Which grouping has the least complex body plan? if you were on a research expedition in the kingdom of tonga, a coral atoll in the south pacific, would you find these organisms?

The Kingdom of Tonga is a Polynesian Archipelago in Oceania consisting of 176 islands. During a month long coral reef research mission in Tonga, the Foundation focused on islands in the Hawaii group, Vava’u, and Niuatoputapu. Haʻapai, directly west of the Tonga trench in the central part of Tonga, is made up of 51 volcanic islands and includes Kao, the highest point in the kingdom (1,046 m). Vavaʻu has one large island and 40 smaller ones and includes the second largest city, a large harbor.  The north side of the main island is lined by 200 m high cliffs and extensive open network of fjord-like channels that stretch inland on the north side. Nearly 300 km north of Vavaʻu, close to the border of Samoa is Niuatoputapu, a sparsely inhabited (population 150)  eroded remnant of a volcano surrounded by a large uplifted reef. This island was badly damaged by a tsunami following a submarine earthquake off Samoa in 2009. And for the last question, yes! I would definitely find organisms.