They burrow by means of zones of muscle contractions which move along the body and they swim by undulating their body from side to side.
ðeɪ bˈɜːɹoʊ baɪ mˈiːnz ʌv zˈoʊnz ʌv mˈʌsəl kəntɹˈækʃənz wˌɪtʃ mˈuːv ɐlˈɔŋ ðə bˈɑːdi ænd ðeɪ swˈɪm baɪ ˈʌndʒuːlˌeɪɾɪŋ ðɛɹ bˈɑːdi fɹʌm sˈaɪd tə sˈaɪd.