Palpons

Palpons are specialized zooids found in certain siphonophores, a group of colonial marine hydrozoans. They are one of the distinct types of zooids that make up a siphonophore colony, alongside gastrozooids (feeding polyps), nectophores (propulsors), bracts, and gonophores (reproductive polyps). Palpons are typically smaller and can appear leaf-like or stalked, running along the main stem of the colony. They arise by budding from the same developmental origin as other zooids but function as a separate unit. Unlike gastrozooids, palpons usually lack a full mouth and independent feeding opening.

The primary role of palpons is digestive and circulatory support within the colony. They contribute to digestion by housing enzymes and facilitating the distribution of nutrients through the colony’s gastrovascular system. In addition to digestion, palpons may have sensory functions and participate in maintaining the colony’s internal homeostasis. Their surface can bear cnidocytes for defense, though their main function is related to digestion and nutrient processing rather than prey capture.

Variation in palpons is common among species and colonies; their presence, number, and arrangement reflect the overall architecture of the siphonophore. As integral components of the colony’s integrated body plan, palpons help coordinate digestion and nutrient transport across the multiple interconnected zooids.