The word archiannelid is playable in Words With Friends™, no blanks required. Because it is longer than 7 letters, you would have to play off an existing word or do it in several moves.
Words With Friends™ Letter Score: 21
Highest Scoring Words With Friends™ Play In The Letters archiannelid
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Seven Letter Word Alert: (45 words)
achiral, adrenal, aedilic, airhead, airline, alanine, anilide, aniline, annelid, archeal, archean, cairned, caldera, candela, candler, cannier, carinae, carinal, chained, chainer, chaired, channel, charade, chinned, cranial, decalin, decrial, deliria, denarii, echidna, enchain, handcar, handier, handler, hernial, incline, inhaled, inhaler, inreach, lacinia, radical, radicel, radicle, ranched, rechain