Styela panamensis, Barros & Rocha, 2021

Barros, Rodolfo Corrêa De & Rocha, Rosana Moreira Da, 2021, Two new species of Styela (Tunicata: Ascidiacea) from the tropical West Atlantic Ocean, Zootaxa 4948 (2), pp. 275-286 : 276-277

Styela panamensis sp. nov.

( Figures 1A and 2 )

urn:lsid:zoobank.org:act:07FC9C46-28A5-496C-8D51-93E70FD38B10

Materials examined. Holotype: Sty –164, artificial substrate, Solarte Island, Bocas del Toro, Panama, 9 o 18’0”N 82 o 11’0”W, August 4, 2003 . Paratypes: Sty –282 and Sty –283, artificial substrate, Colon Island, Bocas del Toro, Panama, 9 o 2315”N 82 o 15’30”W, August 9, 2003 ; Sty –284 and Sty –285, artificial substrate, San Cristóbal Island, Bocas del Toro, Panama, 9 o 21’0”N 82 o 14’0”W, August 12, 2003 .

Etymology. The specific name refers to the country where this species was collected.

Habitat and distribution. The species is very common and abundant in Bocas del Toro province, both in natural (mangrove) and artificial (marinas, piers and pilings sustaining buildings) habitats, less than 2 m deep. They attach directly to the prop roots of mangroves or the artificial substrate, but more frequently on bivalve shells attached to those substrates. They can be found isolated or in small groups of 3–5 individuals. Salinity in the region is 32–34 psu.

External appearance. Color ranges from orange brown to reddish brown, some animals very dark in the anterior region. There are few epibionts, among which filamentous algae and polychaetes are common ( Fig. 1A ). Specimens are 22–38 mm in length. Individuals are oval with a leathery tunic with rough appearance, with discrete projections that are concentrated on the siphons ( Fig. 2A ).

Internal morphology. Length without tunic is 14–34 mm, width is 9–16 mm. The body wall is thin and translucent, allowing the visualization of the gonads and, sometimes, the digestive tract ( Figs. 2B and 2C ). The longitudinal muscles are visible in most cases. The siphons are close to each other, the oral is apical and the atrial a little way back on the dorsal line, with similar lengths, more than 7 mm long in the larger specimens. In each siphon, four triangular lobes and eight whitish bands are observed. Numerous 10–30 µm long scale-like siphonal spines are present on the internal side of both siphons. They are flattened and triangular shaped in surface view. The free margin is slightly concave and smooth ( Figs. 2I and 2i ). Between 31–54 simple and filiform tentacles are observed at the base of the oral siphon, distributed in four orders of size ( Fig. 2E ). Short and numerous filiform tentacles are present at the base of the atrial siphon, forming a ring from which two dorsal and elongated regions also covered by tentacles project towards the dorsal tubercle, which they almost reach. The prepharyngeal groove is formed by a simple blade, with the peritubercular area in a ‘V’ shape. The dorsal tubercle is globular, 0.25–0.88 mm in diameter, and with a variable-shape opening, usually as a ‘U’ ( Fig. 2E ).

The dorsal lamina is simple and continuous until the perioesophageal region, where it moves to the left side of the oesophageal opening, with the lower portion being wider. The pharynx has four well-developed folds on both sides, with 58–111 longitudinal vessels on the right side and 58–103 on the left side. There are 7–15 longitudinal stigmata per mesh. Parastigmatic vessels are present. The formula for the longitudinal vessels of the holotype and the four paratypes follows (from right to left side):

E5(16)6(20)5(21)5(24)9DL3(23)5(20)5(21)5(16)5 (Holotype)

E2(9)3(14)4(12)4(13)5DL1(15)3(10)4(11)4(9)2

E6(15)8(20)9(20)8(18)8DL6(17)8(16)7(17)8(14)6

E5(14)7(19)7(18)7(14)4DL5(15)8(17)8(18)6(14)7

E5(13)5(17)5(15)5(16)4DL4(18)6(16)5(17)4(14)3

The oesophagus is relatively long, slightly curved. The stomach is elongated, 4.3–7.4 mm long, yellow to orange in color, with 19–28 internal longitudinal folds, running from the distal portion of oesophagus to the beginning of intestine, frequently visible on the exterior surface. The stomach has a longitudinal flat region along the side touching the body wall, with internal transverse grooves. A ligament is observed between the posterior portion of the stomach and the first loop, but there is no gastric caecum. The intestine is isodiametric and forms primary and secondary loops, the secondary loop being wider than the primary ( Fig. 2D ). The anus opens near the base of the atrial siphon, with a generally multilobed margin, although some specimens have no clear lobes in the anus. The digestive tube attaches to the body wall through thin ligaments which are easily broken during dissection. Endocarps of varying sizes and quantities (usually abundant) protrude from the body wall, but never on the gonads or digestive tract ( Fig. 2D ). Hermaphroditic gonads are on both sides, two to five on the right side ( Figs. 2D and 2F ) and two to three on the left side. The ovaries are elongated, light yellow, straight to sinuous in shape with cylindrical cross section, usually filled by numerous oocytes. The length of the ovary is 4.0– 20.9 mm on the right side and 2.8–10.5 mm on the left side. The ovaries end with the orifice directed toward the atrial siphon into a free and short oviduct. Bifurcations in the ovarian tubes may be present in the distal portion of some ovaries ( Fig. 2G ). Most dorsal ovary on the left side is usually shorter than the rest and lies partially within the second intestinal loop. The diameter of the oocytes is 0.141 –0.242 mm. The testicular follicles are whitish and distributed besides the ovaries, usually along the posterior 2/3 of the elongated ovary on both sides. Follicles are attached to the body wall by the basal part only, protruding into the peribranchial cavity as one long digitiform (more rarely globose) structure or branched in the base to form up to five long lobes ( Fig. 2H ). Common sperm duct gathers the ducts of many testicular follicles and runs along the atrial surface of each ovary to open close to the oviduct aperture on a small papilla.

Figures

FIGURE 1. A. Styela panamensis sp. nov. in situ. B. Styela multicarpa sp. nov. in the laboratory right after collection. Legend: os. oral siphon; as. atrial siphon.

FIGURE 2. Styela panamensis sp. nov. A. external appearance; B. right side body; C. left side body; D. overview of specimen dissected without the pharynx; E. detail of pharynx and anterior region; F. specimen with four gonads on the right side; G. bifurcated ovary; H. digitiform testicular follicles; I. siphonal spines; i. two views of the siphonal spines shape. Scale bars = 10 mm.