Phascolosoma (Phascolosoma) perlucens Baird, 1868
This species has been considered a circumtropical species and the most common intertidal sipunculan species in the Caribbean, inhabiting coral ruble or in crevices of calcareous rocks. The main characters that distinguish this species from its congeners are the reddish brown conical pre-anal papillae, some of which are posteriorly directed, the secondary rounded tooth on the edge (concave side) of the hook, and differences in the internal pattern of the hook visible when examined via transmitted light.
(From Cutler and Cutler 1990 and Cutler 1994)
Introvert is shorter than or equal to the trunk length, usually with patches of dark reddish pigment on the dorsal surface and papillae widespread over the surface. The base of the dorsal introvert and the preanal region has a concentration of reddish brown, conical, sometimes sharply pointed papillae, which become smaller and lighter toward the anterior region. On the ventral side of the introvert the papillae become less prominent.
Tentacular crown has 12 to 14 tentacles encircling the nuchal organ (Stephen and Edmonds 1972). A live specimen from Florida (see pictures) has 12 slender, flattened, brownish tentacles surrounding a white nuchal organ.
Hooks are arranged in 15-25 rings (8-10 rings in 5 mm specimens), measuring 30-60 µm tall. A secondary large tooth is present. An internal triangle separate from the clear “C” streak is visible when a hook is observed via transmitted light.
Trunk has thin walls and the longitudinal muscles bands are visible through it. Commonly 35 mm long, but a few can reach to 45-50 mm long. On the anterior half of the trunk, posterior to the anus, the preanal papillae are reddish brown, conical, and some are posteriorly directed.
Internal anatomy
(From Rice and Stephen, 1970)
Trunk wall divided in anastomosing longitudinal bands.
The spindle muscle is attached immediately anterior to the anus and at the posterior end of the trunk.
Nephridia length one-half of the length of the trunk, attached to the trunk wall for three quarters of their length, and opened at the level of the anus.
Retractor muscles arise from the middle of the trunk (Stephen and Edmonds, 1972).
In Fort Pierce, Florida, Phascolosoma perlucens is found inside rocks under the Phragmatopoma reef, associated with Themiste alutacea, or inside vermetid reef conglomerates on a vertical seawall, associated with Phascolosoma nigrescens, and Antillesoma antillarum.
(From Cutler, 1994)
Phascolosoma perlucens is considered a circumtropical species. It is very common in the Caribbean, from Venezuela to southern Florida, and the western Pacific, from Queensland to Vietnam and central Japan. In the Indian Ocean it has been recorded from many locations. Also recorded in the eastern Pacific off Panama and northern Mexico.
The study by Kawauchi and Giribet (2010) discusses the circumtropical cosmopolitan aspect of the distribution of P. perlucens. The author investigated whether this is a true cosmopolitan species or whether it is another case of a cryptic species or an artifact of overconservative taxonomy. Because sipunculan worms have a simple morphology and some of the characters are poorly defined the identification in many cases is dubious. A long list of synonyms reflects the difficulty in determining the species boundary among P. perlucens. The authors examined 56 putative P. perlucens individuals from 13 different localities in the tropics. The molecular analysis of two mitochondrial markers, cytochrome c oxidase subunit I and 16S rRNA, suggested a high level of genetic differentiation between distant populations of P. perlucens. Moreover, the phylogenetic, population genetic, and the demography analyses supported four different lineages, suggesting that P. perlucens is not a cosmopolitan species, but probably another case of overconservative taxonomy.
According to Rice (1975a) P. perlucens is the most abundant species in the Caribbean, constituting 46% of the specimens collected, inhabiting friable rocks and compact structure, containing calcite as well as aragonite. Commonly P. perlucens is found in the same rock with one or more species of sipunculans and usually is the dominant species (Rice, 1975a). Phascolosom perlucens is a large specimen, very active and capable of considerable long and winding extension and contraction, which permit the worm to penetrate very deep into the rock (Rice and Macintyre, 1979). In Carrie Bow Cay, Belize, P. perlucens borings in recent coral limestone are abundant in rubble of Acropora palmata and Agaricia sp., in shallow water or intertidal regions to 3 m of depth (Rice and Macintyre, 1979).
(From Rice, 1975b)
This species follows the developmental pattern IV determined by Rice (1976), which includes a lecithotrophic trochophore and a planktotrophic pelagosphera larva that often remains for several months in the plankton. The shape of a mature egg in P. perlucens is a flattened ellipsoid, wider in the frontal than sagittal plane, and the vitelline envelope is thick and penetrated by narrow pores. The P. perlucens eggs are pink in color with depressions in the egg envelope at both poles, and the animal depression is wider than the vegetal. The average egg size is 112 µm in length by 91 µm in width and 86 µm in thickness. The cleavage is spiral and unequal. After approximately three days at 25ºC the lecithotrophic trochophore metamorphoses into a planktothrophic pelagosphera larva.