H. Milne Edwards, 1837
Diagnosis:
The carapace has the median teeth before the cervical groove blunt and inconspicuous: the rostral tooth is reduced to a tubercle, the pregastric tooth is replaced by a double row of 1 or 2 tubercles and a few inconspicuous median tubercles. The gastric tooth is the most conspicuous, it is broad and blunt and bears a double row of tubercles. The surface of the carapace is very uneven and the tubercles are high. Between the postrostral and branchial carinae there are a few tubercles and many smooth areas. The abdomen shows a distinct median longitudinal carina on somites 2 to 5, that of somite 3 is by far the highest, and (like the one of somite 4) bears numerous tubercles laterally. Somite 1 is quite smooth, and has the transverse groove only slightly noticeable in the extreme lateral parts. The exposed part of the following somites shows no arborescent pattern, but in each somite there is a wide transverse groove there. In somite 2, both before and behind this groove there is a perfectly smooth broad ridge, a character in which the species differs from most others. In the following somites these ridges are tuberculate. In somites 4 to 6 the posterior margin is tuberculate. The fourth antennal segment has a sharp and high oblique median carina. Outside the carina the upper surface of the segment shows a row of tubercles. The outer margin of the segment bears 4 or 5 teeth (apical tooth of the segment not included), the inner margin has 5 to 7 teeth of irregular size. The anterior margin of the thoracic sternum is deeply U-shapedly incised. Each of the thoracic sternites bears a rounded median tubercle. The dactyli of pereiopods 3 to 5 show two short fringes of hair each.
Colour: the dorsal surface of the body is greyish or purplish brown with darker spots. The distal segment of the antenna is often lighter. The first abdominal somite shows dorsally often a dark blue colour (see Chan and Yu, 1986, pls 1, 8A, 10C).
Type:
Type locality of Scyllarus rugosus: " Habite la côte de Pondichéry" ( = Pondicherry, S.E. India, 11°59'N 79°50'E). Holotype in MP, no longer extant.
Type locality of Arctus tuberculatus: "Challenger" "Station 190, between New Guinea and Australia... lat. 8°56'S., long. 136°5'E.; depth, 49 fathoms [= 90 m]; bottom, green mud". Syntypes in BM.
Diagnostic Features:
The carapace has the median teeth before the cervical groove blunt and inconspicuous: the rostral tooth is reduced to a tubercle, the pregastric tooth is replaced by a double row of 1 or 2 tubercles and a few inconspicuous median tubercles. The gastric tooth is the most conspicuous, it is broad and blunt and bears a double row of tubercles. The surface of the carapace is very uneven and the tubercles are high. Between the postrostral and branchial carinae there are a few tubercles and many smooth areas. The abdomen shows a distinct median longitudinal carina on somites 2 to 5, that of somite 3 is by far the highest, and (like the one of somite 4) bears numerous tubercles laterally. Somite 1 is quite smooth, and has the transverse groove only slightly noticeable in the extreme lateral parts. The exposed part of the following somites shows no arborescent pattern, but in each somite there is a wide transverse groove there. In somite 2, both before and behind this groove there is a perfectly smooth broad ridge, a character in which the species differs from most others. In the following somites these ridges are tuberculate. In somites 4 to 6 the posterior margin is tuberculate. The fourth antennal segment has a sharp and high oblique median carina. Outside the carina the upper surface of the segment shows a row of tubercles. The outer margin of the segment bears 4 or 5 teeth (apical tooth of the segment not included), the inner margin has 5 to 7 teeth of irregular size. The anterior margin of the thoracic sternum is deeply U-shapedly incised. Each of the thoracic sternites bears a rounded median tubercle. The dactyli of pereiopods 3 to 5 show two short fringes of hair each. Colour: the dorsal surface of the body is greyish or purplish brown with darker spots. The distal segment of the antenna is often lighter. The first abdominal somite shows dorsally often a dark blue colour (see Chan and Yu, 1986, pls 1, 8A, 10C).
Geographical Distribution:
Indo-West Pacific region from Red Sea, East Africa and Madagascar to Japan, Taiwan, the Philippines, Indonesia and N.E. Australia.
Habitat and Biology:
Inhabits depths from 20 to 60 m, rarely reported from 100 or 200 m. Bottom usually sand and mud, sometimes with coral, shelly grit or rubble
Size:
Total body lengths reported are 2.5 to 6 cm (males), 2.5 to 6 cm (females), 3 to 6 cm (ovigerous females) and carapace lengths of 0.8 to 2.1 cm (males), 0.8 to 2.2 cm (females), 1 to 2.2 cm (ovigerous females).
Interest to Fisheries:
Like the other Indo-West Pacific species of the genus, S. rugosus is hardly of any commercial importance, if at all. It is taken accidentally by trawlers fishing for other species and so get to the fish markets. Chan and Yu (1986:149) reported it from fish markets in Taiwan, brought in by "baby" shrimp trawlers, but Chang (1965) does not list any Scyllarus among the "Edible Crustacea of Taiwan".