Redescription of Deltamysis holmquistae Bowman & Orsi, 1992 (Crustacea: Mysida: Mysidae), a mysid species new to the Atlantic Ocean with observations on the taxonomic status of Kochimysis Panampunnayil & Biju, 2007

Abstract

The first occurrences of the estuarine mysid Deltamysis holmquistae Bowman & Orsi from the Atlantic Ocean are documented from sites on the eastern Florida and northwest Gulf of Mexico (Texas) coasts of North America. Based on examination of type material and specimens from Florida and Texas, considerable morphological variability and additional characters were observed necessitating a rediagnosis of the monotypic genus Deltamysis and a redescription of D. holmquistae. As a result of these new taxonomic criteria, the Indian Ocean species, Kochimysis pillaii Panampunnayil & Biju, described from southwest coastal India, is subsumed as a junior synonym of D. holmquistae. The current distribution of this apparently invasive species is probably due to maritime commerce. The geographical location of the endemic or source populations of D. holmquistae remains undetermined; however, its co-occurrence in California with three introduced Asian mysids suggests a northern Indian Ocean or northwest Pacific origin.

On the mysid crustacean genus Deltamysis (Mysidae: Heteromysinae), with a new species and a new record from Australia

“…Distribution.Western Indo-Pacific. Originally recorded from Sacramento-San Joaquin Estuary in California (Bowman & Orsi, 1992), and later also along the Atlantic US coast (Scripter et al, 2020), where it was supposed to be introduced. With discovery of D. lowryi sp.…”

“…With discovery of D. lowryi sp. nov. on the New South Wales coast, and the transfer of the former Kochimysis pillai from India (Scripter et al, 2020), the former Heteromysoides nana from northern Australian coast and H. songkhlaensis from Thailand to Deltamysis (Daneliya, 2021), it is now clear that the genus is naturally distributed in the Western Indo-Pacific Region (Fig. 1).…”

“…Panampunnayil & Biju (2007) distinguished the genus Kochimysis from Deltamysis on the basis of the male lobe presence on the antennular peduncle, the articulation absence on the antennal scale, the presence of the lacinia mobilis on the mandible and the wide segment 2 of the mandibular palp, equal size of the maxilla 2 endopod segments and the oval shape of its segment 2. Such discrimination was possible partly due to confusion (Scripter et al, 2020), because Bowman & Orsi (1992), describing Deltamysis, 1) did not notice the male lobe on the antennulae; 2) mentioned the presence of the lacinia mobilis on the left mandible and its absence of the right mandible (p. 737); 3) it was also the aspect of the mandibular palp illustration that did not show the width of the segment 2; 4) the maxilla 2 was mistakenly illustrated as 3-segmented with rather short segment 2, and the aspect did not clearly show the width of the segments. The presence or absence of the articulation on the antennal scale is a common intraspecific variation in different groups of mysids.…”

“…Variation. Scripter et al (2020) provided rather detailed information on the variation in D. holmquistae. I will only mention here the most diagnostically important features.…”

“…Deltamysis and Kochimysis found their position in Mysidetini. Scripter et al (2020) collected new material on D. holmquistae from the US Atlantic coast. After a detailed morphological revision of new and the type material they found that originally D. holmquistae males were not carefully studied and revealed that the males had special cuticular prominences on the maxillipeds 2, similar to K. pillaii.…”