Latin-to-English irregular loan plural

A Latin plural is a plural formed according to the language rules in Latin. These were once most commonly found in Latin, though since its demise, not so much. Rather, what we're interested in is Latin loanwords (and loan phrases) in English.

Latin has a whole load of declensions, familiar o everyone who was subjected to it at school. Fortunately, most Latin loanwords in English are based on the nominative case, regardless of their case in English. Also, English loanwords follow natural gender, rather than Latin gender. The following declensions are reasonably common in English:

Latin declension	Singular ending	Plural ending	Example(s)	Notes
First declension	-a	-ae	alga-algae alumna-alumnae formula-formulae
Second declension masculine singular	-us	-i	alumnus-alumni corpus-corpora locus-loci nucleus-nuclei radius-radii
Second declension neuter singular	-um	-a	curriculum-curricula datum-data referendum-referenda stadium-stadia
Third declension masculine	-x	-ces	appendix-appendices axis-axes index-indices matrix-matrices
				Third and Fourth declensions are very confusing
Fifth declension ending -ies	-ies	-ies	series - series species-species	These are invariant

Often a regularised form exists in English alongside the irregular Latin plural, so e.g. stadium has two plurals, i.e. stadiums and stadia.