Mid-Atlantic Ridge. It occurs throughout the Mediterranean Sea, save for the northern waters of the Adriatic and Aegean Seas, and is absent from the Black Sea. This species primarily inhabits the continental slope, at depths of . However, it has been documented from water as shallow as in Norway, and as deep as in the eastern Mediterranean. The depths at which it is most common vary between regions, for example in the Bay of Biscay, off Portugal, in the Strait of Sicily, in the Catalan Sea, and in the eastern Mediterranean. Water temperature does not appear to be an important factor in determining the distribution of this species. Found on or near the bottom, the blackmouth catshark favors a muddy habitat. There is little evidence for segregation by sex. A number of studies in the northern and western Mediterranean have reported that adults occur deeper than juveniles. Other studies though have found no such pattern. It is possible that areas such as the waters off southern France offer a habitat suitable for sharks of all ages. Another explanation with some scientific support is that adults are most common at intermediate depths, while young sharks are restricted to shallower water and both adults and juveniles are found in deeper water. If true, the age-depth inconsistencies observed from previous research could have resulted from incomplete depth sampling. Description The reported maximum lengths attained by the blackmouth catshark varies from for Atlantic sharks and for Mediterranean sharks; a length record of may be dubious. Females attain a larger ultimate size than males. The maximum weight on record is . This species has a slender, firm body with a rather long, pointed snout comprising roughly 6–9% of the total length. The anterior rim of each nostril bears a large triangular flap, which divides the nostril into incurrent and excurrent openings. The eyes are horizontally oval and equipped with rudimentary nictitating membranes (protective third eyelids). Beneath each eye is a subtle ridge, and behind is a small spiracle. The mouth forms a short, wide arch, and bears moderately long furrows around the corners. The upper and lower jaws contain around 69 and 79 tooth rows respectively. Each tooth is small, with a narrow central cusp flanked by one or two smaller cusplets on either side. There are five pairs of gill slits, with the fifth pair over the pectoral fin bases. The two dorsal fins