Thylacodes vandyensis

Invasion History

First Non-native North American Tidal Record: 2014
First Non-native West Coast Tidal Record:
First Non-native East/Gulf Coast Tidal Record: 2014

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General Invasion History:

Thylacodes vandyensis is currently known from only one shipwreck off the Florida Keys. Based on genetic sequences, the overall diversity of the genus, and the origin of other non-indigenous species in the region, the Indo-Pacific is considered the likeliest region of origin (Bieler et al. 2017).

North American Invasion History:

Invasion History on the East Coast:

Thylacodes vandyensis was discovered on a sunken shipwreck, the USNS General 'Hoyt S. Vandenberg' about 11 km off Key West, Florida, on May 10, 2014, at 29 m depth. The worm-shell colonies were rare and scattered in 2014, but in January 2016 they covered much of the current-exposed parts of the wreck. This worm-shell was morphologically distinct from known Atlantic species, and had genetic sequences similar to Indo-Pacific species. The Vermetidae of the Indo-Pacific are highly diverse and include many undescribed species (Kelly 2007). The wreck was heavily colonized by at least two Indo-Pacific species, the cup coral Tubastraea coccinea and the oyster Hyotissa hyotis (Bieler et al. 2017).

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Description

Vermetids (Worm-shells) are sessile gastropods, whose shells are long, coiling tubes attached to hard surfaces, often growing in colonies, The protoconch (initial larval shell) is at right angles to the following whorls (Abbott 1974). In Thylacodes vandyensis*, the protoconch has 1.5 bulbous whorls, with weakly or strongly developed spiral ribs (Bieler et al. 2017). The shell grows in a convoluted irregular fashion, with sharp, elbow-like bends, wrapping over older parts of the tube. Earlier whorls are abandoned and closed off by septa, and its body resides in 2–4 of the newest whorls. The earlier whorls have growth lines and densely spaced transverse ribbing. Later whorls have variable transverse and longitudinal ribs. The last whorl often forms an erect feeding tube, which is thinner walled, lacks longitudinal sculpture, and rises about 9–25 mm above the tube mass. This worm-shell lacks an operculum. The body of T. vandyensis is worm-like, but stocky and tapering posteriorly. The head-foot complex is broad and plug-like, with a pair of small tentacles and eyespots. The overall tube mass is about 25 mm in the longest dimension, and the mouth of the feeding tube is ~4.5–6.5mm. There are two color morphs, orange and gray. The orange morph has a deep-orange head-foot and an overall orange body. The gray morph has a black head-foot, a yellow rim on the mantle edge and an orange lining of the mantle cavity, but is generally gray and brown. The above description is based on Bieler et al. 2017.

Thylacodes vandyensis is much larger and is morphologically distinct from the known vermetids off Florida and in the Atlantic. Gene COI sequences were similar to those of several Thylacodes spp. from the Indo-Pacific, including T. medusae from Japan and T. "imbricatus'' [adamsii] from China. The Indo-Pacific also has a high diversity of undescribed vermetids (Bieler et al. 2017).

*The species name is derived from scuba divers' nickname 'Vandy' for the wreck of the USNS 'General Hoyt S. Vandenberg' (Bieler et al. 2017).

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Taxonomy

Ecology

General:

The appearance and ecology of vermetids is roughly comparable to that of serpulid polychaetes (Abbott 1974). Vermetids are dioecious, with distinct males and females, but some species are protandrous hermaphrodites (male first, then female, Calvo et al. 2005). In another, unnamed species (known as 'Hadfield's vermetid', found in Hawaii) males are rarely seen, but it is not known whether reproduction is parthenogenetic, or whether sperm is released by short-lived males and stored, or whether males are simply rare (Strathmann and Strathmann 2006). Eggs are brooded in egg-capsules, stored in the mantle cavity, and attached by a stalk to the inner wall of tube. The capsules contain 14–16 veligers, which are released as crawling hatchlings with the velum fully resorbed (Bieler et al. 2017). This mode of development was found in five species of Indo-Pacific vermetids (Kelly 2007). Longer-range dispersal can occur by rafting on floating objects, or transport on ships. In addition, hatchlings can produce long mucus threads and can be carried by currents to new habitats (Strathmann and Strathmann 2006).

At this time, Thylacodes vandyensis is known only from the wreck of the USNS ‘General Hoyt S. Vandenberg’, off Key West, Florida, so its biology in natural habitats is unknown. Likely substrates include coral reefs and rocky outcrops. It was found in marine salinities, in 29 m of water, and a subtropical climate. It is expected to spread to other ships, which have been deliberately sunk to create habitat for marine life and attractions for divers. Most of the animals were attached to shells of Hyotissa mcgintyi (McGinty's Oyster), or Spondylus americanus (Atlantic Thorny Oyster), growing on the ship's hull (Bieler et al. 2017). Vermetid gastropods feed by exuding a mucus net, letting it expand in the current, and then drawing it in to ingest the captured particles, including both phytoplankton and zooplankton (Kappner et al. 2000).

Food:

Phytoplankton, Zooplankton

Trophic Status:

Suspension Feeder

SusFed

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Habitats

General Habitat	Vessel Hull	None
General Habitat	Rocky	None
General Habitat	Coral reef	None
Salinity Range	Euhaline	30-40 PSU
Tidal Range	Subtidal	None
Vertical Habitat	Epibenthic	None

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Life History

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Tolerances and Life History Parameters

Maximum Length (mm)	25	Largest length of attached individual adult shell mass, usually 20-25 mm (Bieler et al. 2017).
Broad Temperature Range	None	Subtropical-Tropical
Broad Salinity Range	None	Euhaline

General Impacts

Given its recent discovery and limited range, ecological and economic impacts of Thylacodes vandyensis are unknown. However, vermetids growing on coral reefs are believed to impact corals negatively, by reducing light and water circulation, intercepting food, and irritating corals with the noxious chemicals present in their mucus webs (Bieler et al. 2017).

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References

Abbott, R. Tucker (1974) American Seashells, Van Nostrand Reinhold, New York. Pp. <missing location>

Bieler R, Granados-Cifuentes C, Rawlings TA, Sierwald P, Collins TM. (2017) Non-native molluscan colonizers on deliberately placed shipwrecks in the Florida Keys, with description of a new species of potentially invasive worm-snail (Gastropoda: Vermetidae), PeerJ 5: Published online
https://doi.org/10.7717/peerj.3158

Calvo, M. ; Templado, J. (2005) Reproduction and sex reversal of the solitary vermetid gastropod Serpulorbis arenarius, Marine Biology 146: 963-973
DOI 10.1007/s00227-004-1490-8

Kappner, I., Al-Moghrabi, S. M., & Richter, C. (2000) Mucus-net feeding by the vermetid gastropod Dendropoma maxima in coral reefs., Marine Ecology Progress Series 204: 309–313

Kelly, Walter C., III (2007) Three new vermetid gastropod species from Guam, Micronesica 39: 117-140

Rosenberg, Gary 1995-2023 Malacolog 4.1. http://www.malacolog.org/



Strathmann, Meguni F.; Strathmann, Richard R. (2006) A vermetid gastropod with complex intratracapsular cannibalism of nurse eggs and sibling larvae and a high potential for invasion., Pacific Science 60(1): 97-109

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