González-Vallejo NE and Amador-Carrillo S (2021), Assessment of Megadenus holothuricola Rosén, 19...

ECB-ART-49307

Zookeys 2021 Feb 11;1016:49-61. doi: 10.3897/zookeys.1016.55071.

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Assessment of Megadenus holothuricola Rosén, 1910 (Eulimidae), an endoparasite of Holothuria mexicana Ludwig, 1875 (Holothuriidae) in the southern Gulf of Mexico and the description a new species.

González-Vallejo NE , Amador-Carrillo S .

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As part of a study on holothurians from the southern Gulf of Mexico, some Holothuria mexicana Ludwig, 1875 were obtained for gut analysis. In two of them, a couple of eulimids were located inside the main tube of the respiratory tree. They were identified as Megadenus holothuricola Rosén, 1910, described from the Bahamas Islands, based on five specimens attached to the respiratory tree of H. mexicana. The original description was brief with few details, the type material is lost, and the species has not been found again. In this contribution, this species is confirmed for Campeche Bay, Mexico. The adult shell is globular to conical, transparent, thin, and fragile. Megadenus smithi sp. nov. from Palmyra Atoll, Central Pacific is described based on adult specimens. It differs from its congeneric species in its more robust shell, the pseudopallium does not cover the shell, and its short and contracted proboscis forms a thick disc. Further research on these eulimid parasites is now complicated in the southern Gulf of Mexico because of the holothurian population collapse due to over-exploitation of the fishery.

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References :

Takano, Megadenus atrae n. sp., an endoparasitic eulimid gastropod (Mollusca) from the black sea cucumber Holothuria atra Jaeger (Aspidochirotida: Holothuriidae) in the Indo-West Pacific. 2017, Pubmed, Echinobase

	Figure 1. Megadenus holothuricola Rosén, 1910 A two adults between filaments of the respiratory tree B, C detached adult shells, SL = 5.5 mm and 4.5 mm; right side juvenile attached SL = 1.0 mm D broken adult shell SL = 2.5 mm E subadult SL = 2.0 mm with everted proboscis L = 2.5 mm. Scale bars: 1.6 mm (A); 1.8 mm (B); 1.4 mm (C); 0.2 mm (D); 1.1 mm (E).
	Figure 2. Megadenus holothuricola Rosén, 1910 A adults immersed in the main tube of the respiratory tree B, C two adults showing the mottled skin of the respiratory tree and the pseudopallium covering shell; proboscis slightly rolled, and another adult stretched to the maximum D cephalic view, 40× E two egg capsules, L = 2 mm F view of the distal part of an adult proboscis. Scale bars: 1.2 mm (A); 2.3 mm (B); 1.65 mm (C); 0.8 mm (D); 0.6 mm (E); 0.5 mm (F). Abbreviations: e: eyes; eg: egg capsules; p: proboscis; pg: pedal gland; pp: pseudopallium; rt: respiratory tree; s: shell; t: tentacle.
	Figure 3. Megadenus smithi sp. nov. A holotype female in apertural and posterior views (ECOSUR-0234) SL = 6.5 mm × 4.0 mm wide B paratype male in apertural and lateral view, showing the tentacles SL = 4.0 mm. × 3.5 mm wide C pedal gland view D distal open proboscis view. Scale bars: 1.2 mm (A); 1.0 mm (B); 0.6 mm (C); 0.5 mm (D).