Distaplia stylifera (Kowalevsky, 1874)

Moreno-Davila, Betzabe, Huato-Soberanis, Leonardo, Gomez-Gutierrez, Jaime, Galvan-Tirado, Carolina, Sanchez, Carlos, Alcoverro, Teresa, Balart, Eduardo F. & Turon, Xavier, 2023, Taxonomic identity of Distaplia stylifera (Tunicata, Ascidiacea), a new arrival to the eastern Pacific displaying invasive behavior in the Gulf of California, Mexico, ZooKeys 1157, pp. 109-125 : 109

Distaplia stylifera (Kowalevsky, 1874)

Figs 2 , 3 , 4

Didemnium styliferum Kowalevsky, 1874: 443, pl. 30, figs 1-16.

Holozoa bursata Van Name, 1921: 366-368, figs 44-47.

Distaplia bursata - Van Name 1930: 456, fig. 31.

Distaplia mikropnoa - Hartmeyer 1919: 130.

Distaplia stylifera - Hartmeyer 1919: 135; Michaelsen 1930: 502; Van Name 1945: 147, fig. 71.

Polyclinum mikropnous - Sluiter 1909: 94, pl. 5, fig. 1.

Material examined.

CEAB.ASC.DIST-001: Ensenada de La Paz , Mexico ; two purple colonies, one as epibiont on sea pen A. maura and one attached to a PVC pipe, 1-3 m depth, 03/Dec/2017. CEAB.ASC.DIST-002: Ensenada de La Paz , Mexico ; two white colonies, one epibiont on A. maura and one attached to a buoy, 1-3 m depth, 03/Dec/2017. CEAB.ASC.DIST-003: Ensenada de La Paz , Mexico ; three orange colonies epibiont on A. maura , on a rope and on a buoy, 1-3 m depth, 03/Dec/2017. CEAB.ASC.DIST-004: Ensenada de La Paz , Mexico ; three orange colonies attached to wooden yacht docks, 0.5 m depth, 19/Jun/2021. CEAB.ASC.DIST-005: Ensenada de La Paz , Mexico ; three purple colonies attached to wooden yacht docks, 0.5 m depth, 19/Jun/2021. CEAB.ASC.DIST-006: Ensenada de La Paz , Mexico ; three white colonies on wooden yacht docks, 0.5 m depth, 19/Jun/2021. CEAB.ASC.DIST-007: Ensenada de La Paz , Mexico ; eight orange colonies on wooden yacht docks, 0.5 m depth, 9/Jul/2021. All the colonies examined in the present study have been deposited in the Biological Collection of the Center of Advanced Studies of Blanes (CEAB) with voucher codes CEAB.ASC.DIST-001 to 007 .

Morphological characters.

Colonies can be mushroom-like with orange color and white mottles marking the common cloacal apertures (Fig. 2A ). Purple (Fig. 2B ) or white colonies (not shown) can also be found. They are up to 2 cm in height and 2-2.5 cm in head (cormidium) diameter (Fig. 2C, D ). The basal part of the colonies is less colored, and only the distal region had pigment after preservation. The tunic is firm and sometimes the stalks are branched so that different heads originate from the same base. Each head had one or several zooid systems, each with a central common cloacal aperture to where double rows of zooids converge. Small systems are made up of a simple circle of zooids. Colonies can also be cushion-shaped, spread over the substrate without a stalk.

The zooids are up to 5 mm in length (excluding the gonadal sacs) (Fig. 2E ). They are divided into thorax and abdomen, with two stalked sacs adhered. One sac, smaller than the abdomen and connected to its right posterior side (Fig. 3A ), includes the gonads. The second sac contains embryos and larvae in incubation and can be longer than the zooid itself. It is attached by a thin peduncle joining the zooid at the posterior part of the pharynx, on the right-hand side close to the dorsal line (Fig. 2E ).

The thorax has a smooth-rimmed oral siphon (or with six slight lobulations), with a large atrial aperture exposing most of the branchial sac. An atrial languet, often consisting of a wide flap-like lid with smooth or lobed margins, is placed at the top of the atrial aperture (Figs 3A , 4A ). There are several transverse muscular bands across the atrial languet. Approximately 30 longitudinal muscular bands run over the thorax of each side. The thorax has ~ 14 simple oral tentacles. The pharynx has four stigmata rows clearly divided by parastigmatic vessels (Fig. 4A ). All thoraces examined (except for those recently budded) had these parastigmatic vessels. The number of stigmata per half-row are typically between 18 or 19 (reaching 22 in larger zooids) in the first two rows and 15 or 16 (reaching 18) in the two posterior rows. There are three simple dorsal languets between rows, slightly displaced to the left-hand side (Fig. 3B, C ).

The abdomen has an elongated and curved stomach. Its wall is marked by fine plications (> 20 per side) that, in section, are visible in both the outer and the inner surface of the wall (Figs 3D, E , 4B ). The plications are longitudinal but can be interrupted or divided. There is a short post-stomach that connects to an enlarged mid-intestine located at the bottom of the gut loop. The distal intestine runs anteriorly and ends in a bilobed anus at the base of the atrial aperture. The pyloric gland features a vesicle or reservoir between the stomach and the intestine and continues anteriorly forming sinuous tubules over the intestine in front of the stomach (Figs 3D, E , 4A ).

The gonads lie in a pedunculated sac, with one well-formed oocyte (sometimes a smaller second one) at the bottom and a cluster of five or six elongated or wedge-shaped testes placed vertically. The common sperm duct arises posteriorly from the cluster of testes, but turns anteriorly at its very beginning, without overlapping the oocytes (Figs 3F , 4B ).

All Distaplia colonies examined had larvae incubating in long sacs that reach posteriorly deeper than the zooids themselves in the colonies. Usually, several larvae can be seen in the brooding sacs, containing up to two well-formed larvae plus three embryos. Larvae are ~ 1.3 mm length, and when fully developed their body become elongated, reaching up to 1.5 mm in trunk length. Larvae possess three adhesive papillae, two dorsal and one ventral, with a globular ampulla each in the stalks. The oozooid is well-formed, with four rows of stigmata already present and an incipient abdomen folded under the branchial sac (Figs 3H , 4C ). The sensory vesicle contains two pigmented spots, a larger one (likely corresponding to the ocellus) and a smaller one (likely the otolith) just under it (Fig. 3G ). The pigmented spots are very close and, given that the larvae are not completely transparent, the two pigmented spots can be easily taken as one.

Geographic distribution.

Distaplia stylifera was described in the Red Sea ( Kowalevsky 1874) and has been reported in several areas of the Indo-Pacific. It has been found in Australia (e.g., Brewin 1953; Millar 1963, 1966; Kott 1990, 2002), Philippines ( Millar 1975; Monniot and Monniot 2001), South China Sea ( Lee et al. 2016), Madagascar ( Monniot 2012), and (as D. mikropnoa , a debated synonymy, see Discussion) in Palau Islands ( Tokioka 1955, 1967). There is a dubious report in the Mediterranean Sea ( Pérès 1956). It is also known from the Western Atlantic coast from North Carolina to Jamaica ( Van Name 1921, as D. bursata , Van Name 1945; Villalobos et al. 2017). It has been reported in several Caribbean locations ( Monniot and Monniot 1984; Monniot 1988; Rocha et al. 2010; Streit et al. 2021), and there are recent reports further south in artificial substrates at Sao Paulo region, Brazil ( Rocha et al. 2011; Dias et al. 2013). It therefore appears to have a wide circumtropical distribution (Fig. 5 , but see discussion for potential taxonomic issues), although it has never been documented in the Eastern Pacific.

Molecular analyses.

Despite obtaining positive amplifications with all the primer pairs assayed, no sequence could be obtained that blasted with ascidian mitochondrial COI. Our sequences were closer to algae, mycoparasites or bacteria with an 80-83% similarity. These results may be due to the presence of mutations in the binding sites or contamination. However, we consider contamination unlikely given the care taken during the extraction of the samples.

Figures

Figure 2. Distaplia stylifera A live orange colony B live purple colony C, D typical mushroom-shaped colonies E Zooid. Scales bars: 10 mm (A, B); 2.5 mm (C, D); 1 mm (E).

Figure 3. Distaplia stylifera A zooid (thorax and abdomen) B thorax C dissected thorax D, E stomach F gonads G larvae H enlargement of one larva showing two pigmented spots. Scales bars: 10 mm (A); 0.5 mm (B, C, F, G); 0.25 mm (D, E). All images (except F) correspond to stained zooids.

Figure 4. Distaplia stylifera A zooid (thorax and abdomen) B abdomen C larva. Abbreviatures: a. anus; am. ampullae; ap. adhesive papillae; oc. ocellus; o. oocyte; pv. parastigmatic vessels; pg. pyloric gland vesicle; sc. statocyte, sg. stigmata; st. stomach; t. testes. Scales bars: 1 cm (A); 0.5 mm (B, C).

Figure 5. Sites of previous records of Distaplia stylifera: 1) Red Sea, Kowalevsky 1874 (type locality). Indo-Pacific, 2) Brewin (1953). 3) Millar 1963 (1966); 4) Millar (1975); 5) Kott 1990 (2002); 6) Monniot and Monniot (2001); 7) Monniot (2012); 8) Shenkar (2012); 9) Lee et al. (2016). Mediterranean, 10) Peres (1956). Western Atlantic Ocean, 11) Van Name (1921, 1945); 12) Monniot and Monniot (1984, Monniot 1988); 13) Cole and Lambert (2009); 14) Rocha et al. (2010); 15) Villalobos et al. (2017); 16) Rocha et al. (2011); 17) Streit et al. (2021); 18) Dias et al. (2013). Eastern Pacific Ocean, 19) present study. The type locality in the Red Sea and the record of the present study are indicated with stars.