Characodoma wesselinghi, Martino & Taylor, 2018

Martino, Emanuela Di & Taylor, Paul D., 2018, Early Pleistocene and Holocene bryozoans from Indonesia, Zootaxa 4419 (1), pp. 1-70 : 45-47

Characodoma wesselinghi n. sp.

( Figs 133–136 ; Table 30)

Figured material. Holotype, RGM.1350579, and paratypes, RGM.1350580, RGM.1350581, Holocene, UPGG 041, off South Sulawesi.

Diagnosis. Colony with an encrusting and erect phase of growth. Autozooids hexagonal. Frontal shield granular, with a single row of marginal areolar pores. Orifice cleithridiate. Oral spines absent. Avicularia adventitious, single but commonly paired, placed below and/or lateral to the orifice, elliptical to rounded triangular, with a complete crossbar. A third, lozenge-shaped avicularium may occur on the proximolateral zooidal corner.

Etymology. Named after Dr Frank Wesselingh, fossil mollusc researcher at Naturalis Biodiversity Center (Leiden, The Netherlands), who kindly provided part of the material used in this study.

Description. Colony characterized by an erect phase of growth inferred to arise from the encrusting phase, found usually on small shell fragments, with zooids arranged quincuncially. The isolated erect phase consisting of tubular to club-shaped branches, dichotomizing at right angles with zooids arranged in 4–6 alternate, longitudinal rows. Autozooids distinct, bordered by shallow interzooidal grooves, hexagonal, longer than wide (mean L/W = 1.29). Frontal shield convex, coarsely granular, with a single row of small, circular, marginal areolar pores (15–20 µm in diameter) along the proximolateral zooidal margins. Primary orifice cleithridiate, a horseshoe-shaped anter separated from a narrower, shallow, bowl-shaped sinus by two small, triangular, proximomedially directed condyles. Oral spines absent. Avicularia adventitious, single but commonly paired. When a single avicularium is present, this is suboral, median and transversely placed, elliptical with a complete crossbar, 90–110 µm long by 55–75 µm wide; in zooids with paired avicularia, the second avicularium is placed proximolateral to the orifice, the rostrum is raised and distolaterally directed, rounded triangular with complete crossbar, about 95–105 µm long by 55–70 µm wide. A third, larger (about 115–130 µm long by 90–100 µm large), lozenge-shaped avicularium may occur on the proximolateral zooidal corner on a swollen cystid, distolaterally directed with complete crossbar. Avicularian cystids sometimes outlined by marginal areolar pores. No complete ooecia observed.

Remarks. Thirty specimens of Characodoma wesselinghi n. sp. were found in our samples. Characodoma wesselinghi n. sp. is very similar to the Recent Characodoma biavicularium ( Canu & Bassler, 1929) described from the Philippines. However, examination of the holotype USNM8067 of C. biavicularium proved the two species to be different ( Figs 137–138 ). The constant avicularium present in C. biavicularium is placed parallel and lateral to the orifice and is larger than the proximolateral avicularium observed in C. wesselinghi n. sp. (110–140 µm long by 100 µm wide in C. biavicularium vs 95–105 µm long by 55–70 µm large in C. wesselinghi n. sp.). It is also lozenge-shaped rather than rounded triangular, and the crossbar is much more conspicuous (15–20 µm in width in C. biavicularium vs 10 µm in C. wesselinghi n. sp.). The second, additional avicularium is oval and smaller than those observed in C. wesselinghi n. sp. (ca 80 µm long by 60 µm wide in C. biavicularium vs 90–110 µm long by 55–75 µm wide in C. wesselinghi n. sp.), and although sometimes located and directed in the same way as the constant avicularium in C. wesselinghi n. sp., it is often located medially on the frontal shield and directed proximally. The two growth-form phases, encrusting and erect, have been observed also in the Miocene C. excubans ( Waters, 1881) from Australia. Although in both species the two phases have been observed only isolated, they have identical zooids in all characters. Characodoma excubans differs from C. wesselinghi n. sp. in having a pair of triangular, proximally directed avicularia flanking the orifice, or a single largely spatulate avicularium proximal to the orifice and laterally directed.

N, Number of colonies and number of zooids measured; SD, standard deviation.

Figures

FIGURES 133–136. Characodoma wesselinghi n. sp., Holocene, UPGG041, off South Sulawesi. 133, 134. Holotype RGM.1350579. 133. View of a branch (erect growth phase). 134. Group of zooids with various adventitious avicularia. 135. Paratype, RGM.1350580, close-up of zooids with partly-formed ooecia. 136. Paratype, RGM.1350581, colony on a shell fragment (encrusting growth phase). Scale bars: Fig. 133 = 500 µm; Figs 134, 136 = 200 µm; Fig. 135 = 100 µm.

FIGURES 137, 138. Characodoma biavicularium (Canu & Bassler, 1929), holotype, USNM 8067, Recent, Sulu Archipelago, Philippines. 137. Group of zooids. 138. Close-up of two autozooids. Scale bars: 200 µm.