Reimer, J.D.

Research on the order Zoantharia (Cnidaria: Anthozoa: Hexacorallia) has a long history in the Caribbean Sea, with the first species, Zoanthus sociatus, described by Ellis & Solander (1768). Since then, the majority of worldwide zoantharian research has occurred in the Caribbean, and the fauna and species are generally thought to be well-known. However, over the past 20 years, molecular techniques have brought about a reconsideration of many marine species and their taxonomy, and the Zoantharia are no exception. Despite many species, genera, and family having been described recently, most discoveries have been from the Indo-Pacific, and thus a reconsideration of zoantharian species combined with faunal surveys in the Caribbean is timely. Additionally, recent Indo-Pacific work has shown that surveys in areas of coral reefs not normally examined (e.g. rubble zones, caves and cracks, sand) as well as at depths below the normal recreational range of SCUBA (> 30 m) harbor much unexamined diversity. During this survey around St. Eustatius, we focused on these areas as well as “normal” coral reef habitats (slopes, crests). 

This article was published in the following report:

MARINE BIODIVERSITY SURVEY OF ST. EUSTATIUS, DUTCH CARIBBEAN 2015 by Naturalis Biodiversity Center and the Netherlands ANEMOON Foundation

Crabs of the genus Platypodiella (Brachyura: Xanthidae) are known for their association with zoantharians (Hexacorallia: Zoantharia), predom- inantly of the genus Palythoa (Den Hartog and Holthuis 1984; Den Hartog and Tu ̈rkay 1991). They make cavities inside their zoantharian hosts, which they use as shelter.

During the Statia Marine Biodiversity Expedition to St. Eustatius (Lesser Antilles, Dutch Caribbean) in June 2015, small crabs (~5–10 mm wide) of Platypodiella spectabilis (Herbst, 1794) were most commonly observed either inside or in close proximity to encrusting Palythoa caribaeorum (Duchassaing and Michelotti, 1860) (Fig. 1a, b). A larger crab of the same species (~30 mm wide) was found hiding in between sponges and coral (M.A. Faasse and G.W.N.M. van Moorsel, pers. comm.), whereas crevices in dead coral may also be a common habitat (Martin and Zimmerman 2007). All crabs were characteristically colored in variable patterns of orange, yellow, black and white (Fig. 1; Martin and Zimmer- man 2007).
Unexpectedly, two small P. spectabilis individuals were found in cavities inside Niphates digitalis (Lamarck, 1814) sponges associated with the parazoanthid Umimayanthus parasiticus (Duchassaing and Michelotti, 1860). These crab dwellings were similar to burrows ob- served in Palythoa (Fig. 1c). Although N. digitalis was one of the most commonly observed sponges of St. Eustatius, no P. spectabilis was found in sponges without a zoantharian associate.