Meru phyllisae Spangler and Steiner 2005

Introduction

Meru phyllisae is among the world's smallest and rarest beetles. Less than a millimeter in length, M. phyllisae is known only from the El Tobogán de la Selva cascade in Amazonian Venezuela. There, specimens have been collected clinging to vegetative debris submerged in the stream.

As in other crawling aquatic Adephaga, Meru has a hydrodynamic teardrop shape. The feeding habits of Meru are not known, but lab observations and mouthpart morphology suggest that it may graze on algal filaments or fungal hyphae (Spangler & Steiner 2005). Intriguingly, the population at El Tobogán is dimorphic in wing morphology. Most individuals are brachypterous and flightless but a few have fully developed flight wings, suggesting adaptation to temporary pools or flooding.

The single species is placed in its own family, Meruidae, in the suborder Adephaga. Meruidae is among the newest beetle families, discovered in the 1980s and formally described in 2005 (Spangler & Steiner 2005).

Characteristics

The following diagnosis for the adults is modified from Spangler & Steiner (2005):

1. Size small, total length less than 1 millimeter.
2. Body sculpture rough, and integument covered with flat, wrinkled setae.
3. Tarsal claws pectinate.
   

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   Meru phyllisae tibiae and tarsi. ©

4. Tibial spurs tridentate (inner metatibial spur serrate).
5. Labrum with pairs of overlapping spatulate setae.
6. Legs without swimming hairs.
7. Scapus small and rounded.
8. Antennal flagellum with segments alternately large and small.

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Meru phyllisae antennal flagellum. ©

Discussion of Phylogenetic Relationships

The small size and corresponding reduction of morphological characters complicates the placement of Meru within Adephaga. Nonetheless, the first morphological (Beutel et al 2006) and molecular (Balke et al 2008) phylogenies both infer a sister relationship between Meru and Noteridae, the burrowing water beetles.

Other Names for Meru phyllisae Spangler and Steiner 2005

• Meruidae Spangler and Steiner 2005
• Meru Spangler and Steiner 2005

References

Balke, M., I. Ribera, R. Beutel, A. Viloria, M. Garcia, and A.P. Vogler. 2008. Systematic placement of the recently discovered beetle family Meruidae (Coleoptera: Dytiscoidea) based on molecular data. Zoologica Scripta, 37: 647-650. doi: 10.1111/j.1463-6409.2008.00345.x

Beutel, R.G., M. Balke, and W.E. Steiner. 2006. The systematic position of Meruidae (Coleoptera, Adephaga) and the phylogeny of the smaller aquatic adephagan beetle families. Cladistics, 22: 102-131. doi:10.1111/j.1096-0031.2006.00092.x

Spangler, P.J. and W.E. Steiner. 2005. A new aquatic beetle family, Meruidae, from Venezuela (Coleoptera: Adephaga). Systematic Entomology, 29: 339-357.

Information on the Internet

• Meru on Wikipedia
• El Tobogan de la Selva Hydrophilidae.org's photos and discussion of the only known location where Meru occurs.
• Smithsonian entomologists name a new genus and family of beetles from Venezuela Smithsonian press release announcing discovery of Meru phyllisae.
• Meruidae: New aquatic beetle family Cornell University's Insect Conservation Biology class page on Meruidae.