They have a highly vascularized, red "plume" at the tip of their free end which is an organ for exchanging compounds with the environment (e.g., H2S, CO2, O2, etc.).
Teñen unha "pluma" vermella moi vasclarizada no extremo do seu extremo libre, que é un órgano para o intercambio de compostos co ambiente (por exemplo, H2S, CO2, O2, etc.).