Morphology of seminal receptacle of the harvested golden crab Chaceon chilensis and its implication in the fertilization process

Abstract

The external and internal architecture of crab seminal receptacles are closely associated with mating behavior, sperm transfer, and storage patterns, and ultimately reproductive success. Therefore, describing their anatomy contributes to the development of a greater understanding of crab reproductive biology. In this study, we describe the anatomy and tissue characteristics of the seminal receptacle of the golden crab Chaceon chilensis, a harvested deep-sea species from the Juan Fernandez Archipelago (off central Chile). Females in the late mature stage were used as reference for histological description. Morphological features of the seminal receptacle included: (1) a dorsal receptacle-oviduct connection, (2) velum and septum separating the dorsal and ventral chambers, (3) extensive glandular epithelium in both chambers, (4) a ribbed chitin line, (5) a highly folded, bilobulated ventral chamber, and (6) a simple-type vagina. Some of these traits (2, 3, 4, 5) are novel for crab receptacles and could contradict the generalized idea about the pattern of sperm precedence associated with the location of the receptacle-oviduct connection. External sperm plugs were not found in mature females, but variations in the color of opercula occluding the vulva were used to assess sexual maturity. The seminal receptacle of C. chilensis has an unusual internal morphology with vast sperm storage capacity and separate storage areas for sperm ejaculates, which could allow for cryptic female choice. In cases like these, male-male competition is usually intense and males deliver large quantities of sperm in each mating event, which makes them vulnerable to sperm depletion.