Contributions to Zoology, 83 (2) – 2014Pablo Hernández-Alcántara; Vivianne Solís-Weiss: Anatomical and morphometric analysis of a new species of Leitoscoloplos (Annelida: Orbiniidae) with numerous stomach papillae, from the Gulf of California, Eastern Pacific

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Appendix

Systematics


Orbiniidae Hartman, 1942

Leitoscoloplos Day, 1977, emended

Type species: Haploscoloplos bifurcatus Hartman, 1957: 277-279, designated by Day (1977).

Diagnosis. Prostomium pointed, conical, with an achaetous peristomial ring. Thoracic neurochaetae with only crenulated capillaries; abdominal furcate notochaetae present or absent. Branchiae either present from posterior thoracic, transitional or abdominal chaetigers, or absent. Interramal cirri present or absent. Posterior thoracic neuropodia with up to 6 podal papillae. Subpodal and stomach papillae absent, or with up to 8 subpodal papillae per parapodium and with numerous stomach papillae in the posterior thorax/anterior abdomen.

Remarks. In Leitoscoloplos multipapillatus sp. nov., thoracic chaetigers with up to 2 podal papillae are present, which corresponds well to the generic definition (Mackie, 1987; Eibye-Jacobsen, 2002). However, in this new species, a higher number of subpodal papillae (up to 8 per parapodium) are found, and most of all, numerous stomach papillae (up to 14 on each segmental side). Together, they form ventral fringes on some posterior thoracic and anterior abdominal chaetigers. Because of their position, below the neuropodia or on the ventral region of the body, both types of papillae are usually separated by a gap. However, in Leitoscoloplos multipapillatus sp. nov., when these papillae together make continuous ventral fringes on some chaetigers, it is almost impossible to differentiate them. In such cases, it was assumed that there could be up to 8 subpodal papillae by parapodium, because 8 was the maximum number of subpodal papillae observed in the analyzed specimens, when papillae are not clearly placed on the ventral middle region (stomach papillae). So far , no other morphological distinctions between these structures have been observed in orbiniids. (Based on the redefinition of Mackie (1987), the emendations made by Eibye-Jacobsen (2002), and the remarks made in this study.)

Leitoscoloplos multipapillatus sp. nov. (Figs 4A-G, 5A-I, 6A-H)

Leitoscoloplos panamensis.− Hernández-Alcántara and Solís-Weiss 1999: 27 (in part). (not Monro, 1933)

FIG2

Fig. 4. Leitoscoloplos multipapillatus sp. nov., holotype. A) Anterior end, dorsal view; B) same, lateral view; C) chaetiger 5, posterior view; D) chaetiger 10, posterior view; E) chaetiger 24, posterior view; F) chaetiger 30, posterior view; G) chaetigers 15 to 23, lateral view. (Roman numerals=number of chaetiger; NO =nuchal organs; SbPa=subpodal papilla; StPa=stomach papilla). Scale bars: A 1 mm; B 0.5 mm; C-F 0.1 mm; G 0.2 mm.

FIG2

Fig. 5. Leitoscoloplos multipapillatus sp. nov., paratype. A) Thoracic and abdominal region, ventro-lateral view; B) anterior end, dorso-lateral view; C) transition from thorax (left) to abdomen, dorsal view; D) chaetigers 1 and 2, lateral view; E) notopodium from chaetiger 3, anterior view; F) neuropodium from chaetiger 3, anterior view; G) neuropodium from chaetigers 6-8, anterior view; H) neuropodium from chaetiger 11, anterior view; I) neuropodium from chaetiger 8, frontal view. (Roman numerals=number of chaetiger; NO=nuchal organ; SbPa =subpodal papilla; StPa=stomach papilla). Scale bars: A 1 mm; B, C 0.5 mm; D 0.1 mm; E-I 50 µm.

FIG2

Fig. 6. Leitoscoloplos multipapillatus sp. nov., paratype. A) Chaetigers 8 and 9, anterior view; B) chaetiger 12, frontal view; C) chaetigers 15 to 17, anterior view; D) abdominal region, anterior view; E) notopodium from chaetiger 32, anterior view; F) posterior abdominal region, antero-dorsal view; G) transition from thorax (left) to abdomen, ventro-lateral view; H) anterior abdominal region, antero-lateral view. (Roman numerals =number of chaetiger; SpPa =subpodal papilla; StPa=stomach papilla). Scale bars: A-D, G 0.1 mm; E 50 µm; F 0.2 mm; H 0.5 mm.

Holotype (CNP-ICML: POH-01-001): Expedition ‘Cortés 3’: Station 42, Tepoca Cape, Gulf of California (30°12.4’N, 112°47.2’W), 23 m, fine sand, collected by P. Hernández-Alcántara, 5 August 1985.

Paratypes (12 specimens): CNP-ICML: POP-01-001: 7 specimens, 2 used for SEM studies, same station as holotype; BMNH: NHMUK ANEA 2014.324-38: 5 specimens, same station as holotype.

Additional material examined. Twenty-five specimens (CNP-ICML: PO-01-028): Expedition ‘Cortés 2’: 2 specimens, Station 52, El Fuerte River (25°39.9’N, 109°28.6’W), 28 m, 20 March 1985. Expedition ‘Cortés 3’: 1 specimen, Station 3, Santa María Bay (25°2.4’N, 108°30.5’W), 23 m, fine sand, 9 August 1985; 1 specimen, Station 16, Arboleda Point (26°52.7’N, 110°00.8’W), 18 m, fine sand, 31 July 1985; 1 specimen, Station 27, Northern Tiburón Island (29°28.6’N, 112°26.4’W), 34 m, fine sand, 2 August 1985; 5 specimens, Station 32, Willard Point (29°46.7’N, 114°20.0’W), 21 m, fine sand, 3 August 1985; 7 specimens, Station 42, Tepoca Cape (30°12.4’N, 112°47.2’W), 23 m, fine sand, 5 August 1985; 2 specimens, Station 48, Tastiota (28°15.7’N, 111°35.6’W), 54 m, fine sand, 6 August 1985; 2 specimens, Station 52, El Fuerte River (25°43.6’N, 109°29.3’W), 22 m, fine sand, 8 August 1985. Expedition ‘Estudio Integral de la Bahía de Mazatlán’: 1 specimen, Station C1, VV8, Mazatlán Bay (23°13’N, 106°27’W), 9 m, 26 June 1979; 1 specimen, Station C8, VV6, Mazatlán Bay (23°13’N, 106°27’W), 10 m, 25 January 1980; 1 specimen, Station C10, VV3, Mazatlán Bay (23°13’N, 106°27’W), 10 m, 11 April 1980; 1 specimen, Station C10, VV5, Mazatlán Bay (23°13’N, 106°27’W), 16 m depth, 11 April 1980. All localities are in the Gulf of California. All specimens from expeditions ‘Cortés 2’ and ‘Cortés 3’ were collected by P. Hernández-Alcántara, all those from Expedition ‘Estudio Integral de la Bahía de Mazatlán’ were collected by M. Hendrickx.

Description. Holotype and paratypes incomplete. Holotype with 52 chaetigers, 20 mm long and 2 mm wide. Paratypes with 33 to 73 chaetigers, 13 to 18 mm long and 1.5 to 2 mm wide. Body yellowish in alcohol, divided into a dorso-ventrally flattened thoracic region which consists of the peristomium and 19 chaetigers (18-20 in paratypes), the last one transitional, and a cylindrical abdominal region (Figs 4A-B, 5A). Prostomium conical, sharp, no eyes (Fig. 4A-B). Peristomium achaetous, with a pair of conspicuous lateral nuchal organs in anterior position (Figs 4B, 5D). Branchiae erect, from chaetiger 9 (Figs 4A, 5B), triangular, initially very small but gradually increasing in size along thorax, better developed on abdominal region (Fig. 5C), slightly longer than notopodial postchaetal lamellae, conspicuously fimbriated on both sides (Fig. 6D-F). Parapodia of first chaetiger slightly shifted dorsally (Fig. 5B, D). Thoracic notopodia with a small triangular postchaetal lobe from first chaetiger, increasing in length and thickness towards the posterior thorax (Figs 4A-D, 5B, E). Notopodia with numerous very long camerated capillaries arranged in 3-4 rows (Fig. 5E). Thoracic neuropodia of first chaetiger as low transverse ridges, with a rounded postchaetal lamella bearing a podal papilla from chaetiger 1 to 8 (8-9 in paratypes) (Figs 4C, 5F, G); on the first neuropodia, these papillae are very small, difficult to observe (Fig. 5D). From chaetiger 9 (9-10 in paratypes) to the end of the thorax, neuropodia similar in shape but with 2 podal papillae (Figs 4D, 5H, 6A-C). Thoracic neuropodia with numerous camerated capillaries, more or less arranged in 4-6 rows (Figs 5I, 6B); capillaries located on anterior rows shorter than those on posterior rows (Figs 5F, H). Abdomen incomplete, cylindrical in section, notopodia with numerous crenulated capillaries and a broad and foliaceous postchaetal lamella (Figs 5C, 6D-H). No forked or other modified chaetae. Neuropodia bilobed, inner lobe longer, with clear notch at insertion of a well-developed lateral flange (Figs 4E-F, 6H), and supported by a pair of fine aciculae, slightly protruding from distal margin in some posterior chaetigers; they carry 5-15 crenulated capillaries (Figs 4E-F, 6D-H). Interramal cirri present from chaetiger 18 (17-19 in paratypes) (Figs 4E, 6H), progressively becoming indistinct and disappearing (Figs 4F, 6D, F) at chaetiger 25 (24-28 in paratypes). One subpodal papilla (Figs 5A, 6C) from chaetiger 13 (13-15 in paratypes); increasing to 7 papillae (up to 7-8 in paratypes) on chaetigers 20-22 (Figs 4G, 6D, G-H). With triangular stomach papillae on 6 chaetigers (4-7 in paratypes): from chaetiger 17 (16-18 in paratypes) to chaetiger 22 (20 to 23 in paratypes) (Figs 4G, 5A, 6G). Initially, 2 stomach papillae on each segmental side (1-3 in paratypes), but on 2 or 3 posterior chaetigers (19 to 21) the number of stomach papillae can increase to 9-12 (up to a total of 14 in some paratypes), even forming ventral fringes (Figs 4G, 5A, 6G). Pygidium unknown.

Remarks. Based on the system proposed by Mackie (1987) to organize this genus, Leitoscoloplos multipapillatus sp. nov. can be included into species group 5: branchiae present, more than 10 thoracic chaetigers, and bearing interramal cirri and subpodal papillae. This group also includes by L. fragilis (Verrill, 1873), L. robustus (Verrill, 1873), L. obovatus Mackie, 1987, L. mackiei Eibye-Jacobsen, 2002, L. papillatus Eibye-Jacobsen, 2002 and L. panamensis (Monro, 1933). The last two had been the only species with 4 or more subpodal papillae: L. papillatus has up to 7 subpodal papillae, but only 14-15 thoracic chaetigers and branchiae start from chaetiger 11, while L. panamensis has a maximum of 4 subpodal papillae (5 according to the observations made in specimens of the Gulf of California). Therefore, this new species is just the second one within the genus with numerous subpodal papillae (up to 7-8), but most of all, it is the only species bearing many stomach papillae (up to 14 on each segmental side). Apart from the presence of these stomach papillae, the new species is morphologically similar to L. panamensis, also widely distributed in the study area. The morphometric analyses further validate the establishment of the new species, since most of the parameters evaluated showed significant differences between L. multipapillatus sp. nov. and L. panamensis (Fig. 2). Abundant subpodal papillae (up to 6), are present in Leitoscoloplos sp. but stomach papillae are much fewer (1-2) and restricted to only 1-2 posterior thoracic or anterior abdominal chaetigers (Fig. 2).

Previously, stomach papillae were associated with other orbiniid genera, such as Orbinia, Phylo or Scoloplos. In fact, Blake (2000) suggested that all species with stomach papillae and lacking modified spines on thoracic notopodia be assigned to Orbinia, and that the generic assignations of all species referred to Scoloplos should be reassessed on this basis. However, Orbinia, Phylo and Scoloplos all possess modified chaetae (hooks or spines) in the thoracic neuropodia. Conversely, in the specimens collected in the Gulf of California, only capillary chaetae are found in all neuropodia, irrespective of size. The lack of modified chaetae was investigated thoroughly and corroborated with SEM pictures of some specimens, confirming their inclusion in Leitoscoloplos.

Habitat. In 9 to 54 m, on fine sand and muddy sand; temperature: 16.8 to 30.3°C; salinity: 34.2 to 36 psu; 3 to 5.4 ml/L dissolved oxygen, and 1.9 to 5.3% organic carbon.

Type locality. Tepoca Cape, northeastern Gulf of California.

Geographical distribution. Widely distributed on the eastern coasts of the Gulf of California.

Etymology. The specific name refers to the presence of numerous stomach papillae, which clearly separates the species from other members of the genus.

Leitoscoloplos panamensis (Monro, 1933) (Figs 7A-I, 8A-F)

Haploscoloplos panamensis Monro, 1933: 1045-1046, fig. la-d; Fauchald, 1977:46; not Hartman, 1957: 277, pl. 28, figs 1-3 (= Scoloplos armiger alaskensis fide Mackie, 1987).

Leitoscoloplos panamensis.− Mackie 1987: 19-20, fig. 20a-e; Hernández-Alcántara and Solís-Weiss, 1999: 27 (in part).

FIG2

Fig. 7. Leitoscoloplos panamensis (Monro, 1933). A) Thoracic region, dorso-lateral view, syntype; B) chaetigers 16 to 23, lateral view, syntype; C) anterior end, lateral view; D) anterior and mid-body region, lateral view; E) notopodium from chaetiger 3, frontal view; F) neuropodia from chaetigers 5 and 6, frontal view; G) anterior end, dorsal view; H) parapodia from posterior thorax, anterior view; I) transition from thorax (left) to abdomen, dorsal view. (Roman numerals=number of chaetiger; NO=nuchal organ; SbPa=subpodal papilla). Scale bars: A, D 0.5 mm; B 1 mm; C, H 0.1 mm; E, F 50 µm; G, I 0.2 mm.

FIG2

Fig. 8. Leitoscoloplos panamensis (Monro, 1933). A) Notopodia from chaetigers 8 to 10, dorso-lateral view; B) chaetigers 10 to 14, lateral view; C) transition from thorax (left) to abdomen, dorso-lateral view; D) chaetiger 20, anterior view; E) chaetigers 15 to 18, lateral view; F) chaetigers 20 to 23, lateral view. (Roman numerals=number of chaetiger; IC=interramal cirrus; SbPa=subpodal papilla). Scale bars: A 50 µm; B, D-F 0.1 mm; C 0.2 mm.

Type material examined. Three syntypes deposited in the Natural History Museum, London (BMNH, ZK 1933.7.10.63-64). Collected between Taboga and Taboguilla Islands, Pacific coast of Panama, 11-22 m.

Material examined. Thirty-eight specimens (CNP-ICML: PO-01-018): Expedition ‘Cortés 1’: 6 specimens, Station 42, Tepoca Cape (30°12.4’N, 112°47.5’W), 30 m, muddy sand, collected by V. Solís-Weiss, 10 May 1982. Expedition ‘Cortés 2’: 1 specimen, Station 15, Arboleda Point (26°51.1’N, 110°06.5’W), 49.8 m, 12 March 1985; 1 specimen, Station 34, Willard Point (30°11.5’N, 114°31.7’W), 33 m, muddy sand, 15 March 1985; 7 specimens, Station 42, Tepoca Cape (30°12.1’N, 112°46.9’W), 30 m, fine sand, 17 March 1985; 1 specimen, Station 44, Tepoca Cape (30°02.4’N, 112°55.4’W), 104 m, sand, 17 March 1985; 7 specimens, Station 51, El Fuerte River (25°42.1’N, 109°30.6’W), 49 m, muddy sand, 20 March 1985. Expedition ‘Cortés 3’: 1 specimen, Station 15, Arboleda Point (26°53.2’N, 110°05.9’W), 39 m, fine sand, 31 July 1985; 1 specimen, Station 32, Willard Point (29°46.7’N, 114°20.0’W), 21 m, fine sand, 3 August 1985; 1 specimen, Station 39, Northern Consag Rocks (31°01.83’N, 114°05.3’W), 93 m, fine sand, 4 August 1985; 2 specimens, Station 51, El Fuerte River (25°44.3’N, 109°29.4’W), 42 m, fine sand, 8 August 1985; 10 specimens, two used for SEM, Station 52, El Fuerte River (25°43.6’N, 109°29.3’W), 22 m, fine sand, 8 August 1985. All localities are in the Gulf of California, and all specimens from expeditions ‘Cortés 2’ and ‘Cortés 3’ were collected by P. Hernández-Alcántara.

Description. Incomplete specimens with 20 to 93 chaetigers; 3 to 19 mm long and 0.5 to 2.0 mm wide (syntypes with 37 to 71 chaetigers; 12 to 24.5 mm long and 0.75 to 1.5 mm wide). Body yellowish in alcohol. Prostomium conical, with no eyes (Fig. 7A); peristomium bearing a pair of lateral nuchal organs (Fig. 7C). Thorax consisting of 17 chaetigers, last one transitional (Fig. 7A, D) (3 specimens with 16 chaetigers, 0.75-1 mm wide, and 1 specimen with 15 chaetigers, 1 mm wide; all collected in the Gulf of California). All thoracic parapodia birramous; notopodia with postchaetal lobes from chaetiger 1, increasing in length throughout (Figs 7A, C, E, 8A), becoming broader in posterior thorax (Figs 7G, I, 8C); bearing numerous crenulated capillaries arranged in 2-4 rows (Fig. 7E, H). Neuropodia with 1 podal papilla from chaetiger 2, increasing to 2 papillae from chaetigers 9 or 10 (Figs 7F, 8B-C, E). Abdomen cylindrical in section, notopodial postchaetal lamella broad and foliaceous; neuropodia bilobed, inner lobe longer and more robust (Figs 7I, 8D, F), with a notch at insertion of a lateral flange. Small subpodal papillae from posterior thoracic parapodia (chaetiger 13-15; 15-17 in syntypes), two subpodal papillae on chaetigers 17-18 (16-17 in syntypes), up to 4-5 subpodal papillae on chaetigers 19-23 (3-4 on chaetigers 18-24 in syntypes), decreasing to 1 or 2 in the next 3-4 chaetigers (1-3 chaetigers in syntypes); absent on posterior chaetigers (Figs 7B, D, 8C-F). No stomach papillae. Interramal cirri from chaetigers 15-17 (18 in syntypes), absent after chaetigers 19-29 (24-27 in syntypes) (Figs. 7I, 8C-D). Branchiae from chaetiger 9 (from chaetiger 8 in 1 specimen collected in the Gulf), slender, triangular, initially small, gradually increasing in length towards posterior region (Figs. 7A, G, 8C). All chaetae crenulate capillaries; abdominal neurochaetae weakly crenulate. No forked chaetae.

Remarks. Leitoscoloplos panamensis is included in the group of Leitoscoloplos with more than 10 thoracic chaetigers, bearing interramal cirri and subpodal papillae (Mackie 1987). Revision of available type material deposited in the British Natural History Museum (BMNH) and the specimens collected in the Gulf of California confirmed the occurrence of L. panamensis in this marine region (Hernández-Alcántara and Solís-Weiss 1999), since most of their morphological features agree well with the description (Fig. 2). Besides, we verified that in the type material of L. panamensis, branchiae start at chaetiger 9, as pointed out by Mackie (1987), and not at chaetiger 12 as stated in the original diagnosis (Monro, 1933). In fact, the beginning of branchiae can be considered as a stable feature in this species, since only in one specimen collected in the Gulf did branchiae start at chaetiger 8. Before this study, no other species of the genus had been recorded with more than four subpodal papillae. However, this characteristic is difficult to distinguish in the type material due to the poor condition of the syntypes, as also pointed out by Mackie (1987). In some specimens collected in the Gulf of California, up to five subpodal papillae were observed.

There is not enough material to correlate the morphological variations in size of both groups of L. panamensis (type material from Panama and Gulf of California, this study); however, it is clear that the specimens from Panama are significantly longer than those living in the Gulf of California (Bln: KW= 6.520, p= 0.011; Tln: KW= 7.361, p= 0.007) and that in the type material the interramal cirri (KW= 12.137, p= 0.001) and subpodal papillae (KW= 5.431, p= 0.020) initially appear 2 to 3 chaetigers later than in the specimens from the Gulf (Fig. 2). Differences found in the other morphological features were small and not significant.

Habitat. In 11 to 22 m depth (Mackie 1987). In the Gulf of California, this species was collected in 21 to 104 m, on sand, fine sand and muddy sand; temperature 14.1 to 32°C; salinity 34.2 to 35.9 psu; 1 to 6.5 ml/L dissolved oxygen and 3.6 to 7.2% organic carbon.

Geographical distribution. Taboga and Taboguilla Islands, Pacific coast of Panama (Monro, 1933). In northern and central Gulf of California, mainly on its eastern coasts.

Leitoscoloplos sp. (Fig. 9A-I)

Leitoscoloplos panamensis.− Hernández-Alcántara and Solís-Weiss, 1999: 27 (in part) (not Monro, 1933).

FIG2

Fig. 9. Leitoscoloplos sp. A) Thoracic region, dorso-lateral view; B) anterior end, ventro-lateral view; C) same, dorso-lateral view; D) chaetigers 4 to 8, antero-lateral view; E) neuropodia from chaetigers 9 and 10, anterior view; F) chaetigers 17 and 18, ventro-lateral view; G) anterior abdominal region, ventro-lateral view; H) transition from thorax (left) to abdomen lateral view; I) chaetigers 18 to 20, anterior view. (Roman numerals=number of chaetiger; IC=interramal cirri; NO=nuchal organ; SbPa=subpodal papilla; StPa=stomach papilla). Scale bars: A 0.5 mm; B, D-F, I 0.1 mm; C, G, H 0.2 mm.

Material examined. Twelve specimens (CNP-ICML: PO-01-029): Expedition ‘Cortés 1’: 4 specimens, Station 42, Tepoca Cape (30°12.4’N, 112°47.5’W), 30 m, muddy sand, collected by V. Solís-Weiss, 10 May 1982. Expedition ‘Cortés 2’: 1 specimen, Station 43, Tepoca Cape (30°08.6’N, 112°08.6’W), 69 m, muddy sand, 17 March 1985; 1 specimen, Station 51, El Fuerte River (25°42.1’N, 109°30.6’W), 49 m, muddy sand, 20 March 1985. Expedition ‘Cortés 3’: 2 specimens, one used for SEM, Station 42, Tepoca Cape (30°12.4’N, 112°47.2’W), 23 m, fine sand, 05 August 1985; 4 specimens, Station 52, El Fuerte River (25°43.6’N, 109°29.3’W), 22 m, fine sand, 8 August 1985. All localities are in the Gulf of California, and all specimens from expeditions ‘Cortés 2’ and ‘Cortés 3’ were collected by P. Hernández-Alcántara.

Description. Incomplete specimens with 26 to 102 chaetigers; 5.5 to 32 mm long and 1 to 2 mm wide. Body yellowish in alcohol. Prostomium conical, pointed (Fig. 9A-C), with no eyes. Peristomium with a pair of lateral nuchal organs (Fig. 9B-C). Thorax with 16-17 chaetigers, last one transitional (Fig. 9A, F). Branchiae from chaetiger 9, initially small, gradually increasing in length towards posterior region (Fig. 9A, F, I). All thoracic and abdominal chaetae crenulated capillaries (Fig. 9B, D-E). No forked or modified chaetae. Notopodia with postchaetal lobes from chaetiger 1, increasing in length throughout, becoming broader in posterior thorax, bearing numerous crenulated capillaries (Fig. 9D, H). Neuropodia with 1 podal papilla from first chaetiger (Fig. 9D), 2 papillae from chaetiger 9 or 10 (Fig. 9E-F). Notopodial postchaetal lobe broad and foliaceous in abdomen; neuropodia bilobed, with a notch at insertion of a lateral flange (Fig. 9G-I). Interramal cirri from chaetiger 15-17 (Fig. 9F-I), absent posterior to chaetigers 21-28. Subpodal papillae from posterior thoracic parapodia (chaetiger 13-15), 2 subpodal papillae on chaetigers 15-16 (Fig. 9F), up to 6 subpodal papillae on chaetigers 18-21, decreasing to 1 or 2 in the next 3-4 chaetigers (Fig. 9G-I); absent from chaetigers 22-25. With 1-2 stomach papillae on 1 or 2 posterior thoracic or anterior abdominal segments (between chaetigers 16 and 19), clearly in ventral position (Fig. 9F-I). Pygidium unknown.

Remarks. Leitoscoloplos sp. can be clearly separated from other species of the genus bearing stomach and subpodal papillae, since L. obovatus bears a single small stomach papilla and 1-3 subpodal papillae on 2-3 segments, but has a noticeably lower number of thoracic chaetigers (10-11), and L. multibranchiatus sp. nov. has abundant stomach (up to 14), and up to 8 subpodal papillae. However, it is important to emphasize that, except for the presence of 1-2 stomach papillae on 1-2 chaetigers, Leitoscoloplos sp. is very difficult to separate from L. panamensis. The morphological features in both taxa are almost identical, even if the specimens collected in Panama are longer (Bln: KW= 4.696, p= 0.030; Tln: KW= 5.450, p= 0.020), and their interramal cirri (KW= 12.137, p= 0.001) and subpodal papillae (KW= 5.431, p= 0.020) first appear on 2-3 chaetigers later than in Leitoscoloplos sp. (Fig. 2). In addition, differences between specimens of L. panamensis recorded in the Gulf of California and Leitoscoloplos sp. are even less evident: they can be slightly distinguished because Leitoscoloplos sp. has more subpodal papillae (4 to 6) than L. panamensis from the Gulf (3 to 5). Therefore, and in accordance with the morphometric analyses, we decided not to formally name this material.

The number and distribution of these stomach papillae have been important to identify species in other genera of orbiniids; however, as in other anatomical structures associated with parapodia, their origin and function remain somewhat unknown. For example, the lobe inserted at the base of the neuropodium has sometimes been referred to as ventral cirrus, but it is uncertain that it is homologous to the ventral cirrus of other aciculate polychaetes (Eibye-Jacobsen, 2002).

Habitat. In depths of 22 to 69 m, on fine sand and muddy sand; temperature 14.8 to 30°C; salinity 34.2 to 35.6 psu; 1.8 to 6.5 ml/L dissolved oxygen and 4.8 to 8.9% organic carbon.

Geographical distribution. Eastern coasts of the Gulf of California.