Heterochrony in mandible development of larval shrimp (Decapoda: Caridea)—A comparative morphological SEM study of two carideans

Abstract

Mandible development in the larval stages I-V of two palaemonid shrimp species, Palaemon elegans and Macrobrachium amazonicum, was analyzed using scanning electron microscopy, light microscopy, and confocal laser scanning microscopy. In contrast to the zoea I of P. elegans, first-stage larvae of M. amazonicum are nonfeeding. At hatching, the morphology of the mandibles is fully expressed in P. elegans, while it appears underdeveloped in M. amazonicum, presenting only small precursors of typical caridean features. In successive zoeal stages, both species show similar developmental changes, but the mandibular characters of the larvae in M. amazonicum were delayed compared to the equivalent stages in P. elegans, especially in the development of submarginal setae and mandible size. In conclusion, our results indicate heterochrony (postdisplacement) of mandible development in M. amazonicum compared to that in P. elegans, which is related to initial lack of mandible functionality or planktivorous feeding at hatching, respectively. This conclusion is supported by comparison with other palaemonid zoeae exhibiting different feeding modes. Our data suggest that an evolutionary ground pattern of mandible morphology is present even in species with nonfeeding first-stage larvae.

Description of the zoeal stages of Periclimenes aegylios Grippa & d'Udekem d'Acoz, 1996 (Crustacea: Decapoda: Palaemonidae) reared in the laboratory

“…The setae were distinguishable, according to the length/width ratio and the absence/presence of lateral outgrows, into simple (short or long), plumose, cuspidate (Garm 2004), and serrate (two rows of needle-like outgrowths or denticles, along the seta). The first comb seta under the incisor process of both mandibles was indicated as 'lacinia mobilis', according to Geiselbrecht & Melzer (2010), who proposed the presence of this structure on both mandibles, not only the left one (Sollaud 1923); the setae between the incisor and molar processes, under the 'lacinia mobilis', were indicated as comb setae-the submarginal setae proposed by Batel et al (2014).…”

Morphometric Analysis of Chin Shape in Inverted Mandible and Mid Symphysis Menti Angle

“…They are also being used since olden time to ascertain the sex of an individual, because they show sexual dimorphism (g and Vinay, 2013). It is the largest and strongest bone in the face with horizontally curved body that is convexed forwards with two broad rami, which ascend from the posterior end of the body, Therefore it remains the most durable bone of the facial skeleton and retains its shape better than other bones (g and Vinay, 2013;batel et al, 2014). The human mandible is also found to resist post mortem damage and forms an important source of information about the sexual dimorphism.…”