Tessaradoma sp.

Tessaradoma sp.

( Fig. 13.1–5 View FIGURE 13 )

Material examined. SMF 10370 (St. 257; Fig. 13.1–5 View FIGURE 13 ).

Description. Colonies rigidly erect, cylindrical, multiserial, dichotomously branching ( Fig. 13.1–2 View FIGURE 13 ).Autozooidal outlines not evident frontally. Zooidal peristomes arranged in four alternating rows along cylindrical branches. Ancestrula and early astogeny not observed.

Autozooids supposedly longitudinally rectangular, though zooidal boundaries obscured by secondary calcification. Peristomes projecting. Peristomal orifice circular, 177–236 μm (ẋ = 210 ± 25 µm; CV = 12; N = 4 on 1 specimen) in diameter ( Fig. 13.3 View FIGURE 13 ). Frontal shield with longitudinally aligned striae, raised around peristome and spiramen, pierced by circular areolar pores at the lateral margins and by infrequent slit-like pores. Spiramina projecting, single; outer opening proximal to the orifice at about one-third the autozooid length, circular, 56–66 μm (ẋ = 60 ± 5 µm; CV = 8; N = 4 on 1 specimen) in diameter ( Fig. 13.3 View FIGURE 13 ). Spine bases absent. Ovicells not observed .

Avicularia monomorphic, adventitious, located inside circular pores usually at the margin of an autozooid, bilaterally symmetrical, ovate, 59–87 μm (ẋ = 73 ± 8 µm; CV = 11; N = 15 on 1 specimen) long by 40–80 μm (ẋ = 62 ± 10 µm; CV = 15; N = 15 on 1 specimen) wide, with incomplete crossbar at about one-third the avicularian length ( Fig. 13.4–5 View FIGURE 13 ). Rostrum rounded, strongly elevated, proximally or distally directed .

Kenozooids not observed.

Remarks. One specimen from the Gulf of Aden, collected from a deep-sea station, exhibits strong secondary calcification. However, marginal areolar pores and projecting spiramina proximal to the orifice remain clearly recognisable ( Fig. 13.3 View FIGURE 13 ), allowing its assignment to Tessaradoma , a genus that currently comprises only a few species known from deep-sea environments worldwide.

The type species, Tessaradoma boreale ( Busk, 1860) , is recorded from deep-sea waters of the Atlantic Ocean and the Mediterranean Sea. This species displays significant morphological variability, as secondary calcification alters its surface features over time, particularly in older parts of the colony (see Souto et al. 2016, figs 84–90). Due to this variability, Winston (2005) suggested that the specimens currently identified from the Atlantic Ocean might represent a species complex.

From the Indian Ocean, David & Pouyet (1986) reported specimens from the deep sea southeast of Madagascar as Tessaradoma boreale , though the poor preservation of the imaged specimens raises doubts about their conspecificity. Another species from the same region, Tessaradoma sinulabiata David & Pouyet, 1986 , is distinguished by a sinuate proximal primary orifice. Additionally, two species initially assigned to Tessaradoma , Tessaradoma bispiramina Hayward & Cook, 1979 and Tessaradoma circella Hayward & Cook, 1979 , were described from deep waters off KwaZulu-Natal, South Africa. These species, characterised by two spiramina and bilamellar colonies, respectively, were later transferred to Galeopsis Jullien in Jullien & Calvet, 1903 by Boonzaaier-Davids et al. (2020). However, their current taxonomic status remains uncertain due to a lack of further study and reimaging.

The specimen from the Gulf of Aden closely resembles Tessaradoma boreale , but it differs in one key characteristic: its avicularia possess an incomplete crossbar ( Fig. 13.5 View FIGURE 13 ), a feature not observed in any known Tessaradoma species. However, given that only a small colony fragment is available, we refrain from proposing a new species and instead refer to the Aden specimen in open nomenclature.