Psednos Barnard 1927

Psednos Barnard 1927

Diagnosis (modified from Chernova and Stein, 2002). Ventral disk absent. Pseudobranchiae absent. One pair of nostrils. Mouth oblique, superior or terminal. Infraorbital sensory canal widely interrupted behind eye, consisting usually of six (5+1) or five (5+0) pores. Nasal pores widely spaced, the upper nasal pore opening higher and behind vertical through nostril. Suprabranchial pore far above top of gill opening. Pectoral fin of 13–17 rays, usually with a notch. Pectoral girdle with three (rarely four) radials, rounded or notched. Interradial fenestrae present or absent. Vertebrae 40–58. Vertebral column often but not always sharply curved dorsally, usually resulting in a humpbacked body deep at occiput, with anteriormost vertebrae forming a distinct angle with cranium. Pleural ribs absent. Hypural plate single, unslit. Caudal fin rays usually six, rarely five.

Two subgenera, Psednos sensu stricto and Protopsednos Andriashev 2003. Psednos s.s. is defined by V 40 –47, D 34–42, A 28–35, having three evenly spaced radials lacking notches and interradial foramina. Protopsednos has V 56 –58, D 48–50, A 41–43, and three radials (2+0+1) with notches and 1–2 interradial fenestrae. Validation of these subgenera awaits examination of more specimens.

Distribution. Eighteen species known from the Southern Hemisphere, of which at least eight are from New Zealand waters (Fig. 24). Six of the 18 are in Psednos s.s. and three more in P. Protopsednos. Assignment of the New Zealand species is problematic; all could be in Protopsednos but several do not fit well.

Psednos individuals are rare and usually very difficult to identify because they are often similar and differ in non-quantitative details. Frequently, valuable characters are damaged or destroyed during capture and examination. Three of the species included below were badly damaged and were distinguished by only a few characters (see Methods, above). Therefore, the following key should be used with caution and should not be considered definitive.