Which of the following properties is unique to echinoderms within higher invertebrates

This is s cute awee : (( . well if she's showing you signs that she may like you , then shoot your shot ! don't be afraid . & if you're unsure that she's giving you these signs , then wait out for a little bit . most girls are different . some may act really sweet , but only bc you're a good friend of hers . that , or she might like you . you just never know . but i think you should sit down with her & tell her how you feel . but don't be awkward & shy . just be straight up & tell her how you feel . if the feelings aren't mutual , then don't cry about it . you need to respect her decision & look for others in the world . feelings can be difficult & confusing , but don't be afraid to show them . i say you play it out & if you're still unsure about it , talk to her . - rach

Carbon monoxide is the answer: )