Abertella miskellyi Kroh, Mooi, Río & Neumann, 2013, n. sp.
Creators: name: Kroh, Andreas
name: Mooi, Rich
name: Río, Claudia Del
name: Neumann, Christian
Publisher: name: Zenodo
Year: 2013
Subjects: Biodiversity
Taxonomy
Animalia
Echinodermata
Echinoidea
Clypeasteroida
Abertellidae
Abertella
Abertella miskellyi

description: Abertella miskellyi n. sp.
Figures 2 A–F, 3A–B, 4, 5A–B, 6A–F
Diagnosis. Abertella with heterogeneous interambulacral basicoronal plates (small in interambulacrum 5, largest in interambulacra 2 and 3) and disjunct oral interambulacra involving two ambulacral plates rather than one in some of the interambulacral areas.
Etymology. Named after Ashley Miskelly, a fellow echinologist from Australia, for his continuous support and help in echinoid matters.
Types. Holotype is MB E.7463, from P. Camarones, Chubut Province, southern Argentina. Camarones Formation, Miocene. Paratype MB E.7462 has the same provenance as the holotype.
ZooBank LSID. urn:lsid:zoobank.org:act:A0132110-360E-4FCF-AD24-99631D10DC70
Description. Adult test size exceeding 60 mm in length (Table 1). Aboral surface slightly domed, oral surface flat (Fig. 2 C, F). Highest point of test located at apical system. Outline slightly angular when viewed from the aboral aspect. Test distinctly widened laterally (TW 115–120 per cent of TL), almost alate (sensu Mooi et al. 2000). Two very broad, but very shallow marginal indentations present in ambulacra I and V. Moderately deep anal notch at posterior interambulacral interradial suture opening at an angle of about 110–120° (Figs. 2, 3, 6 D).
Apical system monobasal, slightly anterior, with numerous hydropores scattered over the madreporic plate (Fig. 6 A). Four gonopores, one in each of the paired interambulacra and located at the suture between the madreporic plate and the first adapical plates of the interambulacral column.
Ambulacra petaloid adapically, extending about 50–58 per cent of the corresponding test radius. Petals almost closed distally, with three to five trailing podia (sensu Mooi 1989) at the distal end of each column of respiratory podia (Fig. 3 A). Posterior paired petals longest, anterior paired petals intermediate in length, and anterior unpaired petal shortest. Respiratory podial pairs strongly conjugated, inner pore circular or almost circular, outer pore distinctly elongate (Fig. 6 C). Only one or two occluded plates present at the tips of the petals (Fig. 4), sometimes none. Occasionally, a supernumerary interambulacral plate present where the petals end (Fig. 4). At the ambitus, ambulacra strongly widened, forming strip-like ambital plates (Fig. 3 A). Ambulacrum III of both specimens (Fig. 5 A-B) and ambulacrum II of specimen MB E.7462 (Fig. 5 B) apparently disagreeing with Lovén’s Rule (David et al. 1996). In specimen MB E.7462 a tiny plate seems to be present, wedged in between the basicoronal plates of ambulacrum III, re-establishing Lovén’s pattern. Ambulacral basicoronal plates all similar, narrow and relatively short (Fig. 5). Interambulacral basicoronal plates unequally developed, shortest in interambulacrum 5 and longest in interambulacra 2 and 3, where they are strongly enlarged and almost twice as long as the ambulacral basicoronal plates (Fig. 5).
Apex Position (from anterior edge of test to anterior edge of madreporic plate) 27.7 28.6 Petaloid I Length 19.4 19.2 Petaloid I Width (at widest point) 7.6 7.6
Petaloid I Interporiferous Zone Width (at widest point) 2.7 2.3
Petaloid II Length 17.2 16.5 Petaloid II Width (at widest point) 8.2 8.2
Petaloid II Interporiferous Zone Width (at widest point) 3.0 2.8
Petaloid III Length 15.2 15.1 Petaloid III Width (at widest point) 8.4 7.9
Petaloid III Interporiferous Zone Width (at widest point) 4 3.3
Peristome Diameter 2.9 3.1
Peristome Position (anterior edge of test to anterior edge of peristome) 29.2 30.0 Periproct Position (anterior edge of test to anterior edge of periproct) 52.9 55.4 Interambulacra narrow and straight, with four post-basicoronal plates in each half of interambulacral column on the oral surface. Interambulacra only about one-seventh the width of the ambulacra at the ambitus and forming narrow bands of radially elongated plates on the oral side. Interambulacrum 5 extremely narrow at the ambitus, being only about one quarter of the width of the other interambulacra. All interambulacra discontinuous, separated from the basicoronals by the first post-basicoronal pair and (in interambulacra 2, 3, 4, and 5 of specimen MB E.7463 and interambulacra 4 and 5 of specimen MB E.7462) one plate of the second ambulacral post-basicoronal plates (Figs. 3, 5). In the cases in which only one ambulacral plate is involved in the disjunction this plate has a pronounced, distally directed, curved extension that joins the proximal edges of the first interambulacral postbasicoronal plate.
Peristome (Fig. 6 B) circular, almost central on the oral side, with a distinct perradial process in each ambulacrum extending into the peristome beyond the slight bulge containing the sphaeridium. Periproct small, close to the posterior margin, but placed distinctly on the oral surface, approximately four times its own diameter from the ambitus, and surrounded by second pair of interambulacral post-basicoronal plates. Area around the periproctal opening slightly raised (Fig. 6 E).
Both aboral and oral tuberculation homogeneous. A clear differentiation of the oral tubercles in geniculate and locomotory spine fields cannot be observed (Fig. 6 D).
Food grooves well developed (Fig. 6 D–F), with primary bifurcation near the distal ends of the ambulacral basicoronal plates (Fig. 5 A). After this branch point, grooves continuously diverge as they approach the ambitus, but secondary bifurcations apparently absent (Fig. 6 E), or at least not discernible, even under very low-angle light conditions.
In the paired interambulacra very shallow channels are present extending from close to the peristome to the margin. They are visible under low-angle light conditions only (Fig. 6 F). The margins of these depressions coincide with the strongly parallel buttresses on either side of this narrow interambulacral region known from other species of Abertella. It is possible that these depressions are taphonomically induced, due to sediment compaction deforming this relatively thin part of the test. Similar depressions occur in the region around the peristome in other fossil scutellines as well, and although they look very natural, are here interpreted as preservational artifact.
Occurrence. Known only from the type locality.
Discussion. Abertella miskellyi n. sp. is easily distinguished from all congeners by its heterogeneous interambulacral basicoronal plates. From its geographically nearest congener, A. gualichensis (lower to middle Miocene of Argentina), it additionally differs by its slightly deeper anal notch, narrower interambulacrum 5 at the ambitus, and lack of prominent, secondary branching of the food grooves.
The type species of the genus, Abertella aberti (Conrad, 1842) (= Abertella floridana (Cooke, 1942)) (middle Miocene of Maryland, USA), differs by its less widened outline, deeper marginal indentations and anal notch, larger petaloids, higher number of occluded plates at the ends of the petals, and wider oral interambulacra with hexagonal plates. The latter are strongly elongate in A. miskellyi n. sp.
Abertella cazonensis Kew in Dickerson & Kew, 1917 (upper Oligocene or lower Miocene of Mexico) is very similar to A. miskellyi n. sp., but differs by its more homogeneous interambulacral basicoronal plates, more circular test, much higher number of occluded plates at the ends of the petals, and interambulacral disjunctions involving only a single pair of adjacent ambulacral plates (based on re-examination of CAS material).
Abertella dengleri Osborne & Ciampaglio, 2010 (upper Miocene of Florida, USA) has a much wider test and narrower petaloids than A. miskellyi n. sp. From drawings in the original description and re-examination of CAS material, it would appear that there are at least 4 or 5 occluded plates at the ends of petals. Otherwise, the plate pattern of A. dengleri is largely unknown due to the strongly agatized mode of preservation of all known specimens.
Abertella? habanensis (Sánchez-Roig, 1949) (Oligocene to Miocene of Cuba) is very poorly known, but clearly differs from A. miskellyi n. sp. by its small, semicircular anal notch, homogeneous petaloid length, and sharply truncated posterior margin. The attribution of this species to Abertella is uncertain due to the fact that its plate pattern is unknown.
“ Abertella ” kewi Durham, 1957 (middle (?) Miocene of Mexico) is similar in shape to A. miskellyi n. sp., but was found to possess continuous oral interambulacra (R. Mooi, unpubl. data, UCMP material) and therefore differs not only from A. miskellyi n. sp. but from any other member of the genus Abertella.
Abertella palmeri Durham, 1957 (lower Miocene of Guatemala) has a deep and narrow anal notch, deeper marginal indentations, trapezoidal outline, three or four occluded plates at the ends of the petals, and wider interambulacra at the ambitus.
Abertella pirabensis (Marchesini Santos, 1958) (= A. complanata Brito, 1981) (lower Miocene of Brazil) additionally differs from A. miskellyi n. sp. by its much deeper anal notch and different periproct position as illustrated by Marchesini Santos (1958), who showed the periproct as being framed by 5a2 and 5b2, as opposed to 5a3 and 5b 3 in A. miskellyi).
description: Published as part of Kroh, Andreas, Mooi, Rich, Río, Claudia Del & Neumann, Christian, 2013, A new late Cenozoic species of Abertella (Echinoidea: Clypeasteroida) from Patagonia, pp. 369-378 in Zootaxa 3608 (5) on pages 371-375, DOI: 10.11646/zootaxa.3608.5.5, http://zenodo.org/record/218135