436


Journal of Paleontology 92(3):432–441 Type.—Holotype, MLP 35702. Four paratypes, MLP 35703.


Diagnosis.—Aspidostoma with a bilaminar colony, a concave quadrangular process on the proximal margin of the opesia-orifice, and frequent interzooidal avicularia of relatively large size (30% of zooid length).


Occurrence.—Early Miocene, Monte León Formation (see Parras et al., 2012). Type locality. Cabeza de León (Fig. 2).


Description.—Colony erect, bilaminar, robust. Autozooids ordered in quincunx, subhexagonal to rounded, limited by well-marked, slightly crenulated sutures. Autozooid length = 697 (653–752) µm; width = 523 (475–574) µm; length-to-width ratio = 1.3. Frontal surface consisting of a coarsely granular cryptocyst, convex, with protruding lateral margins, pierced by small, scattered pores. Cryp- tocyst distal to the opesia-orifice with a pair of inconspicuous dis- tolateral processes that are eroded in most zooids. Cryptocyst proximal to the opesia-orifice with amedian ridge formed by several indistinct umbos, depressed laterally. Opesia-orifice wider than long, 120–140µmlong × 140–180µmwide, D-shaped; proximal margin concave, everted, with a broad quadrangular process having a notch at each side for the passage of muscles depressing the frontal mem- brane. Interzooidal avicularia frequent, 208 × 131µm, the length attaining almost one-third of autozooid length, directed distolaterally, located at the level of the opesia-orifice of two adjoining autozooids, with triangular rostra, one pair of condyles, and a small transversely elliptical opesial foramen separated from the rostral foramen by a slender bridge. Avicularian cystide in contact with two lateral and one distal autozooids. Autozooids in some parts of the colony with orifices obliterated by secondary calcification. Ovicells not seen.


Etymology.—From Latin, meaning armed, referring to the large size of the interzooidal avicularia.


Other materials.—MLP 570, Bahía Sanguinetto. MLP 544, Cañadón al Deseado, Santa Cruz Province, Argentina.


Remarks.—The distolateral processes of the cryptocyst are well preserved in the material from Bahía Sanguinetto. The colonies from Cañadón al Deseado are characterized by the good pre- servation of the avicularia. This species differs from A. ortmanni and A. tehuelche by the much larger size of its interzooidal avicularia (Table 1).


Aspidostoma tehuelche new species Figure 4.2–4.4


1904 Aspidostoma ortmanni nom. nov.; Canu, p. 14 (part, only material from Punta Borja [‘Boya’ sic], Comodoro Rivadavia).


1908 Aspidostoma giganteum Busk, 1854; Canu, p. 276, pl. 7, figs. 4–12 (non Eschara gigantea Busk, 1854; part, only material from Punta Borja, Comodoro Rivadavia).


Type.—Holotype MPEF-PI 6348. Three paratypes, MPEF-PI 6349.


Diagnosis.—Aspidostoma with a bilaminar colony, a straight quadrangular process and avicularia attaining almost one-fifth of autozooid length, and avicularian cystide in contact with two autozooids.


Table 1. Morphological differences among species of Aspidostoma discussed in the text. Character


Zooidal form*


Zooid length* µm, mean (min–max, n)* Central cryptocyst* Cryptocystal pores* Quadrangular process* Median ridge*


Avicularium length* µm, mean (min–max, n)* (% of zooid length)* Avicularian rostrum*


Avicularian cystide location* *Diagnostic feature.


A. ortmanni Hexagonal


Slightly depressed Small, scattered Concave,* broad Inconspicuous


A. incrustans


802 (673–911, 10) 570 (475–673, 5) Almost flat


A. armatum


Very large,* abundant* Straight


Replaced by a granular cryptocystal thickening*


131 (119–139, 5) — (16 %)*


Triangular


In contact with 3 autozooids


— —


Slightly depressed Small, scattered Concave,* broad


Formed by several indistinct umbos


208 (178–238, 8) (30%)*


Relatively long, triangular In contact with 3 autozooids


A. tehuelche


Irregular* or subhexagonal Subhexagonal or rounded Hexagonal 697 (653–752, 10)


906 (812–970, 10) Slightly depressed


Moderately developed


165 (139–178, 6) (18%)


Protruding,* relatively more rounded


In contact with 2 autozooids*


A. roveretoi


Hexagonal or rhombic* 754 (713–812, 10)


Medium-sized, scattered Medium-sized, infrequent Straight


Strongly depressed* Straight


With two distinct umbos*


243 (139–356, 7) (32%)


Triangular, relatively short


In contact with 3 autozooids


A. giganteum Hexagonal


1168* (970–1307, 10) Strongly depressed Small, scattered Slightly concave With one umbo


347 (277–416, 10) (30%)


Relatively more rounded


In contact with 2 autozooids


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