Camachoaster maquedensis, Mooi & Martínez & Del Río & Ramos, 2018

Mooi, Rich, Martínez, Sergio A., Del Río, Claudia J. & Ramos, Maria Inês Feijó, 2018, Late Oligocene - Miocene non-lunulate sand dollars of South America: Revision of abertellid taxa and descriptions of two new families, two new genera, and a new species, Zootaxa 4369 (3), pp. 301-326 : 310-316

Camachoaster maquedensis n. sp.

Figures 1 , 5–8 .

Diagnosis. As for the genus.

Etymology. Named for the type locality of Punta Maqueda, Santa Cruz Province, Argentina, where the sand dollars occur in the Chenque Formation, which is exposed about 2 km south of the point. Type material studied. Material is housed at the Museo Argentino de Ciencias Naturales Bernardino Rivadavia (MACN). Holotype is MACN-Pi 5809, from shoreline deposits about 2 km south of Punta Maqueda, Santa Cruz Province, southern Argentina. These deposits form part of the Chenque Formation, lower Miocene. There are two paratypes, MACN-Pi 5859 and MACN-Pi 5860. These have the same provenience as the holotype.

Description. Holotype and largest specimen ( Fig. 5 ) 59.3 mm TL. Measurements for all known specimens given in Table 1. All ensuing percentages, calculated to facilitate comparisons with other descriptions herein, are from holotype. Aboral surface slightly domed, oral surface flat. Highest point of test 11% TL, located at apical system. Very shallow but distinct posterior notch, depth just over 5% TL, width 16% TL, notch widening significantly near ambitus. Broad, shallow marginal indentations present where perradial suture meets ambitus in each ambulacrum.

Apical system monobasal, pentagonal (not star-shaped), 49% TL from ocular III to anterior edge of test, length 8% TL, numerous hydropores scattered over madreporic plate. Four gonopores, one in each of paired interambulacra and located at suture between madreporic plate and first adapical plates of interambulacral column ( Fig. 8A ).

Ambulacra petaloid adapically. Posterior paired petals (I and V) not noticeably longer than any other petals, each extending 56% of corresponding test radius, but 30% TL; anterior paired petals (II and IV) 51% of corresponding test radius, but 29% TL; anterior unpaired (III) 56% of corresponding test radius, but 29% TL. Petal V width at widest point 12% TL, interporiferous zone 4% TL; petal IV width 12% TL, interporiferous zone 5% TL; petal III width 13% TL, interporiferous zone 6% TL. Petals lyrate, almost closed distally ( Figs. 5 , 8A, B ), with two or perhaps as many as three trailing tube feet (sensu Mooi 1989) at distal end of each column of respiratory tube feet ( Fig. 8A ). Respiratory tube foot pore pairs strongly conjugated, inner pore slightly elongated, outer pore extremely elongated, comprising about half length of pore pair, apparently subdivided by stereom septae ( Fig. 8A, B ). Five or six occluded plates present at tips of petals ( Fig. 8A ). At ambitus, ambulacra greatly widened, forming strip-like ambital plates that follow contour of shallow indentation at each perradius, and curving adapically to form test wall along each side of posterior notch ( Fig. 7 ). Ambulacra all in agreement with Lovén’s Rule (sensu David et al. 1996). Ambulacral basicoronal plates all similar, narrow and straight with almost parallel radial sutures on each side ( Figs. 6 , 7 ).

Interambulacra narrow and straight on oral surface, narrowing towards ambitus, but containing paired, zig-zag plates right up to madreporic plate. On oral surface, three or four postbasicoronal plates in each halfinterambulacrum in interambulacrum 5, four or five in in other interambulacra. Widest point of each interambulacrum about one third of way from basicoronal to ambitus, narrowing distally so that paired interambulacra about 22% width of adjacent ambulacra at ambitus. In each paired interambulacrum, first postbasicoronal greatly elongated, about four times as long as wide, about twice length of corresponding second postbasicoronal. In interambulacra 1 to 4, basicoronals broadly in contact with both corresponding first postbasicoronals. Unpaired, posterior interambulacrum 5 discontinuous, separated from basicoronal by adjacent ambulacral postbasicoronals ( Figs. 6 , 7 ).

Peristome circular, relatively small, about 5% TL, with distinct perradial process in each ambulacrum extending into peristome beyond slight bulge containing sphaeridium ( Fig. 8C ). Anterior edge of peristome 51% TL from anterior edge of test. Periproct small, about 3% TL, on oral surface between second and third pair of postbasicoronals.

Aboral tuberculation homogeneous. Very slight enlargement of tubercles in oral interambulacral regions relative to those in ambulacral regions. In specimens with best preservation of surface detail, distinct tube foot pores visible in food grooves ( Fig. 8C ).

Food grooves well developed ( Figs. 5 , 7 , 8C ), restricted to oral surface, with primary bifurcation near adapical ends of ambulacral basicoronal plates. After this branch point, food grooves continuously diverging as they approach ambitus. Secondary branching well developed ( Fig. 5 ). Extremely shallow depressions along perradial sutures on oral surface.

Occurrence. Known only from the type locality.

Geologic setting. The shallow marine deposits in which the new species was found have been described in Mooi et al. (2016). In summary, the rocks of the Chenque Formation in the Golfo San Jorge Basin (Chubut and Santa Cruz Provinces, Argentina) exposed near Punta Maqueda have been described as early Miocene (del Río 2004). The type specimens of Monophoraster telfordi Mooi et al., 2016 were collected from the same thin bed (up to 15 cm thick) of fine-grained sandstones from which the new species of non-lunulate was recovered.

Remarks. Although Camachoaster maquedensis n. sp. is found in the same strata as Monophoraster telfordi Mooi et al., 2016 , the former is immediately recognizable as a different species, as well as representing a different major scutelliform clade, by its complete lack of an anal lunule. Camachoaster resembles the Abertellidae only in the possession of a shallow notch, and in the discontinuity of the posterior interambulacrum. However, the continuity of the paired interambulacra immediately invites favorable comparison with Placatenella , as do the similar shapes and dimensions of the petals.

Nevertheless, Camachoaster differs from Placatenella in having the posterior interambulacrum discontinuous. Camachoaster 's combination of continuous paired interambulacra with a discontinuous posterior, unpaired interambulacrum, is unique among South American forms. A small species of Vaquerosella from California seems to have a similar oral plate pattern. However, among large scutelliforms with a posterior notch, this condition seems to be shared only with a Mexican species previously ascribed to Abertella , A. kewi Durham, 1957 . The original description of A. kewi lacks figures of, or any reference to, oral plate architecture, likely due to the condition of the specimens. However, access to material from UCMP locality B8562, collected from the same locality as the types (Simojovel, Chiapas, Mexico) allows reconstruction of this architecture for comparison with Camachoaster maquedensis n. sp. ( Fig. 7 ). This suggests that A. kewi is not an Abertella . Aspects of the oral plate pattern are reminiscent of some abertellid species, notably Abertella miskellyi Kroh et al., 2013 , such as the periproct placement, the reduced posterior interambulacral basicoronal, and discontinuity of the posterior interambulacrum. However, A. kewi is unlike any abertellid in the continuity of the paired interambulacra, and the insertion of very small first postbasicoronals in either the "a" or the "b" column of each of the ambulacra. The latter situation is seen in the Pliocene Scutellaster Cragin, 1895 , the Miocene and Pliocene Kewia Nisiyama, 1935 , and in the Eocene Eoscutella , all from the northwest Pacific coasts of North America. The occurrence of these small postbasicoronals has not yet been analyzed in a phylogenetic context in order to determine its overall significance. The aforementioned differences between Camachoaster maquedensis n. sp. and A. kewi might suggest that they are not congeneric, but we here provisionally place A. kewi in Camachoaster as Camachoaster ? kewi pending full revision of all the relevant North American taxa associated with the Abertellidae and Placatenellidae.

Figures

FIGURE 1. Localities for taxa discussed in the text. Inset at lower left centers on the Santa Cruz region of Patagonia. Numbered occurrences correspond to unequivocal Iheringiella patagonensis localities (inside boxed region in main map): 1. Pampa Castillo, Chile (Andre Wyss, pers. comm.); 2. Cañadón El Lobo, Santa Cruz, Argentina (CPBA 16493-95); 3. Oven Point/Sholl's Tomb, Santa Cruz, Argentina (Ortmann 1902), Punta Cuevas, Santa Cruz, Argentina (MACN 4586 and Cuitiño 2011), Playa La Mina, Santa Cruz, Argentina (Cuitiño 2011); 4. Meseta Chica, Bajo de San Julián, Santa Cruz, Argentina (MACN 5144 and Cuitiño 2011); 5. Upper Rio Chalia, Santa Cruz, Argentina (Ortmann 1902); 6. Puerto Santa Cruz, Santa Cruz, Argentina (ROM 5433M, 5468M, 5469M); 7. Sector Flamenco, Tierra del Fuego, Chile (Larrain 1984)—reported to be from Eocene strata, but this is questionable (Mooi et al. 2000).

FIGURE 6. Camachoaster maquedensis n. sp., photographs of the oral surfaces of paratypes. A: MACN-Pi 5859, prepared specimen with pencil marks indicating plate architecture. B: MACN-Pi 5860, partially prepared specimen with pencil marks indicating plate architecture, faint tuberculation, and main branches of food grooves. Scale bars 10 mm in length.

FIGURE 7. Comparison of oral plate architecture of Camachoaster maquedensis n. sp. (based on paratypes MACN-Pi 5859 and 5860) and Camachoaster? kewi (= Abertella kewi Durham, 1957) (based on specimens from UCMP locality B8562, Chiapas, Mexico).Food grooves indicated by dotted lines, peristome and periproctin solid black, interambulacra shaded, scale bars 10 mm in length.

FIGURE 8. Camachoaster maquedensis n. sp., details of test features. A: Holotype MACN-Pi 5809, pencil marks indicating partialaboral plate architecture in regionwithin andaround petal in ambulacrum II, gonoporesindicated by white arrows, pores of trailing tube feet by black arrows. B: Paratype MACN-Pi 5859, complete aboral ambulacrum IV showing shape of petal. C: Holotype MACN-Pi 5809, details of tuberculation, food groove (black arrow), and peristome (peristomial projection indicated by white arrow).All scale bars 10 mm in length.

FIGURE5. Camachoaster maquedensisn. sp., photographs of the holotype MACN-Pi 5809.Oral surface shows pencil marks indicating some of the plate architecture.Scale bar 10 mm in length.