Thysanopoda spinicaudata Brinton, 1953
Etymology: Thysanopoda - tassel foot; spinicaudata - spiny tailed.
Eye: The eye is very small and oval (T. spinicaudata eye & rostrum). The eye diameter : carapace length is about 0.09.
Peduncle of 1st Antenna: The heavily setose, elevated dorsal lobe on the 1st segment extends forward over the 2nd segment and terminally has an acute tooth which is bulbous at its base and is directed upward and laterally. The 2nd and 3rd segments are without processes (T. spinicaudata,).
Rostrum: The dorsal anterior end of the frontal plate extends about to the most forward part of the eye and is armed with a long, strong vertical spine (T. spinicaudata eye & rostrum). Viewed laterally, the length of the dorsal spine is about equal to the distal thickness of the frontal plate. The anterior margins of the frontal plate, lateral to the spine, are slightly upturned.
Carapace: The carapace is without lateral denticles in the adult. A cervical groove crosses the dorsal part of the carapace. Lateral furrows are continuous with the cervical groove. A low middorsal keel is present on the carapace, extending from the vertical spine to the cervical groove. A longitudinal submarginal ridge extends along the lateral margin of the carapace posterior to the subvertical grooves (T. spinicaudata).
Abdomen: The 5th and 6th segments are near equal in length. The 4th and 5th segments each bear three small posterior keels (one dorsal, two subdorsal), each adjacent to an elongate groove containing what appear to be sensory or secretory pits (T. spinicaudata dorsal abdomen). On each side of the 6th segment, below the midline, there is a heavy, posteriorly directed spine (T. spinicaudata abdomen). The posterior dorsal surface of the 6th segment is a flat trough bordered laterally by ridges. The telson is robust and armed with numerous (>100) dorsal spines in indistinct rows; the postero-lateral pair of telson spines are heavy and more than 0.5x the length of the telson. Photophores are not evident.
Length: Adults are up to 150 mm.
Petasma: The terminal and proximal processes are slightly curved, similar to those in T. cornuta and T. minyops but thicker. The median lobe is broad and spadelike, as inT. cornuta, and the lateral and additional processes are undistinguished (T. spinicaudata petasma).
Thelycum: Not yet described.
Comments: T. spinicaudata is brilliant red in color (T. spinicaudata photo). The frontal plate in dorsal view, is more broadly oblique anteriorly than inT. cornuta. The body, and particularly the 6th abdominal segment and telson, are generally spiny and robust.
ECOLOGY
T. spinicaudata is the largest known euphausiid and is bathypelagic. Of the two stomachs examined, one contained fish scales and the other, crustacean parts and chaetognaths.
HORIZONTAL DISTRIBUTION
The few records from the Pacific are between 35°N and 43°S, and there is one record from the Arabian Sea in the Indian Ocean. It is not known from the Atlantic (T. spinicaudata distribution).
VERTICAL DISTRIBUTION
Adults and immatures have been caught in tows reaching the 2000-3000 m depth stratum (T. spinicaudata depth range).
LARVAE
Undescribed.