In this paper, the morphology, development and behaviour of a brown-green turbellarian, collected from the sea near Shenzhen Bay Sports Center in Shenzhen City (22°30′58″N, 113°56′1″E) Guangdong Province, was carefully observed. Its taxonomy and geographical distribution was also discussed. The results indicated that, symbiotic Zooxanthella microadriatica and hyphal brown granules were within the epiderm. Its head was blunt round shape, with a pair of granular brown ocellus and a statocyst. Two caudal lappets laid coordinately on both sides of the tail. The shape and size of the caudal lappets were related to the stretch status of the tail. It was hermaphrodite, with two genital openings behind the mouth, and the female genital opening was anterior to the male one. The paired oocyte laid in ventral body and paired testes laid in dorsal body. Seminal bursa was dumbbell shape, within 2-12 bursal nozzles. The vagina was inverted T-shaped, and its epiderm consisted of prismatic cells. Sperm in testis gathered into bundle, extended towards the rear of the body to false seminal vesicle, and gathered into seminal vesicle. The penis was surrounded by seminal vesicle. It moved under the water with the swing of cilia, or wiggled both sides of the body appearing papilionaceous swimming. It preferred to prey on miniature turbellarians and rotifer. When artificial feeding, it could ingest Cladoceran. Through contrastive study, this turbellarian was identified as Heterochaerus australis Haswell, 1905 of the genus Heterochaerus (Acoela, Convolutidae), and it is a newly recorded order and species of turbellarian in China.