DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



81 



Material. 



Fig. 133 Portlandia abyssorum. Lateral views of three shells from 

 the right side to show variation in shape. Dorsal view of a shell 

 and detail of the hinge-plate of a left valve. Specimens taken from 

 a, Sta. 24, Galathea Expedition, Sierra Leone Basin (Type 

 specimen); b, c & d, Sta. 8528 1 , Cape Verde Basin; e, Sta. 8521 6 , 

 Cape Verde Basin. (Scales = 1.0 mm). 



Portlandia abyssorum (Knudsen 1970) 



Type locality. R.V. Galathea, Sta. 24, E., Atlantic off W. 

 Africa, 1950, 3°54'N, 8°22'W, Trawl, 3196 m. 



Type specimen. Holotype: Zoological Museum, University 

 of Copenhagen. 



Yoldiella abyssorum Knudsen 1970, 47, Fig. 29, pi. 1, Fig. 17. 



Cruise Sta DepthNo Lat Long Gear Date 



(m) 



CAPE VERDE BASIN 



Discovery 8521 6 3070- 6+2v 20°47.9'N 18°53.4'W WS 26. 6.74 

 3064 

 8528 1 3155- 72+2v 17°38.7'N 18°35.8'W WS 2.7.74 

 3150 - 17°38.3'N 18°34.9'W 



Atlantis II 148 31114-1 10°37.0'N 18°14.0'W ES 7.2.67 



31 3828 



149 3861 3 10°30.0'N 18°18.0'W ES 7. 2.67 



ANGOLA BASIN 















Atlantis II 195 



3797 



45 



14°40.0'S 



9°54.0'E 



ES 



19. 5.68 



42 196 



4612- 

 4630 



1 



10°29.0'S 

 - 10°29.0'S 



9°54.0'E 

 9°04.0'E 



ES 



21. 5.68 



CAPE BASIN 















Jean Charcot DS05 4560 



1 



33°20.5'S 



2°34.9'E 



DS 



30.12.78 



(Walvis) CP13 3550 



1 



32°18.1'S 



13°15.9'E 



CP 



12. 1.79 



Occurs at abyssal depths off the west coast of Africa, Cape 

 Verde, Angola & Cape Basins. Depth range: 3064-4630 mm. 



Shell description (Figs. 133 & 134). An accurate descrip- 

 tion is given by Knudsen (1970). Populations of this species 

 vary somewhat in the shape of the shell outline from that of 

 the type specimen to specimens with a more straight or 

 slightly concave postero-dorsal margin and a more convex 

 postero-ventral margin with intermediates between these two 

 extremes. 



Internal morphology (Fig. 135). In contrast to the 

 description of Knudsen (1970) there is an inhalent as well as 

 an exhalent siphon. The short ventral inhalent siphon is not 

 particularly obvious being much shorter than the exhalent, 

 however, sections show a twin siphon, the inhalent being 

 open ventrally. A siphonal tentacle originates on the left of 

 the siphon and there is a fairly well-developed feeding 

 aperture below. The adductor muscles are large, the anterior 

 being approximately twice the size of the posterior. The gills 

 are well-developed with up to 24 gill filaments. The labial 

 palps are large with a large number of internal ridges (up to 

 30), the number depending on the size of the individual. The 

 foot is large and extends anterior and ventral to the anterior 

 adductor muscle. It also has a large byssal gland. The cerebral 

 and visceral ganglia are elongate with a moderately thick 

 commissure. The pedal ganglia are large, elongate with large 

 associated statocyts. The hind gut forms a single loop on the 

 right side of the body and has a typhlosole along its length. 



Prodissoconch length: 187-198 |xm. Maximum recorded 

 shell length: 4.76 mm. 



This species at first sight might be confused with Yoldiella 

 biscayensis, however there are a number of differences. 

 These include: - the presence of a lunule and escutcheon; the 

 umbo is raised only slightly above the dorsal margin; the 

 posterior and postero-dorsal margin is faintly rostrate; the 

 prodissoconch is much narrower and is shorter in length; the 

 palps have many more ridges. 



