This 25 November 2018 video says about itself:
Colorful Marine Flatworms – 20 species / Turbellaria
Free-living marine flatworm (German: freilebende Meeresstrudelwürmer) are some of the most fascinating although simple creatures in the world´s oceans. The bright coloring advertises their toxicity to predators, making many species reasonably safe in open areas.
Aside from their toxins, flatworms have simple body structures. They have no respiratory or circulatory systems, so their bodies are a flat shape to allow for diffusion of carbon dioxide and oxygen. Their digestive system consists of a straightforward but many-branched intestine which allows nutrients to be spread throughout the body.
Marine flatworms are hermaphroditic, meaning they have both male and female reproductive organs.The life span of marine flatworms is generally between three weeks to three to four months long.
From Zootaxa, 12 April 2019:
Two new species of marine flatworm from southern China facilitate determination of the phylogenetic position of the genus Nerpa Marcus, 1948 and the histochemical structure of the nervous system in the genus Paucumara Sluys, 1989 (Platyhelminthes, Tricladida, Maricola)
IA-JIA CHEN, WEI-XUAN LI, RONALD SLUYS, MING-QI WU, LEI WANG, SHUANG-FEI LI, AN-TAI WANG
Two new species of flatworm, collected from a beach at eastern Shenzhen, China, were studied through an integrative approach by combining morphological, histological, histochemical (acetylcholinesterase, AChE), and molecular (18S r- DNA) data. These species belong to two genera of marine triclads, previously unrecorded from China, viz. Nerpa Marcus, 1948 and Paucumara Sluys, 1989.
Nerpa fistulata Wang & Chen, sp. nov. is characterized by: transparent body; principally pentamerous intestine with three distinct commissures; two very large, prepharyngeal testis follicles; a semi-circular lens in each eye cup; a penis papilla provided with a chitinized, pointed stylet; lateral bursae communicating with the oviduct and opening ventrally to the exterior via a duct. Phylogenetically N. fistulata groups with one member of the family Bdellouridae. This new, Chinese species of Nerpa introduces a major geographic disjunction, as the type species N. evelinae was described from the bay of Santos, Brazil, so that the genus is now known from both Atlantic as well as Pacific coasts.
The species Paucumara falcata Wang & Li, sp. nov. is characterized by: three distinct pale yellow transverse pigmentation bands on its dorsal side, between which some snowflake-like specks are randomly distributed, and a brown transverse band anteriorly to the eyes; 8–11 testicular follicles on either side of the body, the follicles extending from immediately behind the ovaries to half-way along the pharyngeal pocket; a musculo-parenchymatic organ with a sclerotic, curved tip projecting from the anterior wall of the male atrium, ventrally to the root of the penis papilla. Phylogenetically P. falcata groups with its congener P. trigonocephala, with the genus Paucumara forming the sister taxon of the genus Ectoplana. Comparison of the nerve structure of P. falcata, as revealed by AChE histochemistry, with that of eight other species of triclad suggested that the nervous system of marine planarians is simpler than that of species of freshwater planarians, but revealed also that the nerve structure is rather variable among species.
The copulatory position exhibited by two partners in Paucumara falcata is remarkable in that they intertwine, with their heads pointing downwards and the tails pointing upwards, the entire process lasting about 10 min. Such a copulatory position has never before been reported for triclad flatworms.
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