Ochrophyta

Question 1

Answer 1

Ectocarpus sp.

Ectocarpales are considered to be the most primitive order of the Phaeophyceae

Uniseriate branched filaments
e.g. Ectocarpus sp.

Filamentous, with one of the simplest thalli among brown algae
It is very common, living on rocks or on larger algae, as an epiphyte

Question 2

Answer 2

Dictyota dichotoma
Order: DICTYOTALES

Thalli with regular dichotomous branching pattern:
Growth occurs by division of an apical cell, at the end of each branch, which at almost regular intervals undergoes a longitudinal division giving rise to two equivalent initials, from which two identical branches are formed.

Question 3

Answer 3

Padina pavonica also called pavonia or peacock tail

It shows a typical fan-shaped thallus with a peduncle anchored to the substrate by rhizoids.

The thallus has a hard texture. It is one of the few brown algae with thallus encrusted with calcium carbonate, in the form of aragonite crystals.

Question 4

Answer 4

Padina pavonica also called pavonia or peacock tail

It shows a typical fan-shaped thallus with a peduncle anchored to the substrate by rhizoids.

The thallus has a hard texture. It is one of the few brown algae with thallus encrusted with calcium carbonate, in the form of aragonite crystals.

Question 5

Answer 5

Desmarestia sp. (Flattened Acid Kelps)
Order: DESMARESTIALES

Specialized genus, widespread in cold temperate waters (North Pacific from the Aleutian Islands to Kodiak Alaska)
Desmarestia cells are able to produce and accumulate sulfuric acid in intracellular vacuoles. The sulfuric acid protects the alga from attack of herbivores.

Question 6

Answer 6

Desmarestia ligulata alga able to change its colour
Vacuoles with pH 0.8-1.8

Under different environmental stress (air exposure or temperature) it releases sulfuric acid, which causes damage not only to its own tissues but also to those of other nearby algae.

Question 7

Answer 7

Himantothallus grandifolius

Among Desmarestiales there is the species Desmarestia antarctica and two endemic genera of Antarctica: Himantothallus and Phaeurus. These two genera, moreover, are monospecific.

Question 8

Answer 8

Saccharina latissima (syn. Laminaria saccharina)

It shows the basic structure typical of the order:
thallus 3 m or more long
blade: of various shapes
stipe: cylindrical, can vary considerably in length
holdfast: consisting of digitations, called haptera, growing in the cracks of the substrate (it is not the typical discoid holdfast of brown algae)

Question 9

Answer 9

Organization sporophytes

MER: meristoderm
COR: cortex
MED: medulla

Question 9

Answer 9

Trumpet hyphae in medulla

The transverse walls in the filaments are perforated by areas of plasmodesmata, so that they look like sieve plates and for this reason they are called sieve cells.

Question 10

Answer 10

Trumpet hyphae in medulla

The transverse walls in the filaments are perforated by areas of plasmodesmata, so that they look like sieve plates and for this reason they are called sieve cells.

Question 11

Answer 11

Alaria sp.

shows a long primary blade which secondarily forms small spatula-shaped sporophylls at the base

Question 11

Answer 11

Laminaria digitata

It has a finger-like blade for the action of the waves that split the thallus along predetermined areas

Question 11

Answer 11

Alaria sp.

shows a long primary blade which secondarily forms small spatula-shaped sporophylls at the base

Question 11

Answer 11

Dictyoneurum sp.

Stipe dichotomously branching as a result of longitudinal splitting which extends through the blades

Answer 12

Egregia sp

Conical holdfast with branched haptera. Stipe cylindrical to flattened, irregularly branched near base. Blade bears outgrowths on each margin throughout most of the length, with different forms and functions: pneumatocysts, sterile blades and some small blades bearing sori (sporophylls).

E. menziesii may develop very long seaweeds up to 8 m in length.

Question 13

Answer 13

Corda sp.
shows the most primitive condition
the thallus is constituted by a long unbranched cylinder not differentiated into lamina and stipe
The holdfast is discoidal and without haptera

Question 14

Answer 14

Agarum sp.
Single blade with distinct perforations

Question 16

Answer 16

Nereocystis luetkeana

In this species, below the blade stipe has swellings with gas vesicles form

Question 17

Answer 17

Nereocystis luetkeana

In this species, below the blade stipe has swellings with gas vesicles form

Question 17

Answer 17

Juvenile thalli of Undaria pinnatifida

Answer 17

Nereocystis luetkeana

Question 18

Answer 18

Adult thalli of Undaria pinnatifida

Question 19

Answer 19

Temporal development dynamics of Undaria pinnatifida

Question 20

Answer 20

Fucus sp. It is a widespread genus. It has a flattened thallus less than 1 m long and with a dichotomous branching pattern The tip of each branch is invaginated and at the bottom of the notch is present an apical cell. This cuts off cells laterally which become two new branches. Internally, the thallus is differentiated into cortex and medulla The branches have a thick midrib.

Question 21

Answer 21

Fucus vesiculosus At regular intervals the thallus bears pairs of vesicles, called bladders. As the bladders are full of gas, the thalli stand erect when submerged. The development of the vesicles depends on the environmental conditions. They are much more abundant in the populations that live in calm waters

Question 22

Answer 22

Fucus virsoides

Question 22

Answer 22

Ascophyllum sp The seaweeds belonging to this genus are common in intertidal areas, especially in the North Atlantic, but also in the Mediterranean. It can reach 3 m in length and has a variable appearance depending on the wave motion. Gas vesicles form annually at regular intervals along the thallus. This allows us to calculate the age of the alga which normally reaches 8-10 years.

Question 23

Answer 23

Sargassum sp This genus is widespread with a high number of species. It has thin and long stipe that support blades with the appearance of pointed leaves They have gas vesicles that look like berries

Question 24

Answer 24

Sargassum thalli Among the photosynthetic epiphytes on Sargassum thalli there are some rhodophytes and numerous benthic diatoms. In these large tangles of thalli live a unique community of fish and invertebrates that often camouflages itself resembling the thalli of Sargassum

Question 25

Answer 25

Sargassum muticum Accidentally introduced to Europe probably with Japanese oysters. The first report dates back to 1973 since then it has spread quickly along the coasts of France and Great Britain In 1992 it also settled in the Venice Lagoon. In many areas during the favorable period it reaches such densities as to appear as continuous belts around banks and shallow waters. The thalli reach the surface even on bottoms higher than 1.5 m, thanks to the buoyancy ensured by the characteristic spherical vesicles.

Question 26

Answer 26

The first report dates back to 1973 since then it has spread quickly along the coasts of France and Great Britain In 1992 it also settled in the Venice Lagoon. In many areas during the favorable period it reaches such densities as to appear as continuous belts around banks and shallow waters. The thalli reach the surface even on bottoms higher than 1.5 m, thanks to the buoyancy ensured by the characteristic spherical vesicles.

Question 27

Answer 27

Temporal development dynamics of Sargassum muticum