Author : Baylon, Juliana C.;Alcantara-Creencia, Lota B.

Summary : There were reports of the existence of horseshoe crabs in Palawan, Philippines, but there is a need to identify and confirm these species. A total of 128 adult horseshoe crabs were collected from Honda Bay, Palawan, Philippines. These were identified as Tachypleus tridentatus (68 males, 40 females) and Carcinoscorpius rotundicauda (2 males, 18 females). Morphology, morphometric measurements, and ratios of male and female of each species were described. Morphological characteristics in differentiating a male from a female crab involve examination of the appearance of the genitalia. Morphological characteristics in identifying the species include the presence or absence of notches in the frontal margin, arching in the frontal view, appearance of the chelae of the 2nd and 3rd prosomal appendages, number of lateral spines and the immovable spines in the opisthosoma, the presence of spinnerets on the surface of the telson, and shape of the telson and its cavity in cross-section. This study confirmed the identification of the two species found in Palawan, Philippines, and the morphological characteristics of the male and female of each species. In addition, a comparison was made of the size of the horseshoe crab species in Palawan with those found in other locations in the Asia-Pacific region.