A new species of Pompholyx (Rotifera: Monogononta: Testudinellidae) from the United States Author Araujo, Thiago Q. Department of Biology, University of Massachusetts Lowell, Lowell, MA, USA; Author Walsh, Elizabeth J. Department of Biological Sciences, University of Texas at El Paso, El Paso, TX, USA; Author Wallace, Robert L. Department of Biology, Ripon College, Ripon, WI, USA Author Hochberg, Rick Department of Biology, University of Massachusetts Lowell, Lowell, MA, USA; text Journal of Natural History 2024 J. Nat. Hist. 2024-07-09 58 25 - 28 784 795 http://dx.doi.org/10.1080/00222933.2024.2345927 journal article 10.1080/00222933.2024.2345927 1464-5262 13219746 Pompholyx faciemlarva Araújo, Walsh, Wallace and Hochberg sp. n. ( Figures 2–6 ) ZooBank: urn:lsid:zoobank.org:act: 99CBE73C-C91C-42E2-9C98-1CAEB5C30387 . Material examined Eleven specimens were examined using light microscopy; measurements were taken with an ocular micrometer. All specimens were mounted and photographed and/or digitally recorded. The type specimen was documented, as is permitted digitally recorded: digital type documentation is allowed by The International Code of Zoological Nomenclature , namely in article 73.1.4 ( The International Commission on Zoological Nomenclature 1999), even when the documented specimen has been lost. The type photomicrographs are available at the Smithsonian National Museum of Natural History under accession numbers USNM 1606876 ( holotype ) and USNM 1606877 , USNM 1606878 , USNM 1606879 , USNM 1606880 , USNM 1606881 ( paratypes ). Ten other specimens were examined using SEM. Differential diagnosis Pompholyx faciemlarva sp. n. can be distinguished from P. complanata , P. sulcata and P. triloba by the presence of transverse furrows on its lorica, the structure of the stalk gland (3-lobed), and the number and symmetrical arrangement of unci teeth in the trophi. There are 17 teeth on each side in the new species, compared to 17–20/18–21 (right/left) in P. sulcata (the only other species with a complete description). Etymology The species name is an adjectival name derived from the form of the rotifer’s corona, which resembles the mask used by scuba divers (∞-shaped) ( Figure 3B ): face (Latin: faciem ) and mask (Latin: larva ). Description The description is based on an adult specimen of 110 µm (95–125 µm) body length. The body shape is ellipsoid, but with a flat anterior margin and rounded triangular posterior end. The corona is complete, ∞-shaped, and bears two dorsolateral red eyes ( Figures 2A , 3B , 4D , 6A ). Coronal cilia are approximately 8–20 µm long. In cross section, the smooth and mostly featureless lorica is arched dorsally and with flared lateral edges ( Figures 2A , 3B , 6 ). SEM reveals a fine network of fibres across parts of the lorica, but these may be artefacts of fixation ( Figure 6 ). A large transverse furrow extends laterally across the body on both dorsal and ventral sides around mid-body length. The furrow is present in all living specimens when swimming and does not change when animals are anesthetized; the furrow remains in preserved animals. An occipital convexity (edge) is present just posterior of the corona on the dorsal side. The ventral lorica surface is smooth, but narrower in width than the dorsal surface: it is 80 µm long and has an inverted triangle shape with a 53 µm wide anterior border and a 19 µm wide posterior tip. A pectoral concavity (notch) just posterior to the corona is present on the ventral surface ( Figures 2B , 3C ). A ciliated sub-labium extends from the pectoral concavity during locomotion. The posterior end has a terminal 6 µm diameter cavity that leads to the cloaca ( Figure 6B–D ), which is rectangular in shape and ~20 µm long ( Figures 2C , 4B ). The cloaca has three openings to the blastocoel: one for the stalk gland, one to the anus, and one for oviposition ( Figure 2C ). Figure 2. Schematic illustrations of Pompholyx faciemlarva sp. n. (A) Dorsal view; (B) ventral view; (C) internal view; (D) trophus. Abbreviations: bt, buccal tube; cf, lorica furrow; cl, cloaca; co, corona; e, eye; f, fulcrum; gg, gastric glands; gt, Gossesche thread; i, intestine; m, manubrium; mo, mouth; pn, protonephridia; r, rami; rc, round (unidentified) cells; sg, stalk gland; st, stomach; t, trophi; vit, vitellarium; vs, ventral surface; u, unci. Figure 3. DIC microphotograph of Pompholyx faciemlarva sp. n. (A) Dorsal arch view; (B) middle dorsal view; (C) ventral view; (D) lateral view. Abbreviations: cf, lorica furrow; cl, cloaca; co, corona; e, eye; gt, Gossesche thread; i, intestine; mo, mouth; pn, protonephridia; rc, round (unidentified) cells; st, stomach; t, trophi; vs, ventral surface. Figure 4. DIC microphotograph of internal anatomy of Pompholyx faciemlarva sp. n. (A–D) Different focal planes of ventrolateral body view. Abbreviations: co, corona; e, eye; i, intestine; n, nucleus; pn, protonephridia; rc, round (unidentified) cells; sg, stalk gland; st, stomach; t, trophi; vit, vitellarium. Corona. The corona is ∞-shaped (i.e., it resembles a number 8 lying on its side or a scuba diving mask) and ciliation is complete. Cilia appear to be of a mostly uniform length of 6– 18 μm. Small patches of presumable sensory cilia are present in the apical field. A ciliated sub-labium is present on the ventral surface just posterior of the mouth within the pectoral notch. Digestive tract. Terminal mouth is somewhat ventral in position, but still within the coronal field. The mouth leads to a 30 µm long ciliated buccal cavity that has an inverted pear-shape. The ciliated stomach has two salivary/gastric glands connected to the anterior part of the stomach. The intestine is 20 µm in total length and has two sphincters: one sphincter demarcates the transition from the stomach to the intestine; the second sphincter demarcates the transition from the intestine to the cloaca ( Figures 2C,D , 3B , 4B,E , 6B,C,D ). No bladder was observed. Trophi. Trophi malleoramate. The rami are 13 µm long and have an elongatetriangular shape with rounded latero-ventral margins, delimiting large latero-ventral fenestrae ( Figure 5D ). The fulcrum is elongate and straight (11 µm). The unci plates consist of 16 right and 17 left (frontal view) weakly curved and strongly webbed asymmetrical teeth (lengths: 5–7 µm). The crescent-shaped manubria are 15 µm long and composed of superimposed dorsal, median, ventral, and small sub-ventral chambers ( Figures 2C,D , 5 ). Figure 5. Trophi of Pompholyx faciemlarva sp. n. (A–C) DIC microphotographs. (A) Frontal view; (B) focal plane between frontal and caudal view; (C) caudal view. (D,E) SEM false colour-coded microphotographs. (D) Caudal view; (E) slightly internal view of the ramus. Abbreviations: as, arched rami scleropili; dc, dorsal chamber; fu, fulcrum; mc, median chamber; r, ramus; rf, ramus fenestra; svc, subventral chambers; u, uncus; vc, ventral chamber. Female reproductive system. Vitellarium is syncytial with at least 12 nuclei ( Figures 2C , 4D ). Germarium not observed. Amictic eggs are oviposited one at a time and retained by the female at her posterior end. Each egg is approximately 50 µm in diameter and connected to an adhesive string that is secreted internally by a stalk gland and protrudes out the cloaca ( Figures 2 , 3 , 4A,D ). Protonephridia. One pair of protonephridia is present in each lateral body margin; these extend to the region around the posterior intestinal sphincter ( Figures 2C , 4C ). Other structures. An interconnected chain of large cells (6 µm) is located close to the stomach and appears to attach to the stomach wall ( Figures 2C , 3D , 4B ). The cells are not ova; their function is undetermined. A stalk gland is present on the ventral side. The gland has at least three apical lobes (total length: 8 µm) and secretes a sticky thread (‘Gossesche thread’) approximately 80 µm long that passes through the cloaca to attach to a single amictic egg. At least two muscles insert on or close to the stalk gland and function to release or retract the adhesive thread, thereby moving the egg farther from or closer to the cloaca ( Figures 2C , 3B , 4A,D ). No more than one amictic egg was ever observed being carried by an adult female. Figure 6. SEM microphotographs of Pompholyx faciemlarva sp. n. (A,B) Dorsolateral view; (C) ventrolateral view; (D) ventral view. Abbreviations: cl, cloaca; co, corona; dao, dorsal antennae opening; lao, lateral antennae opening. Ecology and distribution Pompholyx faciemlarva sp. n. was found in Flint Pond, Tyngsborough, MA, USA , during the summer months ( June–September 2022 ). This pond has a rich submerged macrophyte community and the plankton was abundant, comprising at least 11 genera of rotifers and numerous other zooplanktonic taxa. The new species is common, but not abundant. Its collection from the surface waters (< 1 m depth) of the pond suggests it is fully planktonic. Other common rotifers from the same collections include the following: Asplanchna priodonta Gosse, 1850 , Asplanchnopus multiceps ( Schrank, 1793 ) , Brachionus angularis Gosse, 1851 , Hexarthra sp. , Keratella cochlearis ( Gosse, 1851 ) , Kellicottia sp. , and Polyarthra spp.