Anoplodactylus monotrema

Invasion History

First Galapagos Record: 1934

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General Invasion History:

The sea-spider Anoplodactylus monotrema is native to the Western Atlantic from Florida to Brazil, where it inhabits coral reefs, grass beds, and rocky areas (Stock 1979; Lucena, and Christofferse 2018). Its only occurrence in the Pacific is in the Galapagos Islands.

Invasion History in the Galapagos:

Anoplodactylus monotrema was first collected off Isla Floreana (formerly Santa Maria) Island in 1934, by dredge in 0–5 m of water (USNM 125191, U.S. National Museum of Natural History 2021). It was initially identified as the Mediterranean species Anoplodactylus robustus (Dorhn 1882). In 1962, it was collected at Isla Santa Cruz (USNM 125175, U.S. National Museum of Natural History 2021). In these early collections it was regarded as cosmopolitan. Caribbean and the Galapagos specimens were later identified as the Western Atlantic species A. monotrema (Stock 1979; Child 1979). The likely vector of introduction is ship fouling or ballast water since this species does occur in the fouling community of pilings (Stock 1979).

Invasion history elsewhere in the world:

Aside from records in the Galapagos, we have found no records of Anoplodactylus monotrema outside the Western Atlantic.

Description

Pycnogonids (sea-spiders) are arthropods belonging to the subphylum Chelicerata, marked by sucking mouthparts. The class Pycnogonida has a single order, Pantopoda, meaning 'all-legs'. These animals have such a tiny body that many of the vital organs are in the legs. The body is small and segmented, with a narrow neck and head that bears a pair of chelicerae and a pair of palps, which surround a robust proboscis, and with four eyes mounted on a central tubercle. The trunk has four segments, with lateral extensions to which the four pairs of walking legs are attached. In Anoplodactylus monotrema, trunk segments 3 and 4 are fused. The ocular tubercle is low and rounded and the abdomen is vestigial. The first pair of legs are modified for grooming, and in males carry the egg masses as males of this species brood the eggs. The third segment of the ovigerous legs bears a small appendage, the oviger, with 5 segments. The body length of the type specimen (Stock 1979) was 1.2 mm, and with the 3rd pair of legs pulled straight, the whole animal would be about 3.4mm. The animal is yellow-to orange in color (Barnes 1983; Stock 1979; Montoya Bravo et al. 2009).  

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Taxonomy

Ecology

General:

Pycnogonids have separate sexes. The gonads and male and female gonopores are located on the legs. During mating, males hang beneath the female, so they are ventral in the opposite direction and their surfaces are opposed. The eggs are extruded and fertilized by the male and are carried by the ovigers on the first pair of their legs. The eggs hatch into a protonymphon, with three pairs of appendages. Larvae of different species are carried on the legs of the male or live independently in the plankton or on the epibenthos (Barnes 1983).

Food:

Bryozoans, hydroids (by sucking body fluids)

Trophic Status:

Carnivore

Carn

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Habitats

General Habitat	Coral reef	None
General Habitat	Grass Bed	None
General Habitat	Rocky	None
General Habitat	Marinas & Docks	None
Salinity Range	Polyhaline	18-30 PSU
Salinity Range	Euhaline	30-40 PSU

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Life History

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Tolerances and Life History Parameters

Minimum Length (mm)	2	Rough estimate form photo in Montoya Bravo et al. 2009)
Maximum Length (mm)	1.2	Body length (Stock 1979)
Maximum Width (mm)	3.4	Estinmated by adding length of leg joints and width of body extensios (Stock 1979)
Broad Temperature Range	None	Tropical
Broad Salinity Range	None	Polyhaline-Euhalibe

General Impacts

Impacts for Anoplodactylus monotrema are unknown.

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References

Aviz, Daiane; Da Silva, Roseanne Figueira; Filho, José Souto (2018) Sabellaria wilsoni (Polychaeta: Sabellariidae): an ecosystem engineer and promoter of zoobenthos diversity in the Brazilian Amazon coast, Journal of the Marine Biological Association of the United Kingdom 99(5): 1099-1109
DOI: https://doi.org/10.1017/S0025315418001157

Barnes, Robert D. (1983) Invertebrate Zoology, Saunders, Philadelphia. Pp. 883

Child, C. Allan (1979) Shallow-water pycnogonida of the isthmus of Panama and the coasts of middle america, Smithsonian Contributions to Zoology 293: 1-86

Lucena, Rudá Amorim; Christoffersen, Martin Lindsey (2018) Anoplodactylus (Pycnogonida: Phoxichilidiidae) from Brazil, ew records and two new species, Turkish Journal of Zoology 42: 372-388

Montoya Bravo, Maria Fernanda; Müller, Hans-Georg; Arango, Claudia P.; Tigreros, Paulo; Melzer, Roland R. (2009) Morphology of shallow-water sea spiders from the Colombian Caribbean, Spixiana 32(1): 9-34

Stock, Jan. H. (1979) Pycnogonida from the mediolittoral and infralittoral zones in the tropical western Atlantic, Studies of the Fauna of Curacao and other Caribbean Islands 184: 1-32

U.S. National Museum of Natural History 2002-2021 Invertebrate Zoology Collections Database. http://collections.nmnh.si.edu/search/iz/

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