Concept:
Medical terminologies frequently stem from Greek or Latin roots. Words related to blood utilize the prefix hemo- or haemo- depending on the regional variation (American vs. British English). Inversion or displacement of these vowels results in a misspelling.
Step 1: Analyze options A, C, and D.
* Gastroenterologist: Spelled correctly. A medical practitioner qualified to diagnose and treat disorders of the stomach and intestines.
* Neurologist: Spelled correctly. A specialist in the anatomy, functions, and organic disorders of nerves and the nervous system.
* Endocrinologist: Spelled correctly. A medical practitioner qualified to diagnose and treat disorders of the endocrine glands and hormones.
Step 2: Identify and correct the mistake in option B.
* The word "Hemaetologist" contains a vowel transposition error where 'ae' is written as 'ae' in an illegal sequence following 'm'.
* The correct British English spelling is Haematologist (with 'ae' at the beginning), and the correct American English spelling is Hematologist. The hybrid form "Hemaetologist" is completely wrong.
* Meaning: A medical specialist who studies, diagnoses, and treats blood diseases and disorders.