Loxosoma discoides, Roldán & Villalba & Viéitez, 2019

Roldán, Carmen, Villalba, Antonio & Viéitez, José M., 2019, A new solitary, interstitial species of Loxosomatidae (Entoprocta) from the coast of Galicia (NW Spain), Loxosoma discoides n. sp., Zootaxa 4604 (2), pp. 388-394 : 390

Loxosoma discoides n. sp.

Figs. 2–15

urn:lsid:zoobank.org:act:2470BF85-F6E0-41C4-813B-CC712D2BB822

Type material. Holotype: MNCN 26.01/10 Combarro Beach ( Ria of Pontevedra ) 42 o 26’N, 8 o 42’ W, intertidal, February 1976 . 24 Paratypes: MNCN 26.01 /11 Combarro Beach ( Ria of Pontevedra ) 42 o 26’N, 8 o 42’ W, intertidal, February 1976 . 3 Paratypes: MNCN 26.01/12 Meira Beach ( Ria of Vigo ) 42 o 17’ N, 8 o 43’W, intertidal, June 1976.

Etymology. The specific epithet refers to the disc shape of the calyx.

Description. Body length of 500–1300 µm and stalk length of 307–450 µm. Regarding the holotype ( Fig. 2 ), its body length is 1264 µm long and the stalk length 441 µm. The calyx is large, with two wide wings conferring disc shape, thus giving the whole specimen a “table-tennis bat” appearance ( Figs. 2–4 ). The wings arise as lateral expansions from the basal area of the stalk, totally surrounding the atrium. The calyx and the wings show an epidermis covered with a cuticle and an internal mesenchyme ( Fig. 5 ). The atrium is enclosed by a crown with 16–21 tentacles ( Figs. 5, 6 ). The long stalk slightly enlarges at the end forming a sucking disc ( Figs. 2–4, 7 ). A foot gland was not observed but small lappets with gland cells were seen in radial array at the stalk end ( Figs. 8, 9 ). The whole body has strong, mainly longitudinal musculature, but well-developed crossed diagonal musculature occurs in the transition between calyx and stalk ( Fig. 10 ). Six rows of gland cells are found along the stalk, three of them frontal and the other three abfrontal ( Fig. 11 ). The stomach is a large sac ( Fig. 12 ), with two well-developed lateral pockets ( Fig. 4 ).

Buds of different developmental stages are found in many specimens ( Figs. 2, 4, 6 , 13 ). The buds arise in the anterolateral areas, at the level of the upper part of the stomach. No seasonal pattern of bud occurrence was observed. One or two pedunculated, elongate, drop-shaped structures are found at the frontal side near the basal end of the stomach of some specimens ( Figs. 2 , 14, 15 ). They consist of a monolayer of epidermal cells covered with a cuticle, like that of the calyx. The epidermal layer is very thin in the distal part, but quite thick at the peduncle. Below the epidermal cells, the structures have a cavity divided in two chambers by a transverse wall; the cavity is filled with tightly packed, acidophilic granules. The mesenchyme of these organs is continuous with that of the calyx ( Fig. 15 ).

Habitat. The specimens of this new species, which is interstitial, were collected in the intertidal zone of the beaches of Meira and Combarro (Galicia, NW Spain) ( Fig. 1 ) at tidal level between +0.5 and + 1.6 m. The substrate consisted of fine or medium sand with moderate selection coefficient; it showed an average organic content of 0.5%, and its porosity oscillated between 44% and 47%; the recorded salinity of interstitial water was around 34%.

Figures

FIGURE 1. Map of the Iberian Peninsula showing the locations, Combarro and Meira beaches, where the specimens of Loxosoma discoides n. sp. were collected.

FIGURES 2–7. Morphological features of Loxosoma discoides n. sp. 2. Light micrograph of a frontal view of the holotype specimen MNCN 26.01/10 showing the stalk (S), with a shucking disc (Sd) at the end, and the calyx with two wings (W), one bud (B) and two pedunculated, pointed structures resembling flasks organs (Fo). 3. Scanning electron micrograph of the frontal view of another specimen. 4. Light micrograph of the frontal view of another specimen in which the lateral pockets (Lp) of the stomach are shown. 5. Light micrograph of a histological transversal section showing the atrium (A) enclosed by a crown of tentacles (T) and a section of the rectum (R) containing faecal material. 6. Light micrograph of the frontal view of an area of the calyx showing two buds (B) and the atrium (A) enclosed by tentacles (T). 7. Light micrograph of a histological longitudinal section showing the large stomach (St), containing ingested food, and tentacles.

FIGURES 8–15. Morphological features of Loxosoma discoides n. sp. 8. Light micrograph of a frontal view of the end of the stalk showing the sucking disc (Sd) with lappets (L) in radial array. 9. Light micrograph of a histological longitudinal section at the sucking disc (Sd) level showing abundant gland cells (Gc). 10. Light micrograph of a frontal view of a specimen at the stalk-calyx transition level showing crossed diagonal musculature (Cdm). 11. Light micrograph of the stalk showing two rows of gland cells (arrows) along the stalk. 12. Light micrograph of a histological longitudinal section showing the digestive tract, including the mouth (M) in the atrium (A), the oesophagus (O), the stomach (St) and the rectum (R) enclosing faecal material, which leads to the atrium through the anus. 13. Scanning electron micrograph showing a bud. 14. Scanning electron micrograph showing a pedunculated, pointed structure resembling a flask organ. 15. Light micrograph of a histological longitudinal section showing a pedunculated, pointed structure resembling a flask organ; the arrows point out the continuity between calyx epidermis and that of the flask organ-like structure; note the continuity (arrowhead) between the calyx mesenchyme and the inside of the flask organ-like structure.