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Synonymy:
Possibly
Vallentinia adherens (Hyman 1947).
Potentially Misidentified Species:
Vallentinia
adherens (Hyman 1947), a possible conspecific (Vannucci Mendes 1948), was
collected from Pacific Grove, CA (Hyman 1947). The remarkable morphological
similarity between V. gabriellae and V. adherens, has led some to believe that they
may be the
same species (see Foster 1973).
Voucher Specimens:
Voucher specimens (#'s 91938 and
91939) from the Indian River Lagoon, FL, identified by
Dr. Ron Larson, were deposited in the National Museum of Natural History,
Smithsonian Institution, Washington, DC (Rey et al. 1992).
II. HABITAT AND
DISTRIBUTION
Regional Occurrence:
V. gabriellae has been
described from the southern coast of Brazil (Vannucci Mendes (1948), Bimini (Kramp
1959; Krumholz 1963), the Gulf coast of Louisiana (Lytle 1964), the northern
coast of Yucatan, Mexico 1969 (Foster 1971), and the Indian River Lagoon, FL (Rey
et al 1992).
IRL Distribution:
Vallentinia gabriellae was found in a mosquito impoundment (19 A)
perimeter ditch in mangrove wetland on the barrier island side of the Indian
River Lagoon, FL, 6.5 km north of Fort Pierce and 17.5 km south of Vero Beach.
This first time discovery in 1990 was somewhat surprising because these areas
had been previously sampled extensively (Rey et al 1992).
III. LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan:
Rey et al (1992) described medusae collected from the Indian
River Lagoon, Florida ranging in size from 4.0 - 12.0 mm in diameter. Large specimens had
80 - 90 marginal tentacles and 8 exumbrellar tentacles with adhesive disks. The
marginal tentacles, containing gravity detecting statocysts at the base, can be extended for 30 mm
(Foster 1973). Polyps 0.1 - 1.0 mm in length, grow permanently attached to
substratum (Lytle 1964) and contain the same type of nematocyst (microbasic
heterotrichous euryteles) as the marginal tentacles (Vannucci Mendes 1948). An
ultrastructural study of the adhesive tentacles of Vallentinia gabriella
suggested that detachment of the adhesive organ is under nervous control (Honegger
1984).
According to Foster (1973), newly
settled polyps metamorphosing from the frustule are 0.5 - 0.8 mm in length, with
two tentacles. Older polyps measure 1.0 - 3.0 mm in length with 3 to 5
tentacles. Lytle (1964) described permanently attached polyps 0.1 - 1.0 mm,
usually with 4 tentacles.
Medusae can live 3 - 4 months in
the laboratory . Older, senescent medusae become square in shape and gonads
atrophy (Vannucci Mendes 1948; Foster 1973).
Abundance:
As many collections of Vallentinia are made inadvertently, it is
somewhat difficult to state how abundant this species may be.
Locomotion:
Swimming in Vallentinia
gabriellae is accomplished by the rhythmic pulsation of the bell, while marginal
tentacles are contracted.. Medusae, when not swimming, can become sedentary by
attaching themselves by the adhesive organs located on the terminus of the
exumbrellar tentacles (Foster 1973).
Reproduction:
The life cycle of Vallentinia
gabriellae has two distinct phases, the medusa or sexually producing phase and
the polyp, or asexually producing phase. Gonochoristic medusae release eggs and
sperm.
Polyps can produce more medusae, or more
polyps by budding asexually. Three types of buds are produced:
1) Frustules - (0.5 mm in length) are produced
in mucous encased clusters of 4 or more and can mature into a polyp in about 3 -
4 weeks. It appears that the frustule stage is capable of withstanding adverse
conditions of temperature and salinity (Foster 1973). Polyps metamorphosing
from
the frustule can also continue the life-cycle by producing more medusae and/or
polyps (Foster 1971; 1973).
2) Hydranth buds are rarely produced. When these do appear they
generally contain only
one hydranth per polyp.
3) Medusa buds are located on the sides of the polyp and are
produced after several weeks in culture. When released from buds, medusae were
easily reared on an Artemia diet and matured sexually in 3 - 4 weeks, with a
maximum diameter of 6.5 mm (Lytle 1964). Medusae are formed one at a time from
buds but a polyp may simultaneously have more than one medusa forming bud
(Foster 1973). In the Indian River Lagoon, FL, temporal variation in
reproduction was seen. Gravid medusae of Vallentinia gabriellae were sampled in
September and October (1990), non-gravid individuals in May (1991) and juvenile
and gravid individuals in July (1991). Despite intensive sampling efforts, no
polyps were found and no specimens of V. gabriellae were observed during the
winter (Rey et al 1992).
Embryology:
Fertilized eggs develop into planula larvae which in turn develop into
sedentary polyps.
IV. PHYSICAL TOLERANCES
Temperature:
The original species description of V. gabriellae
(Vannucci Mendes 1948) was made from medusae which appeared
inadvertently in a
collection of algae (Ulva, Sargassum, and Enteromorpha) and
empty mollusk shells that had been maintained in the laboratory for
about a month. Laboratory cultures of
Vallentinia gabriellae have been maintained successfully at 20.0 +/- 5.0 °C
(Vannucci
Mendes 1984) and 27.0 +/- 1.0 °C (Foster 1973). Temperature of source water for
Vallentinia gabriellae collected in a mangrove lagoon along the northern coast
of the Yucatan, was 30 °C. Medusae appeared in this source water several weeks
later after Cladophora algae was brought back to the
laboratory and maintained in culture using artificial seawater of 35 ppt
salinity (Foster 1973). In collections of Vallentinia made at North
Bimini Island, pond temperatures were estimated to be 35.0 - 36.7 °C (Krumholz 1963).
Salinity:
Vallentinia gabriellae is a euryhaline
species, well adapted to fluctuations in salinity. In Florida, Vallentinia has been found in
mosquito impoundments where salinity has been recorded to be 41 ppt. Specimens from the island of North
Bimini originated from a man-made pond with a salinity of 28 ppt. In
Louisiana, Vallentinia was transferred from normal seawater to 17.5 ppt salinity in the
laboratory with no harmful effects (Foster 1973), and has been maintained in culture using artificial seawater of 35 ppt
salinity (Foster 1973).
V. COMMUNITY ECOLOGY
Trophic Mode:
Vallentinia immobilizes prey by
nematocysts located along tentacles. It may also use nematocysts to discourage
potential predators (Foster 1971). Laboratory cultures of Vallentinia gabriellae
were fed newly hatched Artemia salina (Foster 1973) as well as copepods, small
crustaceans and flagellates (Vannucci Mendes 1948).
It has been suggested that when
abundant, Vallentinia gabriellae could be a significant predator of wetland
zooplankton because of the voracious appetite displayed by this hydrozoan in
laboratory feeding experiments (Rey et al 1992). In one feeding study (Rey
et al 1992), Vallentinia gabriellae was presented a wide array of food items,
ranging in size from 4.0 to 10.0 mm. These items included rotifers, numerous
species of copepods as well as crab zoeae, nematodes, gastropod veligers and
Artemia nauplii as well as juvenile mullet (12 - 15 mm standard length). V.
gabriellae showed a preference for larger food items (>0 .2 mm). No rotifers
or dead organisms were consumed in feeding trials. After immobilizing prey items
with nematocysts, medusae would detach from the substratum and swim about. This
behavior enabled medusae to dislodge prey items from tentacles with subsequent
engulfment. Entanglement and immobilization of juvenile mullet by V. gabriellae
was also described in this study. Eventually the manubrium would come to
surround the fish prey and the medusa would swim about. The fish would remain in
the gut for 10 - 12 hours and undigested material was expelled the following day
(Rey et al 1992).
Habitat:
Vallentinia gabriellae specimens from the
Louisiana coast originated in aquarium material collected from an eel grass bed.
VI. SPECIAL STATUS
Special Status:
None.
Economic Importance:
None.
Report by: J. Dineen,
Smithsonian Marine Station
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irl_webmaster@si.edu
Page last updated: July 25, 2001
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