**3. Results**

Twenty-seven host-coral species, consisting of 25 scleractinians (Anthozoa) and two milleporids (Hydrozoa), were recorded for the coral-associated feather duster worm, divided over 10 families and 16 genera (Table 1; Figures 2–7). In addition, the species was found in association with the encrusting octocoral *Erythropodium caribaeorum* (Figure 8A,B), the colonial tunicate *Trididemnum solidum* (Figure 8C,D), phaeophyceaen algae, in particular *Lobophora* sp. (Figure 8E,F), and various sponge species (Figure 9). The records were from the southern Caribbean islands of Bonaire and Curaçao and the Eastern Caribbean island of St. Eustatius (Table 1).

**Figure 1.** Map of the eastern part of the Caribbean showing the position of Curaçao, Bonaire, and St. Eustatius, where the presence of coral-associated feather duster worms was investigated.

The symbiotic worms, identified as split-crown feather duster worms of the genus *Anamobaea* Krøyer, 1856 [22,27,29], showed some variation in coloration, ranging from white to dark red and various combination patterns of these colors (Figures 2, 3 and 9A). Two species from the Caribbean have been described, which can be distinguished by two morphological characters [27,29,32] that are not clearly visible in the photographs: *Anamobaea phyllisae* Tovar-Hernández & Salazar-Vallejo, 2006 has two dorsal kidney-shaped shields over the anterior margin of the base of its crown and smooth flanges (without papillae) and *Anamobaea orstedi* Krøyer, 1856 does not have such shields, and its flanges are wrinkled (with papillae). The former species has so far only been reported from the type locality in the British Virgin Islands, whereas the latter has a wider geographic range [29,32]. Because we are not sure about the identity of the associated worms, we refer to them as *Anamobaea* sp.

Most observed worms were withdrawn in their tubes; only a few of them were observed with extended radioles protruding from the tube (Figures 2 and 3). Some extended worms appeared to be shy and quickly retracted into the tube when their pictures were taken (Figure 3). On some occasions, the worms showed high densities, either inside a living host (Figures 2A,B,D, 4E and 6A) or on dead coral (Figure 3C,D).

Some host coral species showed peak-shaped deformities around the worm tubes (Figure 4). In the foliaceous coral *Agaricia lamarcki,* the deformity resembles a sleeve that continues to grow upward and in thickness around the worm's tube, allowing the top to remain free (Figure 4A,B). Peak-shaped deformities in various sizes were most abundantly found in *Pseudodiploria strigosa* (Figure 4C–E) and less commonly in *Orbicella annularis* and *O. franksi* (Figure 4F,G). When the largest peak found in *P. strigosa* (Figure 4C) was removed, the worm tube appeared to be at least 8 cm long and deeply embedded inside the remaining part of the host coral (Figure 5).

Coral injuries were abundant around worm tubes in various coral species (Figures 6 and 7). The wounds, visible as dead lesions, were either at the periphery of live coral tissue (Figure 6A,B) or more toward the middle and surrounded by live coral tissue (Figures 6C,D and 7). Some dead patches were used as substrates by algae and sponges (Figures 6 and 7). In some coral species, the live tissue around the gash showed a discoloration, suggesting that it was spreading from the wound centered around the worm (Figure 7C,D,F).


**Table 1.** Records of stony corals and other sessile invertebrates as host species (by family) for sabellid worms (*Anamobaea* sp.) based on photographs taken at Curaçao (a: 2021 and 2022; b: 2017; c: 2015; and d: 2014), Bonaire (e: 2019), and St. Eustatius (f: 2015).

**Figure 2.** Split-crown feather dusters (*Anamobaea* sp.) hosted by scleractinian corals in the Dutch Caribbean. (**A**) *Diploria labyrinthiformis* at St. Eustatius (2015) hosting five extended worms (one next to the coral colony) and three contracted ones (arrows). (**B**) *Siderastrea siderea* at St. Eustatius (2015) with four extended worms (two next to the coral colony). (**C**) *Porites astreoides* at St. Eustatius (2015) showing two extended worms. (**D**) *Meandrina jacksoni* at St. Eustatius (2015) hosting seven extended worms. (**E**) *Madracis decactis* at Bonaire (2019) with two extended worms. (**F**) *Helioseris cucullata* at St. Eustatius (2015) with one extended worm.

**Figure 3.** Split-crown feather dusters (*Anamobaea* sp.) at Curaçao (2021). (**A**) A single worm on dead coral in the extended condition, showing its radioles. (**B**) The same worm withdrawn inside its tube, overgrown by filamentous algae. (**C**) Four worms on dead coral, one extended. (**D**) The same worms, all withdrawn. (**E**) Two extended worms in association with a *Millepora alcicornis* coral. (**F**) Both worms retracted. Arrows indicate worms that had just retracted. The maximum width of the worm tubes is ca. 5 mm.

**Figure 4.** Coral deformations caused by the presence of split-crown feather dusters (*Anamobaea* sp.) in various host coral species. (**A**,**B**) The host coral *Agaricia lamarcki* at Curaçao (2021) with two peaks in their initial phase (**A**: arrows) and a large peak (**B**: arrow). (**C**) Close-up of the coral *Pseudodiploria strigosa* at Curaçao (2021) showing a large peak. (**D**,**E**) Corals of *P. strigosa* at St. Eustatius (2015), one showing a peak with an extended worm inside (**D**: arrow) and another one with five worm peaks (**E**: arrows). (**F**) *Orbicella annularis* at Curaçao (2021) with one worm peak (arrow). (**G**) *Orbicella franksi* at St. Eustatius (2015) with a small worm peak (arrow), next to a serpulid Christmas tree worm (*S. giganteus*). The maximum width of each sabellid tube is ca. 5 mm.

**Figure 5.** Tube of a split-crown feather duster (*Anamobaea* sp.) after removal of the peak-shaped deformation in a *Pseudodiploria strigosa* coral (see Figure 4C). The visible part of the tube is 8 cm long.

Feather duster worms of two other species were not observed inside living corals but in dead skeleton directly next to a living coral or in a patch of dead coral surrounded by healthy coral tissue. They are the magnificent feather duster *Sabellastarte magnifica* (Shaw, 1800) (Figure 10) and the social feather duster *Bispira brunnea* (Treadwell, 1917) (Figure 11). *Sabellastarte magnifica* was found in or next to live coral colonies of the corals *Diploria labyrinthiformis*, *Madracis auretenra*, *Meandrina meandrites*, *Millepora alcicornis*, *Orbicella annularis*, *Pseudodiploria strigosa*, and *Stephanocoenia intersepta*. Their tubes reached diameters of nearly 2 cm and could therefore be distinguished from the tubes of *Anamobaea* sp., which reached up to 0.5 cm in width. *Bispira brunnea* was only found on dead patches of *Montastraea cavernosa* and *Orbicella annularis* (Figure 11). A published photograph from the Mexican Caribbean shows *B. brunnea* in a coral injury on top of a colony of *Siderastrea siderea* [54]. This worm species can be distinguished from the other two because it occurs as colonies instead of single individuals and because its tubes and radioles are much smaller than those of the others. Because all *Bispira* and *Sabellastarte* worms appeared to live on dead coral skeleton, near live coral, or at a distance, it is unclear whether they were symbionts or part of pseudo-associations.
