Potentially Misidentified Species:
At least three other synaptid sea cucumbers (Epitomapta roseola,
Leptosynapta inhaerens, Leptosynapta tenuis) also occur in the
IRL. Hendler et al. (1995) note that body wall coloration and, if necessary,
ossicle shape, are useful in distinguishing Synaptula hydriformis from
II. HABITAT AND DISTRIBUTION
Synaptula hydriformis occurs in shallow marine environments of Bermuda,
Florida and portions of the Caribbean and Latin America including the Greater
and Lesser Antilles, the Bahamas, Belize, Panama, and Brazil. Museum holdings
also confirm the presence of the species in Texas (Hendler et al. 1995).
The literature is lacking in detailed IRL distribution information, but
Synaptula hydriformis is likely to occur in seagrass habitats throughout
the estuary. Although it is considered a tropical species, it is common in
Florida as far north as Pensacola (Cooley 1978).
III. LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan:
Reported to reach a maximum body length of 10 cm, but most adult Synaptula
hydriformis specimens are less than half that size and juveniles are often
less than 1 cm (Hendler et al. 1995). The literature is lacking in information
regarding the lifespan of this animal.
Information is lacking in the literature, possibly owing to the cryptic nature
of the species. Congeneric species form the central Philippines can form
aggregations so dense as to completely cover the sponges they reside upon (Kerr
et al. 2006), but such dense assemblages have not been reported for
Compared to other holothuroids, reproduction in Synaptula hydriformis is
atypical is several ways. The female broods its young internally, a trait
exhibited by approximately 30% of holothuroids but relatively rare in tropical
specimens (Hendler et al. 1995, Hendler 2001). Moreover, it is a simultaneous
hermaphrodite and is believed to be self-fertilizing as well (Fricke 1998).
Ovulation involves the release of ~250 µm eggs from the germinal epithelium to
the lumen of the gonadal tubule, remaining for a short time at the junction
(basis) of the tubules before being released (through rupture of the junction
wall) into the perivisceral coelom. Eggs removed from the perivisceral coelom
are revealed to be covered with sperm, suggesting that the species is
self-fertilizing (Fricke 1998).
Fricke (1998) notes individual brood sizes of up to 254 young in populations
from the Indian River Lagoon and from Lake Surprise on Key Largo. The study
revealed that brooded young were present year-round, corroborating earlier
findings (e.g., Clark 1907) that reproduction occurs throughout the year.
Synaptula hydriformis is viviparous; rather than a free-living larval
stage, eggs and embryos develop while freely suspended within the maternal
perivisceral coelomic space until they emerge as small, fully-formed juveniles.
Studies by Fricke (1998) also reveal that developing S. hydriformis also
exhibit matrotrophy, receiving maternal nutrition well in excess of that
supplied by egg yolk. This trait, unusual for an invertebrate, was confirmed
experimentally, both through observation of ingestion by brooded young of
synthetic microspheres from the maternal perivisceral coelom and also by
documenting incorporation of radiolabeled palmitic acid into the tissues of
developing young. A greater than one hundred-fold increase in both dry and
organic weight from egg to 8-mm juvenile was observed. The additional
nutrition is supplied in the form of coelomocytes and organic molecules present
in ingested maternal coelomic fluid, and possibly yolk granules or degraded
eggs as well (Hickman 1978, Frick et al. 1992, Fricke 1998).
A final reproductive curiosity exhibited by S. hydriformis is the trait
of superfetation, in which the brooded young ranging in size from 0.5-10 mm
typically belong to more than one cohort (Fricke 1998).
Juveniles, usually 2-3 mm long but sometimes larger, are released through a
rupture in the body wall near the anus (Clark 1907, Hendler et al. 1995). The
lack of a free-swimming larval stage limits the dispersal ability of this and
other brooding holothuroids, but the ability of individuals to cling to
seagrass fragments and other flotsam offers an alternative dispersal strategy
that is of likely ecological importance.
IV. PHYSICAL TOLERANCES
The distribution of Synaptula hydriformis is restricted to
tropical/subtropical waters. The northern distributional limits are most
likely dictated by thermal tolerance of the species.
Synaptula hydriformis is a year-round resident of vegetated estuarine
habitats that may experience pronounced seasonal salinity fluctuations.
V. COMMUNITY ECOLOGY
Stomach analysis reveals that the diet is composed primarily of benthic diatoms
with a smaller amount of fleshy macroalgae (Martinez 1989).
As with many holothuroids, synaptids appear to possess chemical defenses
against most would-be predators in the form of toxic or noxious secondary
metabolites (Kuznetsova et al. 1989, Delbeek and Sprung 1994, Ponomarenko et
Synaptula hydriformis is a cryptic species that inhabits coral reefs,
seagrass beds, mangrove marshes, and isolated brackish ponds and typically
occurs as an epibiont on marine plants such as seagrass blades, mangrove prop
roots, and fleshy and calcareous macroalgae. It is a shallow-water animal
typically inhabiting depths of 1-7 m (Pawson 1986, Hendler et al. 1995).
Although observational reports are lacking in the primary literature, several
marine aquarium hobby authorities support the claim that most medusa worms,
including Synaptula hydriformis, are primarily nocturnal (Toonen 2002).
VI. SPECIAL STATUS
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Publishing, Philadelphia. 893 p.
Clark HL. 1907. The apodous holothurians: a monograph of the Synaptidae and
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collections of the United States National Museum). Smithsonian Contributions to
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echinoderm Synaptula hydriformis. Invertebrate Biology 117:169-179.
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Press, Washington DC. 390p.
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from the holothurians Synapta maculata, Cladolabes bifurcatus and
Cucumaria sp. Comparative Biochemistry and Physiology Part B:
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Sewell MA. 1994. Reproduction of the intraovarian brooding apodid
Leptosynapta clarki (Echinodermata: Holothuroidea) in British Columbia.
Marine Biology 121:285-300.
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Class Holothuroidea: A reassessment of the "tubule recruitment Model."
Biological Bulletin 192:17-26.
Toonen R. 2002. The medusa worms. Advanced Aquarist's Online Magazine Volume
1, November 2002. Available online.
J. Masterson, Smithsonian Marine Station
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