Metrarabdotos sergipensis, Santana, Flávia T., Ramalho, Laís V. & Gumarães, Carmen P., 2009

Santana, Flávia T., Ramalho, Laís V. & Gumarães, Carmen P., 2009, A new species of Metrarabdotos (Bryozoa, Ascophora) from Brazil, Zootaxa 2222, pp. 57-65 : 61-63

Metrarabdotos sergipensis sp. nov.

( Fig. 3 A–H)

Material examined. Type material. MNRJ-358 (holotype), MNRJ-430–435 (paratypes), Sergipe State, Station 5.3 (10°45’ S, 36°36’ W), June 2003, collector Oceano 1 team.

Diagnosis. Colony erect, dichotomously branched, bilaminate; frontal shield with irregularly disposed tubercles; primary orifice with broad, shallow U-shaped sinus; primary orifice with two strong acuminate condyles slightly curved proximally. Avicularia dimorphic, comprising near-triangular ordinary avicularia and enlarged avicularia with bilobate rostrum. Maternal zooid large, with crescent-shaped orifice; proximal border denticulate; avicularia absent. Ovicell slightly convex, perforated by small pores; ribs absent.

Description. Colony erect, dichotomously branched, 0.7–2.5 cm long x 0.2–3.0 cm wide, attached to an ascidian. Violet-purple colour when alive and in alcohol. Ancestrular region not found. Branches bilaminate, comprising up to 15 rows of zooids on each side, with a maximum of seven zooids per row ( Fig. 3 A).

Autozooids alternately disposed ( Fig. 3 B), rectangular, longer than wide, 640–720 (656) µm long x 240– 320 (288) µm wide ( Fig. 3 C), back to back; marginal zooids not different from axial zooids in shape or size. Frontal skeletal wall coarse owing to prominent tubercles, irregularly scattered, varying in shape and number; areolar pores rounded, 40–60 (49) µm diameter, numbering 13 to 16 in a single row, except in marginal zooids where a second row is present ( Fig. 3 C, upper right zooid). Secondary orifice slightly longer than wide, 160– 200 (180) µm long x 160–200 (164) µm wide, with a broad, shallow U-shaped sinus. Peristome slightly elevated, surrounded by 1–7 small, thick tubercles proximally and laterally ( Fig. 3 C–E). Primary orifice elliptical, longer than wide ( Fig. 3 E) with two acuminate condyles directed inwards, slightly curved towards the proximal region, their tips 40 µm apart ( Fig. 3 D, E).

Dimorphic avicularium situated lateral to peristome ( Fig. 3 C). Ordinary avicularia elongate, 50–75 (69) µm long), distal end acuminate, directed proximally and slightly curved along the orifice; crossbar complete ( Fig. 3 D). Twenty percent of zooids have paired avicularia, 12% have only one, and 68% have no avicularia ( Fig. 3 D). Special avicularia elongate; on marginal zooids 200–400 (310) µm long x 75 –100 (89) µm wide, mandible 200–375 (250) µm long; on axial zooids 450 µm long x 150 µm wide, mandible 300 µm long; larger than ordinary avicularia. Special avicularia situated lateral to orifice, starting near the distal margin of the zooid and ending at or near the proximal region of the orifice ( Fig. 3 C, G); these avicularia lacking on zooid adjacent to maternal zooid and rarely paired with ordinary avicularia. Premandibular region wide with elevated processes, wall crenulated; mandibular portion elongate, rounded at tip; crossbar complete ( Fig. 3 G). Mandible of special avicularia bilobate; when closed, inner tip of mandible rests on peristome ( Fig. 3 F).

Maternal ovicell-bearing zooid large, 910–1040 (996) µm long x 585–650 (628) µm wide; orifice crescent-shaped, wider than long, 120–160 (146) µm long x 440–480 (466) µm wide; proximal rim with small, thick tubercles; ordinary and special avicularia absent ( Fig. 3 H). Ovicell weakly convex, slightly longer than wide, 585 µm long x 520 µm wide, perforated by numerous pores of different sizes (smaller in proximal region, larger in distal) ( Fig. 3 C–D, H). Ovicell with small tubercles; areolar pores forming a single row; ribs absent ( Fig. 3 C, H).

Etymology. The name sergipensis is a reference to the type locality Sergipe State.

Remarks. Metrarabdotos comprises an estimated 40 species (Recent and fossil) worldwide, five of which are Recent from the Atlantic: M. cookae Cheetham, 1968 , M. auriculatum Canu and Bassler, 1923 ; M. tuberosum ( Canu & Bassler, 1928b), M. gulo ( Marcus, 1955) , and M. unguiculatum ( Canu & Bassler, 1928a); the four last species are also recorded from Brazil. Among the species of Metrarabdotos , only M. tuberosum and M. gulo have special avicularia with bilobate mandibles. Cheetham et al. (2007) published a wide review of the family Metrarabdotosidae Vigneaux, 1949 , but M. gulo was not included because the type specimens were lost. Here we consider that M. gulo differs from M. tuberosum in the following respects: M. gulo has larger avicularia (both ordinary and special), the ovicell is slightly longer than wide, special avicularia are lacking in the zooids adjacent to maternal zooids and there are fewer zooids per series.

Metrarabdotos sergipensis sp. nov. is similar to M. tuberosum in the shape and size of the colony, autozooids, areolae and the primary orifice; the secondary orifice and ordinary avicularia are similar in shape; ordinary avicularia are absent on the maternal zooid and special avicularia have a bilobate mandible. However, M. tuberosum differs in having a slightly tuberculate, finely granular frontal wall; ordinary avicularia are larger (86–93 µm long), present in almost all autozooids ( M. tuberosum : paired in 55% of autozooids, simple in 30% and absent in 15%; Metrarabdotos sergipensis sp. nov.: paired in 20% of autozooids, simple in 12% and absent in 68%), and differ in shape, having the tip directed outwards; special avicularia are present in the autozooids adjacent to maternal zooids and paired with ordinary avicularia; the ovicell is wider than long (545 µm long x 618 µm wide), with ribs and a greater distance between the tips of the condyles (50 µm).

Metrarabdotos gulo is similar to the new species in the shape of the colonies, special avicularia have a similar size and are present only in marginal and axillary autozooids, and the ovicell is longer than wide. However, the two species differ in several features: M. gulo has large colonies (6 cm long), with more zooids per series (8–12); the autozooids are larger (500–850 µm long x 200–500 µm wide) and smooth, without tubercles on the frontal shield; ordinary avicularia are longer (94 µm long), with their tips directed proximally; special avicularia are paired with ordinary avicularia; maternal zooid orifices are smaller (79–105 µm long x 395 µm wide), as is the ovicell (513 µm long x 487 µm wide).

Owing to the substantial differences observed between the two species with bilobate mandibles, Metrarabdotos sergipensis sp. nov. is considered to be a new species.

Geographic distribution. Continental shelf off Sergipe State (10°45’36” S, 36°36’08” W) (present study).

Figures

FIGURE 3. Metrarabdotos sergipensis sp. nov. (MNRJ- 358). A, Part of the colony. B, Part of a branch with zooids. C, Ordinary and maternal zooids. D, Secondary orifices and ordinary avicularia. E, Peristome and condyles. F, Special avicularium with mandible. G, Special avicularium without mandible. H, Ovicell. Scalebars: A, 5 mm; B, 1 mm; C, D, 200 µm; E, 50 µm; F, G, H, 100 µm.