Abstract
The cushion–star Parvulastra exigua (Lamarck, 1816) is a widely distributed member of the temperate intertidal fauna in the southern hemisphere. In South Africa, it occurs in sympatry with the endemic Parvulastra dyscrita (Clark, 1923), the two species being differentiated predominantly by gonopore placement. Several recent studies have suggested that there may be additional cryptic species within the Parvulastra exigua complex in South Africa, based variously on color morphology, genetic evidence and the differential placement of the gonopores. This paper attempts to resolve whether one or more species are represented within Parvulastra exigua. A total of 346 Parvulastra exigua and 8 Parvulastra dyscrita were collected from sites on the west and south–west coasts of South Africa; morphological, anatomical and genetic analyses were performed to determine whether cryptic species and/or Parvulastra exigua specimens with aboral gonopores were present. Results show that neither cryptic species nor Parvulastra exigua specimens with aboral gonopores occur at these sites. This study thus refutes previous claims of the existence of aboral gonopores in South African Parvulastra exigua, and suggests that a single species is represented. The distinction between Parvulastra exigua and Parvulastra dyscrita is also confirmed, and features separating these two species are clarified and documented.
Highlights
The dwarf cushion–star Parvulastra exigua (Lamarck, 1816) is a prominent and widespread member of the temperate intertidal fauna in the southern hemisphere (Hart et al 2006), occurring along the entire southern coastline of Africa from Namibia to Mozambique, in southeastern Australia and on several oceanic islands (Clark and Downey 1992)
Of the 354 specimens included in the analysis, eight were identified as Parvulastra dyscrita and the remainder as Parvulastra exigua
The gonopore position was not externally visible in any of these specimens, but once dissected it was clear that all had aboral gonopores
Summary
The dwarf cushion–star Parvulastra exigua (Lamarck, 1816) is a prominent and widespread member of the temperate intertidal fauna in the southern hemisphere (Hart et al 2006), occurring along the entire southern coastline of Africa from Namibia to Mozambique, in southeastern Australia and on several oceanic islands (Clark and Downey 1992). While the larger P. dyscrita has a fairly consistent mottled coloration (Fig. 1), P. exigua demonstrates a high degree of color variation, with two major color morphs in South Africa demonstrating an allopatric distribution (Fig. 1; Branch et al 2010). The mottled morph is found predominantly in the high tidal zone within protected, bare rock, algae–encrusted and under boulder habitats with few algal tufts, while the green and intermediate color morphs were found in the mid tidal zone, with the green color morph inhabiting under boulder and bare rock habitats and tidal pools with little/no algae canopy and coralline algae. The intermediate color morph predominantly inhabited bare rock tidal pools, with little coralline algae, and avoided those with algal tufts and an algal canopy
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