Herre, 1933 - Type locality: tide flats at Jolo, Sulu Islands, Philippines.

Distribution
Western Pacific: Andaman Sea east to Solomon Islands, north to Ryukyu Islands, south to Western Australia and New Caledonia.

Biology
Occurs in shallow lagoons and coastal bays, usually in areas with runoffs. The species does not show sexual dimorphism in height and shape of the first dorsal fin. The species lives in association with alpheid shrimps.

Similar species
Cryptocentrus altipinna (Hoese, 2019) - Reported from Indian Ocean: Tanzania, Sri Lanka and the Andaman Sea off Thailand.
Cryptocentrus cryptocentrus (Valenciennes, 1837) - Reported from: East Africa and Madagascar east to Mariana Islands, north to southern Japan.
Cryptocentrus leptocephalus (Bleeker, 1876) - Reported from New Caledonia - Link to the species (here).

Cryptocentrus melanopus (Bleeker, 1860) - Reported from Eastern Indian Ocean and western Pacific: Singapore, Malaysia, Brunei, Vietnam, Indonesia and Australia.