Gastric Ossicles Research Articles

Exceptional preservation of internal organs in a new fossil species of freshwater shrimp (Caridea: Palaemonoidea) from the Eocene of Messel (Germany)

A new species of extinct freshwater shrimp was discovered in the Eocene deposit of the Messel Pit Konservat-Lagerstätte. This rare find is represented by only a few specimens, one of which showing exceptionally preserved soft tissues and other internal parts like the stomach with possibly gastric ossicles in place, branchiae, the ovary, and the left mandible, never described in a fossil shrimp. The new species Bechleja brevirostris n. sp. is characterized by a short rostrum bearing 6–8 dorsal spines and one ventral tooth, and long second pereiopods with strong chelae. One additional specimen shows a slightly different morphology and might belong to a different species. The systematic position of the species among the superfamily Palaemonoidea is discussed, as well as implications for the knowledge of the paleoenvironment of Lake Messel and the paleobiogeography of the Eocene.

Unusual bromine enrichment in the gastric mill and setae of the hadal amphipod Hirondellea gigas.

The hadal amphipod Hirondellea gigas is an emblematic animal of the Pacific trenches, and has a number of special adaptations to thrive in this 'extreme' environment, which includes the deepest part of the Earth's ocean. One such adaptation that has been suggested is the presence of an 'aluminum gel shield' on the surface of its body in order to prevent the dissolution of calcitic exoskeleton below the carbonate compensation depth. However, this has not been investigated under experimental conditions that sufficiently prevent aluminum artefacts, and the possibility of other elements with similar characteristic X-ray energy as aluminum (such as bromine) has not been considered. Here, we show with new electron microscopy data gathered under optimized conditions to minimize aluminum artefacts that H. gigas actually does not have an aluminum shield-instead many parts of its body are enriched in bromine, particularly gastric ossicles and setae. Results from elemental analyses pointed to the use of calcite partially substituted with magnesium by H. gigas in its exoskeleton, in order to suppress dissolution. Our results exemplify the necessity of careful sample preparation and analysis of the signals in energy-dispersive X-ray spectroscopic analysis, and the importance of analyses at different electron energies.

Directly ageing the Caribbean spiny lobster, Panulirus argus with validated band counts from gastric mill ossicles

AbstractIn crustaceans, ecdysis was long believed to result in the loss and replacement of all calcified structures, precluding the use of conventional ageing methods. However, the discovery of bands in the gastric ossicles of several crustaceans with some correlation with age suggests that direct age estimation may be possible. We applied this method to a tropical spiny lobster, Panulirus argus, one of the most iconic and economically valuable species in the Caribbean. The presence of growth bands was investigated using wild lobsters of unknown age and was validated with captive reared lobsters of known age (1.5–10 years) from the Florida Keys, Florida (USA). Bands were consistently identified in ptero- and zygo-cardiac ossicles of the gastric mill and did not appear to be associated with moulting. Validation with known age animals confirms that bands form annually. Counts between independent readers were reproducible with coefficients of variation ranging from 11% to 26% depending on reader experience and the structure used. This study demonstrates, for the first time, that direct age determination of P. argus is possible.

Muddy waters: An assessment of the suitability of zygocardiac ossicles for direct age estimation in the Giant mud crab Scylla serrata

AbstractA fundamental characteristic of calcified structures commonly used for direct age estimation in animals is that new material is accreted cumulatively and preserved across ontogeny, thus allowing growth marks to be reliably observed and counted. Direct age estimation in crustaceans has been problematic due to molting of calcified structures across ontogeny; however, recent studies suggest that gastric ossicle tissue is retained through molts and can be used for age estimation. We evaluate the use of sectioned gastric ossicles for direct aging of the Giant mud crab Scylla serrata. Sectioned zygocardiac ossicles from crabs collected in northern Australia are analyzed to determine: (1) whether putative annual age estimates can be reliably reproduced; (2) if age estimates are compatible with previous information; and (3) if ossicle growth is cumulative across ontogeny. Our analyses show that readability of putative annual increments in sectioned ossicles is poor and age estimates imprecise in comparison to fish otolith studies. Age‐at‐size estimates are broadly compatible with previous mark‐recapture data from the same regions. However, analyses of ossicle growth morphology suggest that the zygocardiac ossicles are either shed or extensively reworked during ontogeny, thus casting doubt on the utility of gastric ossicles for direct age estimation in this species. We conclude that the ontogenetic growth morphology of structures used for crustacean aging needs to be carefully considered and that detailed information on the timing and frequency of increment formation—and at least some understanding of the underlying processes—is required before this method is widely adopted.

A comparative study of the gastric ossicles of Trichodactylidae crabs (Brachyura: Decapoda) with comments on the role of diet and phylogeny in shaping morphological traits.

The gastric armature of decapod foregut is a feeding structure that sparks controversial debates about the role dietary and historical components have in shaping its morphological traits. Having previous information about the natural diet is an interesting way to gather evidence on this issue. For the present study, we analyzed the morphological traits of gastric ossicles involved directly in the maceration of food in nine species of freshwater crabs of the family Trichodactylidae (Brachyura: Decapoda) representing five genera, three tribes and two subfamilies. The analyzed gastric ossicles were quite consistent among closely related species, suggesting that the observed traits had a clear phylogenetic component. However, it was also noted that the morphological traits of the gastric teeth of trichodactylid crabs match well with the natural diet and presented likeness with general features of other species with a similar trophic habit. We discuss the influence of phylogeny and function on the design of morphological traits and propose to quantify the role of phylogeny and function in shaping morphological traits through the analysis of phylogenetic signals.

Description of ten additional ossicles in the foregut of the freshwater crabs Sylviocarcinus pictus and Valdivia serrata (Decapoda: Trichodactylidae)

The morphology of stomach ossicles of decapod crustaceans provides valuable information on their phylogeny and biology. We herein described ten new ossicles in the foreguts of two trichodactylid crabs, Sylviocarcinus pictus (H. Milne-Edwards, 1853) and Valdivia serrata White, 1847, in addition to previously described 38 ossicles, which are also recognized and listed. Five specimens each of S. pictus and V. serrata were selected for morphological analysis of gastric ossicles. The stomachs were obtained after removing the carapace, and they were fixed in 10% formalin for 24 hours. After this procedure, the stomachs were immersed in a solution of 10% Potassium Hydroxide (KOH) and heated to 100 °C during 60 minutes for tissue maceration. At this point, the clean skeletons were colored by adding 1% Alizarin Red to the KOH solution in order to facilitate visualization of the internal structures such as the setae and ossicles. The ten new ossicles are: dorsomedial cardiac plate; dorsolateral cardiac plate; suprapectineal lateral ossicle; inferior cardiac valve; lateral mesopyloric ossicle; ampullary roof-medium portion ossicle; process of the ampullary roof-upper portion; lateral-inferior post-ampullary plate; pleuro-pyloric valve?s ossicle; and lateral pleuro-pyloric plate. Some ossicles are thin plates that together with the main ossicles assist in the structure and support of the stomach, which are similar in the two species studied herein. The current knowledge on gastric ossicles will be useful in establishing taxonomic characters, which can evaluate phylogenetic relationships among brachyuran crabs.

Direct Age Determination of a Subtropical Freshwater Crayfish (Redclaw, Cherax quadricarinatus) Using Ossicular Growth Marks.

Recent studies have reported that crustacean age determination is possible. We applied a direct ageing method (i.e. transverse cross sectioning of gastric ossicles) to a subtropical freshwater crayfish (Cherax quadricarinatus) sourced from an aquaculture population. Growth mark periodicity and the potential for chronological depositions were investigated by staining C. quadricarinatus with calcein and examining their ossicles a year later. Pterocardiac ossicles were superior to other ageing structures (i.e. other ossicles and eyestalks) and produced repeatable between-reader counts (87% were corroborated and 13% varied by ±1). C. quadricarinatus size-at-age data (for an aquaculture population) was described by a von Bertalanffy growth equation (L ∞ = 32 mm occipital carapace length; K = 0.64; t 0 = –0.18; R2 = 0.81). Ossicular growth marks did not correspond to moult history. The calcein stain was retained over an annual cycle comprising multiple moults, demonstrating that pterocardiac ossicles retain chronological information. The maximum age (3+) corroborated other indirectly-obtained longevity estimates for C. quadricarinatus. Multiple lines of evidence indicate that the growth marks in C. quadricarinatus ossicles are probably deposited annually during winter. The ability to extract age information from subtropical decapods provides substantial opportunities for advancing fisheries and conservation research globally, but further research is needed to provide a definitive validation and elucidate the mechanism governing the accrual of ossicular growth marks.

Determination of evolutionary units in European representatives of the crab genus Pilumnus

Abstract Bristle crabs of the genus Pilumnus (Brachyura: Heterotremata: Pilumnidae) are common inhabitants of European waters. They are easily identifiable as a genus, but with the exception of P. inermis, intrageneric classification turns out to be quite complex. There is no general agreement on the number and distinction of species. Therefore, this genus is well-suited for comparative molecular studies. Specimens of the Pilumnus hirtellus complex, here defined as including Pilumnus hirtellus, P. villosissimus, P. spinifer, P. aestuarii, and an undescribed species, were gathered from throughout the Mediterranean Sea and the eastern Atlantic Ocean. DNA sequence data were obtained from the barcoding region of the cytochrome oxidase 1 mitochondrial gene and used for reconstruction of a phylogenetic tree and a haplotype network. The morphology of the gastric ossicles was compared in the search of separating characters. Our results give evidence for five genetic clusters within the P. hirtellus complex. There is negligible geographic variation within these clusters. Unambiguous mtDNA sequences within morphologically variable local populations argue against possible hybridization. The here encountered evolutionary units are relatively young and possibly allow to study ongoing processes of morphological, genetic, and ecological differentiation, leading to speciation and radiations in the coastal marine environment.