Hexactinellida, Schmidt, 1870

Moser, Julia, Moraes, Fernando C., Castello-Branco, Cristiana, Pequeno, Carolline B. & Muricy, Guilherme, 2022, Manned submersible dives reveal a singular assemblage of Hexactinellida (Porifera) off the Amazon River mouth, Northern Brazil, Zootaxa 5105 (1), pp. 105-130 : 121

Abundance of Hexactinellida off the Amazon River mouth

The three species of Hexactinellida described here were rare to common at the central sector of the Amazon River mouth, off Pará State, with only one specimen of Hyalonema (Cyliconemaoida) alucia sp. nov. being observed on a muddy sand bottom, three specimens of Dactylocalyx pumiceus widely spaced on rocky outcrops, and several specimens of Claviscopulia facunda on coarse sand to gravel bottoms ( Fig. 14A–C ). On the other hand, a dense sponge community dominated by a large population of D. pumiceus was recorded on the upper slope at the southern sector off Maranhão State, colonizing a steep hard bottom ramp partially covered by fine carbonate sediment ( Fig. 14D–E ). Quantitative analysis of 183.2 m 2 of bottom imagery on the upper slope off Maranhão State showed a total of 277 individuals of D. pumiceus and 99 of demosponges (mainly Corallistes sp. ; voucher MNRJ 21293). The highest density of D. pumiceus was recorded between 170 and 175 m depth, reaching 4.5 ind. m-2 ( Fig. 14D ). The maximum density of Corallistes sp. was recorded at 220 m depth (1.5 ind. m-2). Considering the whole depth interval analyzed at this dive site (145–220 m), Dactylocalyx pumiceus accounted for 73.6% of the total number of sponge individuals.

Figures

FIGURE 14. Environment and populations of Hexactinellida off the Amazon River mouth, Northern Brazil. A, Hyalonema (Cyliconemaoida) alucia sp. nov. on muddy sand bottom off Pará State, 378 m depth; B, Claviscopulia facunda population on coarse sand to gravel bottom off Pará State, 250 m depth; C, Dactylocalyx pumiceus on rocky outcrop off Pará State, 260 m depth; D–F, Dense sponge community dominated by Dactylocalyx pumiceus on hard carbonate bottom off Maranhão State, at 170 m depth (D) and 180 m depth (E). Photographs by F. Moraes (A–C) and R. Moura (D–E).