Diagnosis: Somniosus pacificus differs from S. antarcticus by the following characters: interdorsal space about 70% of prebranchial length (vs. 80%); height of first dorsal fin about 3.7% of precaudal length (PCL) (vs. 3.0%); height of second dorsal fin about 3.4% of PCL (vs. 2.9%); number of turns in spiral valve 32-37 (mode 33) (vs. 36-41, mode 39); precaudal vertebrae 28-30 (mode 29) (vs. 30-31, mode 30) (Ref. 50224).

Description: Uniformly greyish-pink with bluish black fins; live specimens probably with white spots on dorsal surface (Ref. 6871). Short rounded snout, heavily cylindrical body and small precaudal fins, equal-sized dorsal fins, asymmetrical caudal fin with a well-developed ventral lobe (Ref. 6871), first dorsal fin on back closer to pelvic fins than pectoral fins, interdorsal space less than distance from snout tip to first gill openings, no short keels on base of caudal fin, upper teeth lanceolate, lower teeth with short, low, strongly oblique cusps and high narrow roots (Ref. 247).