Chalarosthrix gen. nov., a new taxon of the Sphingothrix-Triathrix clade (Harpacticoida: Cletodidae) from the Province of Cortez, Eastern Mexican Pacific.

Seven species of four cletodid genera previously described or reported from Mexico (Cletodes, Enhydrosoma, Geehydrosoma, and Stylicletodes) and an undescribed genus presumably related to Sphingothrix and Triathrix, were found in sediment samples from a coastal system in north-western Mexico. The Bayesian analysis of 95 morphological characters of thirty-four cletodid genera revealed that the new genus, Chalarosthrix gen. nov., is closely related to Sphingothrix. The clade Sphingothrix-Chalarosthrix bears a sister group relationship with Triathrix. These three genera constitute a monophyletic group defined by the presence of a posterior chitinous extension of the cephalothorax with four sensillum-bearing socles, and the presence of a median tube-pore on the anal operculum. Other synapomorphies for Sphingothrix and Triathrix proposed by earlier researchers are re-evaluated upon the latest definition of the Cletodidae. Our analysis supports previous studies in that Sphingothrix can be objectively defined by i) the reduction of the distal outer seta of the last exopodal segment of the first swimming leg being at most as long as the subdistal outer spine, and ii) the distal inner seta of the same segment inclined outwards intersecting the distal outer element at its base. On the other hand, no (aut)apomorphies were detected for Triathrix. The new genus, Chalarosthrix gen. nov., is defined here by the apomorphic secondary loss of the inner element of the second endopodal segment of the first swimming leg. Some comments on the relationships of the new genus are given.

On some deep-sea Stenheliinae from the Gulf of California and the west coast of the Baja California Peninsula (Mexico): the genus Delavalia Brady, 1869 and proposal of Archaeohuysia gen. nov. and Diarthropodella gen. nov. (Copepoda: Harpacticoida: Miraciidae).

Several species belonging to the harpacticoid families Ameiridae Boeck, Ancorabolidae Sars, Argestidae Por, and Rhizothrichidae Por have been described so far as an ongoing long-term project on the diversity of deep-sea benthic harpacticoids collected from the Gulf of California and Mexican Pacific. Amongst the several harpacticoid taxa, the subfamily Stenheliinae Brady (Miraciidae Dana) showed to be one of the most important components to overall species richness in deep-sea sediments. Following the rejection of segmentation pattern of the first swimming leg as the only discriminant for subgeneric assignment of stenheliin taxa, four new species of Delavalia Brady, 1869 and two new genera, Archaeohuysia gen. nov. and Diarthropodella gen. nov. are proposed herein. The new Delavalia species belong to the longicaudata-group with close relatives in shallow-water habitats. The so far monotypic Archaeohuysia gen. nov. showed to be unique in the combination of the general structure of the first swimming leg and retention of the primitive complement of four setae on the second endopodal segment of the same leg. Diarthropodella gen. nov. is the only stenheliin taxon with a two-segmented exopod of the first swimming leg. Some comments are given on probable multiple colonization events of stenheliin taxa.

On some deep-sea Stenheliinae from the Gulf of California and the west coast of the Baja California Peninsula (Mexico): Pseudostenhelia bathyalis sp. nov., and Beatricella calidafornax sp. nov. (Copepoda: Harpacticoida: Miraciidae).

At present, only a handful of harpacticoid species of the families Ameiridae Boeck, Ancorabolidae Sars, Argestidae Por, and Rhizothrichidae Por have been described from the deep sea of the Gulf of California and west coast of the Baja California Peninsula. Recent efforts resulted in the description of a new genus, Wellstenvalia Gmez Cruz-Barraza, 2021, closely related to Muohuysia zdikmen, 2009 and Wellstenhelia Karanovic Kim, 2014 and some new deep-sea species of Delavalia Brady, 1869. Other new stenheliin genera from the Gulf of California and the west coast of the Baja California Peninsula are the subjects of another contribution in this volume. The present contribution deals with the description of the first deep-sea representatives of Pseudostenhelia Wells, 1967 and Beatricella Scott, 1905, two typically shallow brackish water and marine genera. Some comments on their relationships are given.

On some deep-sea Stenheliinae from the Gulf of California and the west coast of the Baja California Peninsula (Mexico): Wellstenhelia euterpoides sp. nov., and Wellstenvalia wellsi gen. et sp. nov. (Copepoda: Harpacticoida: Miraciidae).

At present, only 11 species of harpacticoid copepods have been described from the deep sea of the Gulf of California and the west coast of the Baja California Peninsula. These efforts had until recently been focused exclusively on the families Ameiridae Boeck, Argestidae Por, and Rhizothrichidae Por. Preliminary analyses revealed also an important contribution of the subfamily Stenheliinae Brady (Miraciidae Dana) to the overall species richness and diversity of deep-sea benthic copepods from the west coast of the Baja California Peninsula, and the central and southern Gulf of California. One new species of the genus Wellstenhelia Karanovic Kim, 2014, We. euterpoides sp. nov., and one new genus and species, Wellstenvalia wellsi gen. et sp. nov., are herein described from sediment samples taken at eight sampling stations in the west coast of the Baja California Peninsula and in the central and southern Gulf of California. Wellstenhelia euterpoides sp. nov. seems to be closely related to We. euterpe Karanovic Kim, 2014 with which it shares the reduced armature complement of the baseoendopod of the female fifth leg. The so far monotypic genus Wellstenvalia gen. nov. was found to be closely related to Muohuysia zdikmen, 2009 and Wellstenhelia. Some comments on the relationships between the new genus proposed here and other stenheliin genera and species are provided as a contribution towards the monophyly of the subfamily.

A new species of Paralaophonte Lang 1948 (Harpacticoida: Laophontidae), with notes on the phylogeny of the genus and its relationships with Loureirophonte Jakobi 1953 using Bayesian inference.

Early studies during the 1990s supported a close relationship between the genera Paralaophonte and Loureirophonte. Subsequent studies carried out during the first decade of the 2000s suggested the monophyly of the latter and that it could be nested within Paralaophonte, rendering the latter paraphyletic. However, efforts to synonymize these two genera were hampered by the lack of phylogenetic analyses at the species level. Here we describe a new species of Paralaophonte from north-western Mexico, P. ullama sp. nov., and we formally synonymize Loureirophonte with Paralaophonte for which we propose two monophyletic subgenera, Pa. (Paralaophonte) and Pa. (Loureirophonte). The detection of the species most closely related to P. ullama sp. nov. is controversial. Our Bayesian analysis indicates that the new species might be related to Pa. (Pa.) gurneyi, and to Pa. (Pa.) ormieresi and Pa. (Pa.) septemarticulata, with which they form a larger clade supported by a very low Bayesian Posterior Probability value. However, the precise nature of the relationship between the new species and Pa. (Pa.) gurneyi is hampered by the gap in our knowledge of the armature formulae of the swimming legs of the latter, and by the lack of the male of the new species. On the other hand, the new species share several characters with Pa. (Pa.) problematica, Pa. (Pa.) pacificavicinum, Pa. (Pa.) pacificaemulator, and Pa. (Pa.) pacifica, with which it might be related. Our Bayesian analysis of forty-two morphological characters at the species level confirmed earlier suspicions about the relationships between Paralaophonte and Loureirophonte, the latter being nested within the former, and showed the monophyly of the Paralaophonte-Loureirophonte clade with high Bayesian Posterior Probability value, thus confirming the synonymy of these genera. The Paralaophonte-Loureirophonte clade is defined by the synapomorphic dimorphism in the second endopodal segment of the second swimming leg of the male. We did not detect any (aut)apomorphy for Pa. (Paralaophonte). Paralaophonte (Loureirophonte) is defined by the presence of one seta only on the second endopodal segment of the second swimming leg, and the one-segmented endopod of the fourth swimming leg.

Proposal of Arktourella gen. nov., a new genus of the family Normanellidae Lang 1944 (Copepoda: Harpacticoida) from the Province of Cortez.

A new genus, Arktourella gen. nov., is proposed to accommodate a new member of the harpacticoid family Normanellidae, A. margarethae gen. et sp. nov., from a polluted estuary in north-western Mexico. The new genus was attributed to the laophontoidean family Normanellidae on account of the lack of outer spinous processes on the second antennulary segment, one abexopodal seta on the antennary allobasis, four setae on the one-segmented antennary exopod, endopod of first swimming leg two-segmented with first segment elongated and with two distal elements on second segment, endopods of second to fourth legs two-segmented, distal setae on the male second endopodal segment of second and third legs reduced, and outer spine of the male second endopodal segment of third leg fused to segment. The new, so far monotypic genus, differs from the other normanellid genera in the presence of four elements on the third exopodal segment of the first leg, and two outer spines on the third exopodal segment of second to fourth legs. No synapomorphies were observed for Arktourella gen. nov. and Normanella, but they are unique within the Normanellidae in that the mandibular basis and endopod are not fused. Maximum parsimony analysis and Bayesian inference using 59 morphological characters to assess the relationships between the genera of the family Normanellidae confirmed the affinity of Arktourella gen. nov. and Normanella, and their sister group relationship with Sagamiella. Paranaiara and Pseudocletodes were shown consistently to be closely related and are the sister taxa of Normanella-Arktourella gen. nov.-Sagamiella. Arktourella gen. nov., Paranaiara and Pseudocletodes share the presence of a large spinulose spine on the fifth and sixth segments of the female antennule, but its significance is not clear. Additionally, we propose a key to the genera of the Normanellidae.