Stylocheiron abbreviatum G.O. Sars, 1883
Etymology: Stylocheiron - a column/hand; abbreviatum - short
Eye: The eye is pear-shaped, the upper lobe is much narrower than the lower lobe (~0.55:1.0). There are no enlarged crystalline cones (S. abbreviatum eye & rostrum).
Peduncle of 1st Antenna: As in the generic diagnosis in Higher Taxa (S. abbreviatum,).
Rostrum: The frontal plate is produced horizontally as a slender rostrum reaching about to the anterior limit of the eyes (S. abbreviatum eye & rostrum).
Carapace: The gastric region is strongly domed, with a small median keel (S. abbreviatum).
Thoracic legs: The 3rd thoracic leg is elongated and bears a true chela (Stylocheiron-elongated legs) 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.
Abdomen: The 3rd-4th segments bear low mid-dorsal keels and the 5th-6th segments have small mid-dorsal posterior spines (S. abbreviatum ). The 6th segment length : height varies from about 1.65 to 2.0.
Length: Adults are 12-17 mm.
Petasma: The terminal process is strong, somewhat hollowed distally. The proximal process is shorter, more slender and tapering throughout its length. The lateral process is curved, slender and nearly equal in length to the proximal process (S. abbreviatum petasma).
Thelycum: Described by Costanzo and Guglielmo, 1976b.
Comments: S. abbreviatum is a member of the "S. maximum group", along with S. maximum and S. robustum. The narrow upper lobe of the pear shaped eye and the presence of low keels on the 3rd-5th abdominal segments distinguish this species from S. maximum 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. abbreviatum is consumed by fishes.
HORIZONTAL DISTRIBUTION
S. abbreviatum occurs in the Pacific and Atlantic ocean basins, 40°N-40°S and in the Gulf Stream's northern extension to 50°N near Europe. In the Indian Ocean it is present between about 12°N to 40°S, but it also occurs in the Red Sea, and Gulf of Eilat (S. abbreviatum distribution).
VERTICAL DISTRIBUTION
The adults occur at a depth of 50-300 m day and night.
LARVAE
See the development summary (S. abbreviatum Table) for the stage descriptors and length in stage.
Metanauplius - undescribed
Calyptopis - (3 stages) (S. abbreviatum A)
Carapace:
Shape - There are large lateral lobes in C1.
Marginal spines - absent
Postero-dorsal spine - absent
Lateral denticles - absent
Telson:
Postero-lateral spines - In C1-C2 the PL3 is very long . In C3 it is only slightly longer than PL2.
Terminal spines - There are 6 terminal spines in both C1 and C2.
Furcilia - (5 stages) (S. abbreviatum B), (S. abbreviatum C)
Eye: The eye is large. The pigmented area may be pear-shaped in young furcilia larvae and the eye becomes bilobed in later stages. The anterior facets are distinct.
Carapace:
Shape - The carapace is short in relation to the abdomen length.
Frontal plate / rostrum - The rostrum is acute.
Marginal spines - absent
Postero-dorsal spines - absent
Lateral denticles - absent
Dorsal keel - A distinct dorsal keel is present. It is situted in the posterior half of the carapace in early stages.
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 is situated somewhat proximally and ventrally in F3-F5.
Lateral spines - One pair of lateral spines is present, they are situated relatively proximally in the furcilia stages.
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.
In life S. abbreviatum has very characteristic coloring. Lebour (1949) notes that in a 3.6 mm larva there is red on the rostrum, first antennae, eyes, thorax, at the base of the legs, and ventrally along the abdomen segments 1-5.
Casanova (1974) provides a stage-by-stage comparison of the larvae of S . abbreviatum and S. maximum . S. abbreviatum is about 1/3 the size of S. maximum in comparable stages according to Brinton (1975).
Development
(S. abbreviatum Table), development summary for the stage descriptors and length in stage.
(S. abbreviatum Graph 1) , a histogram of developmental form frequency, from the Mediterranean.
(S. abbreviatum Graph 2), a histogram of length freqency by stage, from the Mediterranean.
Pictures
S. abbreviatum, selected stages
S. abbreviatum A [calyptopis 1-3]
S. abbreviatum B [furcilia 1-3]
S. abbreviatum C [furcilia 4-5]
S. abbreviatum D [juvenile]
key to larval illustrations