Thysanopoda microphthalma G.O. Sars, 1885
Etymology: Thysanopoda - tassel foot; microphthalma - small eyed
Eye: The eye is small (T. microphthalma eye & rostrum). The eye diameter : carapace length is about 0.13.
Peduncle of 1st Antenna: The dorsal lobe on the 1st segment is high, rounded posteriorly, extending forward over a short part of the 2nd segment and, in lateral view, ending as an acute almost spiniform angle. The dorsal part of the 2nd segment extends forward over the base of the 3rd segment as a low cover. The 3rd segment bears a low keel (T. microphthalma,).
Rostrum: There is 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: The margin is without denticles in the adult (T. microphthalma) but a single pair is present in immature specimens.
Abdomen: The posterior margins of the 4th and 5th segments are slightly pointed (acuminate) mid-dorsally, as in T. orientalis (but not T. acutifrons).
Length: Adults are 20-41 mm.
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).
Thelycum: Described by Einarsson, 1942,1945; Guglielmo and Costanzo, 1977.
Comments: T. microphthalma 's similarity to T. acutifrons and T. orientalis has made identification difficult. The petasma of T. microphthalma is distinct in the following ways: In T. microphthalma the tip of the terminal process is sharply curved (it is straight and spoon-like inT. orientalis and gently curved inT. acutifrons) and extends beyond the tip of the proximal process (the proximal process extends a little beyond the terminal process inT. orientalis and well beyond it inT. acutifrons).
The forward dorsal tip of the pedunclar lappet (lateral view) (T. microphthalma,) is more acutely spiniform than in T. orientalis (T. orientalis,) and less elevated above the second peduncular segment than in T. orientalis .
ECOLOGY
T. microphthalma is a food source for demersal fish.
HORIZONTAL DISTRIBUTION
T. microphthalma has been 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. Unless based on the adult males, this species can be confused with T. orientalis and T. acutifrons . The most northern record is west of Ireland and the most southern, off the Cape of Good Hope, 35°S. It is absent from the Mediterranean and is not known from the Pacific (T. microphthalma distribution).
VERTICAL DISTRIBUTION
T. microphthalma is considered a mesopelagic species, probably living below the thermocline to mid-depths, around 500 m or deeper.
LARVAE
Undescribed.
Brinton (1975) suggests that the description and figures of T. acutifrons may prove useful in recognizing larvae of the other members of the acutifrons-orientalis-
microphthalma group.
Einarsson (1945) reports that the pleopod developmental pathway is 3' - 3"2' - 5".