6533b852fe1ef96bd12ab569

RESEARCH PRODUCT

Ontogeny of Heterocypris bosniaca (Ostracoda: Cyprididae): description of postembryonic instars and rediscovery of the neglected A-9 stage

subject

description

Despite being the most common and widespread family of Ostracoda in fresh water, the Cyprididae are still poorly known with respect to species ontogeny. The full series of eight juvenile instars has been described in detail for just five of the approximately 1000 living species, and only in one case did this include the earliest A-9 stage. We aimed to fill this gap with a morphological study of the post-embryonic development of Heterocypris bosniaca Petkowski, Scharf and Keyser, 2000, a species with unusual morphological traits within the genus, including putatively paedomorphic characters such as valves without tubercles and the narrow calcified inner lamella on both valves. Inside the egg, the poorly known stage A-9 (prenauplius) develops and starts the moulting process. After the egg breakage, the juvenile instar A-8, still inside the A-9 exoskeleton, emerges passively from the egg and finishes the moulting process to a free A-8 instar in less than two minutes. The prenauplius stage A-9 has two pair of limbs; the first are the antennules, while the second correspond to the fused group of the antennae and mandibles, observed by checking the homology by formation. This is apparently the first time that such fusion of the second and third pairs of appendages is described in crustaceans. The later juvenile instars (A-8 to A-1) and the adult stage of H. bosniaca follow a growth pattern that is similar to the rest of the Cyprididae, and particularly close to other members of the genus, but notably differing in the development of the maxillular Zahnborsten and the segmentation of the endopod of the fifth limb.