Abstract
Benthocodon pedunculata is a deep-sea benthopelagic medusa
found abundantly in Monterey Bay and Carmel Bay,which has been
virtually ignored since its original description (Bigelow, 1913). Recent
observations from a remotely operated vehicle (ROV), working in the
Monterey Submarine Canyon, reveal that the medusae live primarily
near the deep-sea floor and may be potential predators of benthic or
benthopelagic crustaceans. This study investigates the gross
morphology of the medusae, tentacle types, and nematocyst types.
Phase contrast microscopy and scanning electron microscopy were
used to detect morphological differences between the inner and
outer tentacles and also revealed two nematocyst types previously
undescribed in the literature, the modified-aspirotele nematocyst
and the modified-stenotele nematocyst. The inner tentacles are
annulated, with rings of both nematocyst types, and contain digestive
inclusions, which may aid in digestion or storage. The outer tentacles
have an abscission point and are readily discarded. They are coverec
with both nematocyst types and are possibly used for encountering
and capturing prey. Gut analyses of medusae yielded copepods,
amphipods, foraminiferans, pycnogonid, and other unidentified
organisms which, along with data on distribution and abundance of
crustacean zooplankton in Monterey Canyon (Kelly, 1992), show that
the medusae are feeding on benthic and benthopelagic organisms.
Based on the results of this study, a model of tentacular function in
feeding medusae was generated to show that the outer and inner
tentacles of Benthocodon pedunculata may entrap prey during
different pulsation periods of the umbrella. Further gut analyses and
in situ observations of feeding medusae would be helpful in further
resolving the foraging and feeding biology of B. pedunculata.
Introduction
The benthopelagic medusae Crossota pedunculata was
originally described by Bigelow (1913) and later renamed as
Benthocodon pedunculata (Larson and Harbison, 1990). Dives made
with a remotely operated vehicle (ROV) in Monterey Bay (U.S.A.)
have typically found aggregations of medusae at depths between 500
m and 900 m, within 5 m of the sea floor. This environment is
characterized by an increase in biomass, including medusae
(Wishner, 1980a), with some copepods found exclusively in the
benthopelagic boundary (Wishner, 1980b). Crustaceans are the
dominant arthropods in the deep sea (Gage and Tyler, 1991) and in
terms of density in the Monterey Canyon, the most abundant
crustacean was shown to be copepods (Kelly, 1992). Therefore,
benthopelagic medusae, e.g. Benthocodon pedunculata, may prey on
copepods and other abundant deep-sea crustaceans (Larson et al.,
1992) and have distinctive morphological features which allow them
to live in the deep-sea benthopelagic environment.
There are several characteristic features of the order
Trachymedusa, to which Benthocodon pedunculata belongs (Mayor,
1910; Marshall and Williams, 1971). Trachymedusae are generally
carnivorous and either active or passive predators (Laverack and
Dando, 1987). All members are mobile medusae whose tentacles are
hollow and stem from the margins of the umbrella. These tentacles
are structures that are specialized for prey capture and defense. The
gonads are developed from the radial canals. The body wall has 3
basic layers: epidermis, mesoglea (usually well-developed in
subumbrella), and gastrodermis (Laverack and Dando, 1987; Thomas
and Edwards, 1991). The tentacular epidermis contains nematocysts,
complex organelles each of which contains a shaft and an inverted,
spined tube coiled within a capsule (Westfall, 1970; Harrison and
Westfall, 1991), and interstitial cells that give rise to these stinging
cells (Marshall and Williams, 1971). Different species of cnidarians
have up to 7 types of nematocysts, which affect the prey type
captured. A nematocyst is only used once (Marsical, 1974; Barnes,
1987). Several types of nematocysts have been classified and
described (Marsical, 1974). The nematocysts may adhere to, wrap
around, penetrate, or paralyze prey, but the actual mechanism of
discharge is poorly understood (Laverack and Dando, 1987). It has
been proposed that discharge is dependent on chemical and/or
mechanical stimuli, such as triggers extending from the nematocyst
known as cnidocils.
Recent observations from a remotely operated vehicle (ROV),
working in the Monterey Submarine Canyon, reveal that the
medusae live primarily near the deep-sea floor and may be potential
predators of benthic or benthopelagic crustaceans. Because so little is
known about these specialized structures along the tentacles that are
crucial to the survival of B. pedunculata , the morphology of the
nematocysts are interesting to study, particularly if nematocyst type
affects the type of prey captured. This study investigates the gross
morphology of the medusae, tentacle types, and nematocyst types
using phase contrast and scanning electron microscopy. Prey type
will be determined by gut analysis of collected specimens. It is
hypothesized that because Benthocodon pedunculata are typically
found on or near the bottom of the ocean floor, they would have
tentacles and nematocysts that would allow them to feed on
benthopelagic crustaceans and other benthic organisms.
Materials and Methods
Location
Eighteen specimens of Benthocodon spp. were collected on five
dives using the Monterey Bay Aquarium Research Institute's
(MBARI) ROV Ventana from the RV Point Lobos. Five specimens were
collected using the Johnson Sea Link II manned submersible in the
Atlantic Ocean. (Table 1)
Specimen Collection
Individual medusae were captured in a detritus sampler
[transparent acrylic cylinders with lids; designed by Harbor Branch
Oceanographic Institute, Inc (HBOI)). Additional medusae were
collected using a variable speed suction sampler (HBOI) with five
sample jars. Once the samplers were removed from the ROV, the
medusae were transferred to round tupperware containers and
stored in a cooler maintained at 5°C. Specimens were transferred
within two hours of the initial transfer from the samplers to an
aquarium and kept under controlled conditions.
Eighteen specimens of Benthocodon spp were collected
between April 9, 1993 and May 24, 1993. Fourteen medusae were
maintained for laboratory and microscope studies. Three specimens
that were preserved immediately on board ship and 8 medusae that
were maintained in lab were used for gut content analysis. One
specimen was identified as Benthocodon hyalinus and was not used
for this study.
Laboratory studies
Four organisms were maintained in an aquarium with 50C
running sea water in the deep sea lab under dark conditions; ten
specimens under light conditions. Two medusae were kept in a .62 m
*42 m *.18m aquarium; the remaining 2 in a 41 m*.2 m *.27 m
aquarium. They were fed 24 hours later with Tigriopus californicus
and Artemia salina. Ten minutes before feeding, water flow was
discontinued. Approximately 20 prey organisms were placed into the
aquarium near the outer tentacles of each medusa. Five minute
observations of medusa behavior were made every fifteen minutes
for 1 hour. Dead specimens were immediately removed from the
aquarium and preserved in 3% glutaraldehyde.
Gut Contents
Eleven medusae from the Soquel Canyon and five specimens
collected from the western Atlantic using the Johnson Sea Link II
manned submersible on October 29, 1991 (described in Larson et al.,
1992). The entire digestive system--mouth, stomach, and peduncle--
was removed from the subumbrella and transferred to filtered sea
water for microdissection using a Nikon SM2-U Type 104 dissecting
scope with light field/dark field illumination and fiber optic lights
(Bausch & Lomb Fiber-Lite). Photographs of some samples were
taken using a Nikon 35 mm camera and a Nikon HFX-DX electronic
camera system. The grooves of the stomach were examined for prey
All items found were identified to the lowest taxonomic level
possible and transferred to glass vials filled with 70% ethanol.
Microscope studies
Eight specimens were fixed in 3% glutaraldehyde and then
placed in successive ethanol concentrations up to 100%. The general
structure of the medusa was examined under a dissecting microscope
and the structure of 22 outer tentacles and six inner tentacles from 6
different specimens were examined with a light compound
microscope. Squash preparations of eight preserved tentacle margins
from 4 different medusae were made on slides after rinsing the
entire specimen in freshwater and replacing the water with 30%
ethanol. Nematocyst structures were examined using a Zeiss
Axioskop compound microscope under 100x oil immersion phase
contrast and photographs were taken using an Olympus OM2S 35mm
SLR with Ektar 100 and Ektachrome 160T films. Unpreserved outer
and inner tentacles from two specimens were transferred from the
aquarium into a vial of distilled water. After five minutes the
tentacles were squashed onto slides. Uncollected tentacles were
placed into a petri dish filled with sea water and maintained at 50C
temperature and analyzed for nematocyst activity.
Measurements of the lengths and widths of nematocysts from
22 unpreserved outer tentacles and 3 unpreserved inner tentacles
from two specimens were taken using a Dage-MTI digital 81 series
high resolution camera with a TECON frame grabber board version
2.0 and the Bioscan OPTIMAS image processing program for
Microsoft Windows. Nematocyst lengths were measured from the
opening of the nematocyst or base of shaft directly to the other end.
Widths were measured from the widest points of the nematocyst.
The ultrastructure of nematocysts and tentacles of this
trachymedusa was studied using an Hitachi S-450 scanning electron
microscope. Tentacles fixed in 5% glutaraldehyde were transferred to
30% ethanol and dehydrated in a graded ethanol series to 100%
ethanol, 10 minutes in each concentration. Following dehydration, the
samples were critical point dried with CO2 and sputter coated with a
100A layer of gold in a Denton vacuum evaporator.
For histological study, five outer and seven inner tentacles
were dehydrated in a graded ethanol series: from 50%, 60%, 70%,
80%, 90%, to 95% ethanol in scintillation vials at room temperature
for15 minutes at each concentration. Following the dehydration
series, 10 mL of 50% LR white resin solution (mixed 1:1 with 100%
ethanol) was added to each sample and the vials were rotated at 40(
for 2 hours. The supernatant was replaced with 10 mL of a 75% resin
solution, followed by rotation 4°C for 2 hours. The procedure was
repeated with a 100% solution, then the sample was kept in fresh
100% resin solution overnight. The following day, the samples were
placed into a100% resin solution in plastic capsules and heated until
the plastic solidified. A Sorvall ultramicrotome was used to make 0.5
u sections along the longitudinal axis of two outer tentacles and four
inner tentacles from two medusae. The sections were then fixed onto
slides by heating over a bunsen burner. Basic fuchsin and methylene
blue dyes were used to stain the samples. Slides were examined
using the Zeiss Axioskop compound microscope under 100x oil
immersion phase contrast and photographs were taken using an
Olympus OM25 35mm SLR.
Results
Observations of Benthocodon pedunculata in situ (Fig. 1)
revealed that these reddish-brown pigmented trachymedusae hover
near or sit on the ocean floor. They are generally found in patches in
the Soquel Canyon. Characteristic of this species is the presence of
three types of tentacles (Fig. 1) that seem to differ in morphology
(Fig. 1, 2). There appears to be two types of outer tentacles, although
structural differences were difficult to detect with the ROV because
the medusae rapidly swam away from view. One group of outer
tentacles curved downward and in toward the subumbrella while the
other group seemed to extend upward and outward (Fig. 1). The
inner tentacles are the third type, those closest to the subumbrella
and shorter and thinner than the outer tentacles (Fig. 3, 4). The outer
tentacles have an abscission point, which is absent on the inner
tentacles (Fig. 5). Even when fully extended in the uncontracted
medusa, the tentacles are numerous and closely spaced (Fig. 1).
Morphological differences between the two outer tentacles were
indistinguishable in the lab and the two types were therefore
grouped together as outer tentacles.
Laboratory observations of 14 specimens of Benthocodon
pedunculata showed that they were sensitive to prolonged exposure
to fluorescent light. The two medusae maintained in the deeper tank
under dark conditions survived for six days, the ten medusae in the
shallow tank under light conditions died in less than two days, and
the two specimens kept in the shallow tank under dark conditions
were alive for three days. The specimens from the .18 m deep tank
were often seen swimming near the surface while the two medusae
in the .27 m deep tank were frequently observed to be resting on the
bottom.
Feeding experiments began within two days of specimen
collection. Observations of medusae after exposure to either
Tigriopus californicus or Artemia salina showed no visible change in
behavior. Dissection of these medusae showed empty digestive tracts.
Further post mortem examinations showed that only the inner
tentacles were left attached to the edge of the subumbrella. All outer
tentacles and a few inner ones were left intact at the bottom of the
aquarium.
Although the dissections of eight medusae that were
maintained in the lab revealed no gut contents, analysis of eight
specimens that were immediately fixed on board ship showed
recognizable prey in six of the eight (Table 2), five of which were
collected during night dives and one during an afternoon dive (Table
1). Copepod and amphipod (Fig. 6) exoskeletons were discovered in
all the dissected specimens. One pycnogonid exoskeleton (Fig. 7), 22
Globigerina foraminiferans, and several unidentified exoskeletons
were also found. The remaining two did not have any gut contents.
Like other trachymedusae, the tentacles of Benthocodon
pedunculata stem from the edge of the subumbrella (Fig. 8 ). There
are 3 or 4 uneven rows of tentacles (Fig. 9). The inner tentacle is
annulated, completely encircled by rings containing nematocysts (Fig.
10a). The rings disappear at the tip of the tentacle, where
nematocysts cover the entire surface (Fig. 10b). Nematocysts within
these rings are at various orientations and are adjacent to
undifferentiated interstitial cells (Fig. 11a, b). Digestive inclusions are
found in the gastrodermis of the inner tentacles (Fig. 11a) but not in
the outer tentacles. The outer tentacle is more heavily pigmented
and nematocysts and interstitial cells are distributed along the entire
surface area (Fig. 12a, b). The nematocysts are positioned at various
orientations, as shown by the orientation of the shaft and the wound
thread (Fig. 12b). The nematocyst types are modified versions of the
stenotele and aspirotele nematocysts (Marsical, 1974). Lengths and
widths of nematocysts from both the tentacle types were measured
and fell into two categories (Fig. 14). Modified-aspirotele
nematocysts (MAN) were measured and ranged from 8-13 u in
length and 4-6 u in width while modified-stenotele nematocysts
(MSN) were measured with a range from 11-15 u in length and 10-
12 u in width. Both types of nematocysts are found on the inner and
outer tentacles (Fig. 11, 12) with a MAN: MSN ratio of about 3:1.
Ultrastructure of extruded nematocysts were observed with
both the phase contrast microscope and scanning electron microscope
(Fig. 14, 15, 16). The average lengths of the extruded shaft of MAN
and MSN are 7.1841.11 u (n=78) and 10.29+1.58 u (n=54),
respectively. Three stylets are visible on the shaft of both
nematocyst types, near the base of the thread (Fig. 14a, 15, 16). Also
common to both types are spiraled barbs that travel the length of the
extended threads (Fig. 15,16). These threads extend up to 261 u in
length.
Discussion
Patches of Benthocodon pedunculata were frequently found
hovering over or resting on the ocean floor, suggesting that they may
feed on benthopelagic organisms, most of which are crustaceans
(Kelly, 1992), and benthic organisms, of which the foraminiferan
Globerigina bulloides constitute 40% of collected animals (Petry,
1992). Attempts to observe feeding in the lab by introducing
medusae to Tigriopus californicus and Artemia salina were
unsuccessful because the gastrovascular cavities of medusae were
completely empty. Nevertheless, it is inconclusive whether the
medusae are not eating because of the conditions of the aquarium or
because Tigriopus and Artemia are not palatable. The specimens
may have been damaged during collection and lack of outer tentacles
may have prevented the medusae from capturing the prey.
Specimens of Benthocodon pedunculata maintained in the
aquarium under controlled conditions showed sensitivity to
10
fluorescent light, as measured by differences in survival time. The
four specimens maintained under dark conditions survived one to
three days longer than those under light conditions. However, the
four that survived longer were collected by detritus samplers while
the others were collected using a variable speed suction sampler.
This apparent sensitivity to light, then, may actually be sensitivity to
the method of collection. The detritus sampler is probably less
damaging to the specimens than the suction samplers. Of the four
medusae collected by detritus samplers and maintained in tanks of
different depths under dark conditions, the two that were in the
deeper tank (.27 m) survived three days longer than the two in the
shallower tank (.18 m). This difference in survival time may be
caused by the slight change in pressure between the two tanks or by
the difference in nutritional state of the medusae upon collection.
The ones that survived the longest may have fed just before being
collected.
Gut content analysis did reveal recognizable prey in six out of
eight specimens that were not used for feeding experiments. Copepod
and amphipod exoskeletons were discovered in five medusae and
exoskeleton debris was found in all six. Because these crustaceans
are non-sessile organisms that inhabit the benthopelagic
environment (Kelly, 1992; Wishner, 1980b; Gage and Tyler, 1991),
the trachymedusae probably have tentacles that allow them to
capture these prey organisms. Sessile benthic organisms that live in
the sediment of the ocean floor, e. g. pycnogonid and foraminiferans,
were also discovered in the gut contents, indicating that Benthocodon
11
pedunculata probably have mechanisms that allow them to feed
while resting on the deep-sea floor.
The two nematocyst types found in collected specimens (MAN
and MSN) are present on the inner and outer tentacles. The MANs
were found to be more abundant than MSNs on both tentacles, with
an approximate MAN to MSN ratio of 3:1. The structural similarities
between the two nematocyst types are the three spicules on the
shaft and the spiraled barbs on the long threads. Observable
differences are the sizes of the nematocyst capsule and the shaft,
both of which is larger in the MSN. The MSN possibly allows
Benthocodon to capture larger prey, although the larger number of
MAN found on the tentacles suggest that Benthocodon may feed
more often on smaller prey. Both stenoteles (Hufnagel et al., 1985)
and aspiroteles have been characterized as probable penetrants
(Kramp, 1935), but those found in B. pedunculata have long barbed
threads that differentiate Benthocodon nematocysts from the
traditional nematocyst description.
Microscope studies of tentacular and nematocyst morphology
assumed to play a crucial role in prey capture reveal properties that
allow Benthocodon pedunculata to capture both small, hard-bodied
organisms and larger, gelatinous organisms. In trachymedusa
Tesserogastria musculosa, the unbarbed thread of the stenotele was
shown to penetrate between two joints of a copepod leg (Hesthagen,
1971). In Benthocodon pedunculata, the barbed thread may both
penetrate exoskeletons of crustaceans and wrap around to and
adhere to soft-bodied prey, because use of penetration exclusively
may tear through the mesoglea and allow gelatinous organisms to
12
escape. Hydrozoans that feed on microcrustaceans often have
nematocysts concentrated in batteries and filiform tentacles whereas
those possessing nematocysts with extremely long threads and thick
tentacles often feed on larger gelatinous organisms (Purcell and Mills,
1988). Nematocysts and tentacles of Benthocodon pedunculata have
both properties. The thin, inner tentacles have nematocysts
concentrated in batteries except for the very tip of the tentacle,
which suggest that they may function in capturing the copepods,
amphipods, and other crustaceans discovered in the gut contents. In
contrast, nematocysts are spread out over the large, outer tentacles,
suggesting that these trachymedusae also feed on gelatinous prey
that are probably more difficult to detect than exoskeleton debris in
gut dissections. Therefore, these medusae may actually be feeding on
other benthopelagic or benthic medusae, even though gelatinous
prey was not observed.
Prey capture is probably determined by swimming pattern,
tentacle posture (Mills, 1981), and nematocyst type (Purcell, 1984;
Barnes, 1987; Purcell and Mills, 1988; Harrison and Westfall, 1991).
Benthocodon pedunculata were observed to swim rapidly upwards
from the deep-sea floor, then drift slowly downwards, extending
their tentacles (Larson et al., 1992), as well as actively swimming
through the water column, although this may be biased by ROV
disturbances in the water current. Prey capture in swimming
medusae, therefore, may depend on vortexes produced by bell
pulsations and the resulting water flow through the tentacles lining
the bell margin and into the subumbrella cavity, similar to the
feeding mode of scyphomedusa Aurelia aurita (Costello, 1992). As
13
Benthocodon contracts its bell, fluid is propelled out of the
subumbrella cavity and through the inner tentacles on the tentacle
margin, where prey is contacted and entangled by nematocyst
threads. When the medusa relaxes, water refills the cavity by
flowing inward through the outer tentacles where prey is again
captured by nematocyst threads. By this mechanism, the close
spacing of tentacles is advantageous to B. pedunculata in sieving out
small organisms (e. g. copepods and amphipods). During each short
upward-swimming and sinking bout, the tentacles are extended to
sieve prey from the vertical water column through a cylindrical
contact space, characteristic of other trachymedusae (Larson et al.,
1989). The inner and outer tentacles that extend downward perform
the initial sieving of the water column and the outer tentacles that
are more widely spaced and extend above the bell margin may serve
to capture organisms that have escaped through the sieve.
The feeding on benthic organisms may involve a slightly
different feeding strategy. Because Benthocodon medusae are
frequently found on the ocean floor, tentacles probing over the
sediment surface may be important in detecting sessile organisms
such as pycnogonids and foraminiferans. Benthic organisms can also
be captured when uncovered and uplifted from the sediment during
disturbances caused by the upward-swimming and sinking bouts,
like hydromedusae Polyorchis penicillatus (Mills, 1981). These
mechanisms assume that these medusae do detect prey are
hypotheses to be further tested with in situ and laboratory
experiments.
14
Aside from their role in prey capture, histological studies on
the tentacles show properties which suggest other functions. Unlike
the inner tentacles, the outer tentacles lack digestive inclusions,
which may aid in digestion and/or storage, even though the fact that
the tentacles extend from the edge of the subumbrella suggests that
they are both extensions of the gastrovascular cavity. However,
because the outer tentacles appear to be easily shed, as evidenced by
the presence of tentacles in the aquarium post mortem and by their
presence in the temporary tupperware containers during collection,
they would be useless as storage or digestive structures. The inner
tentacles, however, remain attached to the subumbrella, so these
activities are maintained. In the case of prey capture, the shedding of
tentacles attached to vigorously swimming prey may be more
beneficial than expending the extra energy needed to subdue the
organism. As a predator avoidance mechanism, medusae whose
tentacles are entangled in mucoid nets produced by predators such
as siphonophores, ctenophores, and other medusae can readily
escape by leaving their tentacles. Again, confirmation of these
hypotheses depends on further behavioral observations.
Feeding behavior, however, has not been observed in situ,
because Benthocodon medusae are most likely sensitive to the lights
from the ROV, just as they are sensitive to light conditions in the lab.
Another hypothesis is Benthocodon may not be feeding in the early
afternoon when observations are made. Gut contents were found in
all five specimens collected during night dives but in only one
collected during dives made in the late mornings and early
afternoons. This suggests a rhythmical feeding pattern that may
15
coincide with the downward and upward migrations of zooplankton.
Benthocodon would then be expected to feed at night and early
morning. Therefore, all the specimens collected later in the day
would lack gut contents, as observed in two of the three fixed on
board ship. This hypothesis, however, needs to be further tested with
dives made at different times of the day.
This study was limited by the number of specimens that were
examined for both gut contents and tentacle structures and the small
amount of time in behavioral observations using the submersible.
The optimal conditions for maintaining Benthocodon pedunculata
were unknown and the handling of medusae during collection may
have stressed the specimens. Morphology revealed by microscope
studies may also be biased by preparation of these fragile, gelatinous
samples. Regardless of these possible sources of error, this study
provides a description of the morphological features of this
benthopelagic medusae that were previously unexamined.
Postulations about their relationship to function requires further
behavioral observations.
This research has contributed new information about the
structural features of this benthopelagic medusae that are found in
high density patches in the Soquel and Carmel Canyons (Larson et al.
1992). The near bottom environment and the organisms that thrive
there are virtually unknown. It is fascinating to study the
morphological adaptations of benthopelagic medusae to this
environment and to explore their interactions with other deep sea
organisms, as more information is collected using ROVs. Information
about these survival mechanisms lead to an understanding of the
16
interactions between organisms of the deep-sea community, of which
so little is known.
Figure Legends
Figure 1. Benthocodon pedunculata medusa as seen with the ROV.
Figure 2. Photo of a medusa of Benthocodon spp showing three
different tentacle types. (kindly provided by G. I. Matsumoto)
Figure 3. View of the entire subumbrella of a Benthocodon
pedunculata medusa. G.C., gastrovascular cavity; L., lips; S.,
stomach; T., tentacles. (kindly provided by G. I. Matsumoto)
Figure 4. Inner and outer tentacles of a medusa of Benthocodon
pedunculata E.U., exumbrella; S.U., subumbrella. (kindly
provided by G. I. Matsumoto)
Figure 5. Outer tentacles of a medusa of Benthocodon pedunculata
A.P., abscission point. (kindly provided by G. I. Matsumoto)
Figure 6. Gut Content of a specimen of Benthocodon pedunculata
(collected by JSL3170 in detritus sampler (DS) 9 at 2779 ft) s
howing amphipod exoskeleton.
Figure 7. Gut Content of a specimen of Benthocodon pedunculata
(collected by JSL3170 in DS-9 at 2779 ft) showing a pycnogonid
exoskeleton.
Figure 8. Tentacle margin of a medusa of Benthocodon pedunculata
E.U., exumbrella; S.U., subumbrella. (kindly provided by G. I.
Matsumoto)
Figure 9. Scanning electron micrograph of the edge of the
subumbrella and tentacle margin of Benthocodon pedunculata
showing uneven rows of tentacle bases. S.U., subumbrella; T.S.,
tentacle stem. (Bar represents 500 u)
Figure 10a. Scanning electron micrograph showing the annulated
surface of an inner tentacle of Benthocodon pedunculata. N.R.,
nematocyst rings. (Bar represents 50 u)
17
Figure 1Ob. Scanning electron micrograph of the tip of an inner
tentacle of Benthocodon pedunculata . N.R., nematocyst rings.
(Bar represents 5 u)
Figure 11a. Section along the longitudinal axis of an inner tentacle of
Benthocodon pedunculata. (1 u thick section) Stained with
methylene blue and basic fuchsin. Oil immersion phase contrast
100x. E.C.T., ectoderm; M.E., mesoglea; E.N., endoderm; M.,
muscle; D.I., digestive inclusions; N., nematocyst; I., interstitial
cells. (Bar represents 10 u)
Figure 11b. Section along the longitudinal axis of the distal end of an
inner tentacle of Benthocodon pedunculata. (1 u thick section)
Stained with methylene blue and basic fuchsin. Oil immersion
phase contrast 100x. N., nematocyst; I., interstitial cells; M.,
muscle; E.N., endoderm. (Bar represents 10 u)
Figure 12a. Section along the longitudinal axis of an outer tentacle of
Benthocodon pedunculata. (1 u thick section) Stained with
methylene blue and basic fuchsin. Oil immersion phase contrast
100x. E.N., endoderm; M.E., mesoglea; N., nematocyst; I.,
interstitial cells. (Bar represents 10 u)
Figure 12b. Section along the longitudinal axis of an outer tentacle of
Benthocodon pedunculata. (1 u thick section) Stained with
methylene blue. Oil immersion phase contrast 100x. E.N.,
endoderm; N., nematocyst. (Bar represents 10 u)
Figure 13. Graph of the lengths and widths of 391 nematocysts found
on the inner and outer tentacles of Benthocodon pedunculata.
They fall into 2 categories, showing 2 different nematocysts.
Figure 14a. Extruded modified-aspirotele nematocyst on an outer
tentacle of Benthocodon pedunculata . Oil immersion phase
contrast 100x. M.A., modified-aspirotele nematocyst; S., shaft;
T., thread. (Bar represents 10 u)
Figure 14b. Extruded modified-stenotele nematocyst on an outer
tentacle of Benthocodon pedunculata . Oil immersion phase
contrast 100x. M.S., modified-stenotele nematocyst; S., shaft; T.,
thread. (Bar represents 10 u)
18
Figure 15a. Scanning electron micrograph of fired modified¬
aspirotele nematocyst of an outer tentacle of Benthocodon
pedunculata. M.A., modified-aspirotele; S., shaft; T., thread. (Bar
represents 5 u)
Figure 15b. Scanning electron micrograph of fired modified-stenotele
nematocyst of an outer tentacle of Benthocodon pedunculata.
M.S., modified-stenotele; S., shaft; T., thread.
(Bar represents 5 u)
Figure 16a. Scanning electron micrograph of fired modified¬
aspirotele nematocyst of an outer tentacle of Benthocodon
pedunculata. M.A., modified-aspirotele. (Bar represents 5 u)
Figure 16b. Scanning electron micrograph of fired modified-stenotele
nematocyst of an outer tentacle of Benthocodon pedunculata.
M.S., modified-stenotele; S.P., spicules; T., thread.
(Bar represents 5 u)
Table Legends
Table 1. Collection Dives.
Table 2. Number of recognizable prey in gut content analysis of 13
specimens of Benthocodon spp.
Acknowledgements
I would like to thank the Point Lobos crew and ROV pilots for
collecting the jellies, Chuck Baxter for his helpful advice and for
taking me out on collecting trips with the ROV. I am grateful to Chris
Patten and Kurt Buck for their microscope expertise, Alan Baldridge
and Susan Baxter for helping me find obscure journals and books,
and Molly Cummings for teaching me how to be a real marine biology
student. Thanks to the many spring students who suffered through
seasickness with me on the Point Lobos and Mamp;M fever on
Thursdays. Most importantly, I thank George I. Matsumoto for his
19
profound insights to my project, numerous advice, critical readings of
my paper, volleyball and walleyball coaching, many encouragements,
and for surpassing all my expectations of what a mentor could be.
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22

a
K
55.4
EU

Hg.



14 +
12
10 +
8
6
O 2 4
Nematocyst Lengths and Widths

6
8
10 12 14 16
length-(u)
Fg.

H4.1
Ra

e