Thursday, December 26, 2019

[Mollusca • 2019] Eulimacrostoma gen. nov. • A New Genus of Eulimidae (Gastropoda, Caenogastropoda) with Description of A New Species and Reevaluation of other western Atlantic Species


Eulimacrostoma microsculpturata
 Souza & Pimenta, 2019

Abstract
A new genus and a new species of Eulimidae are described based on the shell morphology and on the host-parasite relationship of the type species. Eulimacrostoma microsculpturata Souza & Pimenta gen. nov. and sp. nov. parasitizes a starfish of the genus Luidia and has an elongated, conical, straight, or slightly curved shell, a protoconch with a brownish spiral band and convex whorls, a peculiar large and broad aperture with a strongly protruding outer lip, and microsculpture of axial lines on the teleoconch. Four other species are included in the genus, all from the western Atlantic: Eulimacrostoma chascanon (Watson, 1883), comb. nov., Eulimacrostoma fusus (Dall, 1889), comb. nov., Eulimacrostoma lutescens (Simone, 2002), comb. nov., and Eulimacrostoma patula (Dall & Simpson, 1901), comb. nov. Newly available material of Eulimacrostoma patula expands the known geographic distribution of this species in the Caribbean to the north coast of Brazil. Eulimacrostoma chascanon and Eulimacrostoma fusus and Eulimacrostoma lutescens are known only by the type series which was re-examined. A redescription is provided for Eulimacrostoma chascanon and Eulimacrostoma fusus. Species within Eulimacrostoma differ mainly by teleoconch sculpture, the presence or absence of an umbilical fissure, and shell dimensions. Lectotypes are designated for Eulimacrostoma chascanon, Eulimacrostoma fusus, and Eulimacrostoma patula.

Key Words: biodiversity, micromolluscs, parasitic snails shell morphology, taxonomy, Vanikoroidea

Figure 1. Eulimacrostoma microsculpturata gen. nov. and sp. nov. A. Holotype (USNM 429762); B, C. Paratype (USNM 433081); D–G. Paratype (FLMNH uncatalogued.)
A, B, D. Shell in frontal view; C, E. Shell in lateral view; F. Detail of apical whorls in frontal view; G. Specimen attached to the host Luidia ludwigi scotti Bell, 1917 (Echinoderm collection, FLMNH 5042), red ellipse indicates the eulimid.
Scale bars: 1 mm (A–E); 100 µm (F).

Systematics: 
Family Eulimidae Philippi, 1853

Genus Eulimacrostoma Souza & Pimenta, gen. nov.

Type species: Eulimacrostoma microsculpturata Souza & Pimenta, sp. nov. Recent, northwestern Atlantic and Caribbean.

Diagnosis: Eulimids parasitic on asteroids. Shell elongated, conical, straight or slightly curved. Protoconch subcylindrical, smooth. Teleoconch with slightly convex whorls, several incremental scars and microsculpture of axial lines, wide brownish spiral bands, a large and spread aperture, occupying between 60–70% of the body whorl length, and an orthocline outer lip, strongly protruding.

Etymology: Eulima, due to the systematic affinity and for being one of the most common names of the family, in combination with Macros, Gr. = long; and Stomatos, Gr. = mouth; in reference to the broad shape of the shell aperture.

Eulimacrostoma microsculpturata Souza & Pimenta, sp. nov. 
Melanella patula auct. non. 
(Dall & Simpson, 1901): Dall (1927, in part.: 67).

Etymology: The epithet alludes to the microsculpture characteristic of the present species.

Type locality: Puerto Rico: off San Juan, Johnson–Smithsonian Deep-sea expedition stn. 10 (..., 219–293 m), coll. Yacht Caroline, 02/ii/1933.

Diagnosis: Eulimid parasitic on starfish, with an elongated shell, presenting microsculpture of axial lines, dome-shaped apex, a narrow brownish spiral band close to the suture in the protoconch and a wide brownish spiral band along the teleoconch, a high, wide and spread aperture. Umbilicus absent.

Remarks: 
Dall (1927: 67) cited 20 specimens of “Melanella patula” from “off Georgia”. The USNM houses two lots (USNM 108031, USNM 108380, respectively from Fernandina, Florida, USFC stn. 2668, and from Georgia, USFC stn. 2415), that can be attributed to the material studied by Dall (1927) due to the labels. USNM 108031 contains a single shell with a broken protoconch and an eroded surface. Although the shell is not in perfect condition, it is possible to affirm that it is actually Eulimacrostoma microsculpturata sp. nov. by the general shape and teleoconch sculpture. USNM 108380 contains seven shells, most of them immature, which can neither be identified with certainty as Eulimacrostoma patula (Dall & Simpson, 1901), comb. nov. nor as Eulimacrostoma microsculpturata.

Most specimens of Eu. microsculpturata have a straight spire (Figs 1A, 2A), but individuals of the lot USNM 433081 (Fig. 1B) have a slightly curved spire. The curvature is a growth phenomenon related with the position of the incremental scars and usually helps to distinguish species (Bouchet and Warén 1986: 312). However, in the case of Eu. microsculpturata the protoconch, color pattern, shape of the aperture, and dimensions are very similar in all individuals and we consider all of them belonging to the same taxon. The holotype USNM 429762 and paratype FLMNH are young individuals and shows a more rhomboid aperture and angulated body whorl, which is a common feature at this stage of growth (Bouchet and Warén 1986: 310; Souza et al. 2018: 926).


 Leonardo Santos de Souza and Alexandre Dias Pimenta. 2019. Eulimacrostoma gen. nov., A New Genus of Eulimidae (Gastropoda, Caenogastropoda) with Description of A New Species and Reevaluation of other western Atlantic Species.  Zoosystematics and Evolution. 95(2): 403-415. DOI: 10.3897/zse.95.33880