Fransen, C.H.J.M.

The present paper deals with the Anasca and Ascophora Imperfecta of the inland bays of Curaçao and Bonaire. Collections were made by P. Wagenaar Hummelinck (1930, 1936/ 37, 1948/49, 1955, 1963/64, 1968, 1970, and 1973) and by the author (1982), and stored in the collections of the Rijksmuseum van Natuurlijke Historie, Leiden. A total of 25 species – almost all occurring in inland bays – are described here and fully illustrated. Six new species are established: Crassimarginatella harmeri, Scrupocellaria curacaoensis, Scrupocellaria carmabi, Scrupocellaria piscaderaensis, Scrupocellaria hildae and Bugula hummelincki. Attention is given to the ecology of the species. The bays have been compared as to species composition in relation to substrate and conditions during collecting.

A collection of shrimp from deep reefs in the Dutch Caribbean is described. Most material originates from the Bonaire deep reef expedition (2013) by Wageningen Marine Research of Wageningen University. Some additional material was available from dives on Curaçao (2014). A new species of Pseudocoutierea Holthuis was recognized in the material collected off Bonaire. The new species is described and illustrated and its position in the phylogeny of the genus Pseudocoutierea analyzed. A key to the species in the genus is presented.

The anemone shrimp Periclimenes rathbunae Schmitt, 1924 (family Palaemonidae), is a common associate of shallow- water anthozoans in the tropical western Atlantic. It has been reported from several sea anemone species, an octocoral, a corallimorpharian, and a scleractinian coral (Brinkmann and Fransen 2016).

During a coral reef survey in Curacao (1 April 2014), a previously unknown association was found between an individual of P. rathbunae and a lettuce slug, Elysia crispata Mo ̈rch, 1863 (Fig. 1). It occurred on the reef slope (6–8 m deep) of Playa Kalki on the island’s northwestern tip (12°22'30'N, 69°09'28'W), where this slug appeared to be abundant (ca. 40 observed individuals per 1-h dive). The shrimp’s blue coloration matched that of its host, but it is usually dark red-brown (see, e.g., Brinkmann and Fransen 2016; Horka ́ et al. 2016).

Elysia crispata is a polymorphic sacoglossan sea slug (infraclass Opisthobranchia) that eats algae in a wide range of habitats (Krug et al. 2016). In this case, the shrimp was positioned on top of its host between the dorsal frills, as if riding it (Fig. 1a, b).

Periclimenes rathbunae is the second shrimp species recorded as associate of an opisthobranch gastropod and the first one in the Atlantic. The other shrimp, Zenopontonia rex (Kemp, 1922), lives on Indo-Pacific reefs and is famous under its junior synonym, Periclimenes imperator Bruce, 1967. This species lives with echinoderm hosts as a juvenile but changes to nudibranch hosts as it matures (Horka ́ et al. 2016). Periclimenes rathbunae also lives with a range of hosts, but it is not clear whether the association with E. crispata also results from an ontogenetic host switch.