In the following, we describe one of largest specimens (specimen A) in detail. Furthermore, we provide a morphological description of comparable features of the additional seven specimens (specimen B–H). As the latter ones were not dissected, only features that were available in the intact specimens are described.
Specimen A (ZMUC-CRU-8679):
Habitus (Fig. 2). Small arthropod larva with a globose shield, bearing a long, anteriorly directed, rostral spine (slightly shorter than shield length) and lateral spines (similar length as rostral spine).
Body (Fig. 2) differentiated into cephalothorax, pleon and non-somitic telson. Body with 20 segments, ocular segment plus 19 appendage-bearing (post-ocular) segments.
Ocular segment incorporated into the cephalothorax, dorsal area contributes to the shield.
Post-ocular segment 1-13 (Fig. 2) incorporated into the cephalothorax, dorsal area contributes to the shield.
Post-ocular segment 14-19 (Fig. 2) are separate pleon segments, each dorsally forming a tergite.
Cephalothorax (Fig. 2) shield more or less spherical, without setae; large, shield-like, cuticular structure formed by dorsal region of cephalothoracic segments. Anterior rim of the shield drawn out into prominent rostral spine. Posterior rim of the shield slightly convex, with a confined gape, as wide as the posterior gape of the shield. Rostrum unpaired anterior extension of shield, elongated, without spines; anterior region slightly bent upwards. Shield length about 8.5 mm (measured with rostral spine) and 5.1 mm without rostral spine, maximum shield width (measured without spines), about 5.2 mm (about 60 % of shield length with rostral spine). Rostral spine about 40 % of the shield length with rostral spine.
Post-ocular segment 14 (Fig. 2) anterior-posterior dimension about 25 % of the shield length (without rostral spine); total width of the segment 25 % of the maximum shield width, as wide as the posterior gape of the shield; tergo-pleura not developed; anterior region of post ocular segment 15 slightly convex.
Post-ocular segment 15 (Fig. 2) anterior-posterior dimension about 5 % of the shield length (without rostral spine). Total width of the segment 25 % of the maximum shield width, as wide as the posterior gape of the shield. Tergo-pleura not developed. Post-ocular segment 15 armed with one cone-shaped spine in the middle of anterior rim of the segment.
Post-ocular segment 16 (Fig. 2) anterior-posterior dimension about 20 % of the shield length (without rostral spine). Total width of the segment about 25 % of the maximum shield width. Tergo-pleura not developed.
Post-ocular segment 17 (Fig. 2) anterior-posterior dimension about 20 % of the shield length (without rostral spine). Total width of the segment about 25 % of the maximum shield width. Tergo-pleura not developed.
Post-ocular segment 18 (Fig. 2) anterior-posterior dimension about 15 % of the shield length. Total width of the segment 50 % of the maximum shield width, measured on posterior rim of the segment. Axial region 25 % of the maximum shield width (without rostral spine). Tergo-pleura about 40 % of the axial region, on each side.
Post-ocular segment 19 (Fig. 2) anterior-posterior dimension about 10 % of the shield length (without rostral spine). Total width of the segment about 50 % of the maximum shield width. No clear differentiation between axial region and tergo-pleura.
Telson (Fig. 2) in dorsal view more or less rectangular. About 45 % of shield length (without rostral spine) and about 30 % wider than long. Anterior rim slightly concave, posterior rim convex. The lateral rim on each side slightly convex, telson width suddenly increased after about 20 % from anterior to posterior rim. Telson shape in lateral view distally tapering. Tip of telson more or less triangular-shaped from dorsal view, with a flattened tip. Forty-seven simple setae on tip of telson. Further lateral setae shorter than distal ones. The 20th setae counted from each terminal rim are the longest ones, the most central one is about 50 % shorter than the longest. Telson armed with two spines on distal rim as protrusion of lateral rim on each side.
Lateral eyes (Fig. 2) compound eyes, with numerous ommatidia covered by cornea; stalked.
Hypostome-labrum complex (Fig. 2) with more or less triangular-shaped labrum in ventral view, anteriorly surrounded by hypostome.
Appendage 1 (Antennula) (Fig. 3) differentiated into peduncle and one flagellum. Antennula with aesthetascs. Peduncle more or less tube-shaped and curved to outer lateral rim of the shield. With spine-like protrusion on distal part of the inner lateral rim. Not yet divided into elements, future subdivision into three elements visible. Width of broadest part about 50 % of maximum length. Flagellum 1 not yet developed. Flagellum 2 tube-shaped with a rounded tip. About 35 % shorter than peduncle, with a slightly curved inner lateral rim with numerous setae (aesthetascs) arranged in six tiers.
Appendage of post-ocular segment 2 (Antenna) (Fig. 3) differentiated into coxa, basipod (peduncle), endopod and a paddle-shaped exopod; bears opening of antennal gland on basipod. Peduncle not yet divided into elements, with one spine on distal rim of basipod, where endopod arises from it. Endopod pointed and curved, not yet divided into elements, without setae. Exopod paddle-shaped, with 17 plumose setae on the rounded tip and the outer lateral rim.
Appendage of post-ocular segment 3 (Mandible) (Fig. 3) differentiated into coxa with endite and mandibular palp. Coxa elongate in medio-lateral axis, medially ending in a row of about 12 teeth. Row consisting of more or less lobate teeth, short triangular and longer elongate teeth with a pointed tip. Mandibular palp not yet developed, but future palp visible. Sternal protrusion of mandibular segment (paragnaths) u-shaped with two lateral elongate paddle-shaped setae bearing protrusions on distal rim. About 35 % wider than maximum length and about as large as hypostome-labrum complex.
Appendage of post-ocular segment 4 (Maxillula) (Fig. 3) differentiated into coxa with coxal endite and basipod with basipodal endite and endopod. Coxal endite more or less triangular-shaped from proximal to distal, with a rounded tip, with four elongated plumose setae at the tip. Basipodal endite paddle-shaped, elongate, with four spines at the tip, armed with tiny spines; about 30 % longer than coxal endite. Endopod pointed extension on basipod, not subdivided; one elongate, plumose seta, and one smaller seta on the tip.
Appendage of post-ocular segment 5 (Maxilla) (Fig. 3) differentiated into coxa and basipod, both drawn out into two pronounced lobate endites each and exopod. Coxa with two lobate endites with four setae on each lobe. Distal lobe smaller, than proximal one. Basipod with two lobate endites with four setae on each lobe. Distal lobe larger, than proximal one. Endopod not yet developed. Exopod of appendage 5 largest element, bilobed with a distal and proximal lobe; with numerous plumose setae around the rim.
Appendage of post-ocular segment 6 (Maxilliped 1) (Fig. 4) with coxa and basipod, from which endopod and exopod arise. Coxa and basipod with endites. Coxa more or less tube-shaped; with endite. Coxal endite small, more or less triangular from proximal to distal, without setae. Basipod more or less rectangular, with heart-shaped protrusion of anterior part; bears endopod and exopod; about 73 % longer than coxa, about twice as long as wide. Basipodal endite very prominent, slightly curved; with nine plumose setae, and four spines (armed with tiny spines) on inner lateral rim. Endopod with five elements (ischium, merus, carpus, propodus, dactylus); about as long as maximum length of basipod. Endopod element 1 more or less tube-shaped; about 45 % longer than wide, with four plumose setae on distal rim. Endopod element 2 more or less tube-shaped; about as long as preceding element; about 45 % longer than wide, with two plumose setae on distal rim. Endopod element 3 more or less tube-shaped, about 30 % shorter than preceding element; about 40 % longer than wide, with two plumose setae on distal rim. Endopod element 4 more or less tube-shaped; about 20 % shorter than preceding element, about 30 % longer than wide, with three plumose setae on distal rim. Endopod element 5 pointed, about 16 % shorter than preceding element; about 60 % longer than wide, with five plumose setae on distal rim. Exopod tube-shaped, tapering; not yet subdivided into elements; bent backwards. 85 % longer than wide, with about 12 plumose setae on the tip; laterally with one lobate protrusion slightly beyond the inner proximal rim and one lobate protrusion slightly below the tip.
Appendage of post-ocular segment 7 (Maxilliped 2) (Fig. 4) with coxa and basipod, from which endopod and exopod arise. Coxa and basipod with endites. Coxa more or less tube-shaped, without setae; coxal endite small, more or less triangular from proximal to distal, without setae. Basipod more or less rectangular-shaped, with heart-shaped protrusion of anterior part; bears endopod and exopod, about 70 % longer than coxa, about twice as long as wide. Basipodal endite very prominent, slightly curved, with 3 plumose setae, on inner lateral rim. Endopod with four elements, about as long as maximum length of basipod. Endopod element 1 more or less tube-shaped, about 40 % longer than wide, with three plumose setae on inner distal rim. Endopod element 2 more or less tube-shaped; about 45 % longer than wide; about 10 % longer than preceding element; with two plumose setae on inner distal rim. Endopod element 3 more or less tube-shaped; about 50 % longer than maximum width, and about the same length than preceding element; with two plumose setae on inner distal rim. Endopod element 4 tapering with a rounded tip; about 60 % longer than wide; about 25 % shorter than preceding element; with three plumose setae on tip. Exopod of appendage 7 tube-shaped, tapering; not yet subdivided into elements; bent backwards, about 10 % shorter than endopod and about 85 % longer than wide; with about 12 plumose setae on the tip; setae bearing tip bent to the inner lateral side; laterally with one lobate protrusion slightly beyond the inner proximal rim and one lobate protrusion slightly below the tip.
Appendage of post-ocular segment 8 (Maxilliped 3) (Fig. 4) with coxa and basipod, from which endopod and exopod arise; without endites. Coxa more or less rectangular-shaped, without setae; coxal endite not developed. Basipod more or less tube-shaped; bears endopod and exopod. Endopod about 55 % longer than coxa; about twice as long as wide. Endopod with four elements, separation indicated by faint lines, about 15 % shorter than maximum length of basipod and about 70 % longer than wide. Endopod element 1 more or less tube-shaped, about 20 % longer than maximum width; without setae. Endopod element 2 more or less rectangular shaped; about 30 % wider than maximum length; about 40 % shorter than preceding element; without setae. Endopod element 3 more or less tube-shaped; about 50 % longer than maximum width, and about the same length than preceding element; with two plumose setae on inner distal rim. Endopod element 4 tapering, about as long as maximum width; about 15 % longer than preceding element, with two simple setae on tip. Exopod tube-shaped, tapering. Not yet subdivided into elements; slightly bent backwards; about 15 % longer than endopod and about 80 % longer than wide; with about 18 plumose setae on the tip. Setae bearing tip bent to the inner lateral side. Laterally with one lobate protrusion slightly below the tip.
Appendage of post-ocular segment 9 (Thoracopod 4) (Fig. 4) with coxa and basipod (difficult to differentiate in this developmental stage) and endopod; without setae. Endopod of appendage 9 consists of five visible elements (difficult to identify at this early developmental stage) separated by faint lines; distal part of this appendage is modified to a prominent chela. Endopod elements 1–2 probably corresponding to ischium and merus, not yet separated; more or less tube-shaped; about 25 % longer than maximum width. Endopod element 3 (carpus) more or less tube-shaped, curved to the inner side; about 15 % longer than maximum width; about 12 % shorter than preceding element.
Endopod element 4 (propodus) about 45 % longer than maximum width, with outgrowth, which represents the complement of the following element; outgrowth about 35 % shorter than mainpart of the element. Endopod element 5 (dactylus) movable against outgrowth of propodus; tapering, slightly curved; about 50 % of maximum length of preceding element (propodus). Chela is formed by the articulation of element 5 (dactylus) against an outgrowth of element 4 (propodus).
Appendage of post-ocular segment 10 (Thoracopod 5) (Fig. 4) with coxa and basipod (difficult to differentiate in this early developmental stage) and endopod. Without setae. Coxa difficult to differentiate in this early developmental stage; without setae. Basipod difficult to differentiate in this early developmental stage; without setae. Endopod consists of five elements (difficult to identify in this early developmental stage); distal part without chela. Endopod element 1 (ischium) more or less triangular-shaped from proximal to distal; about 25 % longer than maximum width; without setae. Endopod element 2 (merus) more or less tube-shaped, slightly curved to inner side; about 40 % longer than maximum length and 40 % longer than preceding element; without setae. Endopod element 3 (carpus) tube-shaped; about 30 % longer than maximum width and about 8 % shorter than preceding element; without setae. Endopod element 4 (propodus) tube-shaped, about as long as maximum width and about 30 % shorter than preceding element; without setae. Endopod element 5 (dactylus) tapering, with a slightly rounded tip; about 80 % longer than maximum width, and about 60 % longer than maximum width; without setae.
Appendage of post-ocular segment 11 (Thoracopod 6) (Fig. 4) with coxa and basipod (difficult to differentiate in this early developmental stage) and endopod; without setae.
Appendage of post-ocular segment 12 (Thoracopod 7) (Fig. 4) with coxa and basipod and endopod (difficult to differentiate in this early developmental stage, separation indicated by faint lines); without setae.
Appendage of post-ocular segment 13 (Thoracopod 8) (Fig. 4) with coxa and basipod and endopod (difficult to differentiate in this early developmental stage, separation indicated by faint lines); without setae.
Appendage of post-ocular segment 14 (Pleopod 1) (Fig. 4) not found, not documented.
Appendage of post-ocular segment 15 (Pleopod 2) (Fig. 4) differentiated into basipod and endopod. Separation indicated by a faint line. Basipod elongate tube-shaped, about 50 % longer than maximum width. Endopod of appendage 15 tube-shaped, with a rounded tip; about 40 % longer than maximum width, and about 20 % shorter than basipod.
Appendage of post-ocular segment 16 (Pleopod 3) (Fig. 4) differentiated into basipod and endopod. Separation indicated by a faint line. Basipod elongate tube-shaped, about 35 % longer than maximum width. Endopod of appendage 16 tube-shaped, with a rounded tip; about 25 % longer than maximum width, and about 35 % shorter than basipod.
Appendage of post-ocular segment 17 (Pleopod 4) (Fig. 4) differentiated into basipod and endopod. Separation indicated by a faint line. Basipod elongate tube-shaped, about 35 % longer than maximum width. Endopod of appendage 17 tube-shaped, with a rounded tip; about 40 % longer than maximum width, and about 10 % shorter than basipod.
Appendage of post-ocular segment 18 (Pleopod 5) (Fig. 4) differentiated into basipod and endopod. Separation indicated by a faint line. Basipod elongate tube-shaped, about 47 % longer than maximum width. Endopod of appendage 18 tube-shaped, with a rounded tip; about 40 % longer than maximum width, and about 35 % shorter than basipod.
Appendage of post-ocular segment 19 (Uropod) (Fig. 4) differentiated into basipod and endopod and exopod. Basipod tube-shaped, 55 % longer than maximum width. Endopod tube-shaped with a rounded tip, about 40 % longer than maximum width. Without setae. Exopod paddle-shaped, with about 16 plumose setae on the distal rim, and the inner lateral rim of appendage. With one spine representing the delineation of setae and extention of the outer rim of exopod.
Morphological description of comparable features of specimens B–H
Specimen B (ZMUC-CRU-8681) (Fig. 5):
Shield. Shield length about 8.5 mm (measured with rostral spine). Maximum width (measured without spines) about 3.5 mm (about 40 % of shield length).
Rostral spine. Anterior part slightly bent upwards. About 45 % of the shield length.
Telson. Anterior and posterior rim slightly convex. The lateral rim on each side slightly convex, width slowly increasing from anterior to posterior. Rim of telson more or less curly brace-shaped, with a rounded tip. Telson armed with two spines on distal rim as protrusion of lateral rim on each side.
Specimen C (ZMUC-CRU-8680) (Fig. 5):
Shield. Shield length about 7.5 mm (measured with rostral spine). Maximum width (measured without spines, about 3.4 mm (45 % of shield length).
Rostral spine. Anterior part slightly bent upwards. About 35 % of the shield length.
Telson. Anterior rim slightly convex, posterior rim slightly concave. The lateral rim on each side slightly convex, width slowly increasing from anterior to posterior. Rim of telson more or less curly brace-shaped, with a rounded tip. Telson armed with two spines on distal rim as protrusion of lateral rim on each side.
Specimen D (ZMUC-CRU-8683) (Fig. 5):
Shield. Shield length about 5 mm (measured with rostral spine). Maximum width (measured without spines, about 2.3 mm (45 % of shield length).
Rostral spine. Anterior part slightly bent upwards. About 35 % of the shield length.
Telson. Anterior rim slightly convex, posterior rim slightly concave. The lateral rim on each side slightly convex, width slowly increasing from anterior to posterior. Rim of telson more or less triangular-shaped from dorsal view, with a flattened tip. Telson armed with two spines on distal rim as protrusion of lateral rim on each side.
Specimen E (MNHN-IU-2014-5468) (Fig. 5):
Shield. Shield length about 7.4 mm (measured with rostral spine) and about 3 mm (measured without rostral spine). Maximum width (measured without spines, about 2.5 mm (30 % of shield length).
Rostral spine. Anterior part strongly bent downwards. About 120 % of the shield length.
Telson. Anterior rim slightly convex, posterior rim slightly concave. Lateral rim difficult to recognize; apparently slightly convex, probably with lobate structure. Telson width suddenly increasing after about 45 % from anterior to posterior rim. Rim of telson more or less triangular-shaped from dorsal view, with a slightly flattened tip. Telson probably armed with two spines on distal rim as protrusion of lateral rim on each side.
Specimen F (Mu_267) (Fig. 5):
Shield. Shield length about 8.3 mm (measured with rostral spine). Maximum width (measured without spines), about 4 mm (50 % of shield length).
Rostral spine. No bending visible. Not documented from lateral, or ventro-lateral view. About 50 % of the shield length
Telson. Anterior rim slightly convex, posterior rim slightly concave. Lateral rim slightly convex, with lobate structure. Telson width suddenly increased after about 40 % from anterior to posterior rim. Rim of telson more or less triangular-shaped from dorsal view, with a flattened tip. Telson armed with two spines on distal rim as protrusion of lateral rim on each side.
Specimen G (ZMUC-CRU-8684) (Fig. 5):
Shield. Shield length about 5.2 mm (measured with rostral spine). Maximum width (measured without spines), about 2.5 mm (50 % of shield length).
Rostral spine. No bending visible. Not documented from lateral, or ventro-lateral view. About 40 % of the shield length.
Telson. Anterior rim slightly convex, posterior rim slightly concave. The lateral rim on each side slightly convex, width slowly increasing from anterior to posterior. Rim of telson more or less triangular-shaped in dorsal view, with a flattened tip. Telson armed with two spines on distal rim as protrusion of lateral rim on each side.
Specimen H (ZMUC-CRU-8682) (Fig. 5):
Shield. Shield length about 9 mm (measured with rostral spine). Maximum width (measured without spines, about 3.6 mm (40 % of shield length).
Rostral spine. Anterior part slightly bent upwards. About 40 % of the shield length.
Telson. Anterior rim slightly convex, posterior rim slightly concave. The lateral rim on each side slightly convex, width slowly increasing from anterior to posterior. Rim of telson more or less curly brace-shaped, with a rounded tip. Telson armed with two spines on distal rim as protrusion of lateral rim on each side.