DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



127 



Fig. 41. Propeleda carpenteri. External lateral views of the right sides of 

 two small shells to show differences in shape from the specimen 

 illustrated in text-figure 40. Specimens taken from Atlantis II station 239 

 from the Argentine Basin. Scale = I mm. 



The concentric ridges on the shell of the present specimens while 

 not particularly marked are more so than those described by Dall, 

 though the syntypes that we have examined are dead valves that are 

 somewhat worn (Fig. 39). Our specimens also are very slightly more 

 anteriorly extended than the syntypes, though the characteristic 

 antero-dorsal curvature of the shell margin is the same. Our speci- 

 mens correspond well with the figures given by James ( 1 972, figs 67 

 and 68). These latter come are from similar depths (2340-2627m) to 

 some of our own. It would appear that specimens from mid to lower 

 slope differ slightly from those taken at shallower depths however, 

 we regard the differences as being at most infrasubspecific. 



There is a marked change in shape during growth. Juveniles are 

 much shorter than the adults and subsequent growth involves in- 

 creasing elongation of the post-umbonal shell. The prodissoconch is 

 extremely large measuring 630um in length. 



Internal morphology (Fig.42) 



The adductor muscles are oval in cross-section, the posterior being 

 the more fusiform, both are set some distance in from the shell 

 margin. The posterior adductor muscle lies opposite the limit of the 



posterior hinge plate, the anterior muscle is attached to the shell just 

 dorsal of the mid-horizontal shell axis. The siphonal embayment is 

 elongate, the siphons are slender and entire. The anterior sense organ 

 is small in size. 



The foot lies in the anterior half of the mantle cavity in preserved 

 specimens, it is relatively elongate and has numerous small papillae 

 present along the margins of the sole. The palps are small, each 

 bearing an extremely long, narrow, palp proboscis. Depending on 

 the size of the specimen there are up to 17 palp ridges. The gills are 

 elongate, slender, and have up to 17 plates. 



The course of the hind gut is similar to that in Nuculana in that it 

 passes to the right side of the body where it forms a broad loop that 

 passes close to the posterior wall of the anterior adductor muscle. 

 The stomach is large and occupies a vertical position in the posterior 

 part of the visceral mass. The digestive gland is extensive occupying 

 much of the antero-dorsal visceral space. 



Propeleda louiseae (Clarke 1961) 



Type specimen. Hoiotype, MCZ 224958. 



Type locality. R. V. Vema biology station 121, Argentine Basin, 

 1000 miles ESE of Buenos Aries, 5105 metres. 



Cited specimens. BMNH 1995058 



Nuculana (Thestyleda) louiseae Clarke 1961, 375, pl.l, fig. 7. 



Material: 



Cruise 



Sta Depth No Lat 

 (m) 



Long 



Date Gear 



ARGENTINE BASIN 

 Atlantis II 242 4382- 25 

 60 4402 



243 3815- 2 



3822 

 247 5208- 2 



5223 

 256 3906- 3 

 3917 



38"16.9'S 51"56.1'W 13.3.71 ES 



3736.8'S 52"23.6'W 14.3.71 ES 



43"33.0'S 48*58. l'W 17.3.71 ES 



37"40.9'S 52*19.3'W 24.3.71 ES 



Fig. 42. Propeleda carpenteri. Internal morphology as seen from the right side of a specimen taken from Atlantis II station 239 from the Argentine Basin. 

 For identification of the parts see text-figure 7, p. 106. Scale = 0.5mm. 



