Thysanopoda egregia Hansen, 1905
Etymology: Thysanopoda - tassel foot; egregia - surprising, excellent
Eye: The eye is round and, in the adult, very small relative to the large body (T. egregia eye & rostrum). The eye diameter : carapace length is about 0.10. For eye size in relation to developmental stage see Brinton (1987).
Peduncle of 1st Antenna: The dorsal-anterior lobe on the 1st segment consists of a reflexed ridge encasing the elevated proximal part of the 2nd segment. In lateral view, the anterior (inner) limit of the lobe merges with 2nd segment and does not drop down to it angularly. There is an anteriorly-directed, scarely elevated tooth at the anterior limit of the lobe. The 2nd and 3rd segments are without processes (T. egregia,).
Rostrum: The frontal plate has a thick keel which, at its anterior limit, curves conspicuously downward along a 90° arc, terminating as a low, transverse ridge along the almost truncated (in dorsal view) anterior edge of the frontal plate (T. egregia eye & rostrum ).
Carapace: The head and gastric regions are heavily keeled, with a short crest at the highest point. A distinct dorso-lateral transverse cervical groove separates the head from the thorax. There are no lateral carapace denticles (T. egregia).
Abdomen: The 4th and 5th segments each bear three small posterior keels, one mid-dorsal and two subdorsal, each being adjacent to what appear to be elongate grooves containing rows of minute pits --possibly sensory or secretory (T. egregia dorsal abdomen) (T. egregia abdominal keel). The 6th segment is equal in length to the 5th or a little shorter. The posterior dorsal surface of the 6th segment is a flat trough bordered laterally by ridges. The telson bears two dorsal rows of numerous small spines.
Length: Adults are is 51-62 mm.
Petasma: This structure, from the largest male specimens (> ca. 45 mm) appears to be mature, though differing greatly from other species with respect to the median lobe. The median lobe is short, not much longer than the inner lobe and, distally, bears a variable number (2-5) of short curved processes; these may be a lateral process plus additional processes (see Brinton, 1987, for the variability). The terminal process and the longer proximal process are curved, tapering to acute tips (T. egregia petasma).
Thelycum: Described by Guglielmo and Costanzo, 1977.
Comments: Fresh specimens are a brilliant purple-red color, differing from the typically red color of deep-sea species.
ECOLOGY
T. egregia is a bathypelagic species. The food consists mainly of zooplankton and micronecton, notably copepods, chaetognaths, and fish, e.g. Cyclothone (Nemoto, 1977).
HORIZONTAL DISTRIBUTION
T. egregia is known from 40°N to 53°S in the Pacific, from 3°S to 45°S in the Indian Ocean, and, in the Atlantic, from the Gulf of Mexico and west of North Africa (T. egregia distribution).
VERTICAL DISTRIBUTION
Adults have been caught within the 800-2000 m range. Furcilia larvae occur as shallow as 300 m (T. egregia depth range).
LARVAE
See the development summary (T. egregia Table) for the stage descriptors and length in stage.
Metanauplius - undescribed
Calyptopis - undescribed
Furcilia and young Juvenile - (T. egregia A), (T. egregia B)
Eye: The eye is round.
Carapace:
Frontal plate / rostrum - The frontal plate is truncate with a small rostral spine, and reaches to the level of the eye.
Marginal spines - absent
Postero-dorsal spines - absent
Lateral denticles - A pair of denticles is present.
Dorsal keel - A dorsal keel is present.
Lateral surface - The postero-lateral surface has curving ripple marks.
Thoracic legs: There is sequential development without elongate leg (s).
Abdomen:
Mid-dorsal spines - absent
Segments 1-5 - There are partial dorsal sutures on segments 1-5.
Segment 6 - There is a strong spiniform process on the dorso-lateral margin of segment 6.
Pleopods - The developmental pathway is not known, only a few forms with less than 5" pleopods have been reported.
Telson:
Postero-lateral spines - PL3 is longer than PL2.
Lateral spines - A pair of lateral spines is present.
Terminal spines - In a 14.5 mm furcilia larva with 5" and 7 terminal spines, the central terminal spine has lengthened and the 3 spines on either side are smaller.
Comments: The furcilia larvae and juveniles are large and robust. The unique lateral carapace ripple marks and shape of the frontal plate are characteristic of the species. The carapace ripple marks are absent in the adult.
Development
(T. egregia Table), development summary for the stage descriptors and length in stage.
Pictures
T. egregia, selected stages
T. egregia A [furcilia]
T. egregia B [furcilia, juvenile]
key to larval illustrations