Thelphusian is spelled with the letter "th" at the beginning, which represents the voiceless dental fricative sound /θ/. This is followed by the letter "e", pronounced as the short vowel /ɛ/, and then the letter "l", pronounced as the voiced alveolar lateral approximant /l/. The remaining letters are "p", pronounced as the voiceless bilabial plosive /p/, "h", pronounced as the voiceless glottal fricative /h/, "u", pronounced as the short vowel /ʌ/, "s", pronounced as the voiceless alveolar fricative /s/, "i", pronounced as the long vowel /aɪ/, and "a", pronounced as the short vowel /ə/.
The word "Thelphusian" is believed to have originated from the noun "Thelphusidae", which is the scientific name of a family of freshwater crabs found primarily in Central and South America. "Thelphusian" is an adjective form that refers to something relating to or characteristic of this family of crabs. The exact etymology or word formation process for "Thelphusian" is not available, but it likely stems from the taxonomic classification and scientific nomenclature associated with the study of freshwater crabs.