Is this a run-on sentence
Inside its tissues, the spotted jelly—a marine invertebrate native to the South Pacific—grows symbiotic algae that produces food for the jelly and gives it a greenish-brown hue.

Yes

Explanation:

You have multiple dashes and could easily delete them and make this sentence multiple sentences.

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1.the hosts on two opposing mountains stood,  

2.thick as the foliage of the waving wood;  

3.between them an extensive valley lay,  

4.o'er which the gleaming armour pour'd the day,  

5.when from the camp of the philistine foes,

6. dreadful to view, a mighty warrior rose; in the dire deeds of bleeding battle skill'd,

the answer is:

in the fourth paragraph. ( the paragraph that begins with “on friday of my third ”).

hope it !