WOOD' 

 THE GUT OF NEBALIACEA V ^J9if' 



MASS 



By Helen G. Q. Rowett, Grisedale Scholar, Manchester University 



INTRODUCTION 



MUCH attention has been paid by Cannon, Manton, Lowndes and others to the ' feeding mechanisms ' 

 of Crustacea, but no attempt has so far been made to correlate changes in the structure of the gut 

 with the type of food available and the condition in which it is passed into the mouth. For this purpose 

 it is necessary to compare members of one group which have different habits and habitats rather than 

 isolated examples from different groups. A survey of the Nebaliacea has therefore been made with 

 the object of discovering how far the structure of the gut shows group resemblances and how far it 

 may be associated with the environment and habits of the species concerned. 



METHODS 

 With the exception of Nebalia bipes, material for this investigation was limited to Discovery specimens 

 of Nebaliopsis typica and Nebaliella extrema kindly made available by Professor Cannon. 



Reconstructions were made using transverse sections of Nebaliopsis typica specimen E {Discovery 

 Reports, 1931, vol. in) and sagittal sections of half of specimen F2 (op. cit.) and the unsectioned 

 other half of this specimen. From these reconstructions Figs. 4, 5, 6 C and 7 A were made. 



The single specimen of Nebaliella extrema was sectioned transversely, and the reconstructions 

 shown in Figs. 2, 3, 6 B and 7 C were obtained. 



Besides sectioned material the cast skins of Nebalia bipes were examined and living specimens were 

 watched in a jar with sea water and some of the mud from their usual habitat in Rum Bay, Plymouth, 

 and also isolated in dishes under a microscope. Carmine was fed to some and, using strong illumina- 

 tion, the passage of the red particles through the gut was easily seen through the semitransparent body. 



THE STRUCTURE OF THE GUT OF NEBALIA BIPES (Fabricius) 



The structure of the gut of Nebalia was described in great detail by Claus (1889) and later by Jordan 

 (1909, 19 1 2) in papers comparing the pyloric section with that of Idothea, Ganimanis and Astacus. 

 A detailed description need not, therefore, be given here, but for the sake of clarity in making com- 

 parisons with other types Figs, i, 6 A and 7 B have been made which show the various parts and 

 associated musculature. 



In one important respect, however (which is not mentioned by Jordan), Claus's description is 

 definitely incorrect. The structures which he describes as chitinous pads with thickened striations 

 are actually rows of very strong evenly set setae (^.^.1 in Fig. i) which with the spines (g.s.2) form a 

 tube in which grinding takes place. 



THE STRUCTURE OF THE GUT OF NEBALIELLA EXTREMA {i. Thide) 



I. FORE-GUT 

 The structure of the oesophagus and cardiac region of the stomach of A^. extrema is, as Thiele (1905) 

 says, very like that of Nebalia. Certain important differences may, however, be noted. 



There are many fewer setae throughout. The anterior median projection {a.m.p.) is much reduced 

 and the lateral fanlike plate of setae which is found on the right side only in Nebalia {l.p. Fig. i) is 

 absent. The spatial relations of the homologous parts are so altered that there is no grinding tube 

 such as is seen in Nebalia. As shown in Figs. 2 and 3 A, the spines {g.s.o) are ventral instead of dorsal 



