Females average 300mm – 400mm in length, and males average 250mm – 300mm in length (excluding the tail).
The prosoma (cephalothorax) is horseshoe-shaped, with a rounded anterior margin. In males, this margin is slightly indented in the middle. The posterior lateral angles extend to about half the length of the abdomen.
The abdomen is unsegmented, with oblique lateral margins. Each side bears six long, movable spines of approximately equal length and six small, fixed spines arranged alternately. There are three small spines on the posterior margin at the connection with the tail, a key feature distinguishing it from T. gigas (which has only one such spine).
The tail (telson) is sword-shaped with a triangular cross-section.
Biology and Ecology:
Habitat and Behavior: Horseshoe crabs inhabit sandy-muddy bottom environments. They typically live buried in the substrate and move by crawling along the seabed.
Diet: Their diet primarily consists of benthic organisms.
Sexual Maturity and Reproduction: Sex can only be distinguished after three years of age. From approximately March-April to September-October, males and females congregate in sandy intertidal areas within bays or estuaries for mating and spawning.
Spawning: They typically lay eggs on warm sandy beaches, burying them approximately 20cm deep. The female lays eggs in the nest, and the male fertilizes them.
Eggs: The eggs have a thick shell and a maximum diameter of 4.01mm, typically ranging from 2.5mm to 3.5mm.
Larval Development: After 6-8 days, the horseshoe crab larvae molt, becoming the first stage of juvenile horseshoe crabs. They resemble adults in appearance, except for the tail length.
Distribution:
Vietnam: Very common in Vietnamese waters, with the highest concentrations found in the coastal provinces of the central region.
Global: Indo-West Pacific region: From the Red Sea and East Africa to Japan. Also found in the Solomon Islands and Australia.
Value:
Scientific Significance: Beyond its scientific significance as a living fossil from the Ordovician period, horseshoe crabs, particularly T. tridentatus, have pharmaceutical value.
Medical Applications: The blood of horseshoe crabs contains numerous bioactive compounds, capable of highly sensitive detection of endotoxins from Gram-negative bacteria. This makes it useful as a reagent in drug testing and pharmaceutical production.
Status:
Historical Abundance: Prior to 1990, juvenile and adult horseshoe crabs were frequently encountered in intertidal sandy areas of estuaries and coastal regions, particularly in the coastal provinces of central Vietnam, with a distribution area of approximately 5001 – 20000 km².
Recent Decline: In the last 10 years, with the development of coastal aquaculture, human activities have encroached upon the habitats of juvenile horseshoe crabs, destroying and shrinking their spawning grounds by at least 20% of the habitat area. Production is estimated to have decreased by more than 20% in the last 10 years.
Ranking:
VU A1c Ba,b,c (Vulnerable).
Conservation Measures:
Protected Status: Included in the Vietnam Red Book in 1992 and 2000.
Recommendations: The establishment of conservation areas to protect horseshoe crab spawning grounds is recommended.
