Abstract
Most species of Polyplacophora are found in shallow, coastal water, and their distribution and ecology is generally well known. On the contrary, information related with distribution, biology and ecology of deep-sea chitons is scarce. Specimens of the deep-sea mollusks fauna were obtained during sampling operations of western Mexico (TALUD project) aimed at the study of invertebrate fauna occurring under the Oxygen Minimum Zone (OMZ). The material reported herein is part of the Polyplacophora fauna collected with a benthic sledge off the west coast of the Baja California Peninsula, in the eastern Pacific, Mexico. The deep-sea chiton Tripoplax cf. balaenophila Schwabe & Sellanes 2004 was collected in 530–625 m depth, in the following environmental conditions: dissolved oxygen, <0.25 ml/l; temperature, 6.44 °C; salinity, 34.47. It represents a range extension of 63° of latitude (ca 8280 km) to the north for this species previously known only from the type locality, off Concepcion, Chile. Tripoplax cf. balaenophila is associated with the lower boundary of the Minimum Oxygen Zone occurring off western Mexico, an habitat characterized by severe hypoxic conditions and colonized by well-adapted species that are generally abundant. Assignment of species to Tripoplax or Lepidozona is still a conflictive issue. The existing discrepancy in slit number and the assignment of “balaenophila” to Tripoplax cannot be solved without a more thorough review of both genera. The disjunct distribution of the genera Tripoplax in the eastern Pacific is also an interesting biogeographical issue.
Highlights
Most species of Polyplacophora are found in shallow, coastal water, and their distribution and ecology is generally well known
Studies related to deep-water (>200 m depth) species are few and very little is known on their distribution and biology (Stebbins & Eernisse 2009; Galeana-Rebolledo et al 2012)
Tripoplax cf. balaenophila is a member of the deep-sea mollusks fauna associated with the lower boundary of the Oxygen Minimum Zone (OMZ) occurring off western Mexico, an habitat characterized by severe hypoxic conditions and colonized by well-adapted species that are generally abundant (Zamorano et al 2006; Papiol & Hendrickx 2015)
Summary
Most species of Polyplacophora are found in shallow, coastal water, and their distribution and ecology is generally well known. Information related with distribution, biology and ecology of deep-sea chitons is scarce. Polyplacophora include about 900 extant species worldwide, most living in shallow water on rocky substrates (Schwabe & Sellanes 2010; Ávila & Sigwart 2013). Studies related to deep-water (>200 m depth) species are few and very little is known on their distribution and biology (Stebbins & Eernisse 2009; Galeana-Rebolledo et al 2012). Most information on deep-water chitons is found in taxonomic and monographic studies that often provide interesting information related to geographic and bathymetric ranges (Dall 1919; Ferreira 1979; Kaas & Van Belle 1985, 1987, 1990; Clark 2008), but very few data are provided regarding ecological aspects
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