Facetotectan larvae from the White Sea with the description of a new species (Crustacea: Thecostraca)

A new species of the Y-larva genus Hansenocaris Itô, 1985 (Crustacea: Thecostraca: Facetotecta) from the Azores, with notes on its morphology and biogeography

“…The enigmatic Y-larvae represent the last significant group of Crustacea for which the adult forms are still unknown [Grygier, 1996;Kolbasov, Høeg, 2003;Glenner et al, 2008;Høeg et al, 2014;Kolbasov et al, 2021]. Their naupliar and cypridiform larvae have been found in the marine plankton worldwide.…”

“…Different facetotectan nauplii from West Indian, equatorial Atlantic waters and from the Bay of Kiel in the Baltic were first described in detail more than 100 years ago by Hansen [1899]. Subsequently Y-larvae were reported from almost all oceans in the world [Kolbasov, Høeg, 2003;Belmonte, 2005;Ponomarenko, Korn, 2006;Swathi, Mohan, 2019]. A post-naupliar instar or 'Y-cyprid' resembling other thecostracan cypridiform larvae was first described by Bresciani [1965].…”

A new internal structure of nauplius larvae: A “ghostly” support sling for cypris y left within the exuviae of nauplius y after metamorphosis (Crustacea: Thecostraca: Facetotecta)

“…For individual “species,” a para‐taxonomy of Roman‐numeral “Types” developed and continued to expand even after Itô (, , ), Belmonte (), Kolbasov and Høeg (), and Kolbasov, Grygier, Ivanenko, and Vagelli () began to formally describe what now amount to 12 Japanese, Mediterranean, Arctic, and Indonesian species in the genus Hansenocaris Itô, . Some of these species were based on y‐nauplii, others on y‐cyprids, as these larvae are also called, while only H. furcifera Itô, and H. itoi Kolbasov and Høeg, are currently known from both kinds of larvae (Itô, , ; Kolbasov & Høeg, ). Both species have planktotrophic nauplii, but many other facetotectan nauplii are lecithotrophic.…”

“…Grygier (1985) proposed the higher-level taxon Facetotecta for y-larvae; it is currently ranked as an infraclass or subclass within the Thecostraca, as the apparent sister group of Ascothoracida+Cirripedia (e.g., Pérez-Losada et al, 2009). For individual "species," a para-taxonomy of Roman-numeral "Types" developed and continued to expand even after Itô (1985Itô ( , 1986bItô ( , 1989, Belmonte (2005), Kolbasov and Høeg (2003), and Kolbasov, Grygier, Ivanenko, and Vagelli (2007) began to formally describe what now amount to 12 Japanese, Mediterranean, Arctic, and Indonesian species in the genus Hansenocaris Itô, 1985. Some of these species were based on y-nauplii, others on y-cyprids, as these larvae are also called, while only H. furcifera Itô, 1989 andH. itoi Kolbasov andHøeg, 2003 are currently known from both kinds of larvae (Itô, 1989(Itô, , 1990Kolbasov & Høeg, 2003).…”

Identification of Y-Nauplii (Facetotecta) in Andaman Sea, India

“…Due to its close similarity with Ascothoracida and Cirripedia, this Y-larvae/Y-nauplii has been named as facetotecta (subclass) by Grygier [1] [2] [3]. Ito [4] [5] [6] [7] and Kolbasov and Hoeg [8] proposed a genus based on the cypris morphology. Later, different collections from the world's oceans of this larvae necessitated classification of the scheme based on the plate nomenclature of the cephalic shield [9] [10].…”