Fig 1.
Thysanoessa raschii (Euphausiacea), adult morphology and map of sampling sites.
(A) Adult morphology of Thysanoessa raschii (Euphausiacea) (photo by permission from Russel Hopcroft). (B, C) Map of Godthåbsfjord, SW Greenland, with sampling stations indicated by black dots and station numbers. The larvae examined in this study originated from station GF8 (arrow on C).
Fig 2.
Size of nauplii 1–3 (N1-N3) and metanauplius (MN) of Thysanoessa raschii (Euphausiacea).
Illustrated as width plotted against length (in millimeters) based on data shown in Table 1.
Fig 3.
Nauplii 1–3 and metanauplius of Thysanoessa raschii (Euphausiacea), light microscopy.
(A) Nauplius 1. (B) Nauplius 2. (C) Nauplius 3. (D) Metanauplius. The images are not to the same scale. See Table 1 and Fig 2 for size variation of the larvae.
Table 1.
Sizes of nauplii (N1-3) and metanauplii (MN) based on measurements of body length and width (mm) (see text).
Fig 4.
Nauplius 1 of Thysanoessa raschii (Euphausiacea), scanning electron microscopy (SEM).
(A) Posterior view of whole specimen. (B) Lateral view of whole specimen. (C) Ventral view of whole specimen. (D) Ventral view of right side of whole specimen. (E) Antenna 1, distal setation. (F) Antenna 2, distal setation of endopod and exopod. (G) Mandible, right side, endopod and exopod. (H) Anlagen to caudal setae.
Fig 5.
Nauplius 2 of Thysanoessa raschii (Euphausiacea), scanning electron microscopy (SEM).
(A) Ventral view of whole specimen. (B) Lateral view of whole specimen. (C) Incipient mouth opening (?). (D) Antenna 1, right side. (E) Antenna 2, right side, anterior view. (F) Mandible, right side, anterior view. (G) Antenna 2 and mandible, right side. (H) Caudal setae, ventral view. (I) Caudal seta, left side, posterior view.
Fig 6.
Nauplius 3 of Thysanoessa raschii (Euphausiacea), scanning electron microscopy (SEM).
(A) Ventral view of whole specimen. (B) Incipient mouth opening (?). (C) Antenna 1, left side. (D) Tip of antenna 1. (E) Antenna 2, left side. (F) Mandible, left side. (G) Lateral view of whole specimen. (H) Antennae 1 and 2, left side, dorso-lateral view. (I) Antenna 2 endopod and exopod, left side. (J) Tip of antenna 2 exopod. (K) Tip of antennae 1.
Fig 7.
Metanauplius of Thysanoessa raschii (Euphausiacea), scanning electron microscopy (SEM).
(A) Ventral view of whole specimen. (B) Frontal filaments. (C) Antenna 1, left side. (D) Tip of antenna 1, left side. (E) Tip of antenna 1, right side. (F) Cuticular structure of unknown significance on labrum. (G) Antenna 2, left side. (H) Tips of endopod and exopod of antenna 2. (I) Mandible and paragnath, right side, anterior view. (J) Rudimentary palp (endopodal part?) of mandible. (K) Rudimentary palp (endopod and exopod?) of mandible. (L) Ventral view of whole specimen with first and second antennae omitted. (M) Setation/spination of caudal lobe of left side. (N) Anal opening. (O) Setules of long caudal setae.
Fig 8.
Metanauplius of Thysanoessa raschii (Euphausiacea), scanning electron microscopy (SEM).
(A) Lateral view of whole specimen. (B) Caudal view of whole specimen. (C) Appendages (mandible, maxilla 1 and 2, thoracopod 1) of right side, lateral view. (D) Appendages (mandible, maxilla 1 and 2, thoracopod 1) of both sides, ventral view. (E) Frontal view showing antennae 1 and frontal filaments. (F) Marginal spines of posterior part of naupliar shield.
Fig 9.
Overview of setation/spination of appendages and caudal region in nauplii 1–3 and metanauplius of Thysanoessa raschii (Euphausiacea).
(A-D) Antenna 1. (E-H) Antenna 2. (I-L) Mandible. (M-P) Caudal region. * Indicates new structures or structures that are modified compared to the previous larval stage.
Table 2.
Setae and spines of nauplii 1–3 and metanauplius of Thysanoessa raschii (Malacostraca, Euphausiacea) with emphasis on structures useful for identification of different stages.
This table corresponds to the overview of structures in Fig 9.
Table 3.
Summary of naupliar and metanaupliar development in broadcast-spawning species of euphausiaceans.
Only information from papers providing original contributions has been included. Some of the species included in the table are illustrated in Fig 10.
Fig 10.
Overview of naupliar and metanaupliar stages of some of the species of Euphausiacea studied in most detail.
(A-C) Two nauplii and one metanauplius of Thysanoessa raschii (from [43]). (D-F) Two nauplii and one metanauplius of Thysanoessa inermis (from [44]). (G-J) Three nauplii and one metanauplius of Meganyctiphanes norvegica (from [45]). (K-M) Two nauplii and one metanauplius of Meganyctiphanes norvegica (from [46]). (N-P) Two nauplii and one metanauplius of Euphausia superba (from [47]). (Q-S) Two nauplii and one metanauplius of Euphausia pacifica (from [48]).
Fig 11.
Early (= naupliar type) development of two malacostracan taxa and two non-malacostracan.
(A-D) Four naupliar stages of the Cambrian ‘Orsten’ crustacean Rehbachiella kinnekullensis (from [20]). (E-H) Four naupliar type stages of Branchinecta occidentalis (Anostraca) (from [75]). (I-L) Four (out of six) naupliar stages of Metapenaeopsis dalei (Dendrobranchiata Decapoda) (from [73]).
Fig 12.
Evolution of naupliar development mapped on a simplified phylogeny of the Malacostraca based on several papers providing partly conflicting phylogenetic results [76, 77].
The figure summarizes the idea supported in this paper, that the naupliar type of development seen in two malacostracan taxa, Euphausiacea and dendrobranchiate decapods (A and B), in essence is primitive for malacostracans and retained, but modified, from earlier in evolution (red line). C-H show other examples of the variation in developmental type in Malacostraca, both of taxa with free-living larvae and direct developers. (C) Early embryonic-like stage of Nebalia longicornis (Leptostraca) (from [78]). (D) Antizoea larva (Stomatopoda). (E) Zoea larva (Brachyura). (F) Late development stage of Tulumella unidens (Thermosbaenacea) (from [14]). (G) Praunus inermis (Mysida) (from [79]). (H) Idotea baltica (Isopoda) (material collected in Denmark by JO). (I) Three examples of non-malacostracan taxa with free living nauplii early in their development (Branchiopoda, Copepoda, and the Cambrian Rehbachiella).