C. Triterpenoids
23
The trivial names of the five classes in the phylum are descriptive of their
appearance and thereby indicative of the divergence among the classes. No
wonder that a lively controversy exists among marine zoologists with respect
to phylogenetic relationships in the phylum. All chemical indicators that
have so far been studied seem to point to a close relationship between sea
urchins (Echinoidea) and brittlestars (Ophiuroidea), and similarly between
sea stars [popularly called starfish, (Asteroidea)] and sea cucumbers (Holothuroidea). The fifth class, the feather stars or sea lilies (Crinoidea), appears to
be unique. This purely chemical view of crinoid phylogeny receives some
support from the fact that the crinoids are the most ancient—and in some
ways the most primitive—of the living echinoderms.
1. HOLOTHURINS
The sea cucumbers or holothurians are a class of some 500 species. To
the human eye they are perhaps the least attractive of the echinoderms in
shape and color, although the dried body wall of certain large species (e.g.,
Thelenota ananas, Stichopus variegatus, Holothuria atra) is an East Asian
(mostly Chinese) culinary delicacy traded under the name trepang or bêchede-mer. They are further distinguished from the other echinoderms by their
general lack of calcareous body armor. Nevertheless, sea cucumbers possess
some unique features that make them attractive, at least to scientists. One of
these features is a well-documented symbiotic relationship between the pearl
fish (Carapus spp.) and certain sea cucumbers, which play host to the fish in
their cloaca. The fish leaves the host at night while it searches for food, then
returns to its holothurian shelter. Another unusual feature, of greater immediate chemical interest, is a defensive mechanism associated with the
so-called Cuvierian tubules or glands. Some species of holothurian in the
genera Holothuria and Actinopyga possess these tubules, which are attached
to the base of the respiratory system. These sticky tubules are shot out of the
sea cucumber's anus toward a predator who finds himself entangled and
disabled in a sticky mesh of adhesive threads. The tubules will regenerate
after discharge.
According to Halstead (1965) the earliest record of the toxic nature of the
Cuvierian tubules date back to 1880, but modern research into the constituents of sea cucumbers was probably started in 1929 by Yamanouchi*
(1955).
Apparently one of Yamanouchi's earliest observations was related to the
ability of aqueous extracts of Holothuria vagabunda to kill fish when placed
* Yamanouchi's earlier publications on his research (1929,1942,1943) are cited by him,
and occasionally by others. Some are in Japanese and are published in periodicals that
are not readily available in United States libraries.
23
The trivial names of the five classes in the phylum are descriptive of their
appearance and thereby indicative of the divergence among the classes. No
wonder that a lively controversy exists among marine zoologists with respect
to phylogenetic relationships in the phylum. All chemical indicators that
have so far been studied seem to point to a close relationship between sea
urchins (Echinoidea) and brittlestars (Ophiuroidea), and similarly between
sea stars [popularly called starfish, (Asteroidea)] and sea cucumbers (Holothuroidea). The fifth class, the feather stars or sea lilies (Crinoidea), appears to
be unique. This purely chemical view of crinoid phylogeny receives some
support from the fact that the crinoids are the most ancient—and in some
ways the most primitive—of the living echinoderms.
1. HOLOTHURINS
The sea cucumbers or holothurians are a class of some 500 species. To
the human eye they are perhaps the least attractive of the echinoderms in
shape and color, although the dried body wall of certain large species (e.g.,
Thelenota ananas, Stichopus variegatus, Holothuria atra) is an East Asian
(mostly Chinese) culinary delicacy traded under the name trepang or bêchede-mer. They are further distinguished from the other echinoderms by their
general lack of calcareous body armor. Nevertheless, sea cucumbers possess
some unique features that make them attractive, at least to scientists. One of
these features is a well-documented symbiotic relationship between the pearl
fish (Carapus spp.) and certain sea cucumbers, which play host to the fish in
their cloaca. The fish leaves the host at night while it searches for food, then
returns to its holothurian shelter. Another unusual feature, of greater immediate chemical interest, is a defensive mechanism associated with the
so-called Cuvierian tubules or glands. Some species of holothurian in the
genera Holothuria and Actinopyga possess these tubules, which are attached
to the base of the respiratory system. These sticky tubules are shot out of the
sea cucumber's anus toward a predator who finds himself entangled and
disabled in a sticky mesh of adhesive threads. The tubules will regenerate
after discharge.
According to Halstead (1965) the earliest record of the toxic nature of the
Cuvierian tubules date back to 1880, but modern research into the constituents of sea cucumbers was probably started in 1929 by Yamanouchi*
(1955).
Apparently one of Yamanouchi's earliest observations was related to the
ability of aqueous extracts of Holothuria vagabunda to kill fish when placed
* Yamanouchi's earlier publications on his research (1929,1942,1943) are cited by him,
and occasionally by others. Some are in Japanese and are published in periodicals that
are not readily available in United States libraries.