Spirobranchus tetraceros ( Schmarda, 1861 )

Rodrigues, Andrielle Raposo, Skinner, Luis Felipe & Brasil, Ana Claudia dos Santos, 2020, Do Morphological Similarities and human-induced dispersal explain the non-native occurrence of Serpulidae (Annelida) in Southwest Atlantic? Taxonomic detailing is the key, Papéis Avulsos de Zoologia 60, pp. 1-15 : 2-6

Spirobranchus tetraceros ( Schmarda, 1861) ( Figs. 2-4 )

Pomatoceros tetraceros Schmarda, 1861: p. 30 ; Taf. XXI, fig. 179.

Spirobranchus tetraceros: ten Hove, 1970: p. 3 -14; figs.1-6; 7-14; 15-22; 23-27. Ben-Eliahu & ten Hove, 2011: p. 88-94 ; fig. 33A-E; table 5. Kupriyanova et al., 2015: p. 337-339 ; fig. 30C-D.

Examined material: 199 specimens. Rio de Janeiro State, Mangaratiba Municipality: Ilha de Itacuruçá : 22°56′58.6″S, 43°53′13.4″W, MNRJP2184 (105 specimens) . Ilha dos Martins : 22°57′17.0″S, 43°51′39.2″W (3 specimens) . Ilha de Jaguanum : 23°00′08.8″S, 43°56′14.4″W (6 specimens) . Ilha Guaíba : 23°00′13.1″S, 44°03′07.9″W (1 specimen) . Mangaratiba: 22°58′57.1″S, 44°03′04.7″W (2 specimens) . Praia de Muriqui: 22°55′43.4″S, 43°57′17.9″W (10 specimens) . Ibicuí: 22°57′45.3″S, 44°01′28.5″W (4 specimens) . Ilha da Marambaia: Praia de João Emanuel: 23°02′35.4″S, 43°57′42.0″W (7 specimens) . Praia da Armação: 23°02′39.9″S, 43°57′06.6″W (10 specimens) . Praia Suja: 23°03′57.2″S, 43°59′31.3″W (21 specimens) . Praia Grande: 23°03′57.5″S, 43°59′32.2″W (4 specimens) . Praia da Cutuca: 23°04′03.7″S, 43°59′42.2″W (10 specimens) . Rio de Janeiro State, Itaguaí Municipality: Ilha da Madeira: 22°55′06.3″S, 43°51′14.3″W (16 specimens) . Rio de Janeiro State, Angra dos Reis municipality : Piraquara: 23°01′14.0″S, 44°26′24.5″W (8 specimens) . Dois Rios: 23°11′08.0″S, 44°11′24.4″W (2 specimens) .

Description (based on 10 individuals collected from Itacuruçá Island and Marambaia Island, Brazil)

Tube: Externally white/light pink and sometimes violet in smaller tubes, inside light pink ( Fig. 2A ). Subtriangular in cross-section, with a single prominent wavy median and longitudinal ridge, laterally with fine transverse growth markings, lacking alveoli and peristomes ( Fig. 2A ). Anterior end with a fine tooth extending over the opening ( Fig. 2A ). Attached to rocky shores, Perna perna ( Linnaeus, 1758) mussels and artificial substrates, such as PVC plates.

Radiolar crown: Radioles arranged in a circle on each side, with 18 radioles per lobe. Inter-radiolar membrane extending to about ⅓ of radiolar length, smooth and bearing external rounded processes ( Fig. 2B ). Internally, radioles with two rows of pinnules of the same length. Terminal filament without pinnules. Stylodes absent. Eyespots absent. In live specimens, the bases of radioles (including the inter-radiolar membrane) exhibit a mix of black/pink/yellow/white pigments ( Figs. 2B , 3A , C-D). In fixed specimens, the radiolar crown has blue pigments ( Fig. 3B ).

Peduncle: Smooth, inserted left of the radiolar crown, near the medial line; dark pigments with irregular darker stripes on the dorsal side ( Fig. 3 ); fixed specimens with blue pigments. Proximal area smooth and with narrow stem; distal area flattened and with a broad stem below the opercular plate ( Fig. 3 ). Peduncle color extends into lateral wings. Pair of peduncular wings fringed with digitate processes ( Fig. 3 ). Length: mean = 1.12 (SD = 0.38; n = 10).

Operculum: Four distinct morphotypes, all with a circular calcareous opercular plate ( Fig. 3 ). Type A: distal end of operculum conical and with concentric striations, without spines ( Fig.3A ). Type B: initial bifurcation of short non-ramified spines that share the same base and lack spinules, with two spines lying dorso-lateral and a third ventral to the top of the opercular plate ( Fig. 3B ). Type C: four spines, but a group of three shares the same base; two of which are dorso-lateral, larger and forked once, a third is ventral, smaller and also forked once; spines with spinules at their tips and not divided to the opercular plate ( Fig. 3C ). Type D: similar to type C,but the spines are developed totally and exhibit more ramifications at their tips than other types, spinules present. Dorso-lateral spines ramified three or two times, ventral spine ramified twice ( Fig. 3D ). Spines white. Diameter: mean = 0.7 (SD = 0.16; n = 10);Width: mean = 0.71 (SD = 0.18;n = 10).

Collar and thoracic membranes: Collar well-developed ( Figs. 2B , 3C ), covering ½ of the radiolar crown, divided into one ventral and two lateral lobes of the same size. Ventral lobe triangular. Tonguelet present, dark in colour (black) between ventral and latero-dorsal lobes. Laterodorsal lobes extend to thoracic membranes, producing a short ventral apron. Two types of collar chaetae: 1) limbate or 2) bayonet-like with many small teeth at the base of the ‘blade’ ( Fig. 4A ). Collar and thoracic membranes light brown in colour ( Fig. 3C ).

Thorax: Seven chaetigers, six of which are uncinigerous ( Fig. 2B ); collar fascicle without row of uncini. Thoracic chaetae limbate and of two different sizes ( Fig. 4B ). Uncini saw-shaped, with 9-10 teeth and including an anterior-most gouge-shaped peg tooth ( Fig. 4D ).

Abdomen: Number of abdominal chaetigers varies from 32 to 71 (mean = 49.9; SD = 15.93; n = 10). Chaetae trumpet-shaped ( Fig. 4C ). Uncini saw-shaped, with 10-12 teeth and including gouge-shaped peg tooth ( Fig. 4E ).

Measurements: Total length: mean = 5.4 (SD = 2.0; n = 10); Thoracic length: mean = 1.24 (SD = 0.36;

n = 10); Thoracic width: mean = 0.64 (SD = 0.27; n = 10); Abdominal length: mean = 2.6 (SD = 1.35; n = 10).

Remarks: Two species of Spirobranchus have been reported for the Brazilian coast (Amaral et al., 2013), Spirobranchus giganteus ( Pallas, 1766) and Spirobranchus minutus ( Rioja, 1941) . Both of these species are readily discernible from our collected specimens, identified herein as S. tetraceros .

The radioles of the radiolar crown in S. giganteus are spirally arranged, and the wings of the penduncle form a smooth inverted triangle ( ten Hove, 1970). In contrast, the radioles of the radiolar crowns of our specimens are circularly arranged and the wings of the penduncle are fringed. The opercula of our specimens also differ from those of S.giganteus . The opercular spines of S. giganteus (two large ones, as well as other smaller ones) are ramified. The opercula of our specimens present four basic shapes ( Fig. 3 ), varying from conical to a flat disc, and with three spines (one ventral and two lateral) sharing the same base ( Fig. 3D ).

Spirobranchus minutus has three longitudinal ridges and alveoli at the base of the tube ( Rioja, 1941), unlike S. tetraceros , that has serrated ridges along the tube forming a tip without alveoli. Moreover, S. minutus has a triangular opercular penduncle with narrow and pointed wings ( Zibrowius, 1970), whereas that of S. tetraceros is fringed with digitate wings. The operculum of S. minutus is globose, almost transparent, extends over a calcified plate ( Zibrowius, 1970), and lacks spines.

The species of Spirobranchus that occur in Curaçao (Caribbean Sea) were reviewed by ten Hove (1970), resulting in 22 taxa synonymized under the name S. tetraceros . However, Bastida-Zavala & Salazar-Vallejo (2000) re-elevated Spirobranchus dendropoma ( Mörch, 1863) to the species level based on their Mexican Caribbean material, distinguishing it from S. tetraceros based on morphological and biogeographical differences (Perry et al., 2018). In their analyses of the material collected from the Mexican Caribbean, Bastida-Zavala & Salazar-Vallejo (2000) observed that their specimens were morphologically more similar to S. dendropoma than to S. tetraceros , and also considered biogeographic information in identifying the species. Herein, we consider morphological characters for our specimens identifications, including the position of processes extending from the radiolar membrane. These processes occur at the bases of the radioles in S. dendropoma ( Benedict, 1887; ten Hove, 1970). In our examined specimens of S. tetraceros , the interadiolar membrane processes occur between radioles and present a rounded shape.

Spirobranchus tetraceros was originally described from New South Wales in Australia ( Schmarda, 1861), but it has also been recorded in the Red Sea (Perry et al., 2017), Mediterranean Sea, Hong Kong (Sun et al., 2012), Egypt, the Persian Gulf, and Curaçao ( ten Hove, 1970). This species was first recorded in Brazil at Arraial do Cabo (Skinner et al., 2012), and herein we expand its distribution to Sepetiba Bay and Ilha Grande, both of which are in the southeast of the country.

Habitat: The species were found attached to rocky shores, Perna perna mussels and artificial substrates, such as PVC plates in subtidal areas.

Type-locality: New South Wales, Australia.

Distribution: West Pacific Ocean: Philippines; Port Jackson; Pandanon; Ubay; West Indian Ocean: Tanzania; Mozambique; Madagascar; Central Indian Ocean: Pearl Banks of Ceylon; Sri Lankan; Red Sea: Gulf of Aqaba; Red Sea; Djiboutian part of the Gulf of Aden; Persian Gulf; Mediterranean Sea; Lebanese part of the Mediterranean Sea; Greece; West Atlantic Ocean: Gulf of Mexico; Colombia ( Read, 2018b); Brazil, at Arraial do Cabo, misidentified as S. giganteus , see Perry et al., 2017, Sepetiba Bay and Ilha Grande Bay (current work).

Figures

Figure 2. Spirobranchus tetraceros. (A) Tube with longitudinal ridge and projection in the anterior part of the tube; (B) Complete body, lateral view. Scale bars:A-B:2 mm.

Figure 3. Spirobranchus tetraceros, operculum morphotypes. (A) Conical operculum, latero-dorsal view; (B) Initial bifurcation of operculum, dorsal view; (C) Bihorned operculum,latero-dorsalview; (D) Bi-horned operculum,lateral view.Scale bars:A-D:500 µm.

Figure 4. Spirobranchus tetraceros, types of chaetae.(A) Collar chaetae;bayonet chaetae,with tip processes;(B)Thoracic chaetae;limbate;(C) Abdominal chaetae; chaetae trumpet-shaped;(D) Uncini thoracic with8 teeth;(E) Uncini abdominal with 11 teeth.Scale bars:A-E:500 µm.