BASEODISCUS DELINEATUS (DELLE CHIAJE, 1822)

(FIG. 3C–E)

Polia delineata Delle Chiaje, 1822 in Delle Chiaje (1822–29), pl. XXVIII (28, but correctly 29 in position), fig. 4; Delle Chiaje, 1825 in Delle Chiaje (1822–29): 427–428, 444 (Naples, Italy); Grube, 1840: 57–58, fig. 8a, b (Naples and Palermo, Italy); Hubrecht, 1879: 209 (Naples, Italy); Joubin, 1890: 510–511 (Banyuls-sur-Mer, France).

Nemertes delineatus: Kölliker, 1845: 95 (Naples, Italy).

Eupolia delineata: Bürger, 1892: 151 (Naples, Italy); Joubin, 1894: 79–80, pl. I, fig. 11 (Banyuls-surMer, France); Bürger, 1895a: 600–601, pl. 4, figs 4, 6 (Naples, Italy: the specimen in fig. 8 lacks longitudinal stripes in the anterior part of body and is bulkier than that depicted in fig. 6).

Baseodiscus delineatus: Strand et al., 2005: 3787, table II [Ischia, Italy; Rottnest Island, Australia); Schwartz, 2009: 62, fig. 1B (Carrie Bow Cay, Belize; Peanut Island, Florida, USA; Bocas del Toro, Panama); Gonzalez-Cueto et al., 2014: 92, fig. 2C–E (Inca-Inca and Taganga, Colombia); Mendes et al., 2016: 149, fig. 2-3 (Caucaia, Brazil); Kajihara, 2017: 423, fig. 16.2b (Misaki, Japan); Ikenaga et al., 2019: 348–353, figs 1–4 [Misaki, Japan).

Baseodiscus cf. delineatus: Kvist et al., 2014: 291, table 1 (Australia).

? Baseodiscus delineatus: Coe, 1947: 104–105 (Bogoni Island, Marshall Islands); Corrêa, 1958: 442–443 (Brazil); Gibson, 1979: 139–146, figs 1–3 (Low Isles, off Port Douglas, Great Barrier Reef, Australia).

? Baseodiscus curtus: Stiasny-Wijnhoff, 1925: 102 (Curaçao).

? Eupolia delineata: Bürger, 1893: 230, pl. 8, fig. 4 (Java, Indonesia); Punnett, 1900c: 825 (Torres Straits).

? Taeniosoma delineatum: Coe, 1901b: 226 (Ensenada).

Material examined: Five specimens (extracted total DNA and remaining body preserved in 99% EtOH): four specimens (including ICHUM 6325), 22 February 2014, rocky intertidal, under stone, near Misaki Marine Biological Station (35°09′30″N, 139°36′45″E), collected by H. Kajihara; one specimen (ICHUM 6326), 26 March 2014, rocky intertidal, under stone, Araihama (35°09′33″N, 139°36′40″E), Misaki, Kanagawa, Japan, collected by H. Kohtsuka.

Sequences: From ICHUM 6325: LC178621, 28S (1136 bp); LC178665, 16S (521 bp). From ICHUM 6326: LC178647, H3 (331 bp); LC178666, 16S (521 bp).

Description: Body up to 56 cm long, 3 mm wide (ICHUM 6325); background body colour pale beige, with pale-brown longitudinal stripes covering entire body (Fig. 3C, D) except near mouth (Fig. 3E).

Distribution: Warm waters worldwide: France (Joubin, 1890, 1894), Italy (Delle Chiaje, 1822–29; Grube, 1840; Hubrecht, 1879; Bürger, 1895a; Strand et al., 2005), Australia (Strand et al., 2005; Kvist et al., 2014), Japan (Kajihara, 2017; Ikenaga et al., 2019), Florida, USA (Schwartz, 2009), Belize (Schwartz, 2009), Panama (Schwartz, 2009), Colombia (Gonzalez-Cueto et al., 2014), Brazil (Mendes et al., 2016).

Remarks: In accordance with Article 12.2.7 of the Code (ICZN, 1999), the year of publication for B. delineatus should be 1822, rather than 1825 as previously regarded (e.g. Magarlamov & Chernyshev, 2011; Ikenaga et al., 2019). The species was originally established as Polia delineata in Delle Chiaje (1822– 29), a work comprised of plates published in 1822 and four text volumes, with Volumes 1 and 2 issued in 1825 [or, Volume 2 may have been published in 1827 (Neave, 1940: 344)], Volume 3 in 1828 and Volume 4 in 1829. The description in words appeared in Volume 2 on p. 409 (as ‘ P. lineata ’) and pp. 427–428 (Delle Chiaje, 1825 in 1822–29), although the species name Polia delineata had already appeared as the caption for an plate illustration published in 1822. Delle Chiaje’s 1822 plate numbers are discontinuous in several places: plate numbers XXX (30), LXIII (63) and CII (102) are missing; in addition, for each of the four numbers I (1), II (2), XXVIII (28) and XXXIV (34), two different plates exist. Polia delineata is depicted on the second of the two plates labelled XXVIII.

Baseodiscus delineatus has a pale background body colour with numerous brown longitudinal stripes. The broad range of variation in colour pattern has obscured the species identity of B. delineatus, especially in relation to a similar form, B. curtus (Hubrecht, 1879). Baseodiscus curtus was previously regarded as a variety of B. delineatus (Coe, 1940, 1944; Corrêa, 1958, 1961, 1963) and thus as synonymous with it (Gibson, 1979, 1995). Moreover, Bürger (1904) and Gibson (1979, 1995) synonymized the following six nominal species originally described from the Indo-Pacific with B. delineatus: Baseodiscus insignis Punnett & Cooper, 1909 (Zanzibar, Tanzania); Borlasia striata Quoy & Gaimard, 1833 (Guam); Eupolia amboinensis Staub, 1900 (Ambon, Indonesia); Eupolia ascophora Bürger, 1890 (Ambon, Indonesia); Eupolia marmorata Bürger, 1890 (Ambon, Indonesia); and Eupolia reticulata Staub, 1900 (Ambon, Indonesia). This synonymization was probably an excessive lumping, as Strand et al. (2005) discovered a new species, B. jonasii, from Guadalcanal (Solomon Islands) that resembles, but is genetically distinct from, B. delineatus.

Owing to the 16S gene sequence from Italy (AY955227) provided by Strand et al. (2005), the species identity of B. delineatus has been established more firmly than before, enabling the application of reliable names to material from different localities. The six 16S sequences from four different countries (AY955227, Italy; AY955232, KF935448, Australia; LC178665, LC178666, Japan; EF124861, Belize) were identical (p -distance = 0.00). In addition, recent technological progress in high-quality digital photography allows comparison of subtle differences in body coloration and markings between specimens from different localities (e.g. Schwartz, 2009; Gonzalez-Cueto et al., 2014; Mendes et al., 2016; Kajihara, 2017; Ikenaga et al., 2019). These new data sources now indicate that B. delineatus is distributed circumglobally. The species can reproduce asexually by fragmentation followed by anterior regeneration (Ikenaga et al., 2019).

Bürger (1895a: 600) synonymized Borlasia carmellina Quatrefages, 1846 (type locality, Favignana Island, Italy) with Eupolia delineata, but there are some differences between the descriptions of the two: in Borlasia carmellina, the body is reddish posteriorly and covered with small, elongate patches (‘petites taches allongée’) rather than stripes, and eyes are lacking (Quatrefages, 1846).