Nematobrachion boopis (Calman, 1896)
Etymology: Nematobrachion - thread arms; boopis - "an epithet of the goddess Athena meaning 'ox-eyed' "
Eye: The upper lobe is 1 to 2 times as wide as the lower lobe. The transverse region between the two lobes is scarcely constricted, and has a lightly pigmented band (N. boopis eye & rostrum).
Peduncle of 1st antenna: The lobe on the 1st segment is upright, narrow (in lateral view), distally rounded, and hood-like, extending above the base of the 2nd segment (N. boopis,).
Rostrum: There is no rostrum (N. boopis eye & rostrum).
Carapace: The frontal plate is broadly triangular, extending to the posterior limit of the eye. The gastric region is somewhat elevated anterior to the cervical groove but not domed, and with a short, low keel anteriorly. The carapace is without lateral denticles.
Thoracic legs: The 3rd thoracic leg is greatly elongated (N. boopis).
Abdomen: There are no median spines or keels. The 6th segment is twice as long as high (N. boopis).
Length: Adults are 20-25 mm.
Petasma: The terminal process is broad at the base, then narrows abruptly, with the distal two-thirds broadened and the tip with a shallow fold-like depression which is overhung by a low, short, acute projection. The proximal process is slender, longer, and arcs in a semi-circle. The lateral process is almost straight, and is acutely hooked. The hooked additional process is shorter (N. boopis petasma).
Thelycum: Described by Sebastian, 1966; Guglielmo and Costanzo, 1983.
Comments: The extremely broad upper lobe of the eye, and the absence of a rostrum are conspicuous characters.
ECOLOGY
N. boopis has been reported in the stomachs of planktivorous fishes.
HORIZONTAL DISTRIBUTION
N. boopis is widely distributed in the North and South Pacific 42°N-53°S, in the Atlantic 65°N-53°S, and the Indian Ocean, 10°N to about 50°S (N. boopis distribution).
VERTICAL DISTRIBUTION
N. boopis is the deepest living species of the genus and is considered mesopelagic. Adults are usually below 300 meters. They are not vertical migrators. N. boopis is lacking from the parts of the Eastern Tropical Pacific and northern Indian Ocean which are 02-deficient at mid-depths.
LARVAE
Undescribed.
Because little is known of this species, information is presented in a format different from that for other species. The only picture available for this species is a 7 mm juvenile (N. boopis A).
Mauchline (1985) gives the developmental pathways for furcilia larvae of N. boopis in samples from the Rockall Trough. The common pathway was C3 - 0 - 2' - 2"1' - 3"2' - 5". The following less common pathways were also found:
C3 - 0 - 1' - 1"4' - 5"
C3 - 0 - 2' - 2"2' - 4"1' - 5"
C3 - 0 - 3' - 3"2' - 5".
Mauchline notes that the furcilia larvae are distinguishable by the form of eye and the presence of a large oil globule in the thorax. The globule is about 1/6 of the volume of the thorax.
Pictures
N. boopis, juvenile
N. boopis A [juvenile]
key to larval illustrations