Austrobalanidae Newman and Ross, 1976

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 : 41-42

Family Austrobalanidae Newman and Ross, 1976 stat. nov.

Diagnosis: Small, six or four-plated tetraclitoids with solid parietes with or without chitinous laminae or stringers, intermediate figures or “inflected basal margins”1; radii solid; basis membranous.

Distribution and age: Littoral low to moderate energy often brackish water environments. Eocene to Recent: † Antarctica, Australia, † New Zealand ( Austrobalanus , Epopella and/or Austrominius ); Oligocene, † New Zealand ( Protelminius ); Miocene, †Victoria, Australia (Matellionius); Recent, southern South America ( Elminius ) and New South Wales, Australia ( Hexaminius ); inadvertently introduced into Europe during the 1940s and temporarily to South Africa ( Austrominius ). († denotes that taxon is extinct in this region).

Remarks: A key reason why Elminius s.l. was placed within the archaeobalanids by Newman and Ross (1976) was the presence of a deeply cleft labrum. This feature characterizes some of the earliest balanoids, such as Notobalanus vestitus ( Darwin, 1854) and seemed a good one to demonstrate phylogeny. However, since that time, the tetraclitoid Newmanella has been described and this too has a cleft labrum, so the character no longer remains a defining one for balanoids. On the other hand, the bipectinate nature of the setae of Elminius s.l. is significant, for while this feature is not found in the balanoids, it is also present in both the chthamaloids and tetraclitoids. Add to this a basically membranous base and a tergal spur that is confluent with, or only slightly separated from, the basal angle and one has characters that approximate those of Austrobalanus rather than balanoids, and thus underlie the morphological reasons for the phylogenetic realignment proposed here ( Table 1).

The Austrobalanidae now comprises the Elminiinae ( Austrominius , Elminius, Hexaminius, Matellionius and Protelminius) as well as the Austrobalaninae ( Austrobalanus and Epopella ), based on our morphological

1. Darwin (1854: 45) commented, “… the basal edges of the walls (of Euraphia hembeli ) become inflected, and continue to grow inwards till they entirely take the place of the true membranous basis”. However, it has since been demonstrated by cross-sections of the wall of several chthamalids that the so-called inflection is not part of the wall per se, but the result of secondary calcification to parts or all of the interior of the body chamber, and it may include the opercular plates and/or entire bases, as well as the wall ( Newman, 1961). Among the elminiines, the extinct Matellionius alone has what appears to be a wall with “an inflected basal margin”, but like that of the chthamalid Notochthamalus intertexta ( Darwin, 1854) , a longitudinal section reveals it too to be the product of secondary calcification rather than inward growth of the basal margin of the wall.

analyses, a conclusion well supported by molecular data ( Pérez-Losada et al., 2008) but not by naupliar setation sequencing, where Tetraclita is distinctly separated from the sister-groups Austrobalanus- Tesseropora-Tetraclita and Hexaminius-Elminius ( Newman and Ross, 2001, Fig. 4 ).

Figures

FIGURE 4. Palaeogeographic Setting for the early Austrobalanidae. 4 a: Sketch depicting the oceanic systems that are likely to have operated in the south Pacific region during the late Palaeocene-early Eocene. At this time, the Antarctic continent was kept essentially ice-free by a large south Pacific warm-water gyre; counter-currents operating off Antarctic provided an opportunity for westward dispersal of Austrobalanus (to the McMurdo region and the proto-New Zealand land mass “ NZ ”). The dashed line represents a likely mobile transitional zone between marine regression and transgression. 4 b: Southern ocean conditions during the Oligocene to early Miocene, after the initiation of the Antarctic Circumpolar Current. With the loss of the southern pacific warm-water gyre, glaciation of the Antarctic continent began (e. g. Kennett, 1977), with the resultant regional extinction of austrobalanid barnacles. The heavier dotted blue line represents the likely position of the cold and temperate water systems convergence. (Reconstruction adapted from Markwick et al., 1999; Barron and Peterson, 1991; Nelson and Cooke, 2001).