Living, symbiont-bearing, larger foraminiferids restricted to the phot
ic zone incorporate mechanisms blocking solar radiation and water curr
ent transportation. They can be divided in two groups according to the
ir wall structure: 1. Families with opaque test walls, reducing light
penetration: Peneroplids inhabit shallow-water environments from the i
ntertidal (Peneroplis in large numbers) down to 40 m (Dendritina, pref
erring sandy substrates). Soritids are restricted to subtidal environm
ents with less water turbulence and range from the reef moat down to 6
0 m. Amphisorus and Marginopora are common down to 30 m, whereas Paras
orites is restricted to deeper parts of the reef slope. Alveolinella c
an be found in the upper 40 m of the reef slope. 2. Families with hyal
ine test walls, adjusted for light penetration: amphisteginids inhabit
the whole photic zone, demonstrating a correlation of test flattening
with increasing depth. Calcarinids cling with their spines to firm su
bstrates such as algal thalli or macroids. Baculogypsina is restricted
to high energetic regions on the reef hat. Calcarina inhabits similar
environments, extending its distribution range within fore reefs down
to 80 m. Baculogypsinoides is a dominant calcarinid genus from 30 to
70 m depth. Within nummulitids, Heterostegina prefers hard substrates
on the reef slope, while Assilina (= Operculina) is frequent in deeper
parts and is independent of substrates. Sandy bottoms from 30 to 60 m
are inhabited by the last living representative of the genus Nummulit
es, N. venosus. The giant foraminifer Cycloclypeus, with test sizes up
to 7 cm, is restricted to fore reef areas below 50 m down to the base
of the photic zone.