This is a family of minute molluscs which is divided into the subfamily Ebalinae, containing only the genus Ebala, and the subfamily Murchisonelline, containing the genera Koloonella and Murchisonella. Only a few species exceed 3.5 mm, with most being less than 2 mm. Because of the small size and consequent difficulty of collection and study the family has only recently being closely studied. However, numerous fossil species have been known since the 19th century, and more recently some have been described from Australian Carboniferous deposits.
Traditionally Murchisonella and Ebala were classified in the Pyramidellidae, but Warén (1994) created a family Ebalidae for Ebala and Murchisonella. He based his family on the unique jaw apparatus, which lacks a radula, of the European species Ebala nitidissima. The family was later extended, as Murchisonellidae, to include other genera, particularly the Australian Koloonella.
The family is widely distributed, with species known from the Mediterranean Sea (introduced species M. columna from the Red Sea), the eastern and and western Atlantic, and the eastern Pacific. The Indo-West Pacific appears to have the greatest diversity, with species known from Australia, Thailand, Japan and Philippines.
Specimens are mainly encountered in shallow water, down to about 30 m but nothing is known about the microhabitat or food preferences (Warén, 2013).
Warén, A. 1994. Systematic position and validity of Ebala Gray, 1847 (Ebalidae Fam. N., Pyramidelloidea, Heterobranchia) Bollettino Malacologico 30: 5-9.
Peñas, A. & Rolán, E. 2013. Revision of the genera Murchisonella and Pseudoaclisina (Gastropoda, Heterobranchia, Murchisonellidae). Vita Malacologica 11: 15-64.
Warén, A. 2013. Murchisonellidae: who they are, where are they and what are they doing? (Gastropoda, lowermost Heterobranchia). Vita Malacologica 11: 1-14.
Three well-documented species from NSW are detailed here, but knowledge of the family continues to develop, and it is likely that more species will be described.
The following species of Koloonella are listed by the Australian Faunal Directory as occurring in NSW, but are not treated in detail here:
Koloonella harrisoni (Tate & May, 1900). There are only 2 NSW specimens sorted as this species in the Australian Museum collection. It is doubtful that they are the same species, and neither matches the genus Koloonella.
Koloonella micra (Petterd, 1884). This species was first described from Tasmania. There is only one NSW specimen sorted as this species in the Australian Museum collection. Its identification is doubtful.
Koloonella minutissima (Laseron, 1951). This is known only from the holotype. It is probably a juvenile of K. moniliformis.
Koloonella turrita (Petterd, 1884). This species was first described from Tasmania. Laseron (1951, p. 325) reported it from Balmoral, NSW, but I can find no specimens in the Australian Museum collection.
Koloonella tomacula (Laseron, 1951). This is treated here in the Pyramidellidae as Odostomia tomacula (Laseron, 1951).
Shells are minute, fragile, elongate with many rounded whorls with a deep suture, and the spire nearly straight-sided. The aperture is rounded, the columella is a little reflected, and there is no plait on the columella. Anatomically, the family is distinguished by a complex jaw arrangement without a radula (Warén, 1994).
Copyright Des Beechey 2017