36 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 



of the oesophagus and lateral to the hind gut loop. 



The cerebral ganglia are relatively small and oval while the 

 visceral ganglia are elongate and relatively thickened. The 

 pedal ganglia are large and elongate/oval, conjoined, and 

 each has a large dorsal statocyst associated with it and which 

 contains numerous small refractile crystals. 



The mouth is displaced posteriorly to a small extent. It 

 opens into a relatively long, ciliated oesophagus which curves 

 first anteriorly to the posterior face of the anterior adductor 

 before passing posteriorly to the stomach. The oesphagus is 

 positioned almost centrally rather than dorsally within the 

 body. The longitudinal axis of the stomach and style sac lies 

 diagonally within the body, the style sac penetrating into the 

 upper half of the foot. The stomach and style sac are large, 

 taking up much of the central body space. Externally the 

 stomach is brown in colour. A large gastric shield covers part 

 of the dorsal wall and extends laterally, mainly to the left 

 side. To the right of it are approximately nine sorting ridges. 

 The organization of the stomach appears similar to that 

 described for Ledella (Allen & Hannah, 1989). The stomach 

 is cradled by the pedal retractor muscles. The digestive 

 diverticla are in three parts which for the most part lie 

 anterior to the stomach but also to the right and left of the 

 body. A duct from the right diverticulum joins the stomach 

 on the right anterior face just ventral to the oesophageal 

 opening. Immediately posterior to this, a duct from one of 

 the two left diverticula enters the stomach on the lower left 

 side (Fig. 49b). The third diverticulum opens into the stom- 

 ach immediately below the tooth of the gastric shield. The 

 epithelial cells which line these ducts contain highly refractile 

 golden granules. In the case of the third diverticulum the duct 

 is reduced to a small collar of cells around the aperture. 

 Material was present in the lumen of this diverticulum but not 

 in the other two diverticula. 



From the style sac, the hind gut passes posteriorly into the 

 foot, as far as the pedal ganglia. It then passes anterior for a 

 short distance between ganglia and byssal gland and then 

 takes a dorsal course parallel to the posterior margin of the 

 foot to a point immediately ventral to the ligament. It then 

 forms a loop on the right side of the body which skirts the 

 posterior face of the anterior adductor and then passes 

 dorsally and posteriorly parallel to shell margin to the anus. 

 A deep typhlosole is present along the entire length of the 

 hind gut. Slight variations in the arrangement of the loop of 

 the hind gut are seen in this species. Material in the gut 

 consists of fine clay particles and skeletal fragments of various 

 kinds. 



The sexes are separate. The gonads overlie the lateral and 

 dorsal sides of the viscera of the body. Gonads are present in 

 all specimens over 2 mm in length. Numbers of ova are 

 relatively high and vary with the size of the animal. A 

 maximum of c.730 ova were counted in a specimen 3.54 mm 

 in length. The maximum observed diameter of the ova range 

 from 126-190 |xm. There is some indication of an annual 

 reproductive cycle. Ova of maximum size were present in 

 October and February. April and June samples show little 

 ovarian development, but increasing maturity was observed 

 in July and August. The gonadial apertures open into the 

 supra-mantle cavity, close to those of the kidney, anterior to 

 the posterior pedal retractor muscle. 



The kidney is well-developed. It lies anterior to the poste- 

 rior pedal retractor muscle and extends on either side of the 

 stomach, tapering to its anterior limit close to the lateral 

 pedal retractor mucles. The kidney epithelium is a single 



layer of cuboid cells. The heart, through which the hind gut 

 passes is well-developed in this species with numerous muscle 

 fibres in a relatively thick-walled ventricle. 



Distinctive features include the hind gut on the right hand 

 side of body forming an extended single loop which turns 

 back on itself; the light and dark banding pattern of shell, and 

 the more rounded posterior adductor muscle. The hind gut, 

 although similar, is simpler in form than that in Yoldiella 

 jeffreysi. 



Yoldiella frigida Torrell 1859 



Type locality. Spitzbergen, Ice Sound 55 m. 



Type specimen. Holotype not known; lectotype (desig. A. 

 Waren, 1989) Swedish Museum of Natural History No. 1986. 



Yoldia frigida Torrell 1859, p. 148, pi. 1, Fig. 3; Friele 1878, p. 



222; Leche 1878, pi. 1, Fig. 6 a-d; Sars G.O. 1878, pi. 4, 



Fig. lla-b; Friele 1879, p. 266. 

 Leda frigida Jeffreys 1870, p. 440; Jeffreys 1879, p. 570. 

 Pordandia frigida Norman 1893, p. 344, p. 364; Posselt 1898, 



p. 34-35; Friele & Grieg 1901, p. 15; Hogg 1905, p. 112; 



Jensen 1905, p. 320; Grieg 1909, p. 534; Ohdner 1915, pi. 



1, Figs. 30-32; 

 Pordandia frigida Grieg 1916, p. 8; Ockelmann 1958, pi. 1. 



Fig. 14. 

 Pordandia (Yoldiella) frigida Soot-Ryen 1939, p. 9; Clarke 



1963, p. 100, pi. 2, Figs. 6-8. 

 Yoldiella frigida Soot-Ryen 1958, p. 10; Waren, 1989; Figs. 



7E&F&10G&H. 



Material. 



Cruise Sta Depth No 



Lat 



Long 



Geai 



Date 



(m) 











NORTH AMERICAN BASIN 











Atlantis 4 400 304 



39°56.6'N 



70°39.9'W 



AD 



30. 8.62 



Chain 58 105 530 121 



39°56.6'N 



71°03.6'W 



ET 



5. 5.66 



Chain 88 207 805- 153 



39°51.3'N 



70°54.3'W 



ES 



21. 2.69 



811 



39°51.0'N 



70°56.4'W 







WEST EUROPEAN BASIN 











Thalassa 2425 700 1 



48°28.9'N 



09°44.0"W 



PBS 



25.10.73 



Jean Charcot DS04 619 1 



57°23.0'N 



11°07.0'W 



DS 



17. 6.76 



Incal DS03 609 16 



57°25.1'N 



11°03.7'W 



DS 



17. 6.76 



In addition to the above, material from Ingolf Sta. 115 (det 

 Ockelmann), Spitzbergen, Franz Joseph Fjord, East Green- 

 land (USNM No. 219726 det. Odhner) and off Martha's 

 Vineyard Sta. 934 (USNM No. 193343 det. Verrill & Bush) 

 has been examined. 



Predominantly a North Atlantic high arctic species from 

 shelf seas and upper slope depths (Waren (1989). Clarke 

 (1963) reports it as being present at abyssal rise depths but 

 there must be some doubt about this. There is some indica- 

 tion that in north temperate seas at the southern extremity of 

 its range the population is found deeper at the shelf slope 

 break, thus suggesting a relationship with temperature. 

 Greenland, Jan Mayen, Spitzbergen, Novaya Zemlya, Kera 

 Sea, West Siberia, Iceland, North American and West Euro- 

 pean Basins (see Ockelmann (1958) for other more doubtful 

 records). Depth range: 5-811 m. 



Shell description (Fig. 50 & 51). Shell subelliptical, 



