118 



J.A. ALLEN AND H.L. SANDERS 



Fig. 25. Tindariopsis agatheda. External lateral views of right side of two specimens of differing size to show change in shape with growth, a, from Knorr 

 station 301 and b, from Knorr station 293, both from the Guyana Basin; c, external dorsal view of a shell also from station 293. Scale = 1mm. 



Table 1. Measurements and ratios of shell parameters of the sample from 

 Knorr sta. 293. 



Length (L) 



Height (H) 



Post-umbonal (PL) 



PL/L 



H/L 



(mm) 



(mm) 



length (mm) 







6.00 



4.95 



3.00 



0.50 



0.83 



5.60 



3.95 



2.65 



0.47 



0.71 



5.00 



3.65 



2.20 



0.44 



0.73 



4.90 



3.65 



2.05 



0.42 



0.75 



4.70 



3.15 



1.95 



0.42 



0.67 



4.50 



3.10 



1.85 



0.41 



0.69 



4.45 



3.20 



1.85 



0.42 



0.72 



3.70 



2.55 



1.70 



0.46 



0.69 



3.45 



2.50 



1.45 



0.42 



0.73 



2.35 



1.58 



0.93 



0.39 



0.67 



2.05 



1.43 



0.93 



0.45 



0.70 



1.95 



1.30 



0.88 



0.45 



0.67 



1.83 



1.28 



0.83 



0.45 



0.70 



1.10 



0.88 



0.48 



0.43 



0.80 



Internal morphology (Fig. 26) 



The siphonal embayment is shallow and dorso-ventrally narrow. In 

 contrast, the feeding aperture is broad and well-supplied with radial 

 pallial muscles. The adductor muscles are small, the posterior 

 muscle is oval and the anterior muscle is circular in cross section. 

 The foot is large with a well-developed heel containing a large 

 'byssal' gland. The gland opens into the posterior limit of the pedal 

 groove via a small papilla. The anterior two-thirds of the margins of 

 the divided sole are broadly papillate. The palps are large with up to 

 25 ridges in the largest specimens. The gills are narrow ill-defined 

 with about 16 plates in the largest specimens. 



The mouth lies close to the posterior face of the anterior adduc- 

 tor muscle. The oesophagus opens into a large stomach and style 

 sac. The hind gut passes posterior to the style sac and stomach to 

 the dorsal side of the viscera and thence across the right side of 

 the body where it forms 8 coils before returning along the same 

 path to the dorsal side of the viscera and from there through the 

 heart and then dorsal to the posterior adductor muscle to the anus. 



Usually not more than six coils are visible, the others being 

 overlain by those to the outside of them. The form of the hind gut 

 is derived by 4 complete turns of the closely parallel anterior and 

 posterior lengths of the hind gut on the right of the body. This 

 particular disposition of the hind-gut is to be found in other 

 ledellids (e.g. L. ultima) and yoldiellids (e.g. Y. ella Allen, Sanders 

 and Hannah 1995) (Allen and Hannah, 1989; Allen, 1992; Allen, 

 Sanders and Hannah, 1995). 



The nervous system is similar in its arrangement to that of other 

 deep-sea protobranchs, however the cerebral and visceral ganglia 

 are noticably smaller and the commissures much finer than observed 

 in other species. 



Fig. 26. Tindariopsis agatheda. Internal morphology as seen from the 

 right side of a specimen from Knorr station 293. For identification of the 

 parts see text-figure 7, p. 106. Scale = 1mm. 



