Tetraclitella judiciae, Buckeridge, John S., 2008

Buckeridge, John S., 2008, Two new species and a new subspecies of Tetraclitella (Cirripedia: Thoracica) from the Cainozoic of Australia and New Zealand and a consideration of the significance of tubiferous walls, Zootaxa 1897, pp. 43-52 : 48-50

Tetraclitella judiciae sp. nov.

Figures 1 A–E; 3

1983:? Tetraclitella sp. cf. T. purpurascens (Wood, 1815): Buckeridge, 77–78, (not pl.5c,d). 1985:? Tetraclitella sp. cf. T. purpurascens (Wood, 1815): Buckeridge, 144–146, fig.4a,b. 2008: Tetraclitella sp.: Buckeridge, 70, fig.4.

Diagnosis: Low conic Tetraclitella with orifice large, radii thin-walled, paries with inner ring of larger, elongate, thick-walled pores.

Distribution and age: Southern Victoria, Australia. Late lower Miocene (Batesfordian Stage to Early Pliocene (Kalimnan Stage). For Victorian stages refer to Singleton, 1941.

Holotyp e: P313914, a single specimen ( Figure 1 C–E; Figure 3 ) from the Batesford Limestone, Victoria.

Material: Batesford Limestone: P313914 ( Figure 3 ), a complete shell comprising four compartments (but lacking opercula) from the Batesford Limestone, Victoria, carino-rostral length: 15.5 mm. [The specimen was removed from the old Magistrates' Court building, situated at the corner of Russell and Latrobe Streets, Melbourne, on 6th March, 2006 by J. Buckeridge. The precise locality of the site from where the block of limestone was quarried is unknown, although the Limestone Quarry is close to the Moorabool River, near Geelong, Victoria. Date removed from the quarry, circa 1912 (see Buckeridge, 2008)]; RG77640091 (figure 4a,b in Buckeridge, 1985), an articulated rostrum and latus (rostrum incomplete – apical part and much of the right radius absent), length 4.5 mm, collected in 1977 from 9.8m above the quarry floor, Batesford; R77640090, an incomplete latus, as previous but from 8.2m above the quarry floor; R77640095, a?latus, as previous but from 15.9m above the quarry floor; R77640099, a?latus, as previous but from 21.0m above the quarry floor; RM318 ( Figure 1 A,B), length 2.4mm: a latus collected from a loose block of moderately well cemented limestone in the Batesford Quarry, 38°06.5’S, 144°17.3’E, on 30 January, 2007 by JSB. Age: Early Miocene. Specimens with the prefix “P” are held in the type collection of the Museum of Victoria, Melbourne; those with the prefix “R” are held in the Palaeontology Collection, Bureau of Mineral Resources, Canberra, ACT, Australia; those with “RM” are held in the Palaeobiology Collection of Earth & Oceanic Systems, RMIT University.

Description: Shell of moderate size, possessing a medium-low profile; orifice large, rhomboidal (carinorostral length in holotype: 7mm); exterior with up to six narrow, well-spaced longitudinal ridges separated by slightly more than their own widths, ridges crossed by fine, transverse growth lines; holotype with exterior surface corroded and/or corraded in part, exposing very slightly raised parietal pores, demonstrating an appearance commensurate with that observed in the chitinous lined pores of living tetraclitids ( Figure 1 C,E; Figure 3 ); radii narrow, slightly depressed with respect to paries, relatively flat, more susceptible to being eroded than with paries, such that sub-vertical cavities may form at the radii sites (see Figure 3 ). Sheath weak, extending for approximately half height of paries; pores rounded to oblate in section, becoming significantly larger, flattened, with thickened walls adjacent to the sheath (see holotype, Figure 1 D), less so in other specimens ( Figure 1 B); nature of basis, if present, unknown.

Comparison with other species: Tetraclitella judiciae sp. nov. is easily distinguished from T. depressa by the former’s narrower radii and higher conic shell; it can be distinguished from both subspecies of T. purpurascens by possessing much thinner radii (in no specimens of T. judiciae have complete radii been preserved, and this is considered to reflect a more delicate, thinner structure). The inner row of larger parietal pores is reminiscent of both Tesseropora and Tesseroplax , but these genera are distinguished by possessing a single multitubiferous paries.

Remarks: The presence of horizontal pores within the radii is an important characteristic of Tetraclitella . Pores are not clearly distinguishable in any of the fossil species described in this paper, although the radii in all specimens are poorly preserved. [For example, in T. nodicostata sp. nov. (specimen A177), there are remnants of a radius on the carinal side of the right latus and although there are no definite pores, there is a subtle change in shell texture, both here and on other radii, which is suggestive of pores]. All specimens of T. judiciae have undergone some diagenesis – in the holotype, weak dissolution and crystallisation has occurred and the fine, delicate nature of radial pores would not have survived this process.

Well-developed radii are an important characteristic of Tetraclitella , as is the low profile and multitubiferous paries. As noted, the holotype differs from modern Tetraclitella by possession of an inner row of larger, elongate pores; nonetheless, this may be an ontogenetic feature, as the specimen is large and eroded. The inner pore arrangement however, is similar to what could be expected in an ancestral Tesseropora .

[The history of the holotype is worthy of note. It was found exposed in the limestone wall of “Building 20” fronting Russell Street, Central Melbourne, currently occupied by both the Chancellor and Vice Chancellor of RMIT University. The building, originally the Magistrates’ Law Courts, is one of Melbourne’s grandest; not surprisingly it is “heritage listed” meaning that it cannot be damaged. The saga that culminated in the extraction of this unique specimen was beamed around the world on Sky Television on 7th March 2006, and is fully documented in Buckeridge (2008)].

Etymology: Noun in apposition, [Latin iuris = law (court)] in reference to purpose for which the building in which it was found in was built, and the caution exercised during the extraction of the holotype.

Figures

FIGURE 1. Tetraclitella spp. A – E: Tetraclitella judiciae sp. nov. A: RM 318 – latus (exterior); B: RM 318 – latus (interior), the central, large, ellipsoidal structure is a grain of calcite, that if removed may have damaged the plate. It is not part of the barnacle; C: P 313914 – detail showing eroded radius of left latus (central cavity on image), and ellipsoidal pattern produced by eroded parietal pores intersecting the exterior surface; D: P 313914 – detail showing basal section through the shell wall, with inner row of large, elongate pores and outer multi-porous zone; E: P 313914 – detail showing parietal pores that have been apically infilled; F: Tetraclitella purpurascens purpurascens (Wood, 1815): Basal view of parietes exposing edge of sheath (upper, unpatterned zone) and multi-porous zone that lacks a distinct inner row or larger, elongate pores.

FIGURE 3. Tetraclitella judiciae sp. nov. P 313914 (holotype) – shell with opercular valves absent (the opercular opening is the large central quadrangular structure); carina at top. The dark, “ round ” cavity (c. 1.0 mm in diameter) to right of the opercular opening is an eroded radius, and it is here where the recrystallized shell fabric is suggestive of having had radial pores.