Balanus amphitrite

Balanus eburneus

Chthamalus proteus

Gonodactylaceus falcatus

Ligia exotica

Pachygrapsus fakaravensis

Scylla serrata

Gonodactylaceus falcatus (Forskäl, 1775)

Philippine mantis shrimp

Phylum Arthropoda
Subphylum Crustacea
Class Malacostraca
Order Stomatopoda
Family Gonodactylidae

Description
Individuals may grow to about 6 cm in length and are generally dark green (males) or reddish brown (females). This species can be distinguished from other Hawaiian stomatopods by examination of the last (sixth) abdominal segment and telson (pictured below). The sixth abdominal segment has six inflated carinae or lobes. The telson also with inflated carinae and three pairs of marginal teeth and one pair of accessory teeth. Memebers of the genus Gonodactylaceus do not have spines on dactylus. Another smaller species, G. hendersoni, is also found in Hawaii and is considered also to be introduced. It is typically a mottled beige with some white spots.
Habitat
Dead branching coral heads, clumps of coralline algae, or crevices and small holes in solid reef substrate.
Distribution
Hawaiian Islands
Shallow reefs of Oahu, especially Kaneohe Bay and Waikiki
Native Range
Indo-Pacific
Present Distribution
Indo-Pacific and Hawaiian Islands
Mechanism of Introduction
Unintentional, most likely with fouling on ships' hulls
Impact
An aggressive species, G. falcatus has been shown to drive out the native stomatopod, Pseudosquilla ciliata, from dead coral heads. Since it's introduction, G. falcatus has almost completely replaced the once common P. ciliata in the coral heads on the shallow reefs of Oahu (Kinzie, 1968).
Ecology
Feeding
Stomatopods are generally carnivorous predators, using their powerful raptorial claws to snap up live prey.
Reproduction
Stomatopods have separate sexes. Fertilized eggs are carried by the female until hatching. The free-swimming planktonic larvae undergo several stages of development before settlement in shallow water. G. falcatus appears to reproduce twice a year (see Kinzie, 1968)
Remarks
Kinzie (1968) argued that an lndo-Pacific species of mantis shrimp (which he discussed under the name Gonodactylus falcatus) was introduced to the Hawaiian Islands. Manning and Reaka (1981) subsequently described the same Hawaiian population as a new species, Gonodactylus aloha, and considered it endemic. Kinzie (1984) examined their arguments in detail and concluded that at the least the species was cryptogenic. Barber and Erdmann (2000) proposed that G. aloha is a synonym of G. mutatus, but recently Ahyong (pers. comm.) has synonymized G. mutatus back to G. falcatus.
The first specimens of G. falcatus were observed in 1954 in dead coral heads in Kaneohe Bay. Kinzie (1968) suggested that it was introduced onto Oahu with concrete barges towed back at the end of World War II, particularly from the area of the Philippines and the South China Sea. Kinzie demonstrated experimentally that the more aggressive G. falcatus had displaced the native stomatopod Pseudosquilia ciliata from coral head habitats in Kaneohe Bay. It's continued presence around Oahu has been reported by a number of authors.
References
Barber, P.H. and M.E. Erdmann. 2000. Molecular systematics of the Gonodactilidae (Stomatopoda) using mitochondrial cytochrome oxidase C (subunit 1) DNA sequence data. J. Crust. Biol. 20: 20-36.
Kinzie, R.A. 1968. The ecology of the replacement of Pseudosquilla ciliata by Gonodactylus falcatus (Crustacea: Stomatopoda) recently introduced into the Hawaiian Islands. Pac. Sci. 22: 465-475.
Kinzie, R.A. 1984. Aloha also means goodbye: a cryptogenic stomatopod in Hawaii. Pac. Sci. 38: 298-311.
Manning, R.B. and M.L. Reaka. 1981. Gonodactylus aloha, a new stomatopod crustacean from the Hawaiian Islands. J. Crust. Biol. 1: 190-200.