Chitons (Mollusca: Polyplacophora) - Biological Science - California ...

Page 54 THE FESTIVUS VOL. XLI(6): 2009
of the Southern California Bight (SCB), which ranges
from Point Conception, California, USA to Cabo
Colonet, Baja California, México (see Table 1). Except
for general geographic and bathymetric range
information listed in monographs and other taxonomic
works (e.g., Ferreira, 1978, 1979a, 1979b, 1982, 1983;
Kaas & Van Belle, 1985a, 1985b 1987, 1990, 1994;
Watters, 1990; Clark, 1994, 1999), little information is
available concerning the presence of many species in
these relatively deep southern California waters. Much
of the shelf and slope benthos of the region is composed
of soft sediments, which are the focus of several large
benthic monitoring programs associated with major
municipal wastewater outfalls (see City of Los Angeles,
2007, 2008; Orange County Sanitation District, 2007;
City of San Diego, 2008a, 2008b; Los Angeles County
Sanitation Districts, 2008). Although soft sediments are
typically considered unsuitable habitat for chitons, the
presence of various types of hard substrates scattered
across the sea floor provides refuges for these animals
and also exposes them to incidental capture by regular
benthic or epibenthic sampling activities (e.g.,
Mullineaux, 1987; Eernisse, 1998). In southern
California, these chiton microhabitats often include
small rocks, rocky outcroppings or reefs, mollusk shells
and shell fragments, as well as man-made debris such as
bottles, cans, and larger pieces of glass, metal, plastic or
even rubber (TDS, personal observation). This study
summarizes the SCB benthic chiton fauna collected by
the above monitoring programs over the past two
decades or more.
Methods
Most of the chitons examined in this study were
collected as part of the long-term ocean monitoring
programs conducted by the City of San Diego, City of
Los Angeles, Los Angeles County Sanitation Districts,
and Orange County Sanitation District. Additional
specimens were collected by these or other agencies
during several large-scale regional monitoring projects
that spanned the entire SCB. These bight-wide surveys
included the 1994 Southern California Bight Pilot
Project (SCBPP) and subsequent Bight’98, Bight’03 and
Bight’08 regional monitoring efforts in 1998, 2003 and
2008, respectively (e.g., Bergen et al., 1998, 2001;
SCBPP, 1998; Ranasinghe et al., 2003, 2007). Samples
containing chitons were typically collected using
standard benthic sampling (e.g., Van Veen grabs) or
trawling (e.g., otter trawl) gear and procedures. It is
worth noting that this sampling has not targeted rocky
areas, e.g., using biological (rock) dredge gear, and
such future sampling could turn up additional chiton
species.
All chitons collected were examined and identified
using dissecting and compound microscopes. Body
lengths were measured to the nearest 0.1 mm from the
anterior-most margin of the girdle in front of valve I
(head valve) to the posterior-most girdle margin behind
valve VIII (tail valve) with the chitons flattened as much
as possible. Lengths for excessively curled or damaged
specimens were estimated.
Higher-level chiton systematics and phylogeny have
been in a state of flux and the focus of subsequent
research for a number of years (e.g., Smith, 1960; Kaas
& Van Belle, 1980, 1985a, 1985b, 1987, 1990, 1994,
1998; Van Belle, 1983, 1985, 1999; Eernisse, 1984;
Sirenko, 1993, 1997, 2006; Buckland-Nicks, 1995,
2008; Kaas et al., 1998; Okuso et al., 2003). The
classification expressed in Table 1 follows Eernisse et
al. (2007), which is supported by recent molecular
studies by D. J. Eernisse (unpublished; see also
Eernisse, 2004a, 2004b, 2006, 2007, 2008a, 2008b;
Kelly & Eernisse, 2008; Vendrasco et al., 2008). This
arrangement is similar to the recent system proposed by
Sirenko (2006) but differs in its reassignment of
Dendrochiton and Tonicella to Mopaliidae Dall, 1889,
and not Tonicellidae Simroth, 1894, as in Sirenko’s
classification. Starobogatov & Sirenko (1975) derived
Tonicellidae from Simroth’s (1894: 321) “Tribus” (=
tribe) Tonicelloidea without any proposed change in
composition. Simroth (1894) clearly intended this taxon
to correspond to one of three “Ischnochitoninae”
lineages depicted in Pilsbry’s earlier proposed
phylogeny (reprinted in Simroth, 1894: 326).
Tonicelloidea as envisioned by Pilsbry and Simroth
grouped four disparate genera (including Tonicella)
whose least inclusive grouping would presently
correspond with Chitonida. In contrast, Sirenko’s (2006)
composition of Tonicellidae is similar to
Lepidochitonidae Iredale, 1914, of other authors (e.g.,
Ferreira, 1982, or as subfamily within Ischnochitonidae
in Kaas & Van Belle, 1985b). We use Lepidochitonidae
here instead of Tonicellidae because Lepidochitonidae
sensu Eernisse et al., 2007, is exclusive of Tonicella,
which instead is considered part of Mopaliidae (see