Medium-sized crab, to about 5 cm carapce width. Carapace almost square
(9/10 as long as wide), with its whole surface crossed by prominent, granulated
lines, fringed by hairs lying flat on the carapace. Middle pair of suprafrontal
lobes very prominent and elongate, separated from each other and from
the lateral lobes by broad, deep, hairy furrows.
Rathbun (1907) notes that this species is near P.
plicatus (a native Hawaiian species, pictured below), but is distinguished
by its parallel sides, coarse striation, and great hairiness.
Intertidal, on rocky shores.
Only known from leeward harbors on Oahu
French Polynesia, Japan, and Hawaii
Mechanism of Introduction
Unintentional, perhaps as larvae in ballast water.
Ecological impact unstudied, but probably competes with native intertidal
grapsid crabs for food and shelter.
This crab is a scavenger, feeding on plant and animal debris in the intertidal
With separate sexes. Fertilization is external, with planktonic larval
This rocky intertidal crab, previously known from French Polynesia (the
type locality is Tuamotu) and Japan, was collected in 1996 from Barbers
Point Harbor (Davie 1998). Peter Ng (pers. comm.) found it to be common
at Kewalo, Oahu, in February 2000. Sakai (1976) notes the habitat as "coral
reef, at high tidal mark", but in Hawaii, so far it seems to be rescricted
to harbors and adjacent areas. We regard it as introduced by ballast water.
Davie, P. 1998. New records of crabs in Hawaii (Crustacea: Decapoda: Brachyura).
Bishop Mus. Occ. Pap. 56: 63-64.
Sakai, T. 1976. Crabs of Japan and adjacent seas. Kodansha Ltd., Tokyo.
Rathbun, M.J. 1907. The Brachyura. Mem. Mus. Comp. Zool. 35(2): 21-74.