Upon entering the Arcane Hierophant class you obtain a “Companion Familiar”, the feature description says you have to dismiss your familiar but you may retain your animal companion if you have one.
Companion Familiar: Upon becoming an arcane hierophant, you must dismiss your familiar, if you have one (You do not risk losing XP for doing so.) You may retain any one animal companion you already possess. You add your arcane hierophant class level to your druid or ranger level for purposes of determining your animal companion’s bonus Hit Dice, natural armor adjustment, and Strength/Dexterity adjustment (see the sidebar The Druid’s Animal Companion, page 36 of the Player’s Handbook). For example, a character who is a 4th-level druid/3rd-level wizard/4th-level arcane hierophant has the animal companion of an 8th-level druid (+4 bonus HD, +4 natural armor, and +2 Strength/Dexterity adjustment, or an animal companion chosen from the 4th-level or 7th-level lists). In addition, your animal companion (if any) gains many of the abilities that a familiar would normally possess. You add your arcane hierophant class level to your arcane spellcasting class level, and determine the Intelligence bonus and special abilities of your animal companion accordingly (see the sidebar Familiars, page 53 of the Player’s Handbook). For example, a 4th-level druid/3rd-level wizard/4th-level arcane hierophant has a familiar companion equal to that of a 7th-level wizard and 8th-level druid (Intelligence 9, alertness, improved evasion, share spells, empathic link, deliver touch spells, speak with master, speak with animals of its kind, devotion). The Hit Dice, hit points, attack bonus, saving throws, feats, and skills of the familiar companion are determined as normal for an animal companion. Due to the familiar companion’s unusual Intelligence score, it may very well have more skill points than other animals of its kind. The familiar companion is a magical beast (augmented animal), but you can bestow harmless spells on your familiar companion as if it were an animal instead of a magical beast. If your familiar companion is killed or dismissed, you do not lose XP. You can summon a new familiar companion by performing a ceremony requiring 24 hours of uninterrupted prayer.
It is not clear to me what happens when you become an AH using classes that don’t have the Animal Companion feature (like a Cleric/Scout/Wizard, for example). Do you still get a companion familiar?