(G.O. Sars, 1885)
Description
— Generic features. Carapace with anterior margin either broadly rounded or produced forward into a very short, obtusely triangular rostrum.
Antennal scale oval with distal spine and naked outer margin.
Proximal subsegment of carpo-propodus not swollen, longer than the succeeding sub-segment and separated from the second by a transverse articulation. Endopod of the first thoracic limb with lobes from second, third and fourth segments well developed; no nail. Thoracic limbs 3-8 with tarsus 5-11-segmented, the first of which is the longest and marked by transverse articulation. Pleopods of the male, first and second pairs rudimentary; third pair biramous, with both exopod and endopod short, tapering and unsegmented; fourth pair with exopod composed of five to six elements of the type usually found in the tribe; endopod very small, two-segmented; fifth pair rudimentary as in the female. Telson deeply cleft and exopod of uropod setose all round.
— Species. Telson deeply cleft. Naked outer margin of antennal scale marked distally by a spine or thorn. Antennal scale oval, apex considerably produced; thorn at distal; end of unarmed portion of margin not articualted. Fourth pleopod of male very long; armed distally with two "pincer" setae. Proximal subsegment of carpo-propodus not swollen, longer than the succeeding subsegments and separated from the second by a transverse articulation.
This species so closely resembles S. ornata that it is sufficient to indicate the differences:
1. S. kervillei is on the average a smaller form with the eyes larger.
2. The rostrum is more produced, though this difference may be very slight.
3. The unarmed portion of the outer margin of the antennal scale is longer, and the apex is less produced than in S. ornata.
4. The carpopropodus of the endopods of the thoracic limbs is usually composed of six subsegments in addition to the very small dactylus, whereas in S. ornata there are only five, except on very rare occasions.
5. Spines arming the inner margin of the endopod of the uropod are less even and tend to be grouped in series.
6. Telson somewhat broader and the cleft proportionally narrower than in S. ornata.
7. The colour is greyish white with spots of yellow, dark red or brown in the thoracic region. One dorsal and two lateral pigment spots on each abdominal somite; the proximal fourth of the telson is dark red, and this is succeeded by a white arborescent patch.
Depth range
Most common in depth 40-90 m; coastal, estuarians, but also known from the open ocean.
Remarks
The Genus Schistomysis is in many respects very similar to Paramysis, but may be distinguished from it by the form of the first subsegment of the carpropodus which, in Paramysis, is short and swollen, and in Schistomysis is longer and no more swollen than the more distal subsegments and is always considerably longer than broad.
Schistomysis kervillei is so similar in general form to S. ornata that it is extremely difficult to distinguish it unless one has the two species side by side. It was originally described as Mysis kervillei by G.O. Sars from specimens taken in the estuary of the Seine, and it has since been recorded from various places off the coasts of Britain and Europe. The species habits appear to be similar to those of S. ornata.
Distribution in the North Sea
South-eastern to north-eastern North Sea, shallow waters.
World distribution
E North Atlantic: 33-57°N; coastal; euryhaline, eurythermic.
[After Tattersall and Tattersall, 1951]