ORGANISMS IN THE WATER
(continued)
Common shallow marine, benthic megainvertebrates
readily seen around San Salvador Island include sponges, hydrozoans, sea
anemones, octocorals, scleractinian corals, bryozoans, chitons, bivalves,
gastropods, octopods, annelid worms, crabs, spiny lobsters, sea urchins, heart
urchins, sand dollars, crinoids, starfish, brittle stars, and sea cucumbers.
Phylum Porifera
Haliclona rubens (Pallas, 1766) - red sponge (above left) (Porifera,
Demospongea, Haplosclerida, Chalinidae) & other undetermined sponges (above
right & below). Sponges are parazoan animals (Kingdom Animalia,
Phylum Porifera) - they lack tissues and are essentially well organized
colonies of cells. They construct skeletons generally composed of organic
or calcareous or siliceous spicules. Sponges are sessile, benthic, filter
feeders. They draw in water through small openings (ostia) in the walls of
the skeleton and filter the water for tiny particles of food. Filtered
water is expelled from a large opening (osculum) or openings (oscula) at the
top of the skeleton.
Above left & below: near Bamboo Point, northern Fernandez Bay, western
margin of San Salvador Island. (James St. John photos, 2010)
Above right: near Snapshot Reef, Fernandez Bay, western margin of San Salvador
Island. (Scott Bair photo, 2009)
Phylum Cnidaria
Physalia physalis (Linnaeus, 1758) - Portuguese man-of-war (Cnidaria,
Hydrozoa, Siphonophora, Physaliidae) stranded on an aragonite sand beach
immediately south of “The Thumb”, eastern margin of San Salvador Island.
This organism is not a jellyfish, despite the superficial
similarity. True jellyfish are members of Class Scyphozoa (Phylum
Cnidaria), whereas the Portuguese man-of-war is in Class Hydrozoa (Phylum
Cnidaria). This organism is a colony of hydrozoans. The body
is bluish or purplish or pinkish and consists of a gas-filled float plus many
long tentacles. The tentacles have numerous nematocysts (stinging cells),
used for paralyzing or killing prey. (James St. John photo, 2011)
Patch reefs (above & below) - the highest abundance and diversity of
macroinvertebrates in the waters surrounding San Salvador Island occurs in
reefs. Reefs are readily identified as dark patches in otherwise clear,
turquoise-colored waters. The principal, primary reef builders are
scleractinian corals and crustose calcareous algae.
Above:
patch reefs in Graham’s Harbour, offshore from northern margin of San Salvador
Island.
Below:
patch reefs exposed at low spring tide in western French Bay, near-southwestern
corner of San Salvador Island. The tops
of brain coral, fire coral, and various octocorals are visible.
Patch reef in western French Bay, southwestern San Salvador Island. Organisms visible in this section of patch
reef include Porites porites furcata
clubbed finger corals, Porolithon
pachydermum encrusting red algae, Turbinaria
brown algae, fleshy green algae, >1 species of octocoral, bluehead wrasse,
etc. (James St. John photo, 2011)
Patch reef at Snapshot Reef, Fernandez Bay, offshore from western margin of San
Salvador Island.
Millepora complanata (Lamarck, 1816) - bladed fire coral (Cnidaria,
Hydrozoa, Milleporidae) at Gaulin Reef, northern Graham’s Harbour, offshore
northern San Salvador Island. These upright structures are calcareous
skeletons of colonies of hydrozoan polyps. They are not true stony corals
- fire corals are hydrozoans while true stony corals are anthozoans (see
below). Nematocysts in the tentacles of the small polyps deliver a
painful sting. (James St. John photo, 2010)
Millepora alcicornis Linnaeus, 1758 (above & below) - branching fire
corals (Cnidaria, Hydrozoa, Milleporidae) at Snapshot Reef, Fernandez Bay,
western margin of San Salvador Island. These calcareous, colonial
hydrozoans have a distinctly branching skeletal form, in contrast to the
wrinkled bladed forms of Millepora complanata. The overall
skeletal shape of Millepora alcicornis is often a consequence of the
fire coral encrusting octocoral skeletons. The blue fish above is
Chromis cyanea (blue chromis). The spotted fish below is Lactophrys
triqueter (smooth trunkfish).
(James
St. John photos, 2011)
Condylactis gigantea (Weinland, 1860) (above & below) - giant anemones
(Cnidaria, Anthozoa, Actiniaria) near a small patch reef just west of Cut Cay,
eastern Graham’s Harbour, northeastern San Salvador Island. The tentacles
of sea anemones have stinging cells (nematocysts) that paralyze or kill prey,
which are then drawn toward the mouth at the center of the tentacle
cluster. (James St. John photos, 2010)
Stichodactyla helianthus (Ellis, 1768) - sun anemone (Cnidaria, Anthozoa,
Actiniaria, Stichodactylidae) in eastern Graham’s Harbour, near Cut Cay,
northeastern San Salvador Island. Notice the small shrimp at the center (Periclimenes
sp.) - it has a commensal relationship with the anemone, akin to the
clownship-anemone relationship. (James St. John photo, 2010)
Pseudopterogorgia sp. - sea plume (Cnidaria, Anthozoa, Gorgonacea,
Holaxonia, Gorgoniidae) on biogenic aragonite sand substrate, just offshore
from Rocky Point/Sand Dollar Beach, northwestern San Salvador Island. (James
St. John photo, 2011)
Briareum asbestinum (Pallas, 1766) - corky sea fingers (Cnidaria,
Anthozoa, Octocorallia, Gorgonacea, Scleraxonia, Briareidae) at small patch
reef just west of Cut Cay, eastern Graham’s Harbour, northeastern San Salvador
Island. (James St. John photo, 2010)
Undetermined cnidarian, apparently a plexaurid
octocoral (Cnidaria, Anthozoa, Octocorallia, Plexauridae) in southeastern
Graham’s Harbour, northeastern San Salvador Island. (Mark Peter photo,
2009)
Gorgonia ventalina Linnaeus, 1758 (above & below) - common seafan
(Cnidaria, Anthozoa, Octocorallia, Gorgoniidae) at a small patch reef just west
of Cut Cay, eastern Graham’s Harbour, northeastern San Salvador Island (James
St. John photos, 2010).
Gorgonia flabellum Linnaeus, 1758 - venus seafan (Cnidaria, Anthozoa,
Octocorallia, Gorgoniidae) at Gaulin Reef, northern Graham’s Harbour, offshore
northern San Salvador Island. (James St. John photo, 2010)
Manicina areolata (Linnaeus, 1758) - rose coral (Cnidaria, Anthozoa,
Scleractinia, Faviidae) in southeastern Graham’s Harbour, northeastern San Salvador
Island. Notice that this coral’s slender tentacles are retracted in the
grooves - the coral extends its tentacles and feeds at night. (Mark Peter
photo, 2009)
Stony corals (see rose coral above & other coral
species below) have a patchy distribution in the shallow marine waters
surrounding San Salvador Island. They occur as isolated individual
colonies, in patch reefs, fringing reefs, and barrier reefs. Stony corals
are scleractinian anthozoan cnidarians. They consist of individuals or colonies
of gelatinous polyps that secrete hard skeletons of aragonite (CaCO3).
Most scleractinian corals live in warm, tropical to subtropical, photic zone
environments (the shallow portions of the world’s oceans where sunlight
penetrates). Microbes (Symbiodinium - Protista,
Dinoflagellata/Pyrrhophyta) called zooxanthellae live in their tissues
and need to be in sunlight to make their own food (photosynthesis), which is
shared with the host coral animal. Like sea anemones (see above),
scleractinian corals have stinging cells (nematocysts) in their tentacles that
paralyze prey.
Porites porites porites (Pallas, 1766) - clubbed finger coral (Cnidaria,
Anthozoa, Scleractinia, Poritidae) at Snapshot Reef, Fernandez Bay, western
margin of San Salvador Island. This coral makes a skeleton of relatively
short, stout branches. The living tissues surrounding the skeleton are
typically grayish in color. (James St. John photo, 2010)
Porites porites furcata Lamarck, 1816 - branched finger coral (Cnidaria,
Anthozoa, Scleractinia, Poritidae) at a patch reef in western French Bay, southwestern
San Salvador Island. Some workers
consider furcata to be a separate
species of Porites, while others
consider it a subspecies of Porites
porites (James St. John photo, 2011)
Porites astreoides Lamarck, 1816 - mustard hill coral (Cnidaria,
Anthozoa, Scleractinia, Poritidae) in French Bay, southern margin of San
Salvador Island. Porites astreoides is a stony coral having a
yellowish to greenish-yellow or gray color, with irregularly-shaped & irregularly-sized
pustules (= coral polyps). Colonies form subspherical to subhemispherical
masses, or irregularly encrusting mats. (James St. John photo, 2010)
Agaricia
coral (Cnidaria, Anthozoa, Scleractinia, Agariciidae) at Lindsay Reef,
Fernandez Bay, western margin of San Salvador Island. (Mark Peter photo, 2009)
Dendrogyra cylindrus (Ehrenberg, 1834) - pillar coral (Cnidaria, Anthozoa,
Scleractinia, Meandrinidae) at Telephone Pole Reef, Fernandez Bay, western
margin of San Salvador Island. Large blue fish = blue tang (Acanthurus
coeruleus). Small blue-black-white-yellow fish = bluehead wrasse (Thalassoma
bifasciatum). Purplish seafan at lower right = Gorgonia ventalina.
Small, light-brown, branching coral at lower right = branching fire coral (Millepora
alcicornis). (Mark Peter photo, 2009)
Diploria strigosa (Dana, 1846) - brain corals (Cnidaria, Anthozoa,
Scleractinia, Faviidae) at Lindsay Reef (left) & French Bay (right), San
Salvador Island. Diploria brain corals are easily identified by the presence of
convoluted, labyrinthiform corallites. (Mark Peter photos, 2009).
Diploria labyrinthiformis (Linnaeus, 1758) - grooved brain coral (Cnidaria,
Anthozoa, Scleractinia, Faviidae) at Snapshot Reef, Fernandez Bay, western margin
of San Salvador Island. In this species, the convoluted ridges that make
up the surface have a prominent median groove in this species, while Diploria
strigosa (see above) lacks a median groove. (James St. John photo)
Acropora cervicornis (Lamarck, 1816) - staghorn coral (Cnidaria, Anthozoa,
Scleractinia, Acroporidae) at Gaulin Reef, northern Graham’s Harbour, offshore
northern San Salvador Island. (James St. John photo, 2010)
Acropora palmata (Lamarck, 1816) (above & below) - elkhorn coral
(Cnidaria, Anthozoa, Scleractinia, Acroporidae).
Above:
Gaulin Reef, northern Graham’s Harbour, offshore northern San Salvador Island.
(James St. John photo, 2010)
Below:
patch reef in western French Bay, southwestern San Salvador Island. (James St.
John photo, 2011)
Montastraea annularis (Ellis & Solander, 1786) (above & below) -
boulder star coral (Cnidaria, Anthozoa, Scleractinia, Faviidae).
Above:
Gaulin Reef, northern Graham’s Harbour, offshore northern San Salvador Island.
(James St. John photo, 2010)
Below:
patch reef in western French Bay, near-southwestern corner of San Salvador
Island. (James St. John photo, 2011)
Dichocoenia stokesii Milne Edwards & Haime, 1848 - elliptical star
coral (Cnidaria, Anthozoa, Scleractinia, Meandrinidae) at a small patch reef west
of Cut Cay, eastern Graham’s Harbour, northeastern San Salvador Island. (James
St. John photo, 2010)
Phormidium corallyticum Rützler & Santavy, 1983 - black band disease
(Bacteria, Cyanobacteria, Oscillatoriales) on scleractinian coral near Bamboo
Point, northern Fernandez Bay, western margin of San Salvador Island. (James
St. John photo, 2010)
Phylum Mollusca
Chiton tuberculatus Linnaeus, 1758 - West Indian green chiton (Mollusca,
Polyplacophora, Neoloricata, Chitonidae) attached to rock in intertidal zone
landward of Snapshot Reef, Fernandez Bay, western shore of San Salvador
Island. The red structures are encrusting Homotrema rubrum forams
(Protista, Foraminiferida, Rotaliina, Homotrematidae). Chitons are
bilaterally symmetrical, dorso-ventrally flattened molluscs having 8
overlapping shells (valves) surrounded by a spicule-covered mantle
girdle. Most chitons occupy very shallow marine, rocky shore
environments, where they graze on benthic algae by scraping the substrate with
a radula. (James St. John photo, 2009)
Acanthopleura granulata (Gmelin, 1791) - West Indian fuzzy chiton (Mollusca,
Polyplacophora, Neoloricata, Chitonidae) attached to aragonitic limestone in
intertidal zone immediately east of “The Notch”, eastern part of southern
margin of San Salvador Island. (James St. John photo, 2011)
Strombus gigas Linnaeus, 1758 - empty queen conch shell (Mollusca,
Gastropoda, Strombidae)
in southeastern Graham’s Harbour, surrounded by Thalassia turtle grass
and Syringodium manatee seagrass. The fish at center is a juvenile
Halichoeres bivittatus (Bloch, 1791) - “slippery dick”, a type of wrasse
(Vertebrata, Actinopterygii, Perciformes, Labridae). (Mark Peter photo,
2009)
Cassis flammea (Linnaeus, 1758) - flame helmet snail shell
(Mollusca, Gastropoda, Cassidae) in Pigeon Creek estuary, southeastern San
Salvador Island. Helmet snails are predatory, feeding on regular &
irregular echinoids (sea urchins & sand dollars). They are usually
infaunal during daylight and are epifaunal while feeding at night-time.
(Scott Bair photo, 2009)
Charonia variegata (Lamarck, 1816) - Atlantic trumpet triton snail shell
(Mollusca, Gastropoda, Ranellidae) in Pigeon Creek estuary, southeastern San
Salvador Island. This gastropod is predatory on regular echinoids (sea
urchins) and holothurians (sea cucumbers). (Scott Bair photo, 2009)
Fasciolaria tulipa (Lamarck, 1816) - tulip snail (Mollusca, Gastropoda,
Fasciolariidae) at Snapshot Reef, Fernandez Bay, offshore from the western
margin of San Salvador Island. (James St. John photo, 2011)
Cyphoma gibbosum (Linnaeus, 1758) - flamingo tongue snail (above &
below) (Mollusca, Gastropoda, Ovulidae) at Lindsay Reef, Fernandez Bay, western
margin of San Salvador Island. Flamingo tongues feed on soft tissues of
octocorals (note dark mottled-purplish feeding scars on the octocoral
shown above & very thin skeletal branches on the octocoral shown
below). The shell of flamingo tongue snails is whitish & oddly
shaped. During life, mantle tissue partially or wholly envelops the
whitish shell. The mantle tissue of Cyphoma gibbosum is typically
whitish with brown-outlined orangish patches. (Mark Peter photos, 2009)
Melongenid gastropod (whelk) egg case attached to an octocoral colony at a small patch reef
just west of Cut Cay, eastern Graham’s Harbour, northeastern San Salvador
Island. (James St. John photo, 2010)
Octopus vulgaris Cuvier, 1797 (above & below) - the common octopus
(Mollusca, Cephalopoda, Octopoda, Octopodidae) in a queen conch shell (Strombus
gigas) in South Pigeon Creek estuary, southeastern San Salvador
Island. (Mark Peter photos, 2011)
Phylum Annelida
Hermodice carunculata (Pallas, 1766) - bearded fireworm (Annelida,
Polychaeta, Errantia, Amphinomidae) in a shallow tidal pool at low tide, Singer
Bar Point, Graham’s Harbour, northern shore of San Salvador Island.
Puncture by the spines/bristles of fireworms results in painful wounds. (James
St. John photo, 1999)
Hermodice carunculata (Pallas, 1766) - bearded fireworm (Annelida,
Polychaeta, Errantia, Amphinomidae) feeding on the tips of an octocoral (note
that most of the tips of this octocoral colony are damaged). This is at a
small patch reef due west of Cut Cay, Graham’s Harbour, northeastern San
Salvador Island. This species is known to vary in color from greenish
(see 2nd photo above) to brownish (see below) to whitish to orangish (see
above) to reddish. (James St. John photo, 2010)
Hermodice carunculata (Pallas, 1766) - bearded fireworm (Annelida,
Polychaeta, Errantia, Amphinomidae) at a patch reef offshore from Rocky
Point/Sand Dollar Beach, northwestern corner of San Salvador Island. Greenish
= Microdictyon marinum green algae; pale pinkish = calcareous red
algae (“reef cement”); yellowish-brown = Agaricia agaricites danai
scaled lettuce coral. (James St. John photo, 2011)
Bispira variegata (Krøyer, 1856) - variegated feather duster worms
(Annelida, Polychaeta, Sedentaria, Sabellidae) in southeastern Graham’s
Harbour. The bodies of these worms occupy irregularly cylindrical tubes
composed of organic material and fine-grained sediment. The tubes are
buried in the seafloor. The worms shown above have extended their crowns
of feathery appendages, which extract dissolved oxygen and filter the water for
particles of food (filter feeding/suspension feeding). When disturbed,
the worms quickly retract their feeding appendages. (Mark Peter photo,
2009)
Bispira brunnea (Treadwell, 1917) - social feather duster worms (Annelida,
Polychaeta, Sedentaria, Sabellidae) on small patch reef due west of Cut Cay,
Graham’s Harbour, northeastern San Salvador Island. These feather duster
worms occur in clusters and have parchment-like tubes out in the open (compare
with the hidden tubes of variegated feather duster worms above). (James St.
John photo, 2010)
Anamobaea orstedii (Krøyer, 1856) - split-crown feather duster worms
(Annelida, Polychaeta, Sedentaria, Sabellidae) at a small patch reef just west
of Cut Cay, eastern Graham’s Harbour, northeastern San Salvador Island. (James
St. John photos, 2010)
Spirobranchus giganteus Pallas, 1766 - Christmas tree worm (Annelidae,
Polychaeta, Sedentaria, Serpulidae) at Snapshot Reef, Fernandez Bay, western
side of San Salvador Island. These worms construct a calcareous tube in
which their body resides. They extend two spiraled sets of appendages in
order to filter feed and extract dissolved oxygen from the seawater.
(Mark Peter photo, 2009)
Spirobranchus giganteus Pallas, 1766 (above & below) - Christmas tree
worm (Annelidae, Polychaeta, Sedentaria, Serpulidae) encrusting Millepora complanata fire coral at patch
reef offshore from Rocky Point/Sand Dollar Beach, northwestern San Salvador
Island. The Christmas tree worm’s tube
has been overgrown by the fire coral. (James St. John photos, 2011)
Phylum Arthropoda
Periclimenes (possibly Periclimenes rathbunae Schmitt, 1924) - sun anemone
shrimp (Arthropoda, Crustacea, Decapoda, Natantia, Palaemonidae) in the center
of a Stichodactyla helianthus sun anemone in eastern Graham’s Harbour,
near Cut Cay, northeastern San Salvador Island. (James St. John photo, 2010)
Panulirus argus (Latreille, 1804) - Caribbean spiny lobster
(Arthropoda, Crustacea, Decapoda, Panuliridae) (Gerace Research Centre lab
specimen).
(James St. John photo, 2008)
Panopeus
sp. - rock crab exoskeletons (Arthropoda, Crustacea, Decapoda, Brachyura) found
in Sargassum strand lines on beach landward of Telephone Pole Beach,
Fernandez Bay, western margin of San Salvador Island. (James St. John photo,
2009)
Unidentified crab exoskeleton (Arthropoda, Crustacea,
Decapoda, Brachyura) on rocky shoreline of San Salvador Island. (James St. John
photo)
Carpilius corallinus (Herbst, 1783) (above & below) - batwing coral
crab (Arthropoda, Crustacea, Decapoda, Brachyura, Xanthidae) at Snapshot Reef,
Fernandez Bay, western margin of San Salvador Island. (James St. John photos,
2011)
Phylum Echinodermata
Diadema antillarum (Philippi, 1845) - hatpin urchins (above & below)
(Echinodermata, Echinoidea, Diadematidae).
Above:
live Diadema (+ stoplight parrotfish) at Bimini Island, western Bahamas.
(Lee & Mary Ellen St. John photo, 1964)
Below:
dead Diadema at beach adjacent to Telephone Pole Reef, Fernandez Bay,
western margin of San Salvador Island, eastern Bahamas (James St. John photo).
(James St. John photo, 2009)
Hatpin urchins used to be abundant in the Caribbean
(see 1964 photo above). Their long, sharp spines were a common hazard to
swimmers and snorkelers (I’ve seen spine tips break off in someone's
flesh). In 1983 and 1984, a disease-induced near-extinction of the
species occurred. At any one locality, over 1 or 2 days, numerous dead
hatpin urchin skeletons (tests) washed ashore onto beaches. The sequence
of deaths followed a current in the Caribbean. The near-extinction was
caused by a still-unidentified pathogen. Around San Salvador Island, Diadema
is making a comeback - I saw it for the first time in March 2009. I saw
live specimens on carbonate hardgrounds in very shallow water landward of
Telephone Pole Reef and dead specimens on the adjacent beach (see photo below).
The decline in the health of reefs throughout the
Caribbean since the 1980s has been attributed to, in part, the absence of Diadema
urchins. Diadema is an algal grazer. After its
near-extinction, the lack of algal grazing resulted in reefs being overwhelmed
by benthic algae.
Echinometra lucunter (Linnaeus, 1758) - red rock urchin (Echinodermata,
Echinoidea, Echinometridae) in tidal pool immediately east of “The Notch”,
eastern part of southern margin of San Salvador Island. (James St. John photo,
2011)
Meoma ventricosa Lamarck, 1816 - dead red heart urchins
(Echinodermata, Echinoidea, Spatangoida, Brissidae) washed on beach landward
from Snapshot Reef, Fernandez Bay, western margin of San Salvador Island.
Heart urchins have somewhat globular skeletons (tests) composed of interlocking
calcite plates and covered in short, fur-like spines. The skeleton is
bilaterally symmetrical, not radially symmetrical as in the sea
urchins. The upper side of the skeleton has the pattern of a 5-petaled
star - each petal is an ambulacrum. The mouth and anus are at opposite
ends of the long axis of the skeleton. Heart urchins are infaunal deposit
feeders. (James St. John photos, 2009)
Mellita sexiesperforata (Leske, 1778) - six-keyhole sand dollar
(Echinodermata, Echinoidea, Clypeasteroida, Mellitidae) on seafloor in northern
Fernandez Bay, due west of Bamboo Point, western margin of San Salvador Island.
(James St. John photo, 2010)
Davidaster rubiginosa (above & below) - golden crinoid (Echinodermata,
Crinoidea, Articulata, Comatulida, Comasteridae) at Snapshot Reef, Fernandez
Bay, western San Salvador Island. Crinoids (“sea lilies” & “feather
stars”) are sessile, benthic filter feeders. They are relatively common
in the Paleozoic fossil record, but scarce in modern oceans. Most fossil
crinoids have stems (stalks). Modern stalked crinoids are deep-water
forms. Modern shallow-water crinoids are stalkless. The golden
crinoid shown here lacks a stem and is a moderately cryptic species. Its
body is hidden in cavities or crevices and feathery arms are extended while
filter feeding. (Mark Peter photos, 2009)
Oreaster reticulatus (Linnaeus, 1758) (above & below) - reticulated
starfish (Echinodermata, Asteroidea, Valvatida, Oreasteridae) in Pigeon Creek
estuary, southeastern San Salvador Island. Red individuals above =
adults. Greenish-gray individual below = juvenile. Below
left: aboral side of juvenile. Below right: oral side
(underside) of same juvenile individual. See video.
Most starfish are distinctively pentaradial, with 5
arms. Numerous tube feet occur in the ambulacral grooves running down the
axis of the underside of each arm. Most starfish are predatory and
consume prey by everting their stomachs through their mouths (center structure
on underside) and digest food externally. Oreaster reticulatus is
predatory on a variety of invertebrates and is also a deposit feeder. (James
St. John photos, 2009 & 2011)
Ophiocoma echinata (Lamarck, 1816) brittle star (Echinodermata,
Ophiuroidea) from southeastern Graham's Harbour. (James St. John photo, 1999)
Ophioderma appressum (Say, 1825) banded-arm brittle star (gray)
(Echinodermata, Ophiuroidea, Ophiurida, Ophiodermidae) AND
Ophiocoma echinata (Lamarck, 1816) blunt-spined brittle star
(brownish-black) (Echinodermata, Ophiuroidea, Ophiurida, Ophiocomidae) from
“The Bluff”, southeastern San Salvador Island. (James St. John photo, 1999)
Ophiuroids (brittle stars) have body plans similar to
asteroids (starfish). Asteroids have arms that are generally thick-based
and taper distally. Ophiuroids generally have ~cylindrical, slender, snake-like
arms. The feeding habits of ophiuroids varies from predation to
scavenging to filter feeding to deposit feeding.
Holothuria mexicana Ludwig, 1875 - donkey dung sea cucumber
(Echinodermata, Holothuroidea, Aspidochirotida, Holothuriidae) + reddish and
brownish Oreaster reticulatus starfish from unrecorded locality in the
Bahamas. Holothurians are bizarre animals. They lack the obvious
pentaradial symmetry of other echinoderms (starfish, sand dollars, etc.).
They have soft, elongated, flexible bodies. Their skeletons consist of
numerous, tiny, calcareous sclerites embedded in the body wall or covering the
outer surface of the body. In general, sea cucumbers are benthic and
vagrant, slowly moving around on the seafloor. They use mucus to collect
organic debris from the seafloor and then consume the debris-covered
mucus. Some holothurians can discharge internal organs and toxins from
their posterior in response to potential predators. Rough handling of sea
cucumbers by people can result in the same discharge behavior. (Lee & Mary
Ellen St. John photo, 1964)
More
photos (swimming vertebrates)