Tjalfiella tristoma Mortensen, 1910

Bezio, Nicholas & Collins, Allen G., 2024, Redescription of the deep-sea benthic ctenophore genus Tjalfiella from the North Atlantic (Class Tentaculata, Order Platyctenida, Family Tjalfiellidae), Zootaxa 5486 (2), pp. 241-266 : 252-256

Species Tjalfiella tristoma Mortensen, 1910

Fig. 6 , 8

Grammatical gender— feminine

Etymology— From the feminine noun in apposition formed from Latin tri, “three,” and stoma, “openings.” This name refers to the specimen’s three-body orifices, the mouth, and one opening for each aboral arm.

Pronunciation— Phonetic; “Chae-l-fe-el-ah” “try-stoh-ma” IPA ; /tˈiːd͡Ʒˌaelfɪˈɛlə tɹɪstˈo͡ʊmə/

Material— Seven samples of T. tristoma from the Natural History Museum in Denmark ( NHMD88841 ) and references to Mortensen’s original description and illustrations in his 1912 manuscript “The Danish Ingolf Expedition: TJalfiella tristoma n. g., n. sp. A sessile ctenophore from Greenland”: 249–253, plates. 1–10.

Description

Body— Benthic ctenophore, compressed in the stomodeal axis; and “U” shaped in the tentacular axis; two large highly extendable aboral arms that lack oral grooves on opposing sides of body; distal ends of arms flattened into a disk, contains two openings, a singular gastric accessory opening with serrated edges, and a single smaller tentacular opening; overall body is smooth with no warts or visible papillae, exceptions are four pairs of globular gonads on the aboral face (number of gonads vary between individuals) and two rows of brooding pouches around oral skirt.

Size— Roughly 20mm in length from the tentacular axis, 5mm in length from the stomodeal plane, and 10mm in height; height can be highly variable (6–13mm)

Coloration— Transparent; body is opaque milky white, while tentacles are yellow due to the presence of colloblasts. (These colors are reported from formalin-preserved individuals, which may have lost some color—this cannot be determined after the fact.)

Apical organ— A single sunken statocyst in the center of the aboral face, does not extend beyond the outer epidermal layer; lacks cilia used for balance and positioning; lacks a polar field and no visible anal openings; a large, thickened epithelial floor extends down to the mouth.

Ctene rows— Completely absent in the mature benthic form, while embryos possess eight equally spaced ctene rows of uniform length. See Embryo section (below) for details.

Tentacular apparatus— Two tentacular apparatus (one per aboral arm) located on the innermost facing half; contains a large spherical tentacle bulb (d— 2–3.3mm) with a single tentacle protruding up towards the distal end of the arm; lack tentilla; of an undefined thickness that gradually narrows to the distal end.

Gastrovascular system— Suboral cavity “U” shaped with three openings, a single downward-facing slit mouth, two accessory openings in the arms distal end; suboral cavity houses numerous hanging stomodeal folds that thin out towards the accessory openings; a single protrusion extends upward from the suboral cavity towards the centralized statocyst, two canals extend horizontally from protrusion into the tentacles, each horizontal canal contains four diverticula that imbed into four hermaphroditic gonads; additionally two diverticula extend between each pair of gonadal diverticula along the outer body wall, each diverticulum has numerous dichotomously branching protrusions, all protrusions lack anastomoses.

Reproductive system— Four to eight large globular gonads arranged around a statocyst (d— 3–3.5mm), number varies due to the stage of regeneration, hermaphroditic with separation of reproductive tissues;; Several large brood pouches (variable in number) arranged in 2–3 rows develop on distal ends of each sub-diverticula around the oral foot.

Embryo— Mortensen described the larvae in three stages depending on their development; these stages are described below:

Stage I— Spherical (d— 2mm), numerous small white pigment spots irregularly scattered, large furrow in the transverse plane reaches halfway down the body on oral side, lack of a developed suboral cavity; aboral side with a single statocyst and two elongations; eight rows of costae with clustering cells on aboral half of body, develop into rudimentary tentacle bulbs on tentacular axis; lack ctene rows.

Stage II— Spherical (d— 2mm), without pigmentation, large furrow with visible suboral cavity taking up half body cavity; sunken statocyst with four large elevations; variable number of ctene plates arranged in eight equidistant rows (h— 0.1mm) reaching half length of body; tentacle bulbs developed into “T” shape with simple tentacles, lacking tentilla.

Stage III—Pear-shaped (l— 5mm, d— 2mm); furrow developed into two lobes (similar to Ctenoplana ), pressed together to form tight seal, can flatten on a surface; extends halfway down the oral side of body; suboral cavity is large and voluminous, constitutes half body cavity, fully connected to tentacle bulbs and stomodeum; costae and ctene rows sunken into deep furrows of equidistant around aboral end

Ecology— Known only residing on the surface of pennatuloid octocorals of the genus Umbellula , perhaps in an obligatory symbiotic relationship. Diet may include crustaceans, indicated by an unidentified, partially decomposed, 1-cm “shrimp” lying within the suboral cavity, the tail lying partly within one chimney ( Mortensen 1912:10); additional ecological information unknown.

Habitat— Deeper than 400m in areas dominated by mud flats within the Umanak Fjord and Northern Baffin Bay; 71.001296N, - 54.349333W

Host— Umbellula lindahli ; occupies the upper portion of the central unbranched rachis or within the crown of polyps. Never observed independent of Umbellula .

Remarks— TJalfiella tristoma is unique among the other described species of platyctenes because of the “U”shaped body with projecting arms that lack visible oral grooves, simple tentacles without tentilla, and an arrangement of large globular gonads encircling the statocyst on the aboral face of the species ( Fig. 8 ). Species in Coeloplana , Vallicula multiformis , and Lyrocteis imperatoris do not possess any of these traits.Notably, V.multiformis and Coeloplana spp. lacks externalized gonads, have a flattened body when relaxed, and possess tentacles adorned with fine tentilla that exit out of the distalmost ends of a prominent oral groove. Alternatively, L. imperatoris can be distinguished from T. tristoma based on the presence of a notable oral groove and tentacles adorned with fine tentilla. Additionally, the canal structure and arrangement of gonadal tissue visually varies between TJalfiella , Coeloplana , and Lyrocteis , with both Coeloplana and Lyrocteis possessing a fine network of anastomosing canals while TJalfiella possesses only blind ending canals ( Fig. 9 ). Although certain morphological characteristics used to differentiate species of platyctenes may vary during their development or regeneration, the current valid species have good support based on detailed descriptions of both mature and developmental stages.

Additionally, although Mortensen (1912) observed cilia lining the interior of the suboral cavity in the arms, we failed to detect them utilizing light microscopy and microCT analysis. Additional destructive histological analysis would be needed to verify the presence of cilia in the suboral cavity in the arms.

The geographic distribution of T. tristoma is described by Mortensen (1910) as being strictly in the North Atlantic Ocean on the Western coast of Greenland in the Umanak Fjord and the Northern Baffin Island beginning at about 71.001296N, - 54.349333W. Additionally, Mortensen (1910) described no occurrences of T. tristoma south of Umanak Fjord. However, during Kramp’s visit to the region through the Godthaab expedition in 1928, specimens of T. tristoma were observed only on U. lindahli within the Umanak Fjord, with no additional observations either North or South of the type locality described by Mortensen. Regardless, these sparse observations for T. tristoma could suggest either a tight or spotty distribution for the species. However, due to the brooding nature of TJalfiella , the species may not be as widely distributed as related broadcast spawners.

Figures

FIGURE 6. MicroCT 3D reconstruction of three TJalfiella samples:A. Tentacular view of T. tristoma, B. Tentacular view of T. aff. tristoma (2018), C. Tentacular view of T. aff. tristoma (2022), D. Stomodeal view of T. tristoma, E. Stomodeal view of T. aff. tristoma (2018), F. Stomodeal view of T. aff. tristoma (2022), G. Colorized internal anatomy of T. tristoma with low opacity body overlay, H. Colorized internal anatomy of T. aff. tristoma (2018) with low opacity body overlay, I. Colorized internal anatomy of T. aff. tristoma (2022) with low opacity body overlay, J. Closeup of aboral arms face with centralized opening and tentacle, K. Isolated view of intact larval T. aff. tristoma (2018) within the brood chamber, tentacular view, I. Closeup of developing brood chambers along diverticula protrusions. Blue—gastrovascular cavity (e.g., suboral cavity), Purple—Gonads, Magenta—brood pouches, Pink—tentacular apparatus, Green—canals, Teal—generalized larval anatomy. Scale bar: A–F— 3mm, G–I—1.6mm, J–L—0.3mm.

FIGURE 8. Illustrated Plate of TJalfiella tristoma collected by Kramp: A. representation of specimens in their natural position on the stalk of Umbellula lindahli, B. view of flattened face of aboral arm, C. young specimen of T. tristoma with asymmetrical gonads and no brood pouches, tentacular view, D. mature T. tristoma, tentacular view, E. aboral schematic of arrangement of diverticula and associating canals, F. stomodeal view of mature T. tristoma, G. cutaway illustration featuring internalized anatomy. Tj—TJalfiella tristoma, H—Host coral (Umbellula lindahli), a.a.—aboral arm, a.f.—aboral face, b.—brooding pouch, d.b.—diverticula that transverse along the body, d.g.—gonadal diverticula, d.p.—diverticula protrusions, d.t.—tentacular diverticula, g.—gonads, m.—mouth, o.s.—oral skirt, s.c.—suboral cavity, s.—statocyst, s.f.—stomodeal folds, s.o.—secondary opening (mouth), t.—tentacle, t.b.—tentacle bulb, t.s.—tentacle sheath, t.o.—tentacle opening.

FIGURE 9. Simple schematic of the structure of the canal and reproductive system in three families of Platyctenida viewed from the aboral side; A. Tjalfiellae, B. Coeloplanidae, C. Lyroctenidae. c—canal system, g—gonads, s—statocyst, t—tentacular apparatus.