Potentially Misidentified Species: Although echinoderm taxonomy is a highly specialized science, the general appearance, along with collection information (e.g., location and habitat), should allow unambiguous identification of Ophiophragmus filograneus. The congeneric species Ophiophragmus wurdemani occurs in Florida waters, but is restricted to unvegetated benthic habitats in more saline waters and does not penetrate deeply into Florida's brackish estuaries (Turner and Meyer 1980).
Regional Occurrence: Ophiophragmus filograneus has been reported only from brackish waters of Florida. (Talbot and Lawrence 2002, Pomory 2007).
IRL Distribution: Ophiophragmus filograneus is common throughout the IRL in association with Halodule wrightii seagrass beds (Thompson 1978). The Mosquito Lagoon portion of the IRL system is reported as the northern distributional limit for the species (Turner and Meyer 1980).
Age, Size, Lifespan: The central disc of Ophiophragmus filograneus typically grows to as much as 9-10 mm in diameter, and the long arms attain a length of up to 150 mm (Hendler et al. 1995, Talbot and Lawrence 2002).
Abundance: Clements et al. (1994) sampled natural and planted Tampa Bay Halodule beaudettei beds on a quarterly basis to determine Ophiophragmus filograneus population densities. Mean quarterly densities averaged 10.6 individuals per square meter in natural grass beds (ranging from 0-32 individuals per square meter) and 33.8 individuals per square meter in planted beds (ranging from 0-48.6 individuals per square meter).
Grizzle (1984) lists O. filograneus as among the most common macrobenthic species at two IRL sites, one of which the authors considered to be more environmentally degraded than the other. Brittlestar abundance was approximately 4 times higher at the undegraded site, and the author considers O. filograneus to be an equilibrium species rather than an opportunistic species.
Reproduction: Several authors (e.g., Stancyk 1974, Turner 1974, Turner and Meyer 1980) indicate that Ophiophragmus filograneus forms dense reproductive populations in the Florida Halodule beds in which it occurs beds.
Embryology: Stancyk (1973) hypothesized that Ophiophragmus filograneus exhibits direct development (no planktonic phase), base on egg type. The author suggests direct development as an adaptation for life in a harsh environment, as has been suggested for other direct-developing echinoderms.
Turner (1974) examined the post-metamorphic arm growth of Tampa Bay O. filograneus and revealed the typical pattern to involve a faster rate of growth in two non-adjacent arms and a concurrent slower growth in the remaining arms. The author suggests this pattern may be an adaptation allowing earlier descent of the disc within the substratum and away from predation and salinity and temperature fluctuations, with the two arms displaying concentrated growth remaining long enough to reach up to the sediment surface. Arm lengths are gradually equalized as individuals grow.
Temperature: Restricted to Florida, this is an exclusively subtropical species. Individuals appear to actively burrow deeper within the soft sediment in response to adverse surface conditions, including cold temperature (Stancyk 1970).
Salinity: Although echinoderms are often cited as the only strictly marine major animal phylum, a number of representatives may be encountered at salinities less than full-strength seawater (Stickle and Diehl 1987). Of the approximately 40 echinoderm species reported from brackish waters, Ophiophragmus filograneus is the species with the greatest tolerance for hyposaline conditions, occurring in estuaries but not in the open sea (Turner and Meyer 1980, Talbot and Lawrence 2002). This species appears to be the only echinoderm restricted to estuarine habitats.
Talbot and Lawrence (2002) questioned whether exclusion of O. filograneus from higher open ocean salinities was due to physiological adaptation for reduced salinities or to some other factor. Laboratory experiments revealed that O. filograneus collected from Tampa Bay at 22 ppt was more physiologically stressed (based on measurements of respiration, metabolism, and limb regeneration rate) at 16 ppt than at either 22 ppt or 30 ppt. The findings suggest exclusion from the open ocean may be due to factors other than salinity tolerance, such as dietary resource availability, sediment type, or exclusion due to competition or predation.
Trophic Mode: Ophiophragmus filograneus typically buries its disc in muddy sand and extends one or more of its arms up to the sediment to feed (Stancyk 1974). As with a number of infaunal brittlestars, O. filograneus is capable of functioning as both a suspension-feeder and as a deposit-feeder, likely to routinely ingest significant quantities of detrital material (Clements et al 1994).
As with some other brittlestars, O. filograneus also appears capable of resorbing portions of its own biomass if environment conditions (e.g., starvation) force individuals to catabolize tissue for maintenance (Dobson et al., 1991). Turner and Murdoch (1976) describe a pattern of preferential tissue resorption in which tissues from the disc, oral frame, and arm tips are catabolized before other body tissues, leaving the majority of arm tissue intact to take advantage of favorable feeding conditions should they occur.
Competitors: The exclusively estuarine distribution of this species likely minimizes competitive interactions with other brittlestar species.
Predators: Ophiophragmus filograneus is an important component in the diet of a number of benthic-feeding animals, most notably stingrays of genus Dasyatis and the cownose ray Rhinoptera bonasus (Turner at al. 1982).
The need for individuals to keep portions of their arms exposed at the sediment surface for feeding purposes also exposes brittlestars species to a high degree of sublethal partial predation, and animals often lose portions of their exposed arms to shrimps, crabs, flatfish and other epibenthic predators (Duineveld and Van Noort 1986, O'Connor et al. 1986). Based on a Tampa Bay study, however Clements et al. (1994) indicated that partial predation on seagrass-associated O. filograneus appears low compared to rates reported for other infaunal brittlestars, particularly those from unvegetated habitats.
Habitats: Ophiophragmus filograneus is a common inhabitant of estuarine Florida subtidal unconsolidated substratum environments and seagrass meadows, particularly Halodule wrightii beds (Clements et al. 1994, Rose 1997, Pomory 2007).
O. filograneus is capable of regenerating lost arms from autotomized discs.. The high incidence of O. filograneus regenerating arms in the field suggests a high degree of sub-lethal predation in habitats occupied by this species (Stancyk 1974, Lawrence 1990, Rose 1997). Clements et al. (1994) estimate that 52-94% of brittlestars collected from natural and planted Tampa Bay H. beaudettei beds showed evidence of arm regeneration. Brown (1982) also reported a degree of gut replacement in O. filograneus during regeneration of portions of autotomized discs.
Activity Time: Neanthes succinea is an active forager primarily at night, spending most of the day in a mucous-lined tube (Craig et al. 2003).
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