Calcium Balance and Moulting in the Crustacea

Abstract

Summary 1. Crustaceans have a high content of calcium, which is chiefly located in the skeleton as calcium carbonate. Calcium is generally the most abundant cation in the body. 2. During intermoult, the exoskeleton is usually fully calcified and the animal is in calcium equilibrium with its environment. 3. In the premoult stages calcium is resorbed from the skeleton and may be lost to the environment or stored within the body. Typically, losses are high and storage is small in aquatic species, whilst most terrestrial forms store much larger amounts of calcium and losses are reduced. Loss of calcium in soluble form by aquatic species must be by outward transport across the gills. 4. Calcium is stored in a variety of different ways, usually with a common taxonomic theme. The main forms are as calcium phosphate granules in cells of the midgut gland (Brachyura), gastroliths (Astacidea and some Brachyura), the haemocoel (some Brachyura) the posterior midgut caeca (Amphipoda) and the ventral portion of the body generally in the Isopoda. 5. At ecdysis, the skeleton is shed and the calcium remaining in it is lost from the body. 6. Recalcification begins immediately, or shortly after, ecdysis using calcium mobilized from the stores. Simultaneously, or when the stores are exhausted, other sources of calcium are utilized. These are calcium in the water (aquatic species), the food (aquatic and terrestrial species) and the exuviae (chiefly terrestrial species). 7. Marine species store little calcium and must obtain the bulk of their requirement (ca. 95%) from the water. Fresh‐water species also store little calcium but have, seemingly, adapted to the lower availability of calcium by increasing the affinity of the calcium‐absorbing mechanism. The rates of uptake of calcium are consequently similar in marine and fresh‐water species. 8. A high degree of storage is essential for terrestrial crustaceans as they do not have access to a large aquatic reservoir of calcium. These large reserves enable the animals to reach an advanced stage of calcification, allowing the resumption of foraging and feeding necessary for completion of calcification. 9. The control of calcium metabolism during the intermoult cycle is poorly under stood. β Ecdysone appears to control the resorption of calcium and the formation of calcium stores during premoult, but the mechanism of control of calcium metabolism during postmoult and intermoult is unknown. 10. The concentration of calcium in the haemolymph of most species is high, but a large proportion of this is in non‐ionized form. In premoult, total calcium levels rise as a result of calcium resorption but little change occurs in the concentration of ionized calcium. Postmoult generally sees a fall in blood calcium, sometimes below the intermoult value.

Change in Organic and Inorganic Components of Hepatopancreas, Muscles and Haemolymph of Procambarus clarkii during the Molting Cycle

“…Similar observations were found by Florkin and Scheer [35]. However, magnesium was also involved in molting cycle through mineralization of cuticle [26] and phosphorylase system as co-factor [35]. It was noticed that magnesium concentrations in hepatopancreas takes the same pattern of phosphorous, due to its role in these processes during the course of molting cycle.…”

Influence of soil pH on the toxicity of zinc oxide nanoparticles to the terrestrial isopod Porcellionides pruinosus

“…Calcium plays an important role in terrestrial crustaceans, especially in the formation of the exoskeleton [35]. Such organisms can absorb calcium either from food or from the cuticle itself (i.e., exuviae) [35]. During the premolting period, the calcium from the old cuticle is transported and stored as CaCO 3 deposits, until reuse to form a new cuticle [36].…”

Amorphous and crystalline calcium carbonate distribution in the tergite cuticle of moulting Porcellio scaber (Isopoda, Crustacea)

“…Marine animals store only little calcium within gastroliths and hepatopancreas because they take up calcium ions from the seawater after moult allowing for quick mineralization of the new cuticle to regain its protective function (Neufeld and Cameron, 1993). However, in environments with a lower availability of calcium ions like in fresh water or on land, crustaceans form large CaCO 3 reservoirs that are utilized to mineralize the new cuticle (Greenaway, 1985). An interesting mode to retain calcium during moulting occurs in isopods that are unique in moulting first the posterior and then the anterior half of the body with the border between the fourth and fifth thorax segments (corresponding to the fifth and sixth somites of the pereon).…”