Food acquisition, ingestion and digestion in the Slipper Lobster, Thenus orientalis Lund (Decapoda: Scyllaridae)

Johnston, Danielle Jane (1995) Food acquisition, ingestion and digestion in the Slipper Lobster, Thenus orientalis Lund (Decapoda: Scyllaridae). PhD thesis, James Cook University.

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This study examines food acquisition, ingestion and digestion in the most economically significant scyllarid for Australian fisheries, Thenus orientalis (Lund, 1793). It is a carnivorous scavenger which uses two foraging modes, probing or digging, to locate prey. Bivalves are the preferred food source and are opened efficiently by "wedging". Structural characteristics of the mouthparts and proventriculus are consistent with a predominantly soft flesh diet, with mechanical degradation primarily carried out by the gastric mill, the teeth of which are adapted for tearing and cutting flesh.

Two distinct modes of ingestion are used. The first, for small flesh items <10 mm³, is characterised by alternating action of the second maxillipeds and first maxillae. The second, for large and/or hard items >10 mm³, involves a tearing action between the third maxillipeds and mandibles. Ingestion is rapid, less than 5 s for a 10 mm³ piece of flesh and is facilitated by lubrication with mucus produced by tegumental glands in the paragnaths, membranous lobe and oesophagus. During ingestion, food is passed over the membranous lobe while its anterior lip retracts ventro-posteriorly, thus dilating the preoral cavity to allow quick and efficient swallowing of large food items.

Alimentary tract structure conforms to the general plan exhibited by all decapods, although a posterior pyloric sector appears to be unique to this scyllarid. The digestive gland primary ducts possess extensive musculature, suggesting they have an active role in fluid movement into and out of the glands. Tubule epithelia are differentiated into E-, R-, B- and F-cells, the structural characteristics of which are similar with those of other decapods. R-cells are involved in the storage of lipids and detoxification of metals (Ca, Mg, Al, K, Cr) by their accumulation in residual bodies. An absorptive role of B-cells is evident and immunohistochemical localisation of T. orientalis trypsin conclusively verified that F-cells are responsible for the production and secretion of digestive enzymes. Absence of trypsin from tissues in the oral region, proventriculus and hindgut, revealed that the digestive glands are the primary site of enzyme synthesis and secretion in the alimentary tract of T. orientalis.

The range and concentration of digestive enzymes produced by T. orientalis reflects its carnivorous diet, with the proteases trypsin and chymotrypsin produced in high concentrations. Detection of a-amylase and a-glucosidase indicate potential to hydrolyse glycogen, while N-acetyl-glucosaminidase suggests chitin is also a dietary component. Digestive fluid pH (5.9) is consistent with the acid pH optima of carbohydrases, verifying they are well adapted for extracellular digestion.

Trypsin was purified and shown to be a glycoprotein (35 kDa). The N-terminal amino acid sequence has strong homology to crustacean trypsins revealing their structure is highly conserved. This is confirmed by the cross-reaction of crustacean trypsins to the T. orientalis enzyme. The optimal (k/cat) and (k/cat/K/m), values for N-α-benzoylarginine- p-nitroanalide were 0.91 s⁻¹ and 9.7 x 10³ M⁻¹s⁻¹, respectively, with this specificity constant being lower than those reported for other crustacean trypsins. Inhibition studies indicated the presence of serine and histidine at the active site, which implicates a similar catalytic mechanism with all other serine proteases.

Item ID: 27170
Item Type: Thesis (PhD)
Keywords: Thenus orientalis; Slipper lobster; food acquisition; food digestion; food ingestion; digestive glands; enzyme production; enzyme secretion; digestive enzymes; extracellular digestion
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Appendix 3: Johnston, D.J. (1994) Functional morphology of the membranous lobe within the preoral cavity of Thenus orientalis (Crustacea: Scyllaridae). Journal of the Marine Biological Association of the United Kingdom, 74 (4). pp. 787-800.

Johnston, D. J, Hermans, J. M. and Yellowlees, D., (1995) Isolation and characterisation of a trypsin from the slipper lobster Thenus orientalis Lund. Archiv. Biochem. Biophys., 324(1). pp. 35-40.

Date Deposited: 03 Jun 2013 01:53
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