Umbellula pomona Risaro, Williams & Lauretta, 2020

Risaro, Jessica, Williams, Gary C., Pereyra, Daniela & Lauretta, Daniel, 2020, Umbellula pomona sp. nov., a new sea pen from Mar del Plata Submarine Canyon (Cnidaria: Octocorallia: Pennatulacea), European Journal of Taxonomy 720, pp. 121-143 : 127-132

Umbellula pomona Risaro, Williams & Lauretta sp. nov.

urn:lsid:zoobank.org:act:77FCDEF4-AAE3-4BB5-BAB2-1EDAA4B19439

Figs 2–7

Differential diagnosis

Umbellula pomona sp. nov. is a spiculated Umbellula with three autozooids in its terminal cluster, a central well-developed polyp and two lateral, symmetric and smaller ones. It presents large sclerites in all its tissues as well as siphonozooids all along the rachis. Its central axis is circular in cross section all along its extension, and does not vary throughout the colony.

Etymology

The species is named after the birthplace of the first author (JR), Pomona (Río Negro, Argentina). The word ‘pomona’ is used as a noun in opposition.

Material examined

Holotype

SW ATLANTIC OCEAN • one complete spec. (preserved in 96% ethanol); Mar del Plata Submarine Canyon , “Talud Continental III” exped., stn N° 45; 38°1.913′ S, 53°39.268′ W; 2934 m deep; Sep. 2013; Daniel Lauretta leg.; MACN-IN 42608 .

Paratypes SW ATLANTIC OCEAN • 3 specs (two adult, without the peduncle: paratypes A and B; and one juvenile like, complete: paratype C; preserved in 96% ethanol); Mar del Plata Submarine Canyon , “Talud Continental III” exped., stn N° 46; 38°5.310′ S, 53°39.988′ W; 3282 m deep; Sep. 2013; Daniel Lauretta leg.; MACN-IN 42609 .

Description (holotype MACN-IN 42608)

The colony looks rugous in all its extension, especially the terminal cluster of autozooids. The color of the polyps, rachis and the peduncle is white or light yellow (preserved). The holotype is 214 mm in length. It has a terminal cluster of three autozooids with tentacles, one central and larger polyp growing on the distal-most region of the rachis, and two smaller but well-developed lateral polyps growing at the base of the central one ( Fig. 2 ). The central polyp is 25.3 mm in length and the two lateral polyps’ lengths are 3.0 mm and 2.6 mm. The tentacles of the two types of polyps are larger than its body, the measures are 12.3 mm for the central autozooid, and 1.1 mm and 1.7 mm for the lateral ones. The axis is 178 mm in length and it is circular in cross-section, approximately 0.74 mm in diameter. The rachis is approximately 0.8 mm in diameter in the middle zone between the peduncle and the terminal cluster. The peduncle is 8.68 mm in length, and its appearance is soft and smooth. The autozooids of the cluster grow with a kind of orientation determining a ‘dorsal’ region where the axis inserts and a ‘ventral’ region towards which the polyps come together ( Fig. 2 ). The siphonozooids are numerous and resemble small white dots, and are distributed all along the rachis from the base of the autozooids to the middle of the rachis. These polyps are circular and inconspicuous; and have a diameter of about 393 ± 93 μm (299–486 μm, N = 36).

Sclerites are conspicuous, along much of the length of the colony (polyps, rachis, tentacles and pinnules). They are translucent and colorless, rod-shaped and spindle-shaped with spines ( Figs 4–7 ). Those present in the rachis are spindle-shaped, have triangular protuberances all along their length ( Fig. 4 ) and their sizes are 333.5 ± 71.1 μm (262.4–404.6 μm, N = 10), the body wall of the polyps has different types of sclerites, two of them are rough and rod-shaped, but differ in their measurements, while the others are spindle-shaped with spines along their lengths and also have different sizes ( Fig. 5 ). The largest type is rod-shaped and approximates 1446 ± 32.7 μm (1413.3–1478.7 μm, N = 5) in length ( Fig. 5A ); another type, smaller and spine-shaped, approximates 687 ± 45.6 μm (641.4–732.6 μm, N = 5) ( Fig. 5 B–C). The other types are much smaller, and one type is rod shaped, like the largest one ( Fig. 5D ), and the other type is spine-shaped ( Fig. 5 E–F); these two types of sclerites have similar sizes, length approximates 534 ± 43.4 μm (490.6–577.4 μm, N = 5). Finally, the tentacles have rod-shaped sclerites ( Fig. 6 ) with two sizes: the larger ones are 1223.2 ± 280.1 μm (943.1–1503.3 μm, N = 5) ( Fig. 6 A–C) and the smaller ones are 632.8 ± 96.2 μm (536.6–729 μm, N = 5) in length ( Fig. 6 D–F), and those of the pinnules are rod-shaped with some protuberances along their lengths and their sizes are approximately 269.1 ± 50.3 μm (218.8–319.4 μm, N = 10) ( Fig. 7 ). In both tissues the sclerites are placed along the main axis, not transversally.

Variability

Of the three paratypes (A, B and C), one (paratype C) is significantly smaller than the others, so we consider it could be a juvenile ( Fig. 8 ). The color of the three colonies is white or light yellow when preserved, all of them have three autozooids with the same grade of development as the holotype (as it can be seen in Fig. 2B ) and its central axis is round in all its extension ( Fig. 3 ). The large paratypes (A and B) lack their peduncle. Their general aspect is just like the holotype, they are rugous in all their length because of the presence of conspicuous sclerites in the autozooids and rachis ( Fig. 2B ). The total length of the large paratypes is 134 mm and 231 mm, their central autozooids are 36 mm and 34 mm long (length of the tentacles: 20 mm and 12 mm, length of the columns: 16 mm and 22 mm, respectively) while the dimensions of the lateral ones are 4.8 mm and 5.6 mm in one paratype and 6.4 mm and 7 mm in the other. Their rachis are 97 mm and 200 mm in length and their diameters are 0.9 mm and 2.2 mm at thier widest sections. Their axis’ diameter is 0.83 mm and 1.3 mm. Their siphonozooids are 313 μm and 370 μm (mean) in diameter and look like the siphonozooids of the holotype. Finally, the sclerites of these paratypes look alike and have similar sizes as the sclerites of the holotype. The juvenile paratype’s (C) total length is 110 mm, its central autozooid is 7.9 mm in length (column and tentacles are 4.4 mm and 3.4 mm long, respectively), and the length of the lateral ones is 2.9 mm (column and tentacles are 1.4 and 1.5 mm in length, respectively). The peduncle’s length is 4.6 mm and the rachis’ 95 mm, while its diameter is 0.41 mm at its widest section. Its central axis is 0.35 mm in diameter. Finally, the siphonozooids of this paratype are tiny spots with the same aspect and distribution as those on the holotype and the largest paratypes.

Phylogenetic analysis

Both phylogenetics reconstructions (i.e., BA and ML) agree in the basic topology of the trees (for simplicity we only show BA). Both type specimens of U. pomona sp. nov. were grouped together with low support values within the same group (possibly because we only have one gene sequence for each species). Umbellula spp. were recovered in two clusters, Umbellula clade I including most of the included Umbellula species and a second one ( Umbellula clade II) including only U. monocephalus , Umbellula pomona sp. nov. and Umbellula sp. 2 from Dolan et al. (2013) ( Fig. 9 ).

Figures

Fig. 2. A. General aspect of Umbellula pomona Risaro, Williams & Lauretta sp. nov. A. Holotype (MACN-IN 42608). B. Detail of the terminal cluster of paratype A (MACN-IN 42609), showing three autozooids that form the terminal cluster and amplifications of sclerites (up) and siphonozooids (down). Abbreviations: CP = central polyp; LP = lateral polyp; Pd = peduncle; R = rachis; T = tentacle; S = siphonozooids; Scl = sclerites.

Fig. 3. Transversal section of the central axis of paratype B of Umbellula pomona Risaro, Williams & Lauretta sp. nov. (MACN-IN 42609). A. Transversal section of the central axis between the peduncle and the rachis. B. Transversal section of the central axis near the terminal cluster.

Fig. 4. Variability of sizes and ornamentations of the rachis’ sclerites of the holotype of Umbellula pomona Risaro, Williams & Lauretta sp. nov. (MACN-IN 42608).

Fig. 5. Variability of sizes and ornamentations of the polyps’ sclerites of the holotype of Umbellula pomona Risaro, Williams & Lauretta sp. nov. (MACN-IN 42608).

Fig. 6. Variability of sizes and ornamentations of the tentacles’ sclerites of the holotype of Umbellula pomona Risaro, Williams & Lauretta sp. nov. (MACN-IN 42608).

Fig. 7. Variability of sizes and ornamentations of the pinnules’ sclerites of the holotype of Umbellula pomona Risaro, Williams & Lauretta sp. nov. (MACN-IN 42608).

Fig. 8. General aspect of the unique specimen of a juvenile-like paratype of Umbellula pomona Risaro, Williams & Lauretta sp. nov. (MACN-IN 42609, paratype C). Abbreviations: CP = central polyp; LP = lateral polyp; R = rachis; PD = peduncle; T = tentacles.

Fig. 9. Phylogenetic reconstruction of the concatenated set of the two mitochondrial genes (mtMutS and ND2) based on the Bayesian analysis. Nodes include the Bayesian posterior probabilities. Arrows point to the new specimens of Umbellula Cuvier, 1798 included in the analysis.