The integument of the body is very firm. The carapace is high; in dorsal view it is elongate oval in outline. In adults the carapace measures less than 1/3 of the total body length. The rostrum is narrowly triangular and short; it is depressed and its lateral margins continue for some distance on the carapace as short divergent ridges. The rostrum has no teeth. The carapace ends posteriorly in a distinct posteriorly directed median tooth that overhangs the articulation with the first abdominal somite. The abdomen is long and narrow, more than five times as long as wide in the males, about four times as long as wide in the females. The somites are of about equal width throughout their length, they have a longitudinal carina over the base of the pleura. The telson is about as long as the previous somite, but slightly narrower, the posterior margin is broadly rounded. The uropods are styliform. The eyes are small. The first pair of pereiopods is very strong and asymmetrical, both chelae are subchelate, the larger less conspicuously so than the smaller. The second legs are smaller, also subchelate; the other legs are simple. Epipods are present on the pereiopods.
Colour: the whole body is rather uniformly yellowish or reddish brown.
Type locality of Cancer anomalus: "Das Vaterland dieses Krebses ist völlig unbekannt"; holotype in ZMB, no. 1256, dry, condition reasonable.
Type locality of Thalassina scorpionides not indicated in the original description, evidently likewise unknown; type material in MP, now absent.
Type locality of T. scabra not mentioned either, probably unknown; type material "in the Hunterian Museum", present whereabouts unknown.
Type locality of T. talpa: "Philippine Islands"; holotype in BM, no. 43.6 (in alcohol, condition poor).
Type locality of T. gracilis: "from shores of Telegraph Island, near Singapore"; holotype in USNM.
Type locality of T. chilensis: "Mare Chilense"; holotype in MP, no Th 537, in alcohol, condition mediocre. As pointed out by Holthuis (1952:85-86) the locality label probably is incorrect, as the species since has never been found in Chile.
Type locality of T. maxima: "Sydney", New South Wales, Australia; holotype in SMF, no-ZMG 227, in alcohol, broken, but condition otherwise fair. This locality indication likewise is highly dubious as the species does not occur near Sydney.
Indo-West Pacific region, from the west coast of India to S. Japan (Ryukyu Islands), Vietnam, the Philippines, Indonesia, New Guinea, New Britain Island, N. and N.E. Australia, Fiji, Samoa.
Habitat and Biology:
The species lives in the littoral and supralittoral zones, where it digs its burrows. These can be found in mangrove areas and estuaries. The excavated mud forms a kind of chimney or mound over theopenings of the burrows, and because of their height form a most conspicuous feature in the landscape. The chimneys can be 75 cm high, but sometimes several chimneys together can form complex hills of mud up to 1.5 m high. The burrows go down vertically or obliquely to the water level after which they may make zigzags and side branches; the depths of the burrows has been estimated to be up to 2.5 m. The animals are rarely seen out of their burrows, not even at night, but it seems that after heavy rainfall they may venture outside. They are sluggish and are definitely mud feeders, reports that they also are vegetarian have been doubted. Their burrowing activities take usually place during the night.
Usually up to 16 to 20 cm in total body length, although there are records of up to 30 cm.
Interest to Fisheries:
Minor. Already Rumphius (1705: 6), when dealing with this species from Amboina, Moluccas, Indonesia, remarked on its poor culinary qualities: " Hy heeft weinig ja schier geen vleesch, want het geheele lyf en de staert steeken vol groenachtige modder, en slechts in de scheeren vindmen een weinig wit brokkelig vleesch, van geenen byzonderen smaak.... De Inlanders van Celebes eeten het vleesch van de scheeren, 't welk ik hun willende nadoen, hebbe my niet wel daar op bevonden; dies ik hem voor eenen onnutten Kreeft houde, of hy most in andere Landen beter zyn" (It has little, or almost no meat, as the entire body and the tail are full of a greenish mud, and only in the pincers there is a small amount of white, crumbly meat, without a particular taste. The natives of Celebes eat the meat of the pincers, but when I myself tried this, the meat did not agree with me, therefore I consider this a useless lobster, unless it is of a better quality in other countries). Motoh and Kuronuma (1980: 64) remarked that there is no special fishery for this species in the Philippines and that it is only occasionally picked up by fish pond workers. It appears only rarely on the Philippine fish markets. Ward (1943, Army, 2(4): 30, fig.) in his paper "New Guinea menu" listed Thalassina anomala among the edible crustaceans. Tan and Ng (1988: 85), remarked that in Singapore the animals are considered edible, but are "not popular locally". On a wall chart, issued recently by the Fisheries Division of the Ministry of Primary Industries of Fiji, the present species figures among the "aquatic foods of Fiji ". In Thailand, as I was informed by Prof. Phaibul Naiyanetr of Chulalongkorn University, Bangkok, the species is not eaten but used as medicine against asthma; it is then either dried, ground to powder, and the powder drank with water, or the specimen is placed in a kind of alcoholic liquor and left there for a couple of days, after which the liquor with the beneficial substances dissolved in it is drunk.
The positive qualities of the species from the point of human interest thus are rather small, and its negative qualities seem to be more important. In many areas the species is considered a pest. "The animal is notorious for causing severe damage to bunds [of prawn ponds] by its burrowing activities. The paddy fields and backyards of houses in the proximity of the creeks are also subject to this sort of damage" (Sankolli, 1963: 604). Also earth roads can suffer from the burrowing of the species. Dammerman (1929: 120) reported that "the species has been noticed as destructive to nipa seedlings, which may be protected by surrounding them with small bamboo fences", but the correctness of this observation has later been doubted by Kalshoven and Van der Vecht (1950: 63); the fact that Thalassina is not a vegetarian but mainly a mud feeder supports the view of the latter authors. All in all it seems that Rumphius indeed was right in considering this as a "useless lobster" from an economic viewpoint.