G.O. Sars, 1885
Description
The eye is small and spherical [T.microphthalma eye & rostrum ]. The ratio of the eye diameter and the carapace length is about 0.13.
Peduncle of first antenna: the lappet is a high dorsal lobe on the first segment, rounded posteriorly, extending forward over a short part of the second segment and, in lateral view, ending as an acute almost spiniform angle. The dorsal part of the second segment extends forward over the base of the third segment as a low cover. The third segment bears a low keel [T.microphthalma ped 1st ].
Rostrum with a short forward- and upward-pointing tooth at the apex of the thick, broadly triangular (ca 90° in dorsal view) frontal plate [T.microphthalma eye & rostrum ].
Carapace margin without denticles in the adult but a single pair is present in immature specimens.
Thoracic legs: the eighth thoracic leg is extremely minute, with the endopodite reduced and the exopodite normally developed. Leg 7 is smaller than the sixth, but of the same appearance and with the same number of segments (6). [T.microphthalma-drawing ]
Photophores are present in the eyes, thorax and abdominal segments 1-4.
Abdomen: the posterior margins of the fourth and fifth segments are slightly pointed (acuminate) mid-dorsally.
Petasma: the terminal process is nearly straight but sharply hooked at the distal tip. This hook extends barely beyond the end of the proximal process. The proximal process is obliquely curved, ending acutely; beneath the tip there are fine serrations. The distally hooked lateral process does not extend to the tip of the median lobe. There is a blunt lobe-like additional process [T.microphthalma petasma ].
Size
Adults are 20-41 mm, probably up to 50 mm (Mauchline, 1984).
Larval stages
No illustrations available.
Ecology
T. microphthalma is a food source for demersal fish.
Depth range
Considered as a mesopelagic species, probably living below the thermocline to mid-depths, around 500 m or deeper. Diurnal vertical migration is not likely (see Mauchline, 1984).
Distribution in the North Sea
T. microphtalma is unknown from the North Sea but is recorded from waters north of the North Sea (S. Hay, pers. com.).
World distribution
Reported from the northern temperate, subtropical, and tropical Atlantic and from the tropical Indian Ocean, but many records must be considered uncertain, particularly those from the tropics. Absent from the Mediterranean and not known from the Pacific.
Remark
T. microphthalma is difficult to distinguish from T. acutifrons. The petasma of T. microphthalma is distinct in the following ways: the tip of the terminal process is sharply curved (it is gently curved inT. acutifrons ) and extends beyond the tip of the proximal process (the proximal process extends well beyond it inT. acutifrons ).
[After Brinton et al., 1999].