Pseudopotamilla socialis Hartman, 1944

Tovar-Hernández, María Ana, León-González, Jesús Angel De & Hendrickx, Michel E., 2025, Polychaeta collected during the research cruises TALUD aboard the R / V “ El Puma ” in the Mexican Pacific: Sabellidae and Serpulidae, Zootaxa 5663 (1), pp. 1-80 : 59-65

Pseudopotamilla socialis Hartman, 1944

( Figs 32–35 , Table 4)

Pseudopotamilla socialis Hartman, 1944: 282–283 , pl. 42, figs 53–58.— Tovar-Hernández et al., 2019: 5, fig. 3C.

Potamilla socialis ?. — Gamboa-Contreras & Tapia-García, 1998: 108 (species list).

Material examined. UANL-8275: Gulf of California, Sinaloa, Ahome, Topolobampo, Marina Palmira , 25º35'57"N 109º3'29"W, 06 April 2021, 50 cm depth below dock surface, Coll. Tovar-Hernández, M.A. UANL-8276: same locality, St. TOP-A-Q-20210406-1 (dozens). UANL-8277: St. TOP-A-Q-20210406-2 (10 specimens among Scopalina sp. ); UANL-8278: same locality, St. TOP-A-Q-20210406-3 (dozens among Suberites aurantiaca ); UANL-8279: same locality, St. TOP-A-Q-20210408-9 (dozens among Halichondria aff. panicea ). UANL-8280: Gulf of California, Sinaloa, Ahome, Topolobampo, Embarcadero, 25°35.944'N 109°02.894'W, 10 August 2011, intertidal scraped, Coll. Aguilar-Camacho J.M. & Yáñez-Rivera B., 6 specimens. UANL-8281: Gulf of California, Sinaloa, Mazatlán, dock “El Puma”, St. MZT-S-20210424-1, 23º10'53.47"N 109º25'27.40"W, 24 April 2021, 1 m below dock surface, Coll. Tovar-Hernández, M.A., 2 specimens.

Description of material examined (n: refer to the number of specimens measured). Body long, slender ( Fig. 31A ). Thorax 1.3–2.7 mm long (n: 14), 0.4–1 mm wide (n: 14). Branchial crown 1.5–3.5 mm long (n: 14) with 7–9 pairs of radioles (n: 14). Thorax with 7–11 chaetigers (n: 14). Abdomen with 37–52 chaetigers (n: 2). Radiolar eyes formulae highly variable ( Table 4). Relation between radioles with eyes and total number of radioles: 0/7 to 5/9 (n: 22), being 4/8 the most common pattern (n: 6). Branchial crown asymmetrical with longest radioles dorsally, then decreasing towards ventralmost radioles, which are 1/4 of the length of the dorsalmost radiolar pair ( Figs 32B , 33A ). Radiolar lobes short, with dorsal and ventral flanges: dorsal pair rectangular, erect, ventral pair rounded ( Fig. 33F ). Radiolar flanges and palmate membrane absent. Pinnules arranged in two alternating rows, longest at the mid-radiolar length. Radiolar tips short, as long as space of three pinnules width ( Fig. 33D ). Compound radiolar eyes proximal (basal half of branchial crown), absent in dorsal-most pair ( Fig. 32B ); spherical to oval, unequal in size and number ( Figs 32B , 33C , Table 4). Anterior peristomial ring partially exposed dorso-laterally between dorsal pockets and lateral collar margin ( Fig. 32C–D ). Posterior peristomial ring collar with dorsal margins fused to faecal groove ( Fig. 32D ); mid-dorsal margins low, not longer than the base of radioles ( Fig. 32D ). Ventral lappets triangular, divided mid-ventrally by short incision ( Fig. 32E–F ). Peristomial eyes present ( Fig. 33B ). Dorsal lips triangular, erect, with mid-rib radiolar appendages ( Fig. 33E ); ventral lips short, rounded ( Fig. 33F ). Ventral sacs present. Chaetiger 1: two rows of broadly-hooded notochaetae. Ventral shield of collar rectangular, slightly divided transversely, higher than the following thoracic shields ( Figs 32F , 33A ). Chaetigers 2–7, 8, 9, 10 or 11: ventral shields rectangular, divided transversely in two equal parts; tori not contacting ventral shields (separated by a reduced space) ( Figs 32E–F , 33A ); superior notochaetae elongate narrowly hooded; inferior ones paleate, arranged in two rows, with pointed mucro ( Fig. 34J ). First thoracic torus with 13–15 neuropodial uncini (n: 10), diminishing gradually in number towards the last posterior thoracic chaetiger, where there are 7–9 uncini (n: 10) ( Fig. 35A–C ). Neuropodial avicular uncini with several rows of small, similar sized teeth above main fang, breast well developed. Uncini from anterior thoracic chaetigers with handles as long as 2.25 times the length of main fang, a high crest and short neck (as long as 1/2 the length of main fang) ( Fig. 34B–C, E ). Uncini from the last two thoracic chaetigers with handles longer than those of anterior segments: handle as long as four times the length of main fang, a lower crest than those of anterior segments and a longer neck (as long as 3/4 the length of main fang) ( Fig. 34F–G, I ). Companion chaetae with symmetrical membranes, teardrop-shaped ( Fig. 34D, H ), and long handles, as long as handles of uncini. Abdominal neurochaetae elongate broadly-hooded ( Fig. 34A, M ). Notopodial uncini with several rows of teeth above main fang with a high crest, breast well developed, handles short, as long as the length of main fang ( Fig. 34K–L ). Pygidium bilobed. Tubes 28–34 mm long (n: 4), narrow 0.8 mm diameter (n: 4), composed by fine sand ( Fig. 32A ), some covered with sponges, ascidians, members of Hydrozoa and Bryozoa attached in the external wall. Asexual reproduction by architomy. Posterior part of abdomen were found broken by fission, and some buds were found regenerating branchial crowns and posterior ends.

Methyl green staining pattern. Ventral shield of collar and thoracic shields stains deep blue uniformly. Two remarkable thin, white rectangles in anterior margin of ventral shield of collar ( Fig. 35D–G ). In collar, some scattered blue spots present in lateral areas of lappets.

Variation. Radiolar formula is highly variable in specimens from Topolobampo ( Table 4), not only in the number of eyes per specimen (considering the right branchial lobe only) but also in the number of radioles containing eyes. The highest number of eyes per specimen was 10 (radiolar formula x4321xxx) in a large specimen with thorax 2–7 mm long, 0.7 mm wide, branchial crown 3.4 mm long, compared with only one eye per specimen (radiolar formula x1xxxx), or even zero eyes per specimen (radiolar formula xxxxxxx). The specimen without eyes is small (thorax 1.5 mm long, 0.7 mm wide, branchial crown 1.5 mm long). The number of radioles with eyes varies from only one radiole with eyes (eye present in one of six radioles: 1/6) to five radioles with eyes (eyes present in five of nine radioles: 5/9).

Remarks. Pseudopotamilla Bush, 1905 is a genus characterized by the presence of remarkable compound radiolar eyes, except in the dorsalmost radiolar pair ( Capa et al. 2019). Some species of Pseudopotamilla are known to bore in hard limestone, dead coral, barnacles and mollusks shells ( Chughtai & Knight-Jones 1988; Knight-Jones et al. 2017).

The number of valid species described in Pseudopotamilla is 23 ( Tovar-Hernández et al. 2020) but the status of some nominal species is still questionable. In the case of species of Pseudopotamilla from North America, four were described from Temperate Northern Pacific ( P. debilis Bush, 1905 , P. intermedia Moore, 1905 , P. occelata Moore, 1905 , and P. socialis Hartman, 1944 ). Pseudopotamilla reniformis (Bruguiére, 1798) has been widely reported in the Mexican Pacific (e.g., Hernández-Alcántara & Solís-Weiss 1999 as Potamilla ; Prado-Navarro et al. 2016; Bastida-Zavala et al. 2022) but the distribution of the species seems to be restricted to Iceland, northern Norway, Scotia and Newfound ( Knight-Jones et al. 2017). For the TALUD project, P. intermedia was reported previously by Méndez (2006, 2013).

Tovar-Hernández et al. (2019) included new records of P. socialis as fouler in hulls and docks from La Paz (SW Gulf of California), but a diagnosis or description was not provided due the nature of the publication (an annotated list). In the present study, the records of P. socialis from dock fouling in the Central Gulf of California are reported here in order to provide a description and evidences about the high variability of radiolar eyes formulae, which variation is most probably due to ontogeny; consequently, the number and distribution of eye should be taken with precaution when describing and comparing species in Pseudopotamilla , particularly when few specimens are available for examination.

Pseudopotamilla socialis was originally described from an intertidal habitat, among sponge masses at Tomales Point (Central California, USA) ( Hartman 1944). Specimens from the Gulf of California were also found growing among sponges, ascidians, bryozoans, and hydrozoans in docks. There are no detailed or illustrated reports of Pseudopotamilla socialis since its original description by Hartman (1944) but Contreras & Tapia-García (1998) enlisted “ Potamilla socialis ( Hartman, 1944) ” from the inner continental shelf of the Gulf of Tehuantepec (Oaxaca, SW Mexico), a record than posteriorly was referred to as “ Perkinsiana socialis ( Langerhans, 1884) ” by Bastida-Zavala et al. (2022: 105), thus demanding a clarification.

Abiotic conditions. The specimens of P. socialis were collected in shallow water, 0.5–1.0 m below surface, at the base of three sponges ( Halichondria aff. panicea ( Pallas, 1766) , Scopalina sp. and Suberites aurantiaca ( Duchassaing & Michelotti, 1864)) or among massive mats of the invasive ascidians, bryozoans and hydrozoans, under the following environmental conditions. Temperature: 24–26°C; salinity: 35–40.

Distribution. California, USA ( Hartman 1944), southern Gulf of California ( Tovar-Hernández et al. 2019), and

Central Gulf of California (present study) .

Figures

FIGURE 31. Potamethus pepei sp. nov. A) Thoracic notochaetae, B) superior group of notochaetae (elongate, narrowly hooded), C) inferior group of notochaetae (paleate chaetae), D) thoracic uncini and companion chaetae, E) thoracic acicular uncini, arrow points to hump, F) thoracic uncini and companion chaetae, G) companion chaetae, H) abdominal chaetiger, I) short group of narrowly hooded chaetae, J) abdominal uncini. Scale bars: A, F, H) 100 μm; B) 50 μm; C–E, G, I–J) 20 μm. A–J) holotype ICML-EMU-14048.

FIGURE 32. Pseudopotamilla socialis Hartman, 1944. A) Worm partially inside its tube, B) radiolar crown, dorsal view, C) thorax, lateral view, D) same, dorsal view, E) same, ventral view, F) radiolar crown and thorax, ventral view. Scale bars: A) 0.3 mm, B) 0.7 mm, C) 0.6 mm, D–F) 1 mm. A–D) UANL-8277 specimen 9, E–F) UANL-8277 specimen 10.

FIGURE 33. Pseudopotamilla socialis Hartman, 1944. A) Radiolar crown and thorax, ventral view, B) peristomial eyes, C) compound radiolar eyes pointed with arrows, D) radiolar tip, E) triangular dorsal lip with mid rib support and blood vessel, F) ventral lip and ventral flange of base of radiolar lobe. Abbreviations: dl—dorsal lip, bv—blood vessel, pe—peristomial eyes, vf—ventral flange, vl—ventral lip. Scale bars: A) 0.7 mm, B) 0.4 mm, C) 0.08 mm, D) 0.2 mm, E–F) 0. 4 mm. A–F: UANL- 8277.

FIGURE 34. Pseudopotamilla socialis Hartman, 1944. A) Last four thoracic chaetigers and first abdominal chaetiger, B) uncini from thoracic chaetiger 2, C) detail of crest, main fang, neck and breast from thoracic chaetiger 2, D) companion chaetae from thoracic chaetiger 2, E) detail of crest of thoracic uncini from thoracic chaetiger 2, F) uncini from last thoracic chaetiger (chaetiger 9), G) detail of crest, main fang, neck and breast from last thoracic chaetiger (chaetiger 9), H) companion chaeta from last thoracic chaetiger (chaetiger 9), I) detail of crest from last thoracic chaetiger (chaetiger 9), J) thoracic chaetiger 2 with superior notochaetae elongate narrowly hooded and inferior ones paleate with pointed mucros, K) uncini from first abdominal chaetiger, L) detail of crest of uncini from first abdominal chaetiger, M) abdominal chaetiger with elongate broadly-hooded chaetae. Abbreviations: A1—abdominal chaetiger 1, T6–T9—thoracic chaetigers 6 to 9. Scale bars: A) 0.2 mm, B–D, G–H, K) 22 μm, E, I, M) 10 μm, F) 50 μm, J, L) 30 μm. A–M: UANL-8277.

FIGURE 35. Pseudopotamilla socialis Hartman, 1944. A) Thoracic chaetigers, lateral view, B) detail of torus in chaetiger 2, C) detail of torus in chaetiger 11, D–E) methyl green staining pattern in different specimens. Abbreviations: numbers 1 to 11—refers to number of thoracic chaetigers. Scale bars: A, D–G) 0.4 mm, B–C) 0.2 mm. A–E: UANL-8277.