Simulamerelina gracilis Amati & Giulio & Oliverio 2023, n. sp.
Creators: name: Amati, Bruno
name: Giulio, Andrea Di
name: Oliverio, Marco
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Littorinimorpha
Rissoidae
Simulamerelina
Simulamerelina gracilis

description: Simulamerelina gracilis n. sp.
(Figs 40; 52B; 53Q; Tables 7; 8; 9)
urn:lsid:zoobank.org:act: 8E32B44C-05C8-40AB-AB26-0DE894269DF6
TYPE MATERIAL. — Holotype. Tuamotu • dd (height 2.45 mm, width 1.08 mm, Figs 40 A-C, G-I; 53Q); Moruroa; 21°46’37”S, 138°53’31”W; beached; on the sea-line; MNHN-IM-2000-38726.
Paratype. Tuamotu • 1 dd (height 2.13 mm, width 0.98 mm, Fig. 40 D-F); same locality and data as holotype; coll. MB.
TYPE LOCALITY. — Tuamotu: Moruroa Atoll; 21°46’37”S, 138°53’31”W; on the sea line.
DISTRIBUTION AND SYMPATRY. — The species is known in the South Pacific Ocean from the Tuamotu (Moruroa), from empty shells only, collected on the sea line (Fig. 52B).
Simulamerelina gracilis n. sp. is sympatric with S. australes n. sp. at its type locality (Moruroa) (Table 9).
ETYMOLOGY. — The name is after the appearance of the shell, from the Latin gracilis (meaning slim).
DIAGNOSIS. — Simulamerelina with large shell for the genus (> 2 mm), acute-slender, turriculate and robust. Protoconch paucispiral. Teleoconch with axial and spiral sculpture of the same strength. Axial ribs reaching the base. Teleoconch with three spiral cordlets, seven on the last whorl. Microsculpture of thin and well spaced uneven spiral threads, with sparse microgranules, in the interspaces; thinner and denser threads on the spiral cordlets. Start of 2 spiral cordlets after protoconch-teleoconch boundary. Colouration uniform white with an orange blotch before the varix.
DESCRIPTION OF HOLOTYPE
Shell (Figs 40 A-C, G; 53Q)
Large for the genus, height 2.45 mm, width 1.08 mm height/ width ratio 2.27, slender-acute, turriculate and robust.
Protoconch (Fig. 40H)
Paucispiral with twisted nucleus, of 1.20 convex whorls, height 0.312 mm, nucleus diameter 0.112 mm, first half whorl diameter 0.200 mm, maximum diameter 0.275 mm. Sculpture of 5-6 thin, weak and uneven spiral cordlets. Protoconch-teleoconch boundary well marked.
Teleoconch
Of 4.70 convex whorls, suture evident and impressed. Axial sculpture on the last whorl of 11 orthocline ribs, slightly prosocline, almost as broad as the interspaces, reaching the base. Spiral sculpture of same strength as axial, of non equidistant cordlets: 2 on first whorl, three on subsequent whorls, the adapical very weak and barely visible; 7 cordlets on last whorl, 3 above the aperture. Cordlet I weakest, cordlet II most prominent. Rounded tubercles at the intersections, more acute on first whorls; interspaces quadrangular. Microsculpture (Fig. 40I) of spaced and uneven dense spiral threads in the interspaces, thinner and denser on the cordlets, and sparse microgranules. Umbilical fissure absent. Aperture oval, height 0.85 mm, height/aperture height ratio 2.88, peristome duplicated, internally with 4-5 short and weak denticles, externally thickened by a strong and broad opisthocline varix.
Colour
Colouration uniform white with an orange blotch on the last whorl before the varix.
Operculum and soft parts
Unknown.
VARIABILITY
Only two specimens are available: the paratype has not reached complete maturity, is smaller than the holotype and has an only slightly thickened varix (see Table 8 and Appendix 18).
REMARKS
Simulamerelina australes n. sp. differs from S. gracilis n. sp. in its less slender (maximum diameter: 0.300 - 0.366 mm vs 0.275 mm in S. gracilis n. sp.) protoconch with a single keel on the adapical fifth, and micro granules on the whole surface vaguely arranged in spiral bands vs 5-6 thin and irregular spiral cordlets in S. australes n. sp.; the less slender outline; the less spiny spiral cordlets on the first whorls, with the subsutural one (still very weak) more evident than in S. gracilis n. sp.
Simulamerelina densestriata n. sp. differs from S. gracilis n. sp. in its more pupoid outline with rather obtuse first whorls and broader base; the less robust spirals with more rounded nodules at the intersections; the more numerous axial ribs on the last whorl (13-20 vs 11-12 in S. gracilis n. sp.); the neatly opisthocline outer lip vs barely opisthocline in S. densestriata n. sp.; the broader and less slender protoconch with a maximum diameter of 0.317 -0.366 mm vs 0.275 mm in S. gracilis n. sp.
description: Published as part of Amati, Bruno, Giulio, Andrea Di & Oliverio, Marco, 2023, Shallow-water Rissoidae of the genera Alvania Risso 1826 Haurakia Iredale 1915 Parashiela Laseron 1956 Simulamerelina Ponder 1985 and Subestea Cotton 1944 Gastropoda Caenogastropoda Rissooidea from French Polynesia with the description of a new deep-water genus, pp. 803-892 in Zoosystema 45 (25) on pages 861-864, DOI: 10.5252/zoosystema2023v45a25, http://zenodo.org/record/10458066