Metrarabdotos capanemensis, Ramalho, Tavora. & Zagorsek, 2017

Ramalho, Laís V., Távora, Vladimir A. & Zagorsek, Kamil, 2017, New records of the bryozoan Metrarabdotos from the Pirabas Formation (Lower Miocene), Pará State, Brazil, Palaeontologia Electronica (Weinheim an der Bergstrasse, Germany) 10 (15), pp. 1-11 : 7-8

Metrarabdotos capanemensis sp. nov.

Figure 4.1-3

zoobank.org/ CF64D724-C6F1-44DC-93AA-F32507CE7517

Referred specimens. Holotype: MG-6303-I-t; B-17 Mine; fertile branch fragment; 5 mm long x 3 mm wide; Paratype: MG-6303-I-u, B-17 Mine; fertile branch fragment; 2 long mm x 2 mm wide.

Etymology. The name capanemensis refers to Capanema, the city near B-17 Mine, where this species was found.

Diagnosis. Colony erect, bilaminate; orifice without median denticle. Ordinary avicularia paired, falciform, located proximally, and lining the secondary orifice. Special avicularia large, elongated, narrow and with rounded tip, sparse, apparently not associated to zooecia adjacent to maternal ones.

Description. Colony erect, bilaminate; available branch fragments 2-5 mm long x 2-3 mm wide.

Autozoecia rectangular (489–667 [600] µm long x 222–267 [253] µm wide) with flat frontal wall, often developing a median keel. 14-19 areolar pores on each autozoecium, very large, elliptical, and transversally elongated leaving only a thin medial portion of unperforated frontal surface ( Figure 4.1-3 ). Primary orifice hidden by the peristome; secondary orifice slightly wider than long (120–147 [149] µm long x 133–160 [149] µm wide; N = 6) with proximal border almost straight or sometimes convex ( Figure 4.2-3 ), lacking median denticles.

Ordinary avicularia paired (93–107 [105] µm long), falciform, with extremely curved mandibular part situated proximally, lining the secondary orifice ( Figure 4.2-3 ). Special avicularia very large (440– 467 [453] µm long; N = 3) almost as long as autozooecia, elongated, directed proximally; rostrum elongated, narrow and with rounded tip; pre-mandibular portion and part of the mandibular portion located very distally to the orifice and nearly at the midlenght of the distal zooecium, the tip of the mandibular portion ending near to the proximal margin of the orifice or slightly proximally ( Figure 4.1-3 ). Special avicularia sparse, apparently not associated to zooecia adjacent to maternal ones ( Figure 4.1-3 ).

Maternal zooecia large (911–956 [933] µm long; N = 3) with proximal lip enlarged developing lateral protuberances; ooecium slightly longer than wide (400–467 [433] µm long x 356 µm wide; N = 3) with frontal shield perforated by minute pores and prominent, curved ribs ( Figure 4.2 ).

Remarks. The two available specimens consist of unilaminar fragments, resulting from the separation of colony branches along the median lamina. The presence of special avicularia very large and elongated, straight along the zooidal boundaries and very distally placed, pointed proximally, as well as the ordinary falciform avicularia lining the secondary orifice, distinguish M. capanemensis sp. nov. from all other species of the genus.

Another similar species is M. kugleri Cheetham, 1968 , which has ordinary avicularia directed inward and proximally on proximal margin of the secondary orifice, but the ordinary avicularia are triangulars, usually single and larger (140–152 µm long), special avicularia placed on zooids adjacent to ooecia, orifice with broad, rounded Vshaped sinus, and three deep-set denticles; smaller areolar pores.

Range. Lower Miocene.

Occurrence. Pirabas Formation: B-17 Mine, Capanema city, Pará state.

Figures

FIGURE 4. Metrarabdotos capanemensis sp. nov. 1. General view of a colony showing fertile and infertile zooecia. 2. Detail showing two maternal zooecia bearing complete ooecia, flat ordinary zooecia and a large special avicularium below the maternal zooid. 3. Some zooecia with paired, ordinary proximally located avicularia and one elongated special avicularium. Note the frontal shield with elliptical areolar pores and a median longitudinal keel. Scale bars equal 1: 1000 µm; 2-3: 200 µm. 1-3: MG-6303-I-t. Arrows indicate special avicularia.