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Thysanopoda cornuta Illig, 1905

Etymology: Thysanopoda - tassel foot; cornuta - horned

Eye: The eye is nearly round, and is very small relative to the large body. The eye diameter : carapace length is about 0.08. There is a large rounded tubercle on the eyestalk at the inner anterior-dorsal edge of the eye (T. cornuta eye & rostrum).

Peduncle of 1st Antenna: A dorsal lobe on the 1st segment is heavy, and somewhat reflexed posteriorly, extending forward beyond the midpoint of the 2nd segment and terminating anteriorly as a short, upward-directed tooth situated above the inner dorsal part of the 2nd segment. The 2nd and 3rd segments are without processes (T. cornuta,).

Rostrum: The frontal plate extends forward, almost to the anterior limit of the eyes, as a thick shield, obtusely convex in dorsal view, terminating anterior-dorsally in a short, strong, almost vertical spine (T. cornuta eye & rostrum).

Carapace: The cephalic region is keeled dorsally, and there is a short crest at its highest point. A distinct cervical groove extends transversely across the carapace behind the head and it bifurcates on both sides of the carapace as H-shaped furrows. There are no lateral carapace denticles (T. cornuta).

Abdomen: The 4th and 5th segments each bear three small elevations, or keels, one mid-dorsal and two subdorsal, each supporting an elongate groove in which there are two rows of minute pits that may serve as secretory or sensory loci (T. cornuta dorsal abdomen), (T. cornuta abdominal keel). Lengths of the 5th and 6th segments are nearly equal. The posterior dorsal surface of the 6th segment is a flat trough bordered laterally by ridges. The telson bears 6-8 pairs of small dorsal spines. Photophores appear to be small and rudimentary, possibly not functional.

Petasma: In adult males (>50 mm in length) the terminal and proximal processes are somewhat curving, tapering acutely, and nearly equal in length. The lateral process is shorter, curved but scarcely hooked, and flanked by one or two short additional processes (T. cornuta petasma).

Thelycum: Described by Guglielmo and Costanzo, 1977.

Length: Adults are 50-120 mm.

Comments: Fresh specimens are a brilliant red color. The short stout rostal spine (T. cornuta eye & rostrum) is characteristic. The eye is a little larger than in T. spinicaudata and much larger than in T. minyops.

ECOLOGY
T. cornuta is a bathypelagic species. Stomach contents have been found to contain parts of a wide range of crustacea, commonly copepods, as well as fish vertebrae, chaetognaths and radiolaria (Nemoto, 1977).

HORIZONTAL DISTRIBUTION
T. cornuta is known in the Pacific from the Gulf of Alaska about to 30°S; in the Atlantic from about 40°N to 40°S; in the Indian Ocean from 12°N to 45°S (T. cornuta distribution).

VERTICAL DISTRIBUTION
Adults live below 1200 m, possibly to about 2500 m. Larvae and juveniles are below about 700 m (T. cornuta depth range).

LARVAE
See the development summary (T. cornuta Table) for the stage descriptors and length in stage.

Metanauplius - undescribed

Calyptopis - undescribed

Furcilia - undescribed

Pleopods - The developmental pathway is not known, only one form with less than 5" pleopods has been reported.

Young Juvenile - (T. cornuta A), (T. cornuta B)

Eye: The eye is round.

Carapace:
Frontal plate / rostrum - The frontal plate is broad with a distinct rostral spine, and extends well beyond the eyes.
Marginal spines - absent
Postero-dorsal spines - absent
Lateral denticles - A pair of denticles is present.
Lateral surface - The postero-lateral surface is smooth without ripple marks (seeT. egregia).

Thoracic legs: There is sequential development without elongate leg (s).

Abdomen:
Mid-dorsal spines - absent

Comments: The young juveniles are large and robust. Brinton (1975) notes that it is possible that the specimens described in the literature as T. cornuta may include some of T. spinicaudata .


Development
(T. cornuta Table), development summary for the stage descriptors and length in stage.

Pictures
T. cornuta, selected stages
T. cornuta A [juvenile]
T. cornuta B [juvenile]
key to larval illustrations

Thysanopoda cornuta