DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



123 



right side of the viscera. There is a single typhlosole present along its 

 entire length. The stomach is of moderate size and internally is 

 similar in form to that of shallow water species of Nuculana ( Yonge, 

 1939). The gastric shield lines much of the left wall of the stomach. 

 To the right there is a large posterior sorting area with 13 ciliated 

 ridges. A deep caecum is ventral to the oesophageal aperture. Two 

 digestive ducts open close to the antero-dorsal margin of the poste- 

 rior sorting area and a single duct opens antero-dorsally close to the 

 oesophageal opening. 



As will be seen Nuculana acuta is remarkably similar in its shell 

 features and anatomy to Nuculana commutata. This similarity is 

 discussed under the latter species (p. 123). 



Nuculana commutata (Philippi 1844) 



Type specimen. ZMHU. 



Type LOCALITY. Pliocene, Palermo, Sicily. 



Cited specimen. BMNH 1995212 



Arcafragilis Chemnitz 1784, 199, pl.LV, fig.546. 

 Area pella Gmelin 1790 (non Linne), 3307. 

 Area minuta Brocchi 1814 (non Fabricius), 482, pl.XI,fig.4. 

 Nucula pella Payraudeau 1826 (non Linne), 64. 

 Lembulus deltoideus Risso 1826 (non Lamarck), 320, pi. XI, fig. 



164. 

 Nucula minuta Scacchi 1836 (non Fabricius), 4. 

 Nucula striata Philippi 1836 (non Lamarck), 64. 

 Nucula commutata Philippi 1844, 101. 

 Ledafragilis Jeffreys 1879,575. 

 Leda minuta Jeffreys 1856 (non Fabricius), 25. 

 Leda commutata Hanley 1863, pl.CCXVIII, figs, 80, 81. 

 Lembulus commutatus Monterosato 1 878, 6. 

 Leda (Portlandia) tenuis Sturany 1 896, 6. 

 Nuculana (Jupiteria) fragilis Nordsieck 1969, 9, pi. I, fig.02.25. 

 Nuculana (Jupiteria) commutata Smith and Heppell 1991, 56. 



Material: 









Cruise Sta Depth No 



(m) 



Lat 



Long 



Date Gear 



WEST EUROPEAN BASIN 

 Sarsia S29 119 16 



47'40.0'N 



05"00.0"W 



12.8.67 ES 



Shell description (Fig. 34) 



Shell moderately large, elongate, slightly inflated, rostrate, 

 ornamented with concentric ridges, pale straw-coloured perio- 

 stracum; radial ridge from umbo to antero-ventral margin; rostral 

 ridge well-defined, delimits posterior dorsal area, within this area a 

 faintly outlined escutcheon extending half the length of postero- 

 dorsal margin; lunule elongate, defined by fine ridge; less 

 well-defined ventral rostral ridge extends from umbo to postero- 

 ventral margin; umbos anterior to midline, inwardly directed; 

 antero-dorsal margin proximally straight, distally slightly concave 

 merging with rounded anterior margin to where it meets with ventral 

 limit of anterior radial ridge, ventral margin broadly concave, postero- 

 ventral margin sinuate where ventral rostral ridge meets margin, 

 posterior margin acute, slightly upturned, postero-dorsal margin 

 slightly raised with shallow angulation at limit of hinge plate; hinge 

 plate elongate, relatively broad, acute chevron teeth, 16 on both 

 anterior and posterior hinge plates of specimen 8.3mm total length; 

 ligament internal, amphidetic, triangular, extends slightly ventral to 

 hinge plate. 



Fig. 34. Nuculana commutata. Lateral and dorsal views of a shell, from 

 Sarsia station S29 from the West European Basin. Scale = I mm. 

 Maximum length of present specimens is 8.3mm. 



Internal morphology (Fig. 35) 



The internal morphology differs little from that of A 7 , acuta (Fig.32). 

 The most noticable differences are that N. commutata has less 

 attenuate palps with fewer palp ridges and larger adductor muscles 

 than does N. acuta. 



Other differences between the two species are that in A 7 , commutata 

 the ridge from the umbo to the antero-ventral margin is more 

 marked, the apices of the concentric ridges are less broad, the 

 postero-dorsal margin is not so raised and the shell is somewhat less 

 elongate in relation to its height. 



These differences are of degree and at that point where separation 

 into species rather than subspecies is a subjective judgement. Never- 

 theless, these differences are more marked than those between N. 

 commutata andN. illiricaCanozza 1987 (paratypes BMNH 1995213 

 examined by JAA), a species that has been recently described from 

 the northern Adriatic Sea(Carrozza, 1987). In contrasts commutata 



Fig. 35. Nuculana commutata. Internal morphology as seen from the 

 right side of a specimen from Sarsia station S29 from the West 

 European Basin. For identification of the parts see text-figure 7, p. 106. 

 Scale = 1mm. 



