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Stylocheiron maximum Hansen, 1908

Etymology: Stylocheiron - a column/hand; maximum - largest

Eye: The upper lobe is approximately equal in width to the lower lobe, width of upper lobe : width of lower lobe varies from 0.8 to 1.0 (S. maximum eye & rostrum). There are no conspicuously enlarged crystalline cones, although facets of the upper lobe are somewhat larger than those of the lower lobe.

Peduncle of 1st Antenna: As in generic diagnosis in Higher Taxa (S. maximum lappet lacking).

Rostrum: The frontal plate is produced into an acute rostrum which reaches about to the anterior limit of the eyes (S. maximum dorsal head photo).

Carapace: The gastric region is domed, with a small median keel (S. maximum).

Thoracic legs: The 3rd thoracic leg is elongated and bears a true chela in which the elongate dactyl segment is distally curved and bears a cluster of small grasping teeth. The dactyl segment is opposed by a slender hook of similar length extending from the propodus (S. maximum thoracic leg) (S. maximum chela photo).

Abdomen: There are no mid-dorsal keels present. The 6th segment length : height is approximately 2.4.

Length: Adults are 20-30 mm.

Petasma: The literature reports considerable variability in the shape of the terminal and the proximal process of S. maximum (e.g. Banner, 1950) (S. maximum petasma).

Thelycum: Described by Costanzo and Guglielmo, 1976b.

Comments: This species is the largest in the genus. S. maximum is a member of the "S. maximum group", along with S. robustum and S. abbreviatum. The wide upper lobe and the large size of the eye serve to distinguish S. maximum from S. abbreviatum and S. robustum. These 3 species are the only members of the Stylocheiron genus that have elongated 3rd legs that terminate in true chelae in which the dactylus articulates against a branch of the propodus.

ECOLOGY
S. maximum is consumed by fishes.

HORIZONTAL DISTRIBUTION
S. maximum is a widespread mesopelagic species. It occurs in the Pacific, Atlantic and Indian ocean basins; in the Pacific it occurs as far north as the Gulf of Alaska and as far south as 63°S. In the northeastern Atlantic it has been reported north off Norway and Sweden, to 70°N (S. maximum distribution).

VERTICAL DISTRIBUTION
Adults are rarely found above 140 m, and most are caught below 400 m depth.

LARVAE
See the development summary (S. maximum Table) for the stage descriptors and length in stage.

Metanauplius - undescribed

Calyptopis - (3 stages) (S. maximum A)

Carapace:
Shape - The carapace is short in relation to the abdomen length.
Marginal spines - absent
Postero-dorsal spine - absent
Lateral denticles - absent

Telson:
Postero-lateral spines - PL3 is very long.

Furcilia - (5 stages) (S. maximum B), (S. maximum C), (S. maximum D)

Eye: The eye is large with distinct facets and is bilobed in late furcilia.

Carapace:
Shape - The carapace is short in relation to the abdomen length.
Frontal plate / rostrum - The rostrum is triangular and acute.
Marginal spines - absent
Postero-dorsal spines - absent
Lateral denticles - absent

Thoracic legs: There is precocious development of leg 3, the elongate leg of the adult, in the furcilia phase.

Abdomen:
Mid-dorsal spines - absent

Pleopods: The common developmental pathway is 0 - 1' - 1"2' - 3"2'- 5".

Telson:
Postero-lateral spines - PL2 and PL3 are similar in length. PL1 moves to a proximal position in the furcilia phase.
Lateral spines - A pair of spines is present.

Comments: Lebour (1926b) notes that larvae of the genus Stylocheiron are distinguished by no lateral denticles on the carapace in any stage, a relatively long first antennal peduncle with a short flagella, distinctive large eyes, and a common furcilia stage with 1"2' pleopods.

The larvae of S. maximum are relatively large. Casanova (1974) provides a stage-by-stage comparison of the larvae of S. maximum and S. abbreviatum . S. maximum is about 1/3 again as large as S. abbreviatum in comparable stages according to Brinton (1974).

Lewis (1955) illustrates a form of S . maximum F2 with long eyestalks. The long eyestalk form may be found in association with the more common form of S . maximum but has not been found without the common form present (A. Townsend pers. comm.)

Development
(S. maximum Table), development summary for the stage descriptors and length in stage.

(S. maximum Graph 1) , a histogram of developmental form frequency and length freqency by stage, from the Mediterranean.

Pictures
S. maximum, selected stages
S. maximum A [calyptopis 1-3]
S. maximum B [furcilia 1-3]
S. maximum C [furcilia 1 long eyestalk form]
S. maximum D [furcilia 4-5]
S. maximum E [juvenile]
key to larval illustrations

Stylocheiron maximum