Nicon salinus Hernández-Acántara & Dávila-Jiménez sp. nov.

Materials

Type status: Holotype. Occurrence: catalogNumber: CNAP-POH- 39-003; recordedBy: Yasmín Dávila-Jiménez; individualCount: 1; lifeStage: adult; occurrenceStatus: present; preparations: 70 % EtOH; disposition: in collection; occurrenceID: 1EB9D302-9286-5C39-8966-5C9A5EEC3762; Taxon: scientificName: Nicon salinus Hernández-Alcántara & Dávila-Jiménez; kingdom: Animalia; phylum: Annelida; class: Polychaeta; order: Phyllodocida; family: Nereididae; genus: Nicon; specificEpithet: salinus; taxonRank: species; scientificNameAuthorship: Hernández-Alcántara & Dávila-Jiménez; nomenclaturalCode: ICZN; Location: continent: North America; waterBody: Southern Gulf of Mexico; country: Mexico; countryCode: MX; stateProvince: Yucatán; locality: Río Lagartos, hypersaline coastal lagoon; verbatimDepth: 1.03 m; locationRemarks: hypersaline coastal lagoon; verbatimLatitude: 21°35.74'N; verbatimLongitude: 88°04.28'W; verbatimCoordinateSystem: degrees decimal minutes; Event: samplingProtocol: Ponar standard dredge 0.052 m 2; eventDate: 19-05 - 2005; habitat: 14.3 % silt, 69.9 % sand, 15.8 % gravel, 31.5 ° C, 34.3 psu, 7.21 mg / l, pH 8.16; fieldNumber: 15 - RL 1805; Record Level: institutionCode: ICML-UNAM; collectionCode: CNAP; basisOfRecord: PreservedSpecimen

Type status: Paratype. Occurrence: catalogNumber: CNAP-POP- 39-005; recordedBy: Yasmín Dávila-Jiménez; individualCount: 8; lifeStage: adult; occurrenceStatus: present; preparations: 70 % EtOH; disposition: in collection; occurrenceID: 3C2085B4-BD95-59C5-BF36-EB11CC6B9FC9; Taxon: scientificName: Nicon salinus Hernández-Alcántara & Dávila-Jiménez; kingdom: Animalia; phylum: Annelida; class: Polychaeta; order: Phyllodocida; family: Nereididae; genus: Nicon; specificEpithet: salinus; taxonRank: species; scientificNameAuthorship: Hernández-Alcántara & Dávila-Jiménez; nomenclaturalCode: ICZN; Location: continent: North America; waterBody: Southern Gulf of Mexico; country: Mexico; countryCode: MX; stateProvince: Yucatán; locality: Río Lagartos, hypersaline coastal lagoon; verbatimDepth: 1.09 m; locationRemarks: hypersaline coastal lagoon; verbatimLatitude: 21°36.46'N; verbatimLongitude: 88°08.12'W; verbatimCoordinateSystem: degrees decimal minutes; Event: samplingProtocol: Ponar standard dredge 0.052 m 2; eventDate: 19-05 - 2018; habitat: 6.9 % silt, 66.8 % sand, 26.28 % gravel, 30.5 ° C, 35.19 psu, 9.87 mg / l, pH 8.39; fieldNumber: 12 - RL 1805; Record Level: institutionCode: ICML-UNAM; collectionCode: CNAP; basisOfRecord: PreservedSpecimen

Type status: Paratype. Occurrence: catalogNumber: CNAP-POP- 39-006; recordedBy: Yasmín Dávila-Jiménez; individualCount: 2; lifeStage: adult; occurrenceStatus: present; preparations: coated with gold; disposition: in collection; occurrenceID: 8CCD5200-0822-5099-B539-B648643070C8; Taxon: scientificName: Nicon salinus Hernández-Alcántara & Dávila-Jiménez; kingdom: Animalia; phylum: Annelida; class: Polychaeta; order: Phyllodocida; family: Nereididae; genus: Nicon; specificEpithet: salinus; taxonRank: species; scientificNameAuthorship: Hernández-Alcántara & Dávila-Jiménez; nomenclaturalCode: ICZN; Location: continent: North America; waterBody: Southern Gulf of Mexico; country: Mexico; countryCode: MX; stateProvince: Yucatán; locality: Río Lagartos, hypersaline coastal lagoon; verbatimDepth: 1.09 m; locationRemarks: hypersaline coastal lagoon; verbatimLatitude: 21°36.46'N; verbatimLongitude: 88°08.12'W; verbatimCoordinateSystem: degrees decimal minutes; Event: samplingProtocol: Ponar standard dredge 0.052 m 2; eventDate: 19-05 - 2018; habitat: 6.9 % silt, 66.8 % sand, 26.28 % gravel, 30.5 ° C, 35.19 psu, 9.87 mg / l, pH 8.39; fieldNumber: 12 - RL 1805; Record Level: institutionCode: ICML-UNAM; collectionCode: CNAP; basisOfRecord: specimens coated with gold for SEM studies

Type status: Paratype. Occurrence: catalogNumber: CNAP-POP- 39-007; recordedBy: Yasmín Dávila-Jiménez; individualCount: 5; lifeStage: adult; occurrenceStatus: present; preparations: 70 % EtOH; disposition: in collection; occurrenceID: E0E83DBD-1A2D-57CD-81AF-FA6092D56DB9; Taxon: scientificName: Nicon salinus Hernández-Alcántara & Dávila-Jiménez; kingdom: Animalia; phylum: Annelida; class: Polychaeta; order: Phyllodocida; family: Nereididae; genus: Nicon; specificEpithet: salinus; taxonRank: species; scientificNameAuthorship: Hernández-Alcántara & Dávila-Jiménez; nomenclaturalCode: ICZN; Location: continent: North America; waterBody: Southern Gulf of Mexico; country: Mexico; countryCode: MX; stateProvince: Yucatán; locality: Río Lagartos, hypersaline coastal lagoon; verbatimDepth: 1.03 m; locationRemarks: hypersaline coastal lagoon; verbatimLatitude: 21°35.74'N; verbatimLongitude: 88°04.28'W; verbatimCoordinateSystem: degrees decimal minutes; Event: samplingProtocol: Ponar standard dredge 0.052 m 2; eventDate: 19-05 - 2005; habitat: 14.3 % silt, 69.9 % sand, 15.8 % gravel, 31.5 ° C, 34.3 psu, 7.21 mg / l, pH 8.16; fieldNumber: 15 - RL 1805; Record Level: institutionCode: ICML-UNAM; collectionCode: CNAP; basisOfRecord: PreservedSpecimen

Type status: Other material. Occurrence: catalogNumber: CNAP-PO- 39-034 / 2025 - GMX-LE; recordedBy: Yasmín Dávila-Jiménez; individualCount: 7; lifeStage: adult; occurrenceStatus: present; preparations: 70 % EtOH; disposition: in collection; occurrenceID: 64C2C811-6FA9-5B81-B86A-2EC2325FA5A0; Taxon: scientificName: Nicon salinus Hernández-Alcántara & Dávila-Jiménez; kingdom: Animalia; phylum: Annelida; class: Polychaeta; order: Phyllodocida; family: Nereididae; genus: Nicon; specificEpithet: salinus; taxonRank: species; scientificNameAuthorship: Hernández-Alcántara & Dávila-Jiménez; nomenclaturalCode: ICZN; Location: continent: North America; waterBody: Southern Gulf of Mexico; country: Mexico; countryCode: MX; stateProvince: Yucatán; locality: Río Lagartos, hypersaline coastal lagoon; verbatimDepth: 1.09 m; locationRemarks: hypersaline coastal lagoon; verbatimLatitude: 21°36.46'N; verbatimLongitude: 88°08.12'W; verbatimCoordinateSystem: degrees decimal minutes; Event: samplingProtocol: Ponar standard dredge 0.052 m 2; eventDate: 19-05 - 2018; habitat: 6.9 % silt, 66.8 % sand, 26.28 % gravel, 30.5 ° C, 35.19 psu, 9.87 mg / l, pH 8.39; fieldNumber: 12 - RL 1805; Record Level: institutionCode: ICML-UNAM; collectionCode: CNAP; basisOfRecord: PreservedSpecimen

Type status: Other material. Occurrence: catalogNumber: CNAP-PO- 39-034 / 2026 - GMX-LE; recordedBy: Yasmín Dávila-Jiménez; individualCount: 8; lifeStage: adult; occurrenceStatus: present; preparations: 70 % EtOH; disposition: in collection; occurrenceID: 45D22B06-60DE-5337-8BCE-BC242D073016; Taxon: scientificName: Nicon salinus Hernández-Alcántara & Dávila-Jiménez; kingdom: Animalia; phylum: Annelida; class: Polychaeta; order: Phyllodocida; family: Nereididae; genus: Nicon; specificEpithet: salinus; taxonRank: species; scientificNameAuthorship: Hernández-Alcántara & Dávila-Jiménez; nomenclaturalCode: ICZN; Location: continent: North America; waterBody: Southern Gulf of Mexico; country: Mexico; countryCode: MX; stateProvince: Yucatán; locality: Río Lagartos, hypersaline coastal lagoon; verbatimDepth: 0.61 m; locationRemarks: hypersaline coastal lagoon; verbatimLatitude: 21°35.73'N; verbatimLongitude: 88°04.28'W; verbatimCoordinateSystem: degrees decimal minutes; Event: samplingProtocol: Ponar standard dredge 0.052 m 2; eventDate: 28-02 - 2018; habitat: 49.3 % silt, 50.1 % sand, 0.6 % gravel, 26.7 ° C, 54.46 psu, 8.09 mg / l, pH 8.24; fieldNumber: 15 - RL- 1802; Record Level: institutionCode: ICML-UNAM; collectionCode: CNAP; basisOfRecord: PreservedSpecimen

Type status: Other material. Occurrence: catalogNumber: CNAP-PO- 39-034 / 2027 - GMX-LE; recordedBy: Yasmín Dávila-Jiménez; individualCount: 5; lifeStage: adult; occurrenceStatus: present; preparations: 70 % EtOH; disposition: in collection; occurrenceID: 50C8E210-996E-54B1-86F7-56172AC00AA5; Taxon: scientificName: Nicon salinus Hernández-Alcántara & Dávila-Jiménez; kingdom: Animalia; phylum: Annelida; class: Polychaeta; order: Phyllodocida; family: Nereididae; genus: Nicon; specificEpithet: salinus; taxonRank: species; scientificNameAuthorship: Hernández-Alcántara & Dávila-Jiménez; nomenclaturalCode: ICZN; Location: continent: North America; waterBody: Southern Gulf of Mexico; country: Mexico; countryCode: MX; stateProvince: Yucatán; locality: Río Lagartos, hypersaline coastal lagoon; verbatimDepth: 1.03 m; locationRemarks: hypersaline coastal lagoon; verbatimLatitude: 21°35.74'N; verbatimLongitude: 88°04.28'W; verbatimCoordinateSystem: degrees decimal minutes; Event: samplingProtocol: Ponar standard dredge 0.052 m 2; eventDate: 19-05 - 2005; habitat: 14.3 % silt, 69.9 % sand, 15.8 % gravel, 31.5 ° C, 34.3 psu, 7.21 mg / l, pH 8.16; fieldNumber: 15 - RL 1805; Record Level: institutionCode: ICML-UNAM; collectionCode: CNAP; basisOfRecord: PreservedSpecimen

Description

Holotype complete, with 84 segments, 30 mm long, 2 mm wide at chaetiger 15 (without chaetae). Paratypes incomplete, with 20–56 segments, 4–25 mm long, 0.8–1.0 mm wide. Colour in ethanol light brown. Prostomium slightly wider than long with a frontal cleft; two small frontal digitate antennae (Fig. 1 A). Two pairs of eyes in trapezoidal arrangement, similar in size (Fig. 2 A). Palps biarticulate, palpophore well developed, barrel-shaped, with subspherical palpostyles (Fig. 1 A, Fig. 2 A). Peristomium slightly longer than chaetiger 1, with four pairs of tentacular cirri, short, the longest postero-dorsally reaching to chaetiger 2 (Fig. 1 A). Oral and maxillary pharyngeal rings without paragnaths or papillae; jaws brown, with 5 teeth on the dentate cutting edge. First two chaetigers sub-birramous; notopodia without aciculae, represented by a subulate dorsal ligule and short dorsal cirrus (Fig. 1 B); neuropodia with subulate postchaetal lobe and ventral ligules and short ventral cirrus (Fig. 1 C), only bearing homogomph spinigers (Fig. 2 E-G). Birramous chaetigers from chaetiger 3 (Fig. 1 D-I, Fig. 2 B-D).

Anterior notopodia with short cirriform dorsal cirrus inserted at base of the triangular dorsal ligule; subulate median ligule; cirrus-like prechaetal lobe slightly shorter than the subulate median ligule (Fig. 1 D – F, Fig. 2 B); cirriform prechaetal lobe gradually smaller in middle chaetigers (Fig. 1 D – H, Fig. 2 C, D). Median and posterior notopodia with long, cirrus-like, dorsal ligule and short dorsal cirrus, inserted at base of ligule (Fig. 1 H, I, Fig. 2 C, D); median and posterior chaetigers with short prechaetal lobe, as a small process (Fig. 1 H, Fig. 2 C, D); near to pygidium, the dorsal ligule is shorter (Fig. 1 I).

Anterior neuropodia with a short digitiform postchaetal lobe, projecting beyond end of the acicular ligule (Fig. 1 G, Fig. 2 B), a triangular ventral ligule and a short ventral cirrus (Fig. 2 B). Median and posterior neuropodia with a short postchaetal lobe (Fig. 1 C); subulate neuropodial ventral ligule, gradually smaller until entirely disappearing in posterior chaetigers; short ventral cirrus (Fig. 2 D).

All notochaetae homogomph spinigers, with long, thin blades. Anterior neuropodia with homogomph spinigers, those in the supra- acicular ramus with long-blades and those from the infra-acicular ramus with short-blades (Fig. 2 B, E – G). Median and posterior neuropodia with a supra-acicular ramus having long-bladed homogomph spinigers; infracicular ramus with homogomph spinigers superiorly and homogomph falcigers inferiorly, ending in a blunt curved tooth (Fig. 2 H – K). Pygidium with broad margin and two long cirriform cirri, as long as last 7–8 segments (Fig. 1 B).

Type material

Holotype (CNAP-POH- 39-003) and fifteen paratypes (CNAP-POP- 39-005, CNAP-POP- 39-005, CNAP-POP- 39-006). Only preserved specimens were available for the original description.

Material examined

Holotype (CNAP-POH- 39-003) and paratypes CNAP-POP- 39-005 (5 specimens, Sta. 15 - RL 1805, 21°35.74'N, 88°4.28'W), CNAP-POP- 39-005 (8 specimens, Sta. 12 - RL 1805, 21°36.46'N, 88°08.12'W), CNAP-ICML: POP- 39-006 (Sta. 12 - RL 1805, 2 specimens coated with gold for SEM studies). Other additional specimens were examined: CNAP-PO- 39-034 / 2025 - GMX-LE (7 specimens, Sta. 12 - RL 1805; 21°36.46'N, 88°8.12'W); CNAP-PO- 39-034 / 2026 - GMX-LE (8 specimens, Sta. 15 - RL 1802; 21°35.73'N, 88°04.28'W; CNAP-PO- 39-034 / 2027 - GMX-LE (5 specimens, Sta. 15 - RL 1805; 21°35.74'N, 88°04.28'W).

Type locality

Southern Gulf of Mexico, Río Lagartos, Sta. 15 - RL 1805, 21°35.74'N, 88°4.28'W, collected at 1.03 m depth, in fine sand bottoms.

Diagnosis

Pharynx with two dentate jaws, without papillae or paragnaths. Anterior notopodia with triangular dorsal ligule and short cirriform dorsal cirri; subulate prechaetal lobe, similar in length to median ligule; median and posterior notopodia with dorsal ligule long, cirrus-like. Neuropodia with an acicular lobe and subulate neuroacicular ligule; triangular ventral ligule decreasing in size towards posterior chaetigers until entirely disappearing; short ventral cirrus. All notochaetae homogomph spinigers. Neuropodia with long and short-bladed homogomph spinigers and homogomph falcigers with blades ending in a blunt curved tooth.

Etymology

The species name is derived from the Latin word “ salinus ”, meaning “salty” or “salted”, adjective used to highlight the hypersaline environment that this new nereidid inhabits, tolerating salinities up to 54.46 psu. Gender masculine.

Distribution

Only known from type locality

Ecology

Habitat: At 0.29–1.09 m depth, in fine sand and mud-sandy bottoms (50.08–78.67 % sand). Temperature: 26.5–31.5 ° C; salinity: 34.30–54.46 psu; dissolved oxygen: 6.13–9.87 mg / l; pH: 7.97–8.39.

Taxon discussion

The genus Nicon has eleven valid species, including N. salinus sp. nov. (Read, G.; Fauchald, K. (Ed.) 2024), which can be separated into two large groups, according to presence or absence of notopodial prechaetal lobes (de León-González and Trovant 2013). The species group lacking notopodial prechaetal lobes includes N. ablepsia Wang et al., 2021 (Wang et al. 2021), N. abyssalis Hartman, 1967, N. maculatus Kinberg, 1865 (Kinberg 1865), N. moniloceras (Hartman, 1940) (Hartman 1940), N. pettibonae de León-González & Salazar-Vallejo, 2003 (de León-González and Salazar-Vallejo 2003) and N. yaquinae Fauchald, 1977 (Fauchald 1977) (Table 1).

On the other hand, the species group bearing notopodial prechaetal lobes includes N. salinus sp. nov. from the Gulf of Mexico, N. aestuarensis Knox, 1951 (Knox 1951) from New Zealand, N. japonicus Imajima, 1972 (Imajima 1972) from Ariake Sea, Japan, N. orensanzi de León-González & Trovant, 2013 from Bunche Beach, Ecuador and N. rotundus Hutchings & Reid, 1990 from Port Darwin, Australia. Nicon salinus sp. nov., with the anterior notopodial prechaetal lobes long, only slightly shorter than the median ligule and the neuropodia exclusively bearing homogomph spinigers and homogomph falcigers, can be clearly separated from N. aestuarensis, N. japonicus and N. rotundus, which have heterogomph falcigers and short notopodial dorsal ligules. In addition to heterogomph falcigers, N. rotundus also bears homogomph falcigers, whereas N. aestuarensis and N. japonicus bear heterogomph spinigers (Table 1).

In this group, Nicon orensanzi and N. salinus sp. nov. are the only species having long notopodial dorsal ligules, cirrus-like, on median and posterior parapodia. In N. orensanzi, the anterior notopodia have small triangular prechaetal lobes, which are absent in median and posterior notopodia and the neuropodia bear homogomph and heterogomph spinigers and sesquigomph falcigers. In contrast, the anterior notopodia in N. salinus sp. nov. have subulate prechaetal lobes, similar in length to the median ligules, absent in posterior chaetigers and the neuropodia only bear homogomph spinigers and homogomph falcigers (Table 1).

Previously, N. rotundus and N. abyssalis had been the only species of this genus having neuropodial homogomph falcigers, which were also observed in N. salinus sp. nov., but those species lack notopodial prechaetal lobes and, therefore, belong to the other Nicon species group (Table 1).

Methods

Sampling: The biological material was collected in February and May 2018 along the hypersaline Río Lagartos system, as part of the SALINITY GRADIENT ENERGY project of the Centro Mexicano de Innovación en Energía Océano (CEMIE Océano). It is an estuarine system located in the southern Gulf of Mexico (21 ° 26 ' – 21°38'N; 87 ° 30 ' – 88°05'W), belonging to the Ría Lagartos Biosphere Reserve. The samples were taken with a Ponar standard dredge (0.052 m 2) and the sediments were sieved through a 500 μm mesh size to separate the macrofauna.

Preservation: The individuals were initially anaesthetised with magnesium chloride, fixed in 4 % formaldehyde and later preserved in 70 % ethanol (Dávila-Jiménez et al. 2019).

Morphological methods: The specimens of the new species were examined in detail to compare their morphological characteristics with those observed in close species: anterior, middle and posterior parapodia were dissected and mounted on glass slides to examine their morphological features and chaetal types. The scanning electron photographs were taken with a JEOL JSM 6360 LV microscope, the individuals were dehydrated via a graded ethanol series, critical-point dried with liquid CO 2 and coated with gold.

Terminology: To date, different terms have been given to name the nereidid parapodial structures, so, to standardise them we used the terminology for the atokous parapodial suggested by Villalobos-Guerrero and Bakken (2018) with some modifications made by Villalobos-Guerrero et al. (2021). However, due to the neuropodial lobes in the species of Nicon not being separable into superior and inferior lobes, the neuropodial lobe was named as the acicular lobe in accordance with Pettibone (1971) and Hutchings and Reid (1990), amongst others. The definition of types of articulation to the compound chaetae (homogomph, sesquigomph and heterogomph) suggested by Villalobos-Guerrero and Bakken (2018) was used to classify the observed homogomph falcigers in the new species.

Repository: The holotype and paratypes of the new species and the additional material examined were deposited in the " Colección Nacional de Anélidos Poliquetos " of the ICML, UNAM (CNAP-ICML: DFE. IN. 061.0598).