Tjalfiella aff. tristoma (2022), Bezio & Collins, 2024

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 : 261

Species Tjalfiella aff. tristoma (2022)

Fig. 5 , 6 , 12

Material— Nine samples of T. aff. tristoma collected by the ROV Deep Discoverer on the NOAA Okeanos Explorer and stored in the Smithsonian National Museum of Natural History (EX2205_D05_04B_A03 ; USNM-IZ-1674065 ). Additional pictures of living specimens observed during the same dive were used for morphological analyses and host availability.

Description

Body— Benthic ctenophore, compressed in the stomodeal plane, “U” shaped in the tentacular plane; two extendable aboral arms that lack oral grooves on opposing sides of body; distal ends of arms are flattened with a malleable outer margin that is capable of folding inwards, contains two openings, a singular gastric accessory opening, and a single smaller tentacular opening; overall body surface is smooth with no warts or visible papillae, exceptions are two to four pairs of globular gonads on the aboral face (number of gonads vary between individuals).

Size— 5mm in height, 7.6mm in tentacular length, 3mm in stomodeal length.

Coloration— Body yellow to goldenrod and translucent, intensity varying between individuals; tentacles white.

Statocyst— Sunken into a small pocket in body, not visible in a relaxed state.

Ctene Rows— Absent in specimens (mature and larval).

Tentacular Apparatus— Two tentacular apparatuses (one per aboral arm) within the innermost facing half of the arm; tentacle bulb spherical (d— 1.6mm), near the base of each arm; tentacle is simple, lacks tentilla, even thickness (d— 0.22–0.41mm) that gradually narrows to the distal end, ends in proximally crescentic tentacle root within tentacle bulb; coil counterclockwise when retracted into sheath; the shape and abundance of colloblasts were not documented

Gastrovascular System— Suboral cavity “U” shaped with three openings, a single downward-facing slit mouth, two accessory openings in each of the arm’s distal ends; 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, protrusions in distal end of arm become swollen in larger specimens.

Reproductive System— Six spherical gonads (d— 0.7–0.92mm) protruding from subepidermal pockets, four on one hemisphere, two on the adjacent hemisphere, encircle centralized statocyst on aboral face, do not extend beyond or into the aboral arms, t; male and female gonad tissue on adjacent sides of penetrating diverticula (see gastrovascular section for details); brooding pouches developing on one hemisphere of body (d— 0.46mm) as swollen extensions on the distal ends of the dichotomously branching subdiverticula.

Embryo— Not observed in collected samples

Ecology— Known only residing on the surface of deep-sea octocoral of the genus Adinisis , perhaps in an obligatory symbiotic relationship (it was not seen on nearby corals in the genera). The ecology of this platyctene species is otherwise unknown and requires future study.

Habitat— Azores at 42°20’22.9”N 29°08’59.3”W at a depth of 1061.43m

Host— Undescribed Adinisis sp. Usually occupies the upper third of the host organism.

Remarks— Similarly to T. tristoma and T. aff. tristoma (2018), T. aff. tristoma (2022) has almost identical internal and external morphological features with only slight variations in the size of both the brood pouches and gonads. However, these variations can be explained by the small size of T. aff. tristoma (2022) compared to other TJalfiella specimens, likely inferring an earlier developmental stage. Additionally, T. aff. tristoma (2022) differs from the aformentioned TJalfiella specimens by remaining yellow in color with a preference for Adinisis octocorals compared to Umbellula lindahli of T. tristoma and Acanella sp. of T. aff. tristoma (2018). As in remarks above, T. aff. ttristoma (2022) differs genetically from T. aff. ttristoma (2018) by an amount that is more consistent with the samples representing distinct but closely related species. Either of these putative species could be the true T. tristoma , but it is also possible that they represent two species distinct from T. tristoma .

Figures

FIGURE 5. Still images of living specimens of TJalfiella aff. tristroma (2022) with respect to host coral; A. In situ observation of the host coral Adinisis sp. Scale bar—2cm, B. Close-up still image of the collected host with several platyctenes in a retracted state. Scale bar—0.75cm, C. Tentacular view of two individual platyctenes separated from host coral.Arrows point to individual platyctenes on the collected Adinisis sp. Scale bar—0.5cm.

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 12. Illustrated Plate of TJalfiella aff. tristoma (2022) collected by NOAA: A. representation of specimens in their natural position on the stalk of Adinisis sp., B. mature T. aff. tristoma (2022), tentacular view, C. Stomodeal view of mature T. aff. tristoma (2022), D. cutaway illustration featuring internalized anatomy, tentacular view. E. view of the flattened face of the aboral arm, F. aboral schematic of the arrangement of diverticula and associating canals, Tj—TJalfiella aff. tristoma (2022), H—Host coral (Adinisis sp.), a.a.—aboral arm, a.f.—aboral face, 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.