Linear intermolt growth inAmericamysis bahia(Molenock 1969) (Mysida, Mysidae)

Theoretical considerations in determining allometric growth within instars of crustaceans, with special reference to Americamysis bahia

“…All of the above criteria for determining type of instar allometry, allometric proportions and amounts of growth within periods of instar populations are met in a study by Scarfe and Steele () that examined the theoretical allometric approaches discussed earlier and determined the proportion and amount of allometry through several postlarval instars of A. bahia by sampling individuals in the intermolt stage of instars 1 through 6 and measuring several body regions of each individual. Of primary importance here are abdomen and carapace lengths (mm) because of an observed substantial intermolt expansion in the standard lengths, SL (mm), and because it was necessary to determine whether intermolt expansion occurred in either the abdomen or carapace or both.…”

“…Of primary importance here are abdomen and carapace lengths (mm) because of an observed substantial intermolt expansion in the standard lengths, SL (mm), and because it was necessary to determine whether intermolt expansion occurred in either the abdomen or carapace or both. Scarfe and Steele () also determined the type of instar allometry exhibited by A. bahia and an estimation of the proportion and amounts of period allometry (molt/intermolt allometry) in the abdomen and carapace.…”

“…Of the intermolt growth, about 60% is accomplished in the abdomen and about 40% in the carapace, while ecdysis accounts for the remaining 15% of the total expansion, in which either abdomen or carapace can account for 40–100% of this expansion. The slopes of the intermolt regressions have intercepts different from the regression through all instars (Scarfe & Steele, ). Average molt:intermolt ratio in the carapace expansion is 1:3.16, and in the abdomen, 1:3.71, indicating that proportional growth between the carapace and the abdomen is continuous during both the intermolt and molt phases, but occur at different rates and proportions during the two periods (Scarfe & Steele, ), thus indicating two‐rate continuous allometry (see Figure ).…”

“…In essence, our proposed allometry models free researchers from the limitations of considering only discontinuous growth in crustaceans. The application of these models is illustrated with allometric growth data for A. bahia (Scarfe & Steele ).…”

“…However, recent work by Scarfe and Steele () indicates no obvious discontinuities in the growth curve of Americamysis bahia (formerly Mysidopsis bahia ), as usually associated with ecdysis in crustaceans. Apparently, the majority of the expansion in standard length is accommodated during the intermolt period and not during ecdysis.…”