What about shellfish and crustaceans?

The Quran informs us that all the game in the sea and its food are lawful for believers to eat.

[5:96] All fish of the sea are made lawful for you to eat. During pilgrimage, this may provide for you during your journey. You shall not hunt throughout the pilgrimage. You shall reverence GOD, before whom you will be summoned.

أُحِلَّ لَكُمْ صَيْدُ ٱلْبَحْرِ وَطَعَامُهُۥ مَتَـٰعًا لَّكُمْ وَلِلسَّيَّارَةِ وَحُرِّمَ عَلَيْكُمْ صَيْدُ ٱلْبَرِّ مَا دُمْتُمْ حُرُمًا وَٱتَّقُوا۟ ٱللَّهَ ٱلَّذِىٓ إِلَيْهِ تُحْشَرُونَ

Here is the word-by-word breakdown of the sentence:

1	uḥilla	أُحِلَّ	[It] was made lawful
2	lakum	لَكُمْ	for you [all]
3	ṣaydu	صَيْدُ	game (animals)
4	l-baḥri	ٱلْبَحْرِ	(of) the sea
5	waṭaʿāmuhu	وَطَعَامُهُۥ	and its food
6	matāʿan	مَتَـٰعًا	(as) provision
7	lakum	لَّكُمْ	for you [all]

From this, we see that not only all game of the sea lawful, but also any food they eat.