▁the ▁colon ies ▁maintain ▁their ▁orientation ▁in ▁water . ▁In ▁the ▁c yst on ect ae ▁subgroup , ▁the ▁p neum at op hor es ▁have ▁an ▁additional ▁function ▁of ▁assist ing ▁with ▁fl ot ation ▁of ▁the ▁organ isms . ▁The ▁si phon op hor es ▁exhib iting ▁the ▁feature ▁develop ▁the ▁structure ▁in ▁early ▁lar val ▁development ▁via ▁inv agin ations ▁of ▁the ▁fl atten ed ▁plan ula ▁structure . ▁ ▁Further ▁observations ▁of ▁the ▁si phon oph ore ▁species ▁Nan om ia ▁bij uga ▁indicate ▁that ▁the ▁p neum at oph ore ▁feature ▁potentially ▁also ▁functions ▁to ▁sense ▁pressure ▁changes ▁and ▁reg ulate ▁chem ot axis ▁in ▁some ▁species . ▁ ▁Distribution ▁and ▁habitat ▁ ▁Currently , ▁the ▁World ▁Register ▁of ▁Marine ▁Species ▁( W o R MS ) ▁ident ifies ▁ 1 7 5 ▁species ▁of ▁si phon op hor es . ▁They ▁can ▁differ ▁greatly ▁in ▁terms ▁of ▁size ▁and ▁shape , ▁which ▁largely ▁reflect s ▁the ▁environment ▁that ▁they ▁inhab it . ▁Si phon op hor es ▁are ▁most ▁often ▁pel ag ic ▁organ isms , ▁yet ▁level ▁species ▁are ▁b enth ic . ▁Sm aller , ▁warm - water ▁si phon op hor es ▁typically ▁live ▁in ▁the ▁ep ip el ag ic ▁zone ▁and ▁use ▁their ▁tent acles ▁to ▁capture ▁zo op l ank ton ▁and ▁co pe pod s . ▁Lar ger ▁si phon op hor es ▁live ▁in ▁deeper ▁waters , ▁as ▁they ▁are ▁generally ▁longer ▁and ▁more ▁frag ile ▁and ▁must ▁avoid