Paraphelliactis labiata De Melo & Targino & Gomes 2020, n. sp.

Paraphelliactis labiata n. sp.

(Figs. 2A, 3–5, Tables 1–3)

urn:lsid:zoobank.org:act: 72B664B0-6E14-4610-99FF-42374AD8B8F1

Material examined. Holotype: MNRJ 9095 (one specimen), South Atlantic Ocean, Potiguar Basin, Rio Grande do Norte, Brazil, station MT84 (04° 25.8308’ S, 036° 37.3678’ W), May 6, 2011, 1964-2045m. Paratypes: MOUFPE- CNI 868 (one specimen), South Atlantic Ocean, Potiguar Basin, Rio Grande do Norte, Brazil, station MT 85 (04° 21.3580’S, 036° 44.2730’W), May 4, 2011, 2025–2057m. LC 141 (one specimen), South Atlantic Ocean, Potiguar Basin, Rio Grande do Norte, Brazil, station MT 85 (04° 21.3580’S, 036° 44.2730’W), May 4, 2011, 2025–2057m

Description.

External morphology (Figs. 2A, 3). Column 11 mm to 84 mm in height and 12 mm to 99 mm in width (Figs. 2A, 3 A–B). Body cylindrical, wider than tall. Color a pure white in most of the column, abruptly changing to pale pink towards the aboral side. Base spreads beyond a tapered end but never exceeds the maximum diameter of the animal, hence the body takes a very singular cup shape no matter its size. Column divisible into a strongly tuberculated scapus and a short, smooth scapulus, without cinclides. Tubercles of the scapus conical, pointed, some with very flat with tips withdrawn and longitudinal grooves, not ordered in rows (Fig. 3 A–B). Tubercles are larger at midcolumn and towards the upper scapus, although smaller tubercles are also present near the limbus and at the scapus-scapulus boundary (Fig. 3C). A yellowish cuticle visible between the tubercles in some places. Scapulus thin and concealed due to the retraction of the oral disc. Endocoelic and exocoelic spaces visible as rays running from scapulus to mouth. Oral disc bilobed and broad, with a central oval mouth; mouth remains wide open. Lobes of oral disc unequal in size, usually overlapping (Fig. 3B).

Tentacles slender, short, about 140 in number, without basal mesogleal thickenings, arranged in five peripheral cycles hidden inside the terminal fold of the scapus. Those of the inner cycles longer than those of the outer cycles. In the smaller individual, tentacles number approximately 90, with some clearly missing.

Internal anatomy (Fig. 4). Two deep siphonoglyphs each attached to a pair of directives (Fig. 4C). Slender mesenteries, hexamerously arranged in five cycles (6+6+12+n+n). First three cycles complete, with all mesenteries present. In counterpart, fourth and fifth cycles incomplete, with the number of mesenteries varying among individuals, but always fewer than expected for a regular hexamerous arrangement. More mesenteries distally than proxi- mally. In the smaller individual, there are 80 near the margin, and 72 at the base level and in the larger individual there are approximately 100 at the margin and 78 to 81 at the limbus. Mesenterial filaments more developed on the older mesenteries than on younger ones. The incomplete fourth and fifth cycles have very small mesenteries. The last one is visible as tiny, unpaired projections, merely breaking through the mesoglea and present throughout the column (Fig. 4 D-E). Mesoglea of equal thickness in both endocoelic and exocoelic spaces at the oral disc region. Sphincter mesogleal, weak, restricted to the central part of the mesoglea where it occupies about a quarter of its space at the upper portion but abruptly tapers downwards (Fig. 4A). Muscular processes of the sphincter form somewhat sparse, not very marked bands, tending to align vertically. Longitudinal muscles of the tentacles weak, ectodermal (Fig. 4B). Retractor weak, diffuse, stronger at the distal part of the mesenteries (Fig. 4D). Parietobasilar muscles weak. Radial musculature of the oral disc ectodermal. Acontia present but rare, probably associated with the second cycle of mesenteries. No gametogenic tissues found.

Cnidom. Spirocysts, Basitrichs, Microbasic p -mastigophores (Fig. 5, Table 2).

Type locality. Potiguar Basin, Rio Grande do Norte, Brazil.

Biological characteristics. Individuals originally attached to manganese nodules or slivers of wood (Fig. 3D).

Etymology. The specific epithet “labiata” (from Latin: lips) alludes to the bilobed appearance of the oral disc, resembling a set of lips.

Taxonomic remarks. The presence of a thick cuticle covering most of the body wall has been reported from all species of Paraphelliactis. Although small fragments of a yellowish cuticle were observed in our specimens,

these fragments were few and restricted to the limbus and some cracks between the tubercles. The almost complete lack of cuticle could be explained by high abrasion from sediment, due to the method of collection. Carlgren (1949) stated that Paraphelliactis probably possess more tentacles than mesenteries at the base. An interesting feature not mentioned by Carlgren’s key (1949) but reported for most of Paraphelliactis species is the occurrence of an incomplete fifth cycle of mesenteries (except for Pa. tangi Li & Xu, 2016, which exhibits all five cycles complete). Li & Xu (2016) describe a small paratype for Pa. tangi, with only four cycles of mesenteries. However, this last cycle is fully complete, corroborating the distinct pattern of mesenterial development for the species and showing that the total numbers of such structures may vary according to the individual life stages. Although all our specimens differ in size and development, they have identical body shapes and share the same mesenterial arrangement pattern (five cycles with the last two incomplete), due to this is very unlikely that Pa. labiata is a juvenile of another species of the genus.

Comparison of Pa. labiata n. sp. with other species of Paraphelliactis

The type species of Paraphelliactis, Pa. spinosa Carlgren, 1928, and the later-described Pa. michaelsarsi Carlgren, 1934, were originally recorded for the North Atlantic Ocean. Two more species were registered from the Pacific Ocean, Pa. pabista Dunn, 1982 from the west coast of North America and Pa. tangi, collected near the Yap Trench at the western Pacific, totaling four valid species within the genus.

This newly described species differs from its congeners in having the last two cycles of mesenteries incomplete, rather than just the fifth. In addition, the number of tentacles combined with the arrangement of the tubercles, and also the absence of basal thickenings in the tentacles differentiates the new species from its congeners (see Table 3). Paraphelliactis labiata n. sp. does not exhibit the characteristic hooked tubercles of Pa. spinosa. Although well detailed, the original description of Pa. michaelsarsi was of a single specimen in very poor preservation, and is therefore limited in some aspects, as pointed by the author himself (Carlgren, 1934). Nonetheless, Pa. labiata n. sp. differs from Pa. michaelsarsi by the presence of a smaller category of nematocysts (basitrichs) in the actinopharynx and tentacles and by possessing a very clear differentiation between the scapus and scapulus region vs. indistinct differentiation of the column in Pa. michaelsarsi. Paraphelliactis labiata n. sp. can be easily distinguished from Pa. pabista on the arrangement of the tubercles (not arranged in rows vs. arranged in rows in the latter). Our new species share a few characters with the lately described Pa. tangi (e.g. the absence of mesogleal thickenings at the base of the tentacles), but the latter is distinct from all the other species of Paraphelliactis, including Pa. labiata, in having an equal number of mesenteries throughout the column and a complete fifth cycle of mesenteries.