An interommatidial exocrine gland with a “nail-headed” structure in the water strider Aquarius remigis (Hemiptera, Gerridae)

• The ultrastructure of the interommatidial exocrine glands of Aquarius remigis was described.
• The nail-headed structure (NS) of the gland was described for the first time in arthropod compound eyes.
• The NS consists of two components: a rod-like stalk and a cup-like depression.
• The glands are class 3 epidermal glands (Noirot and Quennedey, 1974).

The fine structure of the interommatidial exocrine glands, found in the compound eyes of the water strider Aquarius remigis, is described using light, scanning, and transmission electron microscopy. The glandular pores of the glands are specialized into minute “nail-headed” structures (NS), which are described for the first time in arthropod compound eyes. Each NS is composed of two components: a rod-like stalk and a cup-like depression. The TEM study shows that the glands are class 3 epidermal glands as defined by Noirot and Quennedey (1974, 1991). Each gland consists of 3 cells: a gland cell, an intermediary cell, and a duct (canal) cell. The gland cell contains abundant electron-lucent vesicles, while the intermediary cell contains a large number of osmiophilic secretory granules. These two cells might secrete different substances which mix together in the dilated sac-like portion of the conducting canal before final release. The possible functions of the secretions released from these glands are discussed.