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Growth, Regeneration, and Damage Repair of Spines of the Slate-Pencil Sea Urchin Heterocentrotus mammillatus (L.) (Echinodermata: Echinoidea )

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Title:Growth, Regeneration, and Damage Repair of Spines of the Slate-Pencil Sea Urchin Heterocentrotus mammillatus (L.) (Echinodermata: Echinoidea )
Authors:Ebert, Thomas A.
Date Issued:1988
Publisher:University of Hawaii Press
Citation:Ebert TA. 1988. Growth, regeneration, and damage repair of spines of the slate-pencil sea urchin Heterocentrotus mammillatus (L.) (Echinodermata: Echinoidea ). Pac Sci (3-4): 160-172.
Abstract:Spines of sea urchins are appendages that are associated with
defense, locomotion, and food gathering. Spines are repaired when damaged,
and the dynamics of repair was studied in the slate-pencil sea urchin Heterocentrotus
mammillatus to provide insights not only into the processes of healing. but also into the normal growth of spines and the formation of growth lines.
Regeneration of spines on tubercles following complete removal of a spine
was slow and depended upon the size of the original spine. The maximum
amount of regeneration occurred on tubercles with spines of intermediate size
(1.6 g), which, on average, developed regenerated spines weighing 0.1, 0.3, and
0.7 g after 4, 8, and 12 months, respectively. Some large tubercles, which had
original spines weighing over 3 g, failed to develop a new spine even after 8-12
Regeneration of a new tip on a cut stump was more rapid than production of
a new spine on a tubercle. Regeneration to original size was more rapid for small
spines than for large spines, but large stumps produced more calcite per unit
time. In 4 months, a small spine with a removed tip weighing 0.15 g regenerated
a new tip weighing 0.09 g, or 63% of its original weight. In the same time, a large
spine with 2.35 g of tip removed regenerated 0.40 g of new tip, or 17% of the
original weight.
Holes were drilled in spines to serve as bench marks to document the production
of new growth lines in response to damage. Blind holes drilled in spines
caused 65% loss over 4 months, but holes drilled completely through spines
caused only a 6% loss. Cutting a spine near its base did not initiate shedding of
the stump. Repair of holes drilled in spines showed that major repair originated
from the spine surface, and regeneration into the hole was over obtuse angles.
For a slanting hole through a spine, filling of the hole carne from the distal edge
for the distal opening and from the proximal edge for the proximal opening.
Spines were tagged with tetracycline, but of 46 spines examined 4-12 months
following treatment, only 1 displayed evidence that the spine surface had been
marked. This suggests that spines usually are not growing.
Abrasion of spines either by wiping with a cloth or sanding with emery paper
failed to induce growth lines to form. Of 57 abraded spines and 64 unabraded
spines, only 2 in each treatment category developed new growth lines. Results
show that some growth lines in spines develop from trauma, but these tend to
be local and do not extend from the base to the tip. Spines of Heterocentrotus
mammillatus usually are not growing but occasionally undergo a growth episode
that produces a growth line that extends from the milled ring to the spine tip.
Such an episode is not related to damage repair from abrasion or breakage and
appears to be endogenous.
The SPINES OF A SEA URCHIN are morphological
parts that serve as the animal's first defense
against assaults from the environment (e.g.,
Fricke 1974, Strathmann 1981), appendages
for gathering and manipulating food (e.g.,
Ebert 1968, Leighton 1968), and braces for
wedging into crevices (e.g., Regis and Thomassin
1982). Spines form an important part of
an urchin's maintenance mechanisms (Ebert
1982), and it is no surprise to find that they
are repaired rapidly once damaged (Ebert
1967, Heat field 1971, Mischor 1975).
Spine sizes vary greatly across taxa. For
example, in St rongylocentrotus purpuratus
(Stimpson 1857), calcite of a large primary
spine weighs only about 0.03 g. In slate-pencil
sea urchins of the genus Heterocentrotus,
spines are substantially more massive. Calcite
in a large H. mammillatus (Linneaus 1758)
spine may weigh over 5 g, and calcite of a
large primary spine of H. trigonarius (Lamarck
1816) may weigh over 11 g.
Although spines from Strongylocentrotus
purpuratus would be expected to be repaired
rapidly (Ebert 1967, Heatfield 1971), it is less
clear whether very large spines from Heterocentrotus
species also would be repaired in just
a few months or whether the benefits of large
spines carry a potential burden of a long regeneration
A second issue associated with damage repair
focuses on growth lines in spines. In
St rongylocentrotus purpuratus, lines form as
a consequence of tip regeneration following
breakage (Ebert 1967, Heatfield 1971 ), but
growth lines in Heterocentrotus spp. have been
interpreted as periodic (Dotan and Fishelson
1985, Weber 1969), an interpretation that has
been disputed (Ebert 1985, 1987).
The purpose of this paper is to present results
of a 1-year study on Heterocentrotus
mammillatus (family Echinometridae), a species
with massive spines. The focus is on the
responses of spines to damage, spine repair
and regeneration in response to trauma, and
the formation of growth lines. Data are presented
on (a) regeneration following total removal
of spines; (b) repair rates of calcite
on cut spine stubs; (c) responses of spines to
small holes drilled into or through them; (d)
responses of spines to abrasion; and (e) results
of tagging spines with tetracycline.
Appears in Collections: Pacific Science Volume 42, Numbers 3-4, 1988

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