Megadenus smithi, González-Vallejo & Amador-Carrillo, 2021

Gonzalez-Vallejo, Norma Emilia & Amador-Carrillo, Stephanie, 2021, Assessment of Megadenus holothuricola Rosen, 1910 (Eulimidae), an endoparasite of Holothuria mexicana Ludwig, 1875 (Holothuriidae) in the southern Gulf of Mexico and the description a new species, ZooKeys 1016, pp. 49-61 : 49

Megadenus smithi sp. nov. Fig. 3A-D

Type material.

Holotype (ECOSUR-0234) female; paratypes (ECOSUR-0235) two males, one juvenile from the type locality found attached in the cloacal chamber of Holothuria (Halodeima) atra Jaeger, 1833 collected on 11 September 2011 by J Smith.

Type locality.

Palmyra Atoll, Central Pacific Ocean, shallow water in reef lagoon.

Etymology.

This species is being named after the collector Mr. J. Smith, as a means of recognition, for his sampling efforts.

Distribution.

Known only from the type locality.

Diagnosis.

Female shell globose to conical, transparent, fragile, glassy, colorless, fine incremental axial stria; apex mucronate glassy white not tilt; proboscis slightly dark; large pedal gland.

Description.

Shell globose, translucent, thin, fragile, colorless, smooth sculpture, with fine axial striae, several growth scars of earlier outer lip positions are irregularly spaced, suture impressed. Adult shell 6.5 mm long; 4.0 mm wide; body whorl 4.5 mm long (holotype Fig. 3A ). Teleoconch 5.5 convex whorls, three flat, small post-larval whorls, the penultimate whorl 1.0 mm. Aperture broad, inner lip smooth, concave at base, outer lip simple, slightly curved in most protruding part. Protoconch mucronate, two whorls, glassy white, no operculum or periostracum; sexually dimorphic, male with a penis behind the eye, female is 30% larger than male (Fig. 3B ).

Soft tissues pale cream with reddish pigmentation, seen through transparent shell. Pseudopallium cauldron-shaped in sub-adults arising from the aperture and covering large part of shell, or short mantle folds not covering female shells, smooth. When skin was removed, a thick, rounded pedal gland was visible in the aperture (Fig. 3C ). Head with a pair of thick long tentacles and black eyes; penis large, placed behind right eye in males. Proboscis slightly dark colored, retractile, separate from the pseudopallium by a deep constriction. Proboscis skin slightly contracted after fixation, forming a thick disc with the mouth distally (Fig. 3D ), almost as long as whole specimen. No egg capsules or juveniles were found.

Remarks.

The new species shares several shell and morphological traits with the other five congeneric species. A comparison of the most important structures, almost all based on the literature, is provided in Table 1 . Megadenus smithi sp. nov. resembles M. voeltzkowi because both have a tall shell (6.5 mm), a swollen and more convex penultimate whorl than M. holothuricola and M. atrae . The protoconch in M. holothuricola is transparent, 1.5 whorls, and is slightly wider than high, while in M. smithi sp. nov. it is two whorls higher than wide much like in M. cantharelloides , M. voeltzkowi , and M. atrae . However, the latter has a slightly tilted protoconch axis. Megadenus oneirophantae has a long thin proboscis, the pseudopallium is missing, and the species exhibits a marked sexual dimorphism with a dwarf male.

Figures

Figure 3. Megadenus smithi sp. nov. A holotype female in apertural and posterior views (ECOSUR- 0234) SL = 6.5 mm x 4.0 mm wide B paratype male in apertural and lateral view, showing the tentacles SL = 4.0 mm. x 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).