Scanning electron microscopy, morphometric and energy dispersive X-Ray analysis of cephalothoracic structures exploring defensive and sensory features in kuruma shrimp (Marsupenaeus japonicus Spence Bate, 1888).

Background: Kuruma shrimp (Marsupenaeus japonicus) is a commercially important crustacean and a valuable global food source. This study employed scanning electron microscopy (SEM) to explore the morphology and morphometric features of the Marsupenaeus japonicus cephalothoracic structures, including antennules, antennas, scaphocerite, rostrums, and eye stalks. The primary focus was on understanding the role of each part, especially through the examination of setae, which are crucial for chemoreception and defense. Additionally, energy dispersive X-ray spectroscopy (EDX) analysis was utilized to identify the elemental composition of these structures.

Material and methods: The samples from the heads of fifteen Marsupenaeus japonicus were studied by gross morphology and morphometry, SEM, and EDX analysis. This study is the first to integrate both SEM and EDX techniques for a detailed analysis of these cephalothoracic structures, offering an innovative approach to understanding both morphological and elemental characteristics.

Results: Marsupenaeus japonicus exhibited two antennules and two antennae. The antenna featured four basal segments: basicerite, ischiocerite, merocerite, and carpocerite, each with distinctive articulations and setae distribution. The antennule, with three segments covered by plumose setae, displayed curved cone-shaped flagellae. The scaphocerite, resembling a paddle, showcased plumose setae, while the rostrum exhibited dorsal and ventral spines, lateral grooves, and unique setal arrangements. Setal measurements across structures revealed diverse lengths and widths, indicating functional specialization. The compound eyes were connected to an optic stalk adorned with plumose setae. EDX analysis revealed higher percentages of calcium and phosphorus in the spear-like structures of the scaphocerite, rostrum, and antenna, respectively.

Conclusion: This investigation provides a thorough examination of the intricate morphological features of the cephalothoracic region of Marsupenaeus japonicus, shedding light on its sensory and defensive capabilities. The novel application of both SEM and EDX not only deepens our insights into these structures but also lays the groundwork for future studies using this dual approach to explore crustacean morphology, with potential advantages for sustainable aquaculture and the conservation of marine ecosystems.