(Pl. 6A–D)
Material examined. Curaçao: 2 ov. females, 1 non-ov. individual (VIMS 08CU3301–3), Caracas Baai, from the canals of Hymeniacidon caerulea. 4 ov. females, 7 non-ov. individuals (VIMS 08CU10601, 11301–2, 11701, 12002), Caracas Baai, from the canals of Xestospongia subtriangularis. 1 ov. female, 1 non-ov. individual (VIMS 08CU1001–2), Piscadera Baai, from the canals of Agelas cf. clathrodes. 1 ov. female, 1 non-ov. individual (VIMS 08CU1101–2), Piscadera Baai, from the canals of H. caerulea. 4 ov. females, 4 non-ov. individuals (VIMS 08CU9201, 9503, 10003–4), Piscadera Baai east, from the canals of X. subtriangularis. 2 ov. females, 2 non-ov. individuals (VIMS 08CU2101, 2501–2), St. Michiel Baai, from the canals of X. subtriangularis. 1 ov. female, 1 non-ov. individual (VIMS 08CU4701–2), Westpunt, from the canals of Xestospongia sp. “soft.” Largest ov. female from Curaçao, CL 4.6 mm, largest non-ov. individual, CL 3.6 mm. Panama: 1 ov. female (VIMS 07P3701–1), Hospital Point (09° 20’ 0.24”N, 82°13’6.84”W), from the canals of H. caerulea.
Color. Body transparent to orange-tinged, females with orange or pinkish-orange ovaries and embryos.
Hosts and ecology. In Curaçao, Synalpheus ul occurred in roughly equal sex ratios, most often as a single pair, and occupied Hymeniacidon caerulea, Xestospongia subtriangularis, Agelas cf. clathrodes , and Xestospongia sp “soft ”. Individuals found in Xestospongia sp. were often morphologically ambiguous (often resembling Synalpheus hoetjesi) and host records from sponges other than H. caerulea and A. cf. clathrodes in Curaçao should be treated with caution (see description for S. hoetjesi for more details). In Panama, S. ul is primarily found in H. caerulea.
Distribution. Belize (Rios & Duffy 2007); Jamaica (Macdonald et al. 2009); Curaçao (this study); Barbados (this study); Panama (this study).
Remarks. In Curaçao, Synalpheus ul from sponge hosts Hymeniacidon caerulea and Agelas cf. clathrodes strongly resembled the original type series described (from H. caerulea) from Belize (Rios & Duffy 2007). Conversely, S. ul living in sponges in the genus Xestospongia were relatively difficult to distinguish from the closely related (and morphologically similar) S. hoetjesi sp. nov., which also inhabited Xestospongia spp., due to occasional convergence of the morphological characters used to separate the species (see S. hoetjesi description for further detail). Here we tentatively assign specimens from these hosts to either S. ul or S. hoetjesi based on a mitochondrial DNA COI gene tree (Fig. 8), i.e., using the maternally-inherited cytochrome c oxidase subunit I locus. Further study is needed, preferably employing a number of different molecular markers, to determine whether similarity of morphological characters in these hosts is caused by species hybridization or by host-related morphological convergence.