Several species of poisonous crabs (of the alimasag varieties) dangerously lurk in Philippine seas. Nine of them are discussed here: distinguishing features for identification, geographical distribution and local habitation. So, the next time you are itching for a bite of succulent crabmeat, stay away from the strange-looking ones; partake only of the varieties known to you or your housemates. The following information should be of great help to local fishermen and consumers to be able to distinguish dangerous species from the midly toxic to the killer crabs.
• The one already mentioned, "kagang-bugtong" also known as "kalambaho" and "kumong-kumong" ranges in size from 50 to 100 millimeters (mm) across, its body is covered with smooth and well-defined lobules. The carapace has crested frontal borders cut into four lobes (the first three are rounded while the fourth is tooth-like). The pincers are equal and rough. Its walking legs, crested above and furrowed longitudinally are fringed with long hairs. It has eye-like spots and spotted with chocolate brown on bluish-gray background.
The crab hides under coral reefs during the day and crawls out at night. It abounds in Ilocos. La Union, Batangas, Quezon, Albay. Sorsogon, Mindoro, Marinduque, Samar, Panay Island, Palawan and Zamboanga.
• Long-armed crab (Dalforfia horrida L.): This horrible looking crab has a carapace which is pentagon in outline, deeply grooved and rough, exceeding 140 mm in width. The body and appendages are covered with tubercular outhgrowths. The pincers are huge and unequal, the length doubling the breadth of the carapace. Spines line the appendages. This crab inhabits the bottoms of rocks and sandy mud from 33 to 125 meters deep and is found in Ilocos, Marinduque and Palawan.
• Rock crab (Carpilius convexus F.): Medium-sized with a front view that is vertically deflexed with two median lobes on the carapace. The pincers are highly unequal and stout. The carapace has the texture and coloration of marble – irregularly cream and red. It has no division and very convex and robust. Mildly, toxic, it is very common in Ilocos, Batangas, Mindoro, Quezon, Bicol Region, Panay Island, Samar and Palawan. It is frequently found under stones or crevices of coral reefs
• Rock crab also known as "calintugas" (Lobozozymus pictor F.): Moderately sized, this crab has a smooth carapace with fairly well-defined regions. A deep gaps separates the front from the side marginal lobe of the carapace which ahs an orange network of lines on a cream background, while the underside has a mat of hair. The walking legs have tuffs of hair on its outer border. Calintugas inhabits rocky bottoms of coral feefs from low tidal mark to a depth of 30 meters. It abound along the reef areas of Batangas, Mindoro, Sorsogon, Negros Oriental, and Samar.
• Rock crab (Atergatis intergerimus L.): Broad oval capace irregularly pitted at the border near the front and towards the side characterizes this midly toxic crab. Its pincers have the same length and looks the same. The other surface of the legs are hardly pitted with hairy dactyls though other joints are generally free of hair. The borders of the carapace are crested. It is pinkish ochre with blackish brown fingers with whitish teeth at the tips. It is found in rocky and sandy bottoms from 10 to 30 meters in Ilocos, Batangas, Quezon, Bohol and Palawan.
• Splendid rock crab (Etisus splendidus R.): Bright red in color, its size exceeds six inches across with smooth, convex carapace with regions well outlined. The front lateral margin has 9 to 13 teeth of different sizes. The pincers are very large and unequal in size with the arm bearing one to three spines on the outer upper border. The fingers are gaping and hollowed out at the tips while the legs are fringed with hairs. It inhabits shallow waters and coral reefs in Ilocos, Negros Oriental and Palawan. It is known to be midly toxic.
• Red-eyed rock crab (Eriphia sebana R.): A medium-sized crab, it is aggressive and nocturnal in habit. The carapace is oval-shaped and is covered towards the front with tubercles and towards the rear with minute granules. Along the frontal margin are six or more spines, decreasing in size towards he side and rear. The pincers are unequal; while they may appear smooth, they are actually covered with microscopic granules. This species can be found in rock crevices in shallow waters in Ilocos, Batangas, Panay Island and Palawan.
• Shoal crab (Platypodia granulose R.): Its surface is rough and covered with small granules and stiff hairs. The crested anterolateral (front and side margin) is separated by closed fissures. The pincers are equal with the fingers that are black at the tips. Small in size, it hardly exceeds 40 mm in width. The crab inhabits coral reefs in shallow water below tidal mark. It is found in Kalayaan Island, Palawan.
• Shoal crab, also locally called "agokoy" or "amumodlong" (Atergatis floridus L.): Compact and robust, it hardly reaches 70 mm across. The carapace is perfectly smooth with broad shallow depressions that faintly defines the regions, the sharp crest at the front and side margins. The cloud-shaped pattern of the carapace adds to the distinct identification of the species. This crab has equal pincers with fluted black tips. It inhabits hard beaches at or below tidal mark of Ilocos, Batangas, Quezon, Bicol Region, Mindoro, Negros, Panay Island, Palawan and Davao.
Beware of these killers crabs! Unfurtunately for unknowing victims, there is no known antidote yet for the kind of poison obtaining from these killer crabs. A person who has eaten a poisonous crab’s meat should induce vomiting and seek medical help. Next time a strange-looking crab is served, examine it well and give it very serious thought.