Hydroides dianthus ( Verrill, 1873 )

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 : 6-7

Genus Hydroides Gunnerus, 1768 Hydroides dianthus ( Verrill, 1873)

( Figs. 5 and 6 )

Serpula dianthus Verril, 1873: p. 620 . Serpula dianthus var. citrine: Verril, 1873: p. 620 -621. Hydroides dianthus: Bastida-Zavala & ten Hove, 2002 :

p. 143-147; figs. 23A-M, 24A-K, 28; Bastida-Zavala

et al., 2017: p. 25-28; figs. 4C, 5.

Examined material: 70 specimens. Rio de Janeiro State, Mangaratiba Municipality : Praia de Ibicuí : 22°57′45.3″S, 44°01′28.5″W, MNRJP2186 (1specimen) . Ilha de Itacuruçá : 22°56′58.6″S, 43°53′13.4″W, MNRJP2185 (18 specimens) . Praia de Muriqui: 22°55′43.4″S, 43°57′17.9″W (9 specimens) . Ilha dos Martins : 22°57′17.0″S, 43°51′39.2″W (11 specimens) . Ilha de Jaguanum : 23°00′08.8″S, 43°56′14.4″W (1 specimen) . Rio de Janeiro State, Itaguaí Municipality: Ilha da Madeira : 22°55′06.3″S, 43°51′14.3″W (31 specimens) .

Description (based on 10 individuals collected from Madeira Island and Muriqui)

Tube: Tube white both internally and externally ( Fig. 5A ), and circular in cross-section. Without longitudinal ridge, laterally with fine transverse growth markings ( Fig. 5A ); alveoli and peristomes absent. Attached to rocky shores, mollusc shells and artificial substrates such as PVC plates.

Radiolar crown: Radioles arranged in semi-circles, with 14-16 radioles per lobe ( Fig. 5C ). Inter-radiolar membrane absent. External side of radioles smooth, internal side with two rows of pinnules of the same length ( Fig. 5C ). Terminal filament without pinnules. Stylodes absent. Eyespots absent. Base of radiolar crown exhibits a mixture of orange and yellow pigments, together with alternating bands of dark brown and white ( Fig. 5C ). In fixed animals, color is light yellow.

Peduncle: Cylindrical, but with a constriction ill-defined at the distal end ( Fig. 5B ); proximal part a smooth narrow stem. Penduncle inserted left side. Pseudoperculum present, smaller, rudimentary and inserted right side. Length: mean = 1.2 (SD = 0.26; n = 10).

Operculum: Bioperculated ( Fig. 5B ); funnel-shaped base with 30-33 radii and a pointed tip; verticil with 10 amber-coloured spines, four dorsal spines curving towards internal face of verticil; ventral spines smaller and with spinules on their external faces ( Fig. 5B ), without central tooth; without internal and lateral spinules. Diameter: mean = 0.33 (SD = 0.08; n = 10); Width: mean = 0.33 (SD = 0.06; n = 10).

Collar and thoracic membranes: Tri-lobed, subdivided into one medio-ventral and two lateral lobes ( Fig. 5C ). Tonguelet absent. Latero-dorsal lobes extend to thoracic membranes with a short ventral apron. Two types of chaetae: limbate or bayonet-like with two blunt elongate teeth, distal blade smooth ( Fig. 6A ).

Thorax: Seven chaetigers, six of which are uncinigerous; collar fascicle without row of uncini. Chaetae limbate ( Fig. 6B ), with two different sizes;uncini saw-shaped with 8-10 teeth including a gouge-shaped peg tooth ( Fig. 6C ).

Abdomen: Total number of chaetigers varies from 31 to 83 (mean = 56; SD = 16.9; n = 10). Chaetae of anterior and mid-abdominal chaetigers trumpet-shaped; uncini saw-shaped, with 6-8 teeth including a gouge-shaped peg tooth ( Fig. 6D ). Posterior chaetigers with capillary chaetae.

Measurements: Total length: mean = 6.2 (SD = 1.35; n = 10); Thoracic length: mean = 1.3 (SD = 0.34; n = 10); Thoracic width: mean = 0.57 (SD = 0.14; n = 10); Abdominal length: mean = 3.8 (SD = 1.2; n = 10).

Remarks: There are 92 described species for the genus Hydroides (Sun et al., 2015) , 13 of which have already been reported the Brazilian coast: H. brachyacantha Rioja, 1941 ; H. cruciger Mörch, 1863 ; H. dianthus ; H. dirampha Mörch, 1863 ; H. elegans ; H. gairacensis Augener, 1934 ; H. norvegica Gunnerus, 1768 ; H. parvus ( Treadwell, 1902) ; H. plateni ( Kinberg, 1867) ; H. sanctaecrucis KrØyer in Mörch, 1863 ; H. similoides Bastida-Zavala & ten Hove, 2002 ; H. lambecki Bastida-Zavala & ten Hove, 2002 ; and H. uncinata ( Philippi, 1844) ( Zibrowius, 1970; Amaral et al., 2013; Schawn et al., 2016).

Among those, only H. sanctaecrucis could possibly be confused with H. dianthus , by the presence of the ventrally curved spines at verticil. However,external spinules are present on the spines of H. sanctaecrucis , wich are lacking in H. dianthus ( Bastida-Zavala & ten Hove, 2002) . All 10 verticil spines of H. dianthus are smooth, with four larger dorsal spines, and six smaller ventrally (Bastida- Zavala & ten Hove, 2002; Lewis et al., 2006).

Hydroides dianthus was originally described for the eastern coast of the United States and from Cape Cod (Connecticut). The species occurs in eastern USA, northern Gulf of Mexico, Curaçao, along the Atlantic coasts of Europe and western Africa, Mediterranean Sea (Bastida- Zavala & ten Hove, 2002), and at Cabo Frio (Rio de Janeiro State) in Brazil (Sun et al., 2017). Here we include the occurrence of H. dianthus in Sepetiba Bay (Rio de Janeiro State), with specimens collected in the intertidal zone, growing on rocks, gastropods, and piers, and co-occurring with other species of the same genus.

Habitat: The species were found attached to rocky shores, mollusc shells and artificial substrates such as PVC plates.

Type-locality: Connecticut (Great Egg Harbor to New Haven and Cape Cod), USA.

Distribution: West Pacific Ocean: Japan ( Otani & Yamanishi, 2010; Link et al., 2009); North Atlantic Ocean: Spain ( Zibrowius, 1983); United Kingdom ( Otani & Yamanishi, 2010; Link et al., 2009); France (Dauvin et al., 2003); Belgium; Mediterranean: Mediterranean (Zenetos et al., 2005; Zenetos et al., 2010); Adriatic Sea; Italy (Marchini et al., 2015; Corriero et al., 2016); Turkey ( Trott, 2004); Greece ( Otani & Yamanishi 2010; Link et al., 2009); East Atlantic Ocean: Gulf of Guinea (Dauvin et al., 2003; Read, 2018a); West Atlantic Ocean, United States: Cobscook Bay ( Trott, 2004); Gulf of Maine ( Otani & Yamanishi, 2010; Link et al., 2009); Massachusetts (Marchini et al., 2015; Corriero et al., 2016); Narragansett Bay, Rhode Island; Chesapeake Bay, Virginia; Charleston, South Carolina; Jacksonville, Indian River, Biscayne Bay, Tampa Bay and Pensacola Bay, Florida; and Galveston Bay and Corpus Christi,Texas (Bastida-Zavala et al., 2017); Mexican Caribbean ( Read, 2018a); West Atlantic Ocean: Cabo Frio, Brazil (Sun et al., 2017), Sepetiba Bay (current work).

Figures

Figure 5. Hydroides dianthus. (A)Tube;(B) Operculum detail;(C) Complete body,dorso-lateral view.Scale bars:A and C:2 mm;B: 500 µm.

Figure 6. Hydroides dianthus, types of chaetae.(A) Collar chaetae;bayonet chateae with rounded process;(B)Thoracic chaetae;limbate; (C) Uncini thoracic with 8 teeth;(D) Uncini abdominal with 6 teeth.Scale bars:A-D:500 µm.