Polysyncraton amethysteum ( Van Name, 1902 )

Oliveira, Livia M., Hoeksema, Bert W. & Rocha, Rosana M., 2019, Polysyncraton (Ascidiacea, Didemnidae): a re-examination of some specimens and descriptions of three new species, European Journal of Taxonomy 519, pp. 1-25 : 4-10

Polysyncraton amethysteum ( Van Name, 1902)

Figs 2–5

Polysyncraton amethysteum Van Name 1902: 366 , pl. 54, figs 62, 64–67.

Polysyncraton amethysteum – Rodrigues 1962: 195. — Millar 1977: 200, fig. 21. — Rocha et al. 2005: 467. — Lotufo & Silva 2006: 228. — F. Monniot 2016: 207 , fig. 4D.

Didemnum (Polysyncraton) amethysteum – Van Name 1921: 333, figs 27–29; 1945: 95, fig. 41, pl. 18, fig. 3. — Moure et al. 1954: 236. — Millar 1958: 499.

Material examined

Paratype

BERMUDA • 1 colony; NHM 1914.5.18.103.

Other material

BRAZIL – Paraíba • 4 colonies; Barra de Camaratuba ; 06°36′12″ S, 34°57′51″ W; 0–0.3 m depth; 13 Mar. 2013; L. M. Oliveira leg.; intertidal zone; DZUP POSC- 23 to DZUP POSC- 25, LIPY UFPB TUN- 395, slides DZUP DID 5.30 to DID 5.31 • 1 colony; same collecting data as for preceding but 6 May 2008; Projeto Biota Paraíba leg.; intertidal zone; LIPY UFPB TUN- 230 • 4 colonies; Baia da Traição , 06°41′15″ S, 34°55′50″ W; 0–0.3 m depth; 12 Mar 2013; L. M. Oliveira leg.; intertidal zone; DZUP POSC- 13 to POSC- 14, slides DZUP DID 5.13 to DID 5.14 • 3 colonies; Quebramar Cabedelo ; 06°57′42″ S, 34°50′34″ W; 0–0.5 m depth; 25 Mar. 2013; L. M. Oliveira leg.; intertidal zone; DZUP POSC- 29 to POSC- 31 • 1 colony; Pomar das Esponjas ; 07°08′04″ S, 34°46′20″ W; 1–5 m depth; 12 Jan. 2009; Projeto Biota Paraíba leg.; snorkeling; LIPY UFPB TUN- 176 • 2 colonies; Ponta do Cabo Branco ; 0 7 o 08′50″ S, 34 o 47′51″ W; 0–0.3 m depth; 28 Mar. 2013; L. M. Oliveira and R.M. Rocha leg.; intertidal zone; DZUP POSC-15 to POSC-16, slides DZUP DID5.15 to DID5.16 • 4 colonies; Praia de Carapibus ; 7°16′19″ S, 34°48′07″ W; 0–0.3 m depth; 26 Mar. 2013; L. M. Oliveira and R.M. Rocha leg.; intertidal zone; DZUP POSC-26 to DZUP POSC-28, LIPY UFPB TUN-396 • 5 colonies; Praia de Coqueirinho ; 07°16′19″ S, 34°48′07″ W; 0–0.3 m depth; 27 Mar. 2013; L. M. Oliveira and R.M. Rocha leg.; intertidal zone; DZUP POSC-18 to POSC-22 • 3 colonies; same collecting data as for preceding but 3 Jun. 2008; Projeto Biota Paraíba leg.; intertidal zone; LIPY UFPB TUN-153, LIPY UFPB TUN-156 . – Pernambuco • 1 colony; Goiana, Pontas de Pedras ; 07°37′17″ S, 34°48′15″ W; 13 Dec. 2013, J. Nogueira leg.; intertidal zone; DZUP POSC-045 . – Espírito Santo • 2 colonies; Carapebus ; 20°13″ 46.02″ S, 40°12′12.67″ W; 0–0.3 m depth; 24 Jan 2012; G.A. Gamba leg.; intertidal zone; DZUP POSC-055, slide DZUP DID5.06 • 3 colonies; Aracruz, Santa Cruz ; 20°01′53.12″ S, 40°09′29.22″ W; 0–0.3 m depth; 25 Jan. 2012; G.A. Gamba leg.; intertidal zone; DZUP POSC-056 to POSC-057, DZUP POSC-059, slides DZUP DID5.07 to DID5.08 , DZUP DID5.10 .

GHANA: 7 colonies; Elmira Gold Coast; 11 Oct. 1938; F.R. Irvine and V.G. Foote leg.; NHM 1959.5.27.23, NHM 1959.5.27.24 • 1 colony; Elmira Gold Coast; 28 Dec. 1932, E.D. Plumptre leg.; NHM 1937.1.5.1.

PUERTO RICO • 1 colony; 10 Jul 1915; AMNH 797 • 1 colony; 30 Jun 1915; AMNH 798 .

UNITED STATES – Florida • several colonies; Atlantic side, Biscayne Bay, banks near Soldiers Keys ; 3 Mar. 1916; W.G Van Name leg.; AMNH 314 • 2 colonies; Gulf of Mexico, St. Teresa , seagrass beds; 29°53′41.3″ N, 84°33′23.4″ W; 2 m depth; 7 Nov 2011; sand; UF 1127 • 1 colony; Gulf of Mexico, north of St. Petersburg ; 29°01′40.8″ N, 83°35′19.3″ W; 18–20 m depth; 12 Mar 2011; G. Paulay, M. Bemis and N. Evans leg.; UF 1037 • 5 colonies; Gulf of Mexico, Hudson ; 28°21′05.4″ N, 82°55′04.8″ W; 6 m depth; 2 May 2011; G. Paulay leg.; UF 1749 , slide DZUP DID5.09 • 1 colony; Gulf of Mexico, Dry Tortugas , n° 23; 10 Jun. 1931; Tandy-Colman leg.; NHM 1931.12.25.2 • 1 colony; Gulf of Mexico , off Florida; 26°16′49″ N, 82°44′01″ W; 30.4 m depth; 19 Jul. 1981; USNM 17364 .

Emended description

The specimen in NHM 1914.5.18.103 ( Bermuda) has not been dissected because of the small size of the colony. It has a gelatinous and transparent tunic, without spicules, through which zooids could be seen on the colony surface without a pattern of organization. The specimen from the Atlantic coast of Florida (AMNH 314) has a brownish colour, is also small (3 cm in diameter and 1 mm thick), with several cloacal apertures and a spicule layer on the colony surface. The zooids are brownish and the atrial languet is bifurcated. The lateral thoracic organ is circular and protruding at the level of the 2 nd row of stigmata. The abdomen has a glandular tissue. The testis has three follicles surrounded by four coils of the sperm duct. Other specimens from the Gulf of Mexico (USNM 17364; Fig. 2 ; UF 1037, UF 1127 and UF 1749) have an atrial languet with a flat tip rather than bifurcated and testis with four follicles surrounded by five coils of the sperm duct. The glandular tissue in the abdomen has not been observed. Larvae were found in sample UF 1749 only. They look like those found in the specimens from São Paulo, Brazil. The specimens from Puerto Rico (AMNH 797 and AMNH 798) are similar in spicule density and zooid morphology to the samples from the Gulf of Mexico.

The colonies from Ghana (NHM 1959.5.27.23-24) are less than 3 cm in diameter. In contrast with the information given about this sample by Millar (1953), the larval trunk is 0.8 mm long. The colonies are pinkish-purple, gelatinous, the colony surface is smooth, shiny and marked with a spicule accumulation around the oral siphons. The zooids are 0.8–1.0 mm long. The oral siphon has six short triangular lobes. The atrial aperture is small. The atrial languet is bifurcated, sometimes with a flat tip. The lateral thoracic organs are circular, not protruding and located in the anterior region of the thorax at the level of the 2 nd row of stigmata, close to the atrial aperture. The pharynx has six stigmata per half row. The abdomen is positioned horizontally in relation to the thorax. The secondary gut loop overlays the stomach. The testis is divided in five follicles surrounded by three coils of the sperm duct. The larvae are present on the colony surface. They are elliptical, gemmiparous, uncoloured, trunk measuring 0.8–1.0 mm. A tail with a diameter of 35 µm winds about halfway around the trunk. Three adhesive papillae are close together. The sucker of the central adhesive papilla is 100 µm in diameter. There are six elongated ectodermal ampullae on each side. The sensorial vesicle lays in the posterior region of the larval trunk. The ocellus is 40 µm long. The distance between ocellus and anterior region of the tail is 200 µm. Larva with two embryos: oozoid dorsal and blastozooid ventral.

The morphological characteristics of the zooids of the Brazilian specimens are very similar to those observed by Van Name (1902), although the variation in colony colour and spicule density is much larger in Brazil. The colour varies from purple to brick. The colonies are 3 to10 cm in diameter and 1 to 3 mm thick ( Fig. 3 ). The atrial languet can be bifurcated or with a flat tip. The pharynx has seven to nine stigmata per half row. The lateral thoracic organ is circular and protruding at the level of the 2 nd row of stigmata. The testis has three to five follicles (even in zooids of the same colony), surrounded by three to five coils of the sperm duct. The larva is gemmiparous, with a trunk that is 0.8 to1.0 mm long. A tail 85 to 90 µm wide winds about three-quarters of the way around the trunk. The peduncles of the adhesive papillae are long, while the sucker of the central adhesive papilla is 63 to 80 µm in diameter. There are six or eight pairs of ectodermal ampullae, but four pairs in different stages of duplication were seen in immature larvae ( Fig. 4 c–f). The sensorial vesicle is in the mid or posterior dorsal region of the larval trunk. The ocellus is 56 to 60 µm long. The distance between the ocellus and the anterior region of the tail is 185 to 238 µm. The pharynx of the oozooid has 8, 7, 6, 6 stigmata on each half row.

Remarks

Lotufo (2002) claimed that Brazilian specimensof this species differ from the ones described by Van Name (1902) in the different arrangement of spicules and in the single cloaca per colony. However, the colonies studied by us showed a huge variation in colour, spicule density and cloaca number as also observed by Pérès (1949) and Millar (1953) in African specimens. Lotufo (2002) also mentioned having studied a sample from the type series deposited in the American Museum of Natural History, with very large larvae (1.5 mm trunk length), but we were not able to find and examine this sample in the museum collection. The only sample close to the type locality with available larvae was one from Florida (UF1749), with larvae whose trunk varies from 0.8 mm to 1.2 mm within the same colony. F. Monniot (2016) compared specimens from French Guiana with those from Bermuda and concluded that they belonged to the same species.

Molecular analyses (ML and IB) also suggest the existence of only one valid species. Samples from Panama to south Brazil grouped in one clade, corresponding to P. amethysteum with a significant bootstrap value (95%) and posterior probability support (IB = 1) ( Fig. 5 ). Although this clade seems to be split in two branches, one of them does not have enough bootstrap support. The intraspecific genetic divergence (p-distance) among haplotypes ranged from 0.7 to 9.8%, while the interspecific divergence with P. lacazei was ~22%, and with P. poro was ~27%. Based on genetic evidence and the lack of clear morphological separation in the samples examined, we consider that they all belong to P. amethysteum , a species with a large phenotypic variation.

The haplotype UPDID096-17 from Rio de Janeiro, in contrast, is a different species with 12.4 to 14.9 % distance from P. amethysteum , and will be commented on later ( Polysyncraton sp.).

Distribution

Type locality: Bermuda ( Van Name 1902). Other localities: United States – Florida ( Van Name 1945), Puerto Rico, Cuba, Belize ( Goodbody 2000; Van Name 1945), Guadeloupe, Martinique ( Gravier 1955), Panama (this study), Colombia ( Van Name 1945), French Guiana (F. Monniot 2016), Brazil – Ceará to Santa Catarina ( Millar 1977; Lotufo 2002; Rocha et al. 2012), Cape Verde, Senegal, Ghana ( Pérès 1948; Millar 1953; C. Monniot & F. Monniot 1967).

Figures

Fig. 2. Polysyncraton amethysteum (Van Name, 1902), Florida (USNM 17364). a. Thorax with bifurcated atrial languet (small arrow) and thoracic organ (big arrow). b. Stained abdomen, sperm duct with five coils (arrow). c. Detail of the testis with four follicles and sperm duct with four coils (arrow). Scale bars: 0.1 mm.

Fig. 3. Polysyncraton amethysteum (Van Name, 1902), Paraíba, Brazil. a–b. Colonies in situ. c–d. Colony surface detail (arrow indicates one cloacal aperture) (DZUP POSC-14 and DZUP POSC- 13, respectively). e. Cross section of the colony, with thin layer of spicules (arrow) (DZUP POSC-14). f. Spicules. Scale bars: e = 1 mm; f = 10 µm.

Fig. 4. Polysyncraton amethysteum (Van Name, 1902), Brazil (DZUP DID-034, POSC-016; LIPY UFPB TUN-293). Structures stained with hemalum. a. Thorax, atrial languet (arrow). b. Abdomen showing the position of the testis (arrow). c–f. Larvae in Brazilian specimens from São Paulo (c) and Paraíba (d–f), different stages in the same colony (e–f). Scale bars: 0.1 mm.

Fig. 5. Maximum likelihood tree of species of Polysyncraton based on analysis of 16 sequences of mitochondrial COI. Numbers on or below branches represent the support value of the bootstrap for Maximum likelihood (> 70%) and posterior Bayesian probabilities (> 0.97). Abbreviations of Brazilian states are explained in Table 1.