TEM image showing phagocytic intracellular digestion in amphioxus

Gut cells (dark grey area) of the sea creature called the amphioxus engulf food particles (light grey circles). Credit: Chunpeng He

Physiology

The sea creature that swallows its food whole — twice

The lancelet’s cells envelop food particles and also offer immune protection.

A simple creature called the lancelet has an unusual way of absorbing nutrients: the cells lining its gut engulf bits of food.

Countless animals — from the sea urchin to the blue whale — break down food particles with digestive enzymes in a hollow digestive organ. But scientists have long suspected that the small ocean-dwelling lancelets rely on a different mechanism.

Zuhong Lu at Southeast University in Nanjing, China, Jun-Yuan Chen at the Nanjing Institute of Paleontology and Geology and their colleagues studied the lancelet Branchiostoma belcheri, feeding it a diet of algae. The researchers’ updated methods for preparing tissue for microscopy helped them to confirm that individual cells in the animal’s gut could encircle an algal particle, essentially swallowing the food whole.

The team also found that in well-fed lancelets, immune genes are active in the digestive cells. This suggests that the animals can mount an immune response to ward off harm from bacteria and other dangerous dinners.