Phoronidea from Brazil

Abstract

1. The demarcation of the species of Phoronidea is difficult because of the great variability of the characters which does not enable the fixing of good differential characters yet. The studies of populations and of life-histories must be undertaken to allow an accurate systematic definition. Within the family Phoronidae, generally considered as composed of only one genus, Phoronis, groups of very divergent species can be distinguished, which must perhaps be considered as genera or at least sub-genera. Owing to the inter gradation of the specific characters within such groups, it is not possible to know if they really represent species of form minor specific units. I. Phoronis hippocrepia Wright 1856 - from Santos, Cananéia and Ubatuba; in the first locality boring in oyster shells; in the second non-boring specimens; and in the third only larvae. a) Phoronis (Figs. 1-33) - The single nephrostome is the main characteristic of the specimens; through the interruption of the lateral mesentery at the level of the nephrostome the communication between the anal and oral cavities is assured. Longitudinal muscle bundles 26-30 in number, arranged according to the formula: ; marginal fibres, three to five in number, on each side of the bundle. Giant fibres of variable diameter: 4.7 to 7.0 microns, the right one, and 3.6 to 10.0 microns, the left. Blood corpuscles from 6.4 to 9.6 microns in diameter. Lophophoral organs also present in specimens with embryos in the tentacular crown. Simultaneous hermaphrodite, at least the specimens from Santos. Eggs: 100 microns. Spermatozoa: 20 microns, with vesicular head. Seven to eight pairs of chromosomes. b) Actinotrocha (Figs. 34-55 )- Primordium of metasoma appears in the larva with one pair of tentacles; peri-anal ciliated ring is present in the larva with four tentacles in which the anlage of the blood-corpuscle mass appears. Ganglion already developed in this larva. Metasoma of the four-tentacle larva forms a small invagination. Nephridia are not terminal any more. Rare glands present in the hood epithelium. In the larva with six tentacles the metasoma forms an ample sac; the primordium of the lophophore coelom appears. Stomach diverticulum absent or single without vacuolization. Nephridia open laterally to the metasoma aperture. In the advanced larva (eight to 10 tentacles) the metasoma forms a series of folds; its longitudinal muscles are differentiated into bundles; a large ventral mass of blood corpuscles is present ventral to the eosophagus and a few corpuscles are grouped on each side at the insertion level of the ventral tentacles. Lophophore coelom well developed; dorsal vessel present; a pair of ventral muscles in the trunk. On the dorsal surface of the hood there is an accumulation of gland cells perhaps the sensory organ. During metamorphosis the evaginated metasoma shows longitudinal muscle bundles. Larval tentacles degenerate. Afferent and efferent vessels are already formed. c) The following observations were made: Maximum survival in aquarium: one year; observed breeding season: July to March; duration of individual reproduction: over 15 days; development: egg to young larva - four days; pelagic perid - 9 to 12 days; metamorphosis - two hours. Irregular blood circulation, with about 10 pulsations per minute (temperature of 24ºC). Food: mostly diatoms, also protozoans and detritus. Not necessarily a boring species. The occurrence in aggregations seems accidental. Maximum of 12 embryos in the brood-pouch. The larvae become free with four tentacles and, exceptionally, in aquarium, shortly before metamorphosis. Swim in more or less large circles, diving often; shortly before metamorphosis, swim on the bottom. Metamorphosis was obtained even without special substratum. Eurythermic species (temperatures from 16 to 27ºC) endures salinities from 30.63 to 37.38 ‰. II. Phoronis ovalis Wright 1856 (Figs. 56-63) - from Santos, in oyster shells. A single median lophophoral organ (Figs. 62, l; 63, b) ; three to four marginal fibres along each side of the longitudinal muscle bundle; two giant fibres 2.5 microns in diameter (Fig. 61, k), not always noticed. Lower lip of the nephridial funnel short or long, prolonged downwards. Larva observed in March. III. a) Actinotrocha bella (new technical name) - from plankton collected off the northeast coast of Brazil. Stage with 18 to 22 tentacles (Fig. 64 A, B) - Metasoma present as a small tube; no mass of blood corpuscles, sensory organ and dorsal vessel. Peri-anal ciliated ring developed. A pair of retractors in the hood; a single diverticulum, vacuolated; nephridia placed above the septum, open laterally the aperture of the metasoma. Stage with 24 tentacles (Fig. 71 A) - Definitive tentacles absent. Stomach diverticulum single. Metasoma represented by a small invagination. Nephridium constituted by a large nephridial canal. Subepithelial muscle layer present. No mass of blood corpuscles and sensory organ. Narrow body cavity. Stage with 38 tentacles (Fig. 71, B, B1) - Definitive tentacles absent. A large blood sinus (Fig. 76, d) ventral to the oesophagus, extending laterally to the mouth; on the lower side it stretches out along the ventral part of the diverticulum (Fig. 77, d) ending near the nephridial canal (Fig. 78, h). Sensory organ (Fig. 83, c) consists of accumulations of basophilous gland cells and a nerve deeply placed. Dorsal vessel (Fig. 79, p) and caecal vessels (l) developed. Metasoma with longitudinal muscles differentiated into bundles (Fig. 79, n). A pair of dorsal retractors in the hood (Figs. 76, 77, b). Two pairs of ventral muscles in the trunk. Peri-anal ciliated ring developed and undulated (Fig. 81). These advanced larvae were related to the young larvae mentioned above by similarities of structure. Only their rearing will enable to confirm they belong to the same ontogenetic sequence. b) Actinotrocha chata n. t. n. (Fig. 90) - This young larva with 16 tentacles was found in plankton from Ubatuba. The metasoma presents itself in the stage of an epithelial thickening; no mass of blood corpuscles and sensory organ; ganglion present. It is probable that this larva represents a young A. wilsoni B with delayed development. c) Actinotrocha wilsoni B - Larva distributed in the coastal waters of Ubatuba (100 km to the NE of Santos) towards the South down to lat. 28º00'S, off Lagoa Mangueira (State of Rio Grande do Sul) ; it is also found in the inlet waters of Cananéia and Paranaguá. Occurs July to February, maximum in October. Euryhaline; it was found at temperatures from 18.5 about 27.0ºC. Larva with eight to 10 tentacles has no metasoma, no diverticulum, no mass of blood corpuscles; terminal nephridia open above the anus. In the 12-tentacle stage the metasoma appears as a thickening. In the stage with 16 to 18 tentacles the ventral pair of blood corpuscle masses appears. Nephridia then open laterally to the metasoma orifice. Metasoma represented by a small tube. The dorsal pair of blood corpuscle masses appears in the larva with 22 tentacles. Usually the definitive tentacles appear in the 22-tentacle larva. They reach a maximum of 26, the maximum of definitive ones being 20. In the mature larva the sensory organ is present (Fig. 118). Stomach diverticulum may be absent, paired or single, rarely vacuolated. Longitudinal muscles of the metasoma are differentiated into bundles. Anomalous metamorphosis may occur in the plankton. Larval tentacles are cast off shortly before metamorphosis. The pairs of blood corpuscle masses conjoin during metamorphosis. The evaginated metasoma showed 48 longitudinal muscle bundles and one nerve. The developed larva is transparent, with orange pigment; it swims on the bottom of the recipient in large circles, resting sometimes in an inverted position; the tentacles are a swimming aid, standing aloof from the body. The developed larvae are identical with Actinotrocha wilsoni B, whose young stages are not known. The present young stages described from plankton, were related to A. ivilsoni B, but only their rearing will confirm that they represent the ontogenetic stages of this larva.

Comparison of the neuromuscular systems among actinotroch larvae: systematic and evolutionary implications

“…The actinotroch listed by Brooks and Cowles (1905) as species “B” is the true larval form of Phoronis architecta. Emig (1982) grouped Wilson's (1881) actinotroch type “B,”Brooks and Cowles' (1905) type “B,”Selys‐Longchamps' (1907) Actinotrocha wilsoni “B,”Forneris' (1959) Actinotrocha wilsoni “B,” and Zimmer's (1964) Phoronis architecta under the name Actinotrocha wilsoni. Emig (1982) also tentatively assigned Actinotrocha wilsoni to the adult of Phoronopsis albomaculata (Gilchrist 1907, collected from False Bay, South Africa).…”

Ultrastructural study of oogenesis in Phoronopsis harmeri (Phoronida)

“…The phylum includes only 12 species of benthos inhabiting animals living in self‐built tubes buried in sand or burrowing in hard substrate. Phoronids lack gonads as constantly presenting organs, the phoronid germ cells mature in the posterior trunk region inside the specialized vasoperitoneal tissue (Benham 1889; Selys‐Longchamps 1907; Pixell 1912; Cori 1939; Marcus 1949; Silen 1952; Forneris 1959; Emig 1983). The vasoperitoneal tissue has an annual cycle of transformation and disappears between spawning seasons (Rattenbury 1953).…”

“…Transformation of the blood vessel peritoneal epithelium into a specialized tissue was observed in early studies (Kowalevsky 1867; Cori 1890; Ikeda 1903; Selys‐Longchamps 1907; Hyman 1959). The light microscope observations of the vasoperitoneal tissue of several species of phoronids include descriptions of the histology of the tissue at different stages of the reproductive cycle: shape and size of cells, morphology and abundance of cell inclusions (Benham 1889; Ikeda 1903; Selys‐Longchamps 1907; Cori 1939; Marcus 1949; Silen 1952; Rattenbury 1953; Forneris 1959; Emig 1983). The vasoperitoneal cells (VPC) are in intimate association with blood vessels and capillaries.…”

Spatial and nycthemeral distribution of the zooneuston off Fernando de Noronha, Brazil

“…This phylum has been cited for the plankton in the following areas of the subtropical Atlantic: São Paulo (Brazil) (FORNERIS, 1959) and Gran Canaria (Spain) (LANDEIRA, et al, 2009). The larvae of these organisms were also registered for the plankton off Reunion Island (Indian Ocean) and for the South China Sea and Black Sea (TEMEVERA, 2009).…”