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Nematoscelis microps G.O. Sars, 1883

Etymology: Nematoscelis - thread leg; microps - small eyed

Eye: The eye is bilobed and medium in size. The height-of-eye/carapace length = about 0.2. The two lobes are approximately equal in width, but the upper lobe is consistently shorter in vertical dimension (N. microps eye photo).

Peduncle of 1st Antenna: The 1st segment ends distally as a short angle, not extending forward of the joint with the 2nd segment (N. microps,).

Rostrum: It is short or lacking in the male, acute in the female and reaching to the anterior limit of the eye (N. microps dorsal head) (N. microps rostrum). Lateral margins of the frontal plate flare upward and outward, providing the plate with an elevated appearance in lateral view (N. microps eye & rostrum).

Carapace: There is a low but prominent dorsal keel on the anterior part of the carapace. A denticle is present on the lateral margin of the carapace in the male, but it is lacking in the female.

Thoracic legs: The dactylus of the 1st thoracic leg is straight, evenly tapering, with a single row of setae, and no additional dorsal setae. The propodus has a strongly convex inner margin bearing 8-9 setae in a single row. The elongate 2nd thoracic leg has a cluster of long apical bristles arising from both the dactylus and propodus (N. microps thoracic leg).

Abdomen: There are no dorsal spines or keels (N. microps).

Length: Adults are 12-20 mm.

Petasma: The spine-shaped and terminal processes extend near equi-distantly, the terminal being a little longer. The proximal process is thicker and longer than the terminal process, terminating bluntly. The lateral process is stout, shorter than the terminal and with a rounded tip (N. microps petasma).

Thelycum: Described by Einarsson, 1942; Sebastian, 1966; Costanzo and Guglielmo, 1980.

Comments: The well-defined dorsal keel on the carapace, the sexually dimorphic rostrum, and the shape of the propodus of the first thoracic leg are particularly useful characters. The eye of this species is slightly larger than in N. gracilis and N. atlantica.

The occurrence of conspicuously enlarged ventral abdominal photophores, together with lens-like dorsal humps on the same abdominal segments, above those photophores, has been observed occasionally in males of N. microps. The phenomenon has been discussed by Einarsson (1942), Taniguchi (1966), James (1973) and Gopalakrishnan (1975).

ECOLOGY
N. microps is a warm-water cosmopolite in all 3 ocean basins. The 13°C isotherm at 200 m depth lies along the approximate limit of distribution. N. microps is a food source for fishes.

HORIZONTAL DISTRIBUTION
N. microps ranges 40°N-35°S in the Atlantic and Pacific but is lacking in the Mediterranean Sea, the California and Peru-Chile current systems and in the Eastern Tropical Pacific's 02-deficient zones. Similarly, it is lacking in most of the Indian Ocean's 02-deficient region north of the equator but extends to about 35°S (N. microps distribution).

VERTICAL DISTRIBUTION
Adults are at depths of 200-400 m at night, rising in the thermocline to about 100-200 m by day.

LARVAE
See the development summary (N. microps Table) for the stage descriptors and length in stage.

Metanauplius - undescribed

Calyptopis - undescribed

Furcilia - (3 stages)

Carapace:
Frontal plate / rostrum - The rostrum is triangular, relatively broad and stout, and acute.
Marginal spines - absent
Postero-dorsal spines - absent
Lateral denticles - A pair of denticles is present.
Dorsal keel - A large, platelike keel is present.

Thoracic legs: There is precocious growth of Leg 2, the elongate leg of the adult. During the furcilia phase the dactylus develops spines.

Abdomen:
Mid-dorsal spines - absent

Pleopods: The developmental pathway is 1'- 1"3'- 4"1' - 5".

Telson:
Postero-lateral spines - PL3 is longer than PL2.
Lateral spines - One pair of lateral spines is present.
Terminal spines - The terminal spines each have a pair of conspicuous sub-spines and have setules proximal to the subspines.

Comments: Brinton (1975) notes that the larvae of the N. atlantica-N.microps-N. gracilis complex of subtropical-tropical Nematoscelis species have proven difficult to identify.

The characters used to identify the furcilia larvae of Nematoscelis species are carapace frontal plate and rostrum, carapace dorsal keel, pleopod developmental pathway, and armature of terminal telson spines. See Nematoscelis larval characters (Nematoscelis A) and (Nematoscelis B).

Development
(N. microps Table), development summary for the stage descriptors and length in stage.

Pictures
N. microps, selected stages
Nematoscelis A [species characters]
Nematoscelis B [species characters]
key to larval illustrations

Nematoscelis microps