Streblospio papillaris, Quintal-Aké & Peraza, 2025

Streblospio papillaris sp. nov.

Figures 2A–H View FIGURE 2 ; 3A–I View FIGURE 3 ; 4A–E View FIGURE 4

Type material. Caribbean Sea: Chetumal Bay, Quintana Roo, mouth of the Hondo River , ( 18°29'18.7"N 88°18'52.4"W) 2 April 2019, coll. Víctor Hugo Delgado Blas, holotype (LACM-AHF-Poly 16670); north of Tamalcab Island , ( 18°37'32.7"N 88°11'27.1"W), intertidal, 9 May 2021, coll. Marisol Betancourt and Víctor Hugo Delgado Blas , 2 paratypes ( ECOSUR-SEM); small square mega-sculpture, 18°30'05.6"N 88°16'51.7"W, intertidal, 9 May 2021, coll. Marisol Betancourt and Víctor Hugo Delgado Blas, 2 paratypes (LACM-AHF-Poly 16671) GoogleMaps .

Description. Holotype complete, 5.9 mm long, 0.3 mm wide with 42 chaetigers; 5 paratypes complete, 2.9–5.5 mm long, 0.6 mm wide with 27–40 chaetigers; 1 paratype incomplete, 4.7 mm long, 0.2–0.6 mm wide with 38 chaetigers. Color in alcohol yellowish ( holotype) to pale white. The entire body is covered in numerous papillae ( Figs 3F View FIGURE 3 ; 4A, B View FIGURE 4 ).

Prostomium fusiform, rounded anteriorly ( Fig. 2A View FIGURE 2 ), with prostomial peak ( Fig. 2B View FIGURE 2 ); posteriorly blunt, extending to anterior margin of chaetiger 1. Eyes absent. Palps in the mid-lateral of prostomium ( five paratypes with palps lost). Palps short, extending to chaetigers 2–3 ( holotype 3), densely ciliated on frontal, latero-frontal and lateral surfaces. Peristomium large, expanded laterally and longitudinally, almost covering anterior region of prostomium ( Figs 2A View FIGURE 2 ; 4B, C View FIGURE 4 ), and extending around base of palps, forming moderate lateral wings, fused dorsally onto chaetiger 1 ( Fig. 4C View FIGURE 4 ).

One pair of thick, flattened branchiae on chaetiger 1, just posterior to palps; inner surfaces wrinkled and heavily ciliated; branchiae long with pointed apexes ( Fig. 2D View FIGURE 2 ), extending up to chaetigers 4–5 ( holotype 5), thicker and longer than palps. Small conical papilla on chaetiger 1 between branchiae ( Figs 2D View FIGURE 2 , 4B View FIGURE 4 ).

Parapodia on chaetiger 1 with neuropodial postchaetal lamellae only; notopodial lamellae lacking, but with 1–2 smooth, short, slender, alimbate capillaries ( Fig. 4C View FIGURE 4 ). Neuropodial postchaetal lamellae on chaetiger 1 short, subtriangular ( Figs 2E View FIGURE 2 , 4C View FIGURE 4 ), with 3–5 capillaries, and with a similar morphology to the notopodial capillaries. Notopodial postchaetal lamellae on chaetiger 2 dorsally rounded, wide ( Fig. 2E View FIGURE 2 ), united across dorsum, forming a low membranous dorsal collar or pouch ( Fig. 2C, F View FIGURE 2 ); anterior margin of pouch hooded and open anteriorly, and posterior edge may extend to chaetiger 3 ( Fig. 2C, F View FIGURE 2 ). Notopodial postchaetal lamellae on chaetigers 3–7 small, rounded ( Fig. 2E View FIGURE 2 ) with dorsal edge elongated and extending further towards dorsal region ( Fig. 2E View FIGURE 2 ), becoming rounded, small on subsequent segments ( Figs 2G, H View FIGURE 2 , 3G View FIGURE 3 , 4D View FIGURE 4 ); from chaetigers 4–5 lamellae progressively reducing in size and disappearing completely around chaetiger 28. Notopodial prechaetal lamellae absent.

Neuropodial postchaetal lamellae largest on chaetiger 2, oval ( Figs 2E View FIGURE 2 , 4C View FIGURE 4 ); abruptly reducing in size on chaetiger 3 ( Figs 2E View FIGURE 2 , 4C View FIGURE 4 ). Neuropodial lamellae rounded on chaetigers 3–5 ( Fig. 2E View FIGURE 2 ), progressively reducing in size from chaetiger 4 until disappearing around chaetiger 11. Neuropodial prechaetal lamellae absent throughout body. Interparapodial pouches lacking.

All notopodial and neuropodial capillaries arranged in one row; capillaries on anterior chaetigers slightly granulated, unilimbate. Notopodial capillaries on chaetiger 1 very small and slender, from chaetiger 2 with very long, pointed, thick, unilimbate chaetae ( Fig. 3A View FIGURE 3 ), longest and thickest on chaetiger 3–7, gradually thinner and smaller on following chaetigers; posterior chaetigers with very long, thin and slightly granulate chaetae ( Fig. 3B View FIGURE 3 ), longer than those on anterior chaetigers. Neuropodial capillaries similar to notopodial capillaries, but smaller and slenderer. First sabre chaeta on chaetiger 2, smaller and slender; sabre chaetae thicker and longer from chaetiger 6; each chaeta thick, long, curved, slightly granulated in middle to distal region and smooth at base, alimbate ( Fig. 3C View FIGURE 3 ), up 2 to per fascicle. Neuropodial hooded hooks from chaetigers 7–8 ( holotype 7), up to 5 per fascicle, accompanied by short, slender, alimbate capillaries only on chaetigers 7–9; on anterior and middle chaetigers all hooks with 4 pairs of small teeth above the main tooth ( Figs 3D View FIGURE 3 , D’; 3E, E’), and on last 2 chaetigers with 3 pairs of small teeth ( Fig. 3D View FIGURE 3 , D’). All hooks without secondary hoods; main hood very large, emerging from the base up to the distal edge ( Fig. 3D, E View FIGURE 3 ); hook shaft thin at the base, gradually thickening distally, thickest at the beginning of the teeth ( Fig. 3D, E View FIGURE 3 ). Notopodial hooded hooks absent.

Pygidium with 2 ventral lappets, without anal cirri ( Fig. 3F View FIGURE 3 ).

Six specimens examined were females with oval-shaped oocytes in coelomic cavities ( Fig. 3I View FIGURE 3 ) from chaetigers 6–8 ( holotype 7). However, only two of them had branchiate brood structures, and these had a large number of long pouches with gametes in their body segments ( Fig. 3G View FIGURE 3 ). Specifically, anterior segments had few oocytes and lacked branchial brood structures, however, large pouches containing more oocytes were found in middle segments, and from chaetigers 14–16 small, nipple-like brood structures ( Fig. 3H View FIGURE 3 ) were observed on lateral body wall; posterior segments up to chaetigers 32–34 were densely laden with oocytes, and had short branchiate brood structures ( Fig. 3G View FIGURE 3 ).

No branchiate brood structures in body segments of other four mature specimens. Few oocytes in coelomic cavities, the oocytes found inside pouches.

Methyl green staining pattern. Prostomium and peristomium stained intensively. Anterior region from chaetigers 2–15 also stained intensively, specifically along the dorso-lateral and ventral sides, forming a ring-shaped ( Fig. 3I View FIGURE 3 ).

Remarks. Streblospio papillaris sp. nov. differs from all the other known Streblospio species due to the numerous papillae scattered throughout the body and the lack of eyes. In addition, S. papillaris sp. nov. has a very long peristomium that extends to the anterior part of the prostomium, unlike other Streblospio species where the peristomium extends to a maximum of 1/2 or 2/3 the length of the prostomium. Furthermore, S. papillaris sp. nov. is the smallest species of Streblospio described up to now Streblospio papillaris sp. nov. has a maximum of 42 chaetigers vs. S. japonica and S. shrubsolli which have 48 chaetigers, S. eridani (50), S. padventralis (54), S. gynobranchiata and S. benedicti (70), and S. eunateae (77). Lastly, Streblospio papillaris sp. nov. can be distinguished from all Streblospio species in that it has sabre chaetae from chaetiger 2, rather than from chaetigers 3–7.

Streblospio papillaris sp. nov. is similar to S. benedicti , S. gynobranchiata , S. japonica , S. eunateae and S. eridani in having a dorsal interbranchial papilla. However, S. papillaris sp. nov. can be distinguished from these species, in that the notopodial postchaetal lamellae on chaetigers 3–5 are rounded with the elongate dorsal edge extending dorsally, whereas in S. benedicti , S. japonica and S. eunateae the lamellae are only rounded, and in S. gynobranchiata and S. eridani the lamellae are flap-like. Furthermore, S. papillaris sp. nov. can be distinguished from S. benedicti , S. gynobranchiata and S. japonica , in that it has no notopodial lamellae on the posterior segments. Also, S. papillaris sp. nov. differs from S. eunateae and S. eridani in that in S. papillaris sp. nov. the notopodial lamellae disappear from around chaetiger 28, whereas in the other two species the notopodial lamellae disappear before chaetiger 20. Another difference between S. papillaris sp. nov. and S. eunateae is that the latter has dorsal crests on the segments and palps with transverse bands. Furthermore, the neuropodial lamellae on chaetiger 1 are subtriangular in S. papillaris sp. nov., whereas they are rounded in S. benedicti and S. japonica , in S. gynobranchiata and S. eridani , flap-like, and oval in S. eunateae .

......continued on the next page ......continued on the next page ......continued on the next page ......continued on the next page

Streblospio papillaris sp. nov. is similar to S. gynobranchiata and S. eridani in that all these species have branchiate brood structures. There are differences, however, in the shape and the starting point of the first branchiate structures: on chaetigers 14–16 in S. papillaris sp. nov., vs. on chaetiger 13 in S. eridani , and chaetiger 20 in S. gynobranchiata ; and the number of paired branchiate structures: 18 pairs in S. papillaris sp. nov., about 10–12 in S. eridani n. sp. and around 15 in S. gynobranchiata .

In S. papillaris sp. nov., four of the six mature females were found to lack branchial reproductive structures. This could be because these specimens were recently pregnant females, and observed with oocytes in the early stages of maturation: the oocytes were few and varied in shape and size. We suggest that at this early stage the females had not yet developed branchial reproductive structures, and possibly as gonadal development increased the reproductive branchial structures for spawning would have developed.

Mahon et al. (2009), Zakas (2022) and Ruskie & Zakas (2023) mentioned that although species placed within the genus Streblospio display only slight morphological differences, there is considerable divergence in their reproductive biology arising from mate preferences is contributing to population divergence and developmental evolution in this species. Mahon et al. (2009) specifically referred to S. benedicti and S. gynobranchiata that can be differentiated only by the reproductive structures of the females: S. gynobranchiata has lateral body wall extensions resembling branchiae, whereas S. benedicti shows specialized dorsal brooding pouches. The males of both species are morphologically similar. Nevertheless, the four most recently described species, S. padventralis , S. eridani , S. eunateae and Streblospio papillaris sp. nov., demonstrate that the Streblospio genus can also exhibit a great deal of variability in the morphological characteristics among species, as well as in their reproductive characteristics.

Schulze et al. (2000) suggested caution when using reproductive morphology alone to identify species, as there has been some overlap reported for the first and last gametogenic chaetiger in females of S. benedicti and S. gynobranchiata . The same applies to the absence/presence of the branchial reproductive structures due to the advancement of pregnancy in the females of S. papillaris sp. nov. Nevertheless, both the shape and length of these reproductive structures are different among S. gynobranchiata , S. eridani and Streblospio papillaris sp. nov.

The description of S. shrubsolli given by Buchanan (1890) is one of the most complete of the genus Streblospio . Munari et al. (2025), however, tried to redescribe a morphotype of S. shrubsolli from the Adriatic Sea, but found that there was a large morphological variability between S. shrubsolli ( Buchanan 1890) , reports of S. shrubsolli by Fauvel (1927) and Rice & Levin (1998), the description of S. dekhuyzeni Horst 1909 , and their own specimens from the Adriatic Sea of Munari et al. (2025, see table 3). All these morphological variations indicate that the specimens reported by Munari et al. (2025), Fauvel (1927), and possibly those described by Horst (1909) that are in subjective synonymy, represent a species different to S. shrubsolli .

Due to the recent morphological and reproductive descriptions given by Delgado-Blas et al. (2018), Martínez & Adarraga (2019), Munari et al. (2020; 2025) and this study, we consider that the species descriptions of S. benedicti (Pacific and Atlantic coasts of Europe), S. gynobranchiata (Mediterranean, Black and Caspian Seas) and S. shrubsolii (Mediterranean Sea) should be reviewed, even though there do not appear to be any morphological differences between these reports and the original descriptions of each of the species.

Other morphological differences between this new species and the other species described are given in the key provided and in Table 1.

Etymology. The specific epithet papillaris of the Latin adjective papillae, refers to the numerous papillae that cover the body and parapodial lamellae of this species.

Type locality. Chetumal Bay , Caribbean Sea .