Hello!

I notice there seems to be some confusion in your question. The passage you're referring to isn't provided, which makes it difficult to find a replacement word for "weight." Additionally, there appears to be some mixing of concepts between species families, elements, plans, and SEO (Search Engine Optimization).

Could you please:

1. Share the complete passage you're referring to?

2. Clarify which specific sentence needs the word replacement?

3. Specify whether this is for a language/vocabulary exercise or something else?

The current question combines biological concepts (species, family) with digital marketing terms (SEO) in a way that's unclear. Also, the phrase "reducing to SEO" doesn't seem to fit the conventional use of either biological classification or search engine optimization.

With more context, I'd be better able to help you find the exact word you're looking for. Please feel free to provide the complete passage and any additional details about your assignment.

Would you mind sharing these details so I can assist you more effectively?