Elminiinae Foster, 1982

Buckeridge, John S. & Newman, William A., 2010, A review of the subfamily Eliminiinae (Cirripedia: Thoracica: Austrobalanidae), including a new genus, Protelminius nov., from the Oligocene of New Zealand, Zootaxa 2349, pp. 39-54 : 42

Subfamily Elminiinae Foster, 1982 (nom correctum, Buckeridge, 1983a).

Diagnosis: Austrobalanids lacking both internal chitinous stringers and arborescent interlaminate figures.

Distribution and age: Littoral, low energy environments. Oligocene to Recent: southeastern Australia, New Zealand, southern Chile around Tierra del Fuegio to southern Argentina and out to the Falkland Islands; introduced into Europe during the 1940s, temporarily to South Africa in the 1950s and questionably introduced to the Azores in the early 1900s ( Figure 1 ).

Remarks: Newman and Ross (1971, copyright 1970), cited by Ross (1970) as “in press”, had discovered chitinous structures in the wall of Elminius simplex similar to those seen in some tetraclitids, and they briefly discussed how this, as well as some previously known characters, suggested tetraclitid rather than balanine affinities. In the discussion of Epopella , the new genus Ross (1970) erected to accommodate Tetraclita (Tetraclita) purpurascens forma breviscutum Broch, 1922 , both Elminius plicatus Darwin, 1854 and E. simplex were transferred to Epopella and thus assigned to the tesseroporan tetraclitids.

As noted in the introduction, Foster (1979) was not aware that Epopella plicata , E. simplex and Epopella breviscutum , had been transferred to the tetraclitid subfamily Austrobalaninae by Newman and Ross (1976). Likely, therefore, he did not feel the need to formalize his new family, the Elminiinae , other than to say, “This species (of Hexaminius ) and of Elminius , seem to constitute a southern hemisphere subfamily as well defined as the northern hemisphere Semibalaninae . I propose the name Elmininae (sic) for this subfamily” ( Foster, 1982a: 22). Foster’s original spelling for the subfamily was “Elmininae” which was derived from the genus Elminius Leach, 1825 , and thus, according to the International Code of Zoological Nomenclature, should have been Elminiinae ( Buckeridge, 1983a; Foster, 1987).

The phylogeny of the elminiines ( Figure 2) draws upon the conclusions reached by Pérez-Losada et al. (2008) plus interpretation of a relatively sparse but nonetheless informative fossil record ( Buckeridge, 1983b, 1984). The main issue with molecular-based reconstructions of phyletic divergence is an assumption that significant changes must occur over considerable time. In Pérez-Losada et al. (2008: 337), it is proposed that the Verrucomorpha-Balanomorpha divergence occurred shortly after the close of the Jurassic c.145 MYBP. However, if the absence of any late Mesozoic balanomorph barnacles is a true reflection of Cretaceous biodiversity (as opposed to an artifact of preservation), and we believe it is, then Protelminius would have arisen from an eight-plated pachylasmatid such as Eolasma only c.50 MYBP.

The absence of Mesozoic balanomorphs is the basis for the broader assessment of balanomorph cirripede divergences as shown in Figure 3 . As the Tetraclitoidea appear first in the late Palaeocene (Thanetian) of the Chatham Islands ( Buckeridge, 1983a), the divergence of the earliest tetraclitoids (e.g. Bathylasma ), from the pachylasmatids, must have occurred in less than 10 million years.

Figures

FIGURE 1. Distribution of the Elminiinae and early Tetraclitoidea. The earliest record of the Elminiinae is the four plated Protelminius pomahakensis from the Rupelian (early Oligocene) of New Zealand. Assuming a six-plated ancestor to this taxon, parsimony requires a Hexaminius - type first occurring in eastern Australia during the Eocene, from which the four-plated form evolved and dispersed across a proto-Tasman Sea to New Zealand. If Hexaminius had occurred in New Zealand, it would not be unreasonable to expect it in the present warmer northern waters. It was most likely during the Oligocene to early Miocene that Elminius dispersed to South America (shaded arrow); with colonization of the Falkland Islands and the eastern seaboard of South America being facilitated by the opening of the Drake Passage, which had occurred by that time (Scher and Morris, 2006). The dotted line shows the very recent distribution path for Austrominius modestus from Australasia to Europe; although there is a report of single specimen of A. modestus from South African waters – a 1949 record in Sandison (1950), there have been no further records from Africa since then, and we can only assume that it has failed to colonise in the area. Uncertainty about the high Austrominius diversity in a restricted region in South Australia necessitates that these taxa be grouped. A further arrow (dotted and shaded), extending from the Antarctic to what would have been the proto-Tasman Sea, delineates a possible westward dispersal route for the tetraclitoid genus Austrobalanus; which has the earliest records from the Bartonian (middle Eocene) of the Antarctic Peninsula (Buckeridge, 2000). Oceanic patterns at and immediately prior to that time (see Nelson and Cooke, 2001) provided an opportunity for Austrobalanus to have dispersed to southern New Zealand (where it is first recorded from the Rupelian (Oligocene). Extinct genera marked †.

FIGURE 3. Sessilia divergence time chronogram. Nodes determined on the basis of the fossil record (figures in nonitalics in MYBP) and molecular and morphological data (figures in italics; after Pérez-Losada et al., 2007). The lack of fossil evidence for sessilian barnacles prior to the Cretaceous boundary is compelling, especially as there is a very diverse and widespread record of Cretaceous scalpelliformes (Newman and Ross, 1976; Buckeridge, 1996). We adopt a parsimonious approach to this, concluding that the Sessilia evolved very quickly during the period following the Cretaceous-Tertiary extinction event, such that all major balanomorph taxa had appeared between the early Palaeocene and the late Eocene. This is a much tighter timeframe than envisaged by Pérez-Losada et al., 2008.