**1. Introduction**

Worm snails of the family Vermetidae are common inhabitants of coral reefs and rocky shores in tropical to warm–temperate marine coastal waters, where they live embedded in dead or live corals or attached to other hard substrata [1]. They have tube-shaped shells, mostly without the regular shell coiling [2,3], which in some species form dense, reef-building aggregations [4–6]. Because of their reef-building capacity in the intertidal or immediate subtidal zone, they play an important role as sea-level and sea-surface temperature indicators in the fossil record [6–8]. The history of Vermetidae systematics is complex, which is partly due to the confusion of their calcareous tubes with those of other organisms, such as serpulid worms [9].

Although there is much literature on coral-associated fauna in the Caribbean, vermetid snails are usually not included [10–13]. Apparently, all host-related information on coral-associated vermetids is from the Indo-Pacific, predominantly involving *Ceraesignum maximum* (G.B. Sowerby I, 1825), previously known as *Dendropoma maxima*, which dwells on scleractinians, blue corals, and fire corals [14–16]. This species is notorious because of its harmful effect on the growth, survival, and photophysiology of host corals [17–20]. There are only a few other coral-vermetid records from the Indo-Pacific, including *Petaloconchus*

**Citation:** Hoeksema, B.W.; Harper, C.E.; Langdon-Down, S.J.; van der Schoot, R.J.; Smith-Moorhouse, A.; Spaargaren, R.; Timmerman, R.F. Host Range of the Coral-Associated Worm Snail *Petaloconchus* sp. (Gastropoda: Vermetidae), a Newly Discovered Cryptogenic Pest Species in the Southern Caribbean. *Diversity* **2022**, *14*, 196. https://doi.org/ 10.3390/d14030196

 Academic Editor: Savvas Genitsaris

Received: 18 February 2022 Accepted: 4 March 2022 Published: 7 March 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

*keenae* Hadfield & Kay, 1972 near Hawaii [21], *Thylacodes hadfieldi* (W.C. Kelly, 2007) near Guam [22], and *Thylacodes* spp. off the west coast of India [23].

During a recent survey of the coral-associated fauna of Curaçao, coral-dwelling worm snails were discovered for the first time in the Caribbean. In order to investigate their preferred habitats, all observed host coral species were recorded. Because the species appears to be cryptogenic, we discuss why no earlier records are known for the Caribbean. The present report serves to create awareness for this cryptogenic species for future research on its origin and its possible effect on the health of Caribbean coral reefs.

#### **2. Materials and Methods**

The survey of coral-associated fauna took place during October–December 2021 along the leeward side of the island of Curaçao. Because the coral-dwelling vermetid was not recorded before in the Caribbean and was overlooked by the first author during earlier surveys, his photo archive was checked for the presence of this snail during fieldwork at Curaçao in 2017, 2015, and 2014, Bonaire in 2019, and St. Eustatius in 2015. Curaçao and Bonaire are located in the southern Caribbean and St. Eustatius in the eastern Caribbean (Figure 1). All association records were listed per island and year (Table 1). Photographic evidence (showing a shell with the operculum present) is presented for each host (Supplementary Materials).

**Figure 1.** Map of the eastern part of the Caribbean showing the position of Curaçao, Bonaire and St. Eustatius, where the occurrence of coral-dwelling vermetids was investigated.
