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Holthuis, 1946

Diagnosis:
Carapace with 2 distinct teeth in the median line before the cervical groove (the gastric and pregastric teeth), the rostral tooth is absent. The region between the postrostral and branchial carinae with only very few tubercles and extensive smooth areas. Abdomen with a distinct sharp median carina on somites 1 to 5, all these ridges of approximately the same height. Somite 1 with the transverse groove interrupted in the middle by the median carina; behind the groove there are no longitudinal grooves, but a transverse row of tubercles. The exposed part of somites 2 to 5 without an arborescent pattern, but with a wide transverse groove (interrupted in the middle) behind which there is a transverse row of tubercles, and before which there are some tubercles and wide short side grooves. The fourth segment of the antenna has a single, distinct oblique median carina; the upper surface has no additional carina or tubercles. The outer margin of the segment has 2 to 4 larger, the inner margin 4 to 7 smaller teeth (not including the apical tooth). The thoracic sternum with the anterior median end gutter-like sunken, not incised in the middle No median tubercles on the sternites. Dactyli of legs 3 to 5 with dorsal fringes of hair.
Colour: body pale brown with the ridges and tubercles pale purple or reddish. First abdominal somite brick red in the anteromedian area (see Chan and Yu, 1986, pls 4, 9A, B).

Type:
Type locality of Arctus orientalis and S. batei (the latter name being a replacement name for the former): "Challenger" "Station 209, between Bohol and Zebu [ = Cebu], ... lat. 10°14'N., long. 123°54'E.; depth, 95 fathoms [=174 m]; bottom, blue mud". Two syntypes in BM.
Type locality of S. batei arabicus: "Gulf of Aden (13°16' - 13°16'36"N 46°20'24"-46°14'E, depth 220 m, "John Murray" Expedition Sta. 194". Holotype in BM, no. 88.22, in alcohol, condition good.

Diagnostic Features:
Carapace with 2 distinct teeth in the median line before the cervical groove (the gastric and pregastric teeth), the rostral tooth is absent. The region between the postrostral and branchial carinae with only very few tubercles and extensive smooth areas. Abdomen with a distinct sharp median carina on somites 1 to 5, all these ridges of approximately the same height. Somite 1 with the transverse groove interrupted in the middle by the median carina; behind the groove there are no longitudinal grooves, but a transverse row of tubercles. The exposed part of somites 2 to 5 without an arborescent pattern, but with a wide transverse groove (interrupted in the middle) behind which there is a transverse row of tubercles, and before which there are some tubercles and wide short side grooves. The fourth segment of the antenna has a single, distinct oblique median carina; the upper surface has no additional carina or tubercles. The outer margin of the segment has 2 to 4 larger, the inner margin 4 to 7 smaller teeth (not including the apical tooth). The thoracic sternum with the anterior median end gutter-like sunken, not incised in the middle No median tubercles on the sternites. Dactyli of legs 3 to 5 with dorsal fringes of hair. Colour: body pale brown with the ridges and tubercles pale purple or reddish. First abdominal somite brick red in the anteromedian area (see Chan and Yu, 1986, pls 4, 9A, B).

Geographical Distribution:
Indo-West Pacific region: Gulf of Aden and East Africa to the South China Sea, Taiwan, the Philippines and Indonesia. It is possible that the western form is a separate subspecies S.b. arabicus.

Habitat and Biology:
Depth range from 160 to 484 m, usually between 170 and 210 m; on sandy and muddy substrates.

Size:
Maximum total body length about 7 cm, carapace length to 3 cm (males 1.4 to 2.9 cm; females 1.5 to 3.3 cm; ovigerous females 2.3 to 3.1 cm).

Interest to Fisheries:
Sometimes taken by trawlers in small quantities (George, 1969: 433), the species is not considered to be of potential commercial interest. Chan and Yu (1986:149) reported the species, from local fish markets in Taiwan; the animals were caught with "baby shrimp trawls".

Soft locust lobster (Scyllarus batei)