No abstract

Hydroids of the Pacific coast of Mexico have been little studied. For the coast of Oaxaca, only five papers provide information on species of the region, with some records included in those publications being questionable. Seven species, Pennaria disticha, Clytia linearis, Clytia cf. gracilis, Obelia dichotoma, Ventromma halecioides, Dynamena crisioides and Tridentata turbinata, were discovered during the study and are reported herein. Of these species, Pennaria disticha and Tridentata turbinata are new records for the Mexican Pacific coast, and Clytia linearis and Ventromma halecioides are new records for Oaxaca. Geographic ranges of other hydroids, recorded in earlier studies, are expanded.

Studies on size changes of Ophiuroidea are limited, despite their importance and implications in taxonomy, phylogenetics, ecology, and distribution. These studies have traditionally been based on descriptive size series seldom integrating quantitative analyses to assess the morphological variability of species, despite their potential use to study size changes in brittle stars. To confirm the latter, size changes of Ophiocomella alexandri were studied here using this approach. The studied size series of O. alexandri included specimens from 1.64 to 23.64 mm disc diameter (DD).Quantitative and qualitative external morphological characters were examined on each specimen, and quantitative analyses (cluster, one-way permutational analysis of variance, and discriminant analysis) were employed to identify size groups within the species. The allometric relationship disc diameter-total arm length (DD-AL) was estimated for each size group and the combined size groups. Two size groups were identified: Group 1, subdivided into Subgroup 1.1 and Subgroup 1.2, and Group 2. Each size group presented particular characters which were described, discussed, and compared with relevant literature. The relationship DD-AL was positively allometric for Group 1 and combined size groups, and isometric for Group 2. The results highlight the potential of quantitative analyses to address size-related morphological changes in ophiuroids, and the importance of conducting this type of study to correctly identify species regardless of their size. This is the first study to describe size-related morphological changes of a brittle star from the Eastern Pacific, and the first one focused on a member of Ophiocomidae globally.

The non-indigenous bryozoan Amathia verticillata (delle Chiaje, 1822) is recorded for the first time from the southern Mexican Pacific. The species was detected between 2014 and 2018 at three locations along the coast of Oaxaca, southwestern Mexico: Puerto Ángel Bay, Santa Cruz Bay, and La Blanca Island. A discussion on the introduction of the species to Oaxaca is also included.

No abstract