Zullobalanus santamariaensis Buckeridge & Winkelmann

Winkelmann, Kai, Buckeridge, John S., Costa, Ana Cristina, Dionísio, Maria Ana Manso, Medeiros, André, Cachão, Mário & Ávila, Sérgio P., 2010, Zullobalanus santamariaensis sp. nov., a new late Miocene barnacle species of the family Archaeobalanidae (Cirripedia: Thoracica), from the Azores, Zootaxa 2680, pp. 33-44 : 36-39

Zullobalanus santamariaensis Buckeridge & Winkelmann sp. nov.

( Figures 2–3 )

Diagnosis. Zullobalanus with shell lacking external apico-basal ribbing; tergum only weakly reflexed apically, but possessing extensive, well-formed crests for depressor muscle attachment; scutum with moderately produced articular ridge and moderate to weak adductor muscle scar.

Distribution and age. Azores; Late Miocene – Early Pliocene.

Type material. Holotype containing 2 sample compositions: DBUA-F 536.1, complete shell (3.23 mm in height and 3.39 mm in basal diameter), carina (5.44 mm in height), carinolatus, (5.36 mm in height), latus (1.84 mm in height), rostrum (2.59 mm in height), scutum (2.50 mm in articular margin), tergum (3.44 mm in articular margin); DBUA-F 536.2, complete shell (6.31 mm in height and 6.63 mm in basal diameter), carina (4.89 mm in height), carinolatus, (4.79 mm in height), latus (3.36 mm in height), rostrum (2.30 mm in height), scutum (2.43 mm in articular margin), tergum (3.61 mm in articular margin); Santa Maria, Malbusca outcrop (25°4'7.04"W, 36°55'45.53"N [30 m asl]); S.P. Ávila & K. Winkelmann, 22–29 June 2008. Paratypes all with same locality, collectors and date as the holotype: Natural History Museum Berlin: MB.A 1733, MB.A 1734; Natural History Museum Vienna: NHMW 2010/0088/0001, NHMW 2010/0088/0002; Royal Belgian Institute of Natural Sciences Brussels: IRSNB 7255a–g, IRSNB 7256a–g; Natural History Museum London: NHM IC 549 – NHM IC 562; Muséum National d’Histoire Naturelle Paris: MNHN A32053, MNHN A32054.

Description. Shell conic, height approximating basal diameter; exterior rough, longitudinal ribbing weak to absent, lateral growth lines weak; orifice rhomboidal ( Fig. 2 A, B); interior with strong ribbing, with minor bifurcation of some ribs near basis; rib cross-section showing simple arborescent interlaminate structures ( Fig. 2 B, C); sheath smooth, well developed, pendant, occupying up to 50% of height of inner surface; basis firmly interlocking with parietal ribs; radii moderately narrow, with oblique summits, growth lines parallel to basis crossed by fine growth striae parallel to alar abutment ( Fig. 2 B); alae with marginal extensions, summits almost horizontal ( Fig. 2 B).

Scutum ( Fig. 3 A, B) very weakly reflexed apically; exterior with strong transverse growth ribs crossed by weak apico-basal striae; interior with articular ridge moderately produced, slightly pendant basally; adductor ridge weak, broadly rounded; adductor muscle scar moderate to weak, pit for lateral depressor muscles well formed lacking any obvious muscle attachment crests. Tergum ( Fig. 3 C, D) moderately elongate, spur wellformed, removed from basi-scutal angle by own width and extending beyond same angle by approximately its own width, furrow well-formed distally, externally with well spaced growth lines, in some areas (especially basally), fine apico-basal striae present; interior with longitudinal furrow on articular margin wide, open, shallow, smooth except for weak growth striae; articular ridge well-formed, concave towards articular margin; crests for depressor muscles well developed basally, extending as a zone of raised papillae nearer the apex; articular ridge gently curved to extend slightly beyond a broadly concave basal margin; apex with approximately 3–4 strong transverse growth lines in adults.

Occurence at Santa Maria Island. All the Late-Miocene and Early-Pliocene outcrops studied in Santa Maria contained the endemic barnacle Zullobalanus santamariaensis sp. nov. Most specimens were found at Malbusca and at “Pedra-que-Pica” outcrops. The beds at “Pedra-que-Pica” contained some well preserved but rare barnacles with opercula cemented to diverse marine molluscs (e.g. Gigantopecten latissimus (Brocchi, 1814) and Lopha plicatuloides (Mayer, 1864)) ; the beds at Malbusca contained a number of loose opercula in a sandy matrix. At Cré outcrop, rare single walls as well as opercula were present. In the more lithified marine sediments of Figueiral and Ponta do Castelo, barnacle fragments were only observed on eroded surfaces. At Ponta dos Frades, a few barnacle fragments were found together with well preserved micro-molluscs on eroded bottom surfaces. Nevertheless, we detected fragments of Zullobalanus santamariaensis sp. nov. in every sampled Miocene/Pliocene outcrop.

Remarks and affinities. There is an extensive archaeobalanid fauna known from western Europe ( Carriol, 2008) and the eastern seaboard of North America ( Zullo 1984; Zullo & Kite 1985; Zullo & Perreault 1989; Zullo & Portell 1991). Of these, species of Actinobalanus are distinguished from this taxon by their porous bases; Hesperibalanus , the terga of which lack the well-formed nodose papillae on the internal surface and the broad spur; Solidobalanus by the externally smooth compartments; and Lophobalanus by their very narrow radii.

Zullobalanus santamariaensis sp. nov. differs from all other Zullobalanus species by a lack of clearly formed external ribbing on the shell. Although there are some weak “ribs” these are somewhat obscured by the generally rough surface of the shell. The weakly reflexed scutal apex is close to that seen in the Australian species Zullobalanus australiae victoriae ( Buckeridge, 1983) and in most respects it is closest to this species. In addition to the lack of external ribbing, it differs from Z. australiae victoriae by the presence of numerous well-formed crests for depressor muscles on the tergum.

The scutal articular ridge is often basally pendant in larger specimens of Zullobalanus species ( Buckeridge 1983), and although this has not been clearly seen in the material available, we should be mindful that all larger scuta are isolated and since shell disarticulation, have been abraded, as such wearing away delicate extensions.

Etymology. Geographic: Island of Santa Maria (noun in apposition).

Figures

FIGURE 2. Zullobalanus santamariaensis sp. nov. All specimens from lower-Miocene / early-Pliocene of Malbusca outcrop (Santa Maria Island, Azores, Portugal); samples DBUA-F (see. Table 1). I: Zullobalanus santamariaensis sp. nov. lateral and apical views. Letters at apical view; C = carina, CL = carinolatus, L = latus, R = rostrum. II: C - R; left interior, right exterior view. III: wall from below. Scale: I = 10 mm, II = 1 mm, III = 200 µm.

FIGURE 3. Zullobalanus santamariaensis sp. nov. All specimens from lower-Miocene / early-Pliocene of Malbusca outcrop (Santa Maria Island, Azores, Portugal), from samples DBUA-F (see Table 1); drawings based on SEM pictures. A: moveable scutum exterior (enlarged area showing detail from the lower part of the exterior of the scutum, accentuating fine apico-basal striae), B: moveable scutum interior, C: moveable tergum exterior, D: moveable tergum interior.