Nematoscelis lobata Hansen, 1916
Etymology: Nematoscelis - thread leg; lobata - lobed
Eye: The eye is bilobed and small-medium in size, slightly larger than in N. atlantica. The upper lobe is about as wide as the lower lobe or a little narrower (N. lobata eye & rostrum).
Peduncle of 1st Antenna: The dorsal part of the 1st segment ends as an angular forward directed tip (N. lobata,), as in N. atlantica.
Rostrum: In the female the rostrum is long, slender, and narrowly acute, reaching almost to the anterior limit of the eye. In the male the rostrum is short but acute, reaching just forward of the posterior limit of the eye (N. lobata rostrum).
Carapace: In the male the frontal plate bears a distinctly elevated keel, unique to this species, curving downward from the small mid-dorsal keel (on the thoracic dome) to the base of the short rostrum. In the female, the keel on the frontal plate is much lower than in the male and also extends to the base of the much longer rostrum. A lateral denticle is present in the male, but is lacking in the female.
Thoracic legs: The 1st thoracic leg has the dactylus with a concave, setae-bearing inner margin, as in N. atlantica. The propodus has a single row of setae on the inner margin. The elongate 2nd thoracic leg has a cluster of long apical bristles arising from both the dactylus and propodus (N. lobata thoracic leg).
Abdomen: The abdomen is slender and there are no dorsal spines or keels (N. lobata).
Length: Adults are 12-14.5 mm.
Petasma: The spine-shaped process is distinctly longer and more slender than the similarly curving terminal process. The proximal process is broad at the base, tapering to a sub-acute tip. The short lateral process sharply tapers distally, and is less than half as long as the proximal process. The median lobe is extremely broad throughout its length, and nearly as broad as high, the inner distal corner terminating in a subacute angle (N. lobata petasma).
Thelycum: Described by Costanzo and Guglielmo, 1980.
Comments: Gopalakrishnan (1975) pointed out that, on the basis of the structure of the first thoracic leg, N. lobata is more closely related to N. atlantica than to N. microps. The strongly keeled male frontal plate and the unique shape of the remarkable median lobe of the petasma are conspicuous specific characters. Apparently, the name lobata derives from this lobe.
ECOLOGY
N. lobata appears to have geographically restricted neritic tendencies, a curious habitat considering the other clearly oceanic, widely ranging Nematoscelis species. (cf. Stylocheiron indicum is similarly restricted, in relation to other Stylocheiron species.) It is a swarming species and is a food source for fishes.
HORIZONTAL DISTRIBUTION
N. lobata is known only from the western slope and shelf waters of the Philippines, from Luzon to Mindanao and to southeast of Mindanao (N. lobata distribution).
VERTICAL DISTRIBUTION
Hansen (1916) reported immense numbers at night at the surface and in similarly shallow tows in embayments and at anchorages. Scattered individuals have been caught in a few deeper offshore tows near the Philippines (Hansen, 1916; Brinton, 1975).
LARVAE
Undescribed.
According to Gopalakrishnan (1975) the furcilia larvae of N. lobata are very similar to those of N. atlantica . (Nematoscelis A)
Pictures
N. lobata, selected stages
Nematoscelis A [species characters]
key to larval illustrations