Question: What animated creatures were the title characters of the film which was based one of the most frequently performed plays written by William Shakespeare early in his career?

Context paragraphs:
Induction (play): An induction in a play is an explanatory scene, summary or other text that stands outside and apart from the main action with the intent to comment on it, moralize about it or in the case of dumb show to summarize the plot or underscore what is afoot.  Typically, an induction precedes the main text of a play.  Inductions are a common feature of plays written and performed in the Renaissance period, including those of Shakespeare.  While Shakespeare plays do not typically have inductions, they are sometimes depicted as part of the device of the play within the play.  Examples include the dumb show in "Hamlet" and the address to the audience by Puck in "A Midsummer Night's Dream".  Another example, in "The Spanish Tragedy" by Thomas Kyd, is the introduction to that play by the ghost of Andrea who preps the audience by laying out the story to come.  Likewise, Shakespeare's "The Taming of the Shrew" opens with induction scenes which involve characters watching the play proper.

History (theatrical genre): History is one of the three main genres in Western theatre alongside tragedy and comedy, although it originated, in its modern form, thousands of years later than the other primary genres.  For this reason, it is often treated as a subset of tragedy.  A play in this genre is known as a history play and is based on a historical narrative, often set in the medieval or early modern past.  History emerged as a distinct genre from tragedy in Renaissance England.  The best known examples of the genre are the history plays written by William Shakespeare, whose plays still serve to define the genre.  History plays also appear elsewhere in British and Western literature, such as Thomas Heywood's "Edward IV", Schiller's "Mary Stuart" or the Dutch genre "Gijsbrecht van Aemstel".

Shakespeare's plays: The plays written by English poet, playwright, and actor William Shakespeare (1564 – 1616) have the reputation of being among the greatest in the English language and in Western literature.  Traditionally, the plays are divided into the genres of tragedy, history, and comedy; they have been translated into every major living language, in addition to being continually performed all around the world.

Romeo &amp; Juliet: Sealed with a Kiss: Romeo & Juliet: Sealed with a Kiss is a 2006 American animated romantic fantasy film loosely following the play "Romeo and Juliet" by William Shakespeare.  The film is about two star-crossed seals, Romeo and Juliet (voiced by Daniel and Patricia Trippet respectively), who fall in love against the wishes of their warring families.  It was released in Europe in mid-2006 and on October 27 in the United States.

Romeo and Juliet: Romeo and Juliet is a tragedy written by William Shakespeare early in his career about two young star-crossed lovers whose deaths ultimately reconcile their feuding families.  It was among Shakespeare's most popular plays during his lifetime and along with "Hamlet", is one of his most frequently performed plays.  Today, the title characters are regarded as archetypal young lovers.

Julius Caesar (play): The Tragedy of Julius Caesar is a tragedy by William Shakespeare, believed to have been written in 1599.  It is one of several plays written by Shakespeare based on true events from Roman history, which also include "Coriolanus" and "Antony and Cleopatra".

Act to Restrain Abuses of Players: The Act to Restrain Abuses of Players (1606) was a censorship law passed by the English Parliament, and introduced fines for plays which 'jestingly or profanely' used the names of God or Jesus.  Plays written after 1606 avoided such terms as a consequence of the act, and new editions of older plays removed profane words.  Some scholars have argued that the Act had an important influence on the revision and publication of the plays of William Shakespeare.

Black (play): Black is a full-length play by Joyce Carol Oates first published in "Twelve Plays" (1991) and reprinted in "The Perfectionist and Other Plays" (1995).  Together with "I Stand Before You Naked", "Tone Clusters", "Ontological Proof of My Existence" and "Bad Girls", "Black" is one of Oates's most frequently performed plays.  The prose version of "Black" appeared in "Witness" in 1989.  A revised version of the play with the title Cry Me a River was first performed in 1997.

The Birthday Party (play): The Birthday Party (1957) is the second full-length play by Harold Pinter.  It is one of his best-known and most frequently performed plays.

African Theatre: The African Theatre was an African-American acting troupe in New York City established by William Henry Brown in the 1820s.  The troupe performed plays by Shakespeare and plays written by Brown, several of which were anti-colonization and anti-slavery.  Its leading actor was James Hewlett.

Supporting paragraphs: Romeo &amp; Juliet: Sealed with a Kiss Romeo and Juliet
Answer: seals