Thursday, 13 November 2014

Three new species of Omalogyrid Snails from the southern West Coast of North America.


Omalogyrid Snails are among the smallest known Gastropods, with adult body sizes often comparable with larger Protozoans (single-celled ‘animals’). As such they tend only to be collected in surveys which directly target them, rather than general surveys of Mollusc faunas, and are often undocumented even in areas where other Molluscs have been studied extensively. Omalogyrid Snails are not well studied, and neither relationships within the group, nor the relationship of the group to other Gastropods are understood. Neither is much known about the ecology or life-histories of these Snails, though they are thought to all be algae consumers, and those species whose reproductive behaviour and life cycles have been observed are hermaphrodites (all individuals poses male and female sexual organs), with the young emerging from the eggs as crawling larvae rather than a separate planktonic phase.

In a paper published in the journal Zootaxa on 7 October 2014, AndréSartori and Rüdiger Bieler of the Field Museum of Natural History in Chicago describe three new species of Omalogyrid Snails from the southern West Coast of North America, all of which are placed in the genus Ammonicera, from the collection of the Natural History Museum ofLos Angeles County.

The first new species described is named Ammonicera sleursi, in honour of Willy Sleurs of the Royal BelgianInstitute of Natural Sciences, for his work on Omalogyrid Snails. The species is described from 92 specimens collected from locations at Mission Bay in San Diego County, California, on the coasts of Jalisco and Baja California States in Mexico, at depths of between 2 and 100 m. Ammonicera sleursi reaches about 0.7 mm in width and has a disk-shaped shell, glossy and fawn on colour, with a broad spiral cord on the early whorls of the shell, which disappears on the outer whorls (as the Snail reaches maturity).

Ammonicera sleursi. (A–B) Apical views; (A) general view; (B) detail of the protoconch (interpreted boundary between protoconch and teleoconch at arrowhead); (C–D) Umbilical views; (C) general view; (D) detail of the protoconch; (E) dorsal view; (G) apical view, showing colouration; (F) apertural view; (H) specimen from Los Arcos, apical view showing wide grooves between spiral cords. Scale bars: (A, C, E–G) are 0.2 mm; (B, D, H) are 0.1 mm. Sartori & Bieler (2014).

The second new species described is named Ammonicera mcleani, in honour of James McLean of the Natural History Museum of Los Angeles County, an expert on eastern Pacific Gastropods, who collected much of the material used in the study. The species is described 19 specimens locations in Baja California State in Mexico, at depths of between 3 and 25 m. Ammonicera mcleani reaches about 0.52 mm in width, and has a disk-shaped glossy amber shell, with inner and outer spiral cords and 19-21 nodules around its outer whorl.

Ammonicera mcleani. (A–C) Apical views; (A) general view; (B) detail of the protoconch; (C) colouration; (D–E) paratype 1, umbilical views; (D) general view; (E) detail of the protoconch (interpreted boundary between protoconch and teleoconch at arrowhead); (F) dorsal view; (G) apertural view. Scale bars: (A, C, D, F, G) are 0.2 mm; (B, E) are 0.1 mm. Sartori & Bieler (2014).

The final new species is named Ammonicera mexicana, in reference to where it was found. The species is described from 24 specimens, from Jalisco State, and the islands of Isabela and Roqueta on the Mexican Pacific Coast, collected at depths of between 1.5 and 20 m. Ammonicera mexicana reaches about 0.57 mm in width, and has a disk-shaped, glossy, amber shell with central and outer spiral cords and 14-20 nodules on its outer whorl.

Ammonicera mexicana. (A–C) apical views; (A) general view; (B) detail of the protoconch (interpreted boundary between protoconch and teleoconch at arrowhead); (C) colouration; (D–E) umbilical views; (D) general view; (E) detail of the protoconch; (F) dorsal view; (G) apertural view. Scale bars: (A, C, D, F, G) are 0.2 mm; (B, E) are 0.1 mm. Sartori & Bieler (2014).

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