I don’t have all the tabs. In the menu ‘animals’, for example, is the last tab that I can use ‘Blood relations’. I use ZooEasy Online at an Apple computer.

The horizontal scroll bar shows up when you click on one of the visible tabs. You can recognize it as a thin gray bar. You take this bar with the mouse button (click at the bar with the left-mouse button and hold the button down) to scroll to the desired tabs. Don’t wait too long because then the scroll bar disappears again.
Tip: when you use Safari as browser you won’t see the horizontal scroll bar at all. In that case you better use Firefox as browser.