Diagnosis: The presence of bicuspid teeth in the outer rows on both the upper and lower jaws and a moderately sloped vomer with a swollen rostral tip place this species in Maylandia (Ref. 119465). Male and female M. flavicauda are distinguished by an elongate body, body depth 23.6-28.5% of standard length, from all other species in Maylandia, body depth 28.8-40.8% of standard length, except M. tarakiki, body depth 25.8-32.9% of standard length, and M. usisyae, body depth 25.9-30.6% of standard length (Ref. 119465). It is distinguished from M. usisyae by a deeper preorbital bone, preorbital depth 18.0-26.9% of head length, and a longer snout, snout length 34.3-47.3% of head length, which are 17.6-21.2% and 32.0-37.6% in head length in M. usisyae respectively; based on the colour pattern, males of M. flavicauda possess 5-6 black lateral bars, black pelvic fins, a black anal fin, a yellow caudal fin, and a black dorsal fin with yellow/orange spots distally; males of M. usisyae have a yellow dorsal fin with a black submarginal band, a yellow pelvic fin and a yellow anal fin with a black leading edge; males of M. tarakikihave 7-9 lateral bars, and gray-blue/dark gray caudal fin (Ref. 119465). Females of M. flavicauda can be distinguished from those of M. tarakiki by a bluish/brown ground colouration without lateral bars; in female M. tarakiki, the ground colour is light brown with blue center-flank scales and dark brown lateral bars; based on colouration alone, females of M. flavicauda cannot reliably be distinguished from those of M. usisyae (Ref. 119465). Maylandia flavicauda also possess a relatively smaller eye than M. tarakiki, horizontal eye diameter 20.5-30.6% of head length vs. 27.2-36.3% in M. tarakiki (Ref. 119465).

Description: Elongate species, body depth 23.6-28.5% of standard length, with greatest body depth at base of fourth dorsal-fin spine (Ref. 119465). Dorsal body profile with gradual curve to caudal peduncle with highest point at fourth dorsal-fin spine; ventral body profile between pelvic fin and anal fin flat with upward curve to caudal fin; anterior head profile straight to slightly convex between snout tip and interorbital; cleft of the upper and lower jaws with 23-39° angle with body axis; then round to dorsal-fin origin (Ref. 119465). Snout short with isognathic jaws; teeth on lower jaw in 3-4 rows; upper jaw in 2-4 rows; outer rows bicuspid; inner rows tricuspid or unicuspid (Ref. 119465). First 3-4 dorsal-fin spines longer posteriorly with first spine less than half length of fourth spine; last dorsal-fin spine slightly longer than fourth spine; dorsal fin with subacuminate tip, fourth ray longest, about to base of caudal fin in both males and females; pectoral fin rounded, paddle-shaped; anal fin with 3 spines progressively longer posteriorly; third or fourth ray longest, length to base of caudal fin in both males and females, tip slightly longer than dorsal fin; caudal fin subtruncate to emarginated (Ref. 119465). Lateral scales large, ctenoid; small, cycloid scales on breast and belly; cheek with 3-5 rows of small scales; rayed section of dorsal and anal fins with narrow band of tiny scales; tiny scales from base to 50% length of caudal fin (Ref. 119465).

Colouration: Males in territorial colour with light blue ground colouration and 5-6 distinct black bars; head black with 2 light blue interorbital bars; throat dark brown; anal fin black with 4-6 yellow ocelli; light yellow marginal band; pectoral-fin rays black with clear membranes (Ref. 119465). Females with beige/brown/light blue ground colouration; belly and breast white/beige; head with beige/brown ground colouration and blue/green highlights; yellow/green opercular spot; interorbital green/light gray; throat white; dorsal fin light brown/light blue without black submarginal band; pectoral, pelvic, and caudal fins beige/brown/light blue proximally, and dark brown distally (Ref. 119465).