Spirontocaris murdochi, Rathbun, 1902, Rathbun, 1902

Sedova, N. A. & Grigoriev, S. S., 2022, Morphology of the larval stages of Spirontocaris murdochi Rathbun, 1902 (Decapoda: Thoridae) from adjacent waters of Kamchatka, Arthropoda Selecta 31 (1), pp. 19-33 : 22-28

publication ID	https://doi.org/10.15298/arthsel.31.1.03
DOI	https://doi.org/10.5281/zenodo.15556831
persistent identifier	https://treatment.plazi.org/id/05088793-BA0A-C632-FCE0-FD32FB44F016
treatment provided by	Felipe
scientific name	Spirontocaris murdochi
status

Treatment

Results View in CoL

ZOEA I

Material examined: larvae were caught on July 6–9, 2016 at three stations in southern part of Western Kamchatka shelf over bottom depths of 21–87 m and off the southeastern coast of Kamchatka in April 2017 in two stations over bottom depth of 560 and 655 m.

Dimensions: TL 4.51±0.06 (4.3–4.9) mm, CL 0.86±0.03 (0.7–0.9) mm, RL 0.54±0.02 (0.5–0.7) mm.

Carapace ( Fig. 2 View Fig , GV, Cp, Cp*, Cp**, Cp***): rostrum long, directed forward (in 1/3 of studied specimens it reaches front margin of eyes, in the majority — not much longer); eyes cylindrical, anterior and posterior dorsomedian papillae present; pterygostomian spine present; anteroventral margin with 3–4 small spines (in 1/3 of specimens in one side of carapace only 2 spines); supraorbital spines absent.

Antennule ( Fig. 2 View Fig , A 1 View Fig ): peduncle unsegmented, with 1 long plumose seta terminally; short outer flagellum with 3 aesthetascs and 1 spinous process.

Antenna ( Fig. 2, A2, A2 View Fig *): protopod unsegmented, with 1 distal spine; endopod shorter than scaphocerite or approximately equal in length; with 1 terminal spine and 1 long terminal plumose setae, base of flagellum is not separated; scaphocerite 5–6-segmented, 4–5 short segments distally, with 7–9 plumose setae in inner margin, 1–2 plumose setae in outer margin, and 1 small simple seta in apex.

Maxillule ( Fig. 2 View Fig , Mx1): coxal endite with 5 papposerrate setae and 2 lateral plumose setae, basial endite with 10 cuspidate setae; endopod with 1 short simple and 5 strong papposerrate setae.

Maxilla ( Fig. 2 View Fig , Mx2): coxal endite bilobed with 8–9+3 and 2+1 papposerrate setae; basial endite bilobed with 4+1 papposerrate setae in each lobe; endopod unsegmented, trilobed, bearing 3+2+3 papposerrate setae; scaphognathite with 5 marginal plumose setae.

First maxilliped ( Fig. 2 View Fig , Mp1): coxa with 3+1+2 setae, very small epipod present; basis with 6+3+4 setae; endopod 4-segmented, with 3, 1, 2, 1+3 papposerrate setae; exopod unsegmented, with 1 or 2 subterminal setae on lateral margin and 3 long terminal plumose setae. Number of setae in right and left appendages differed in half of specimens.

Second maxilliped ( Fig. 2 View Fig , Mp2): coxa with 1 papposerrate setae; basis with 2+3+3 papposerrate setae; endopod 4- segmented with 3, 1, 2, 5+1 papposerrate setae; exopod 2- segmented, with 2 subterminal and 3 terminal long plumose setae.

Third maxilliped ( Fig. 2 View Fig , Mp3): coxa unarmed; basis with 1+1+2 papposerrate setae; endopod 5-segmented with 2, 0, 1, 2, 1, 4+1 papposerrate setae; exopod unsegmented, with 2 subterminal and 3 terminal plumose setae.

Pereopods ( Fig. 2 View Fig , P 1–P View Fig 5 View Fig ): unsegmented, unarmed; pereopods 1–2 biramous, pereopods 3–5 uniramous.

Pleon ( Fig. 2 View Fig , GV): five pleomeres; fourth and fifth pleomeres with a pair of dorsolateral spines, anal spine small.

Pleopods: absent.

Uropods: absent.

Telson ( Fig. 2 View Fig , T): triangular, indented medially, with 7+7 setae (inner 5 plumose and the outer 2 plumose only on proximal axis). In terminal margin a deep and wide semicircular notch.

ZOEA II

Material examined: larvae were caught in 6 stations from April 19 to May 16, 2017 in the Gulf of Avacha (southeastern Kamchatka) over bottom depth of 49 to 655 m.

Dimensions: TL 5.71±0.18 (5.0–6.7) mm, CL 1.36±0.02 (1.2–1.4) mm, RL 0.6±0.05 (0.5–0.7) mm.

Carapace ( Fig. 3 View Fig , GV, Cp, Cp*): eyes stalked, with ocular peduncle shorter than antennal peduncle; rostrum slightly raised up, usually not much short than front margin of eye; supraorbital spines small; pterygostomian spine long, thin; in anteroventral margin 2–4 small spines (in most specimens the number of spines varies in the left and right).

Antennule ( Fig. 3 View Fig , A 1 View Fig ): peduncle 2-segmented, with large spine ventrally and 4 small plumose setae in the outer margin positioned at about two third the length of the first segment and with 1 long plumose seta terminally, distal segment with 4 short plumose setae terminally; outer flagellum with 3–4 aesthetascs and 1 spinous process terminally; small inner flagellum unsegmented, with 1 long plumose seta.

Antenna ( Fig. 3 View Fig , A 2 View Fig , Sc): peduncle 2-segmented; scaphocerite 4–5-segmented, 3–4 short segments distally, with 11– 13 plumose setae on inner margin and 2 small simple setae on apex; spine in scaphocerite not long (usually reaches front margin of scale); endopod with 1 terminal spine and 1 long terminal plumose seta (in some specimens shorter than scaphocerite, in the rest it is approximately equal in length).

Maxillule: coxal endite with 8–9 papposerrate setae, basial endite with 11 cuspidate setae in both limbs; endopod unchanged.

Maxilla ( Fig. 3 View Fig , Mx2): scaphognathite with 9–10 marginal plumose setae; coxal endite, basial endite and endopod unchanged.

First maxilliped ( Fig. 3 View Fig , Mp1): coxa, epipod and basis unchanged; exopod unsegmented, with 1 or 2 setae subterminal and 3 long terminal plumose setae. Number of setae in many specimens differed in right and left appendages.

Second maxilliped ( Fig. 3 View Fig , Mp2): coxa and basis unchanged; endopod 4-segmented with 3+1, 1, 2, 5+1 papposerrate setae; exopod 2-segmented, with 11–12 long plumose setae.

Third maxilliped ( Fig. 3 View Fig , Mp3): coxa, basis and endopod unchanged; exopod unsegmented, with 12 plumose setae. In many specimens 2–4 apical setae in exopod were thin and short ( Fig. 3 View Fig , Mp1*, Mp2*).

First and second pereopods ( Fig. 3 View Fig , P 1–P View Fig 2 View Fig ): long, biramous, unsegmented; without swimming setae; there are rudiments of chela.

Third to fifth pereopods ( Fig. 3, P3–P View Fig 5 View Fig ): long, uniramous, unsegmented.

Pleon ( Fig. 3 View Fig , GV): 6 pleomeres; fourth and fifth pleomeres with a pair of dorsolateral spines, anal spine small.

First pleopods: absent.

Second to fifth pleopods: small buds.

Uropods: absent.

Telson ( Fig. 3 View Fig , T): triangular; not separated from sixth pleomere; 8+8 plumose setae, outer plumose seta in proximal axis only. The telson shape is shown in the figure.

ZOEA III

Material examined: larvae were caught in three stations in the Gulf of Avacha (southeastern Kamchatka) from April 19 to May 16, 2017 over bottom depth of 49 to 2000 m, as well as at 6 stations in the western Kamchatka shelf from June 13 to 24, 2015 over bottom depths of 23–123 m, and in the Bering Sea in August 2010 over bottom depth of 64 m.

Dimensions: TL 6.47±0.1 (5.3–7.4) mm, CL 1.46±0.04 (1.2–1.7) mm. RL 0.58 ±0.02 (0.4–0.7) mm.

Carapace ( Fig. 4 View Fig , GV Cp, Cp*): rostrum thin, slightly raised up; usually not longer than the front margin of eye; pterygostomian spine long; anteroventral margin by 1–2 small spines at least in one side; supraorbital spines large and thin.

Antennule ( Fig. 4 View Fig , A 1, A1 View Fig *): peduncle unchanged; inner flagellum unsegmented, with 1 long plumose seta; in half of larvae outer flagellum unsegmented, with 4–5 terminal and 2 subterminal aesthetascs, in the rest two-segment ones.

Antenna ( Fig. 4 View Fig , A 2, A2 View Fig *): peduncle unchanged; endopodite in most larvae is two-segmented, in some it is unsegmented, nearly equal scaphocerite, with 1 short spine and 1 small reduced seta terminally; scaphocerite 3–4-segmented, 2–3 short segments distally, with 19–20 plumose setae in inner margin; spine on scaphocerite extends beyond edge of plate by at least 1/3 of its length of spine.

Maxillule: coxal endite with 9–10 papposerrate setae, basial endite in 1/ 3 larvae with 12 cuspidate setae in both appendages, in 2/3 of larvae basial endite with 12 setae in one appendage, and with 13 ones in other; endopod unchanged.

Maxilla ( Fig. 4 View Fig , Mx2, Sg): coxal endite bilobed with 9– 10+5 and 2+1 papposerrate setae; basial endite bilobed with 5+1 papposerrate setae in each lobe; endopod unchanged; scaphognathite with 12–16 marginal plumose setae.

First to third maxilliped ( Fig. 4 View Fig , Mp1–3): the first pair of maxillipeds with larger epipod, the rest unchanged; endopod, coxa and basis of second and third pairs unchanged; exopod of second and third pairs of maxillipeds bear 10–12 and 12–13 setae respectively; distal segments separated.

First to second pereopods ( Fig. 4 View Fig , P 1–P View Fig 2 View Fig ): biramous, with protopod; exopod without setae, endopod with 2–3 small setae.

Third to fifth pereopods ( Fig. 4 View Fig , P 3–P View Fig 5 View Fig ): uniramous, unsegmented.

Pleon unchanged.

First pleopod ( Fig. 4 View Fig , pl1): absent in 2/3 studied larvae; rest in form of very small tubercle or absent.

Second pleopod ( Fig. 4 View Fig , pl2, pl2*): small buds in 2/3 studied larvae; rest in form of round bilobed tubercles.

Third to fifth pleopods ( Fig. 4 View Fig , pl3–5, pl3*): bilobed buds in 2/3 studied larvae; rest have long bifurcated tubercles. Uropods ( Fig. 4 T, T View Fig *, T**): biramous; endopod small with 1–2 short plumose setae apically; exopod well developed, reach terminal margin of telson, with 10–12 marginal plumose setae and very small spine in outer margin. One specimen had 3 apical setae in e left endopod, and 2 apical setae in the right.

Telson ( Fig. 4 View Fig , T, T*, T**): separated from sixth pleomere, with a pair of lateral short simple setae followed by 7+7 plumose setae; a wide deep notch in terminal margin.

ZOEA IV

Material examined: larvae were caught it two stations over the Western Kamchatka shelf from June 13 to July 7, 2015 above bottom depth of 69–80 m; two specimens from the Olutoro-Navarinsky region were also studied, which were caught in late August over bottom depth of 27 m and off the coast of southeastern Kamchatka on April 26, 2017 over bottom depth of 86 m.

Dimensions: TL 7.43±0.13 (6.8–7.8) mm. CL 1.74±0.02 (1.5–1.8) mm. RL 0.77±0.04 (0.6–0.9) mm.

Carapace ( Fig. 5 View Fig , GV): unchanged.

Antennule ( Fig. 5 View Fig , A 1 View Fig ): peduncle 3-segmented, first segment with 5–6 small plumose setae distally; second segment with 6 small and 1 long plumose setae distally; third segment with 3 long plumose setae distally; inner flagellum 3- segmented, distal segment with 1 long plumose seta; outer flagellum 4-segmented with 3+3+3+(2–3) aesthetascs.

Antenna ( Fig. 5 View Fig , A 2 View Fig ): endopod longer then scaphocerite; spine at the end of the endopod small; the protopod of the endopod separated; scaphocerite 2–3-segmented, with 20– 30 plumose setae along inner and posterior margin; spine on scaphocerite extends beyond anterior margin of scale (in some specimens in half of its length of spine).

Maxillule: coxal endite unchanged, basial endite with 13–14 cuspidate setae (most of studied larvae bear 13 spines in one maxillule, and 14 in the other), endopod unchanged.

Maxilla ( Fig. 5 View Fig , Mx2, Sg): coxal endite, basial endite and endopod unchanged; scaphognathite with 16–20 marginal plumose setae.

First–third maxilliped ( Fig. 5 View Fig , Mp1–3): coxa, basis and endopod unchanged; exopods of the first–third pairs of maxillipeds bear 5–14–16 setae respectively; in base of all maxillipeds there are underdeveloped gills.

First to second pereopods ( Fig. 5 View Fig , P 1–P View Fig 2 View Fig ): biramous, with 2-segmented protopod; exopod of the first pair with 8– 10 long plumose setae, chela forming, with 6–8 plumose setae available. Chela in the first pair of pereopods is not much larger in size than in P2. In base there are underdeveloped gills.

Third to fifth pereopods ( Fig. 5 View Fig , P 3–P View Fig 5 View Fig ): uniramous, 7- segmented, with elongated distal segments In base there are underdeveloped gills. Next stage is visible through cuticle in six larvae. It is clear that in stage V these segments will be pointed and long.

Pleon unchanged.

First pleopods ( Fig. 5 View Fig , pl1): rounded buds bilobed in the apex.

Second to fifth pleopods ( Fig. 5 View Fig , pl2–5): biramous, protopod naked, endopod of the fourth and fifth pleopods can be with rudiment of appendix interna.

Uropods ( Fig. 5 View Fig , T): biramous; endopod slightly shorter than exopod; exopod reach posterior margin of telson, with 12–15 plumose setae and very small spine in outer margin.

Telson ( Fig. 5 View Fig , T): expands slightly towards the end, with 2 pair of lateral spines and 6 pairs of terminal posterior processes, with notch in terminal margin.

ZOEA V

Material examined: 4 specimens from the western part of the Bering Sea, caught over bottom depth of 27 m.

Dimensions: TL 8.64±0.08 (8.6–8.7) mm; CL 1.9±0.11 (1.8–2.0) mm; RL 0.78±0.07 (0.7–0.8) mm.

Carapace unchanged.

Antennule ( Fig. 6 View Fig , A 1 View Fig ): peduncle unchanged; inner flagellum 4-segmented, distal segment of inner flagellum much longer than others; outer flagellum 5-segmented.

Antenna ( Fig. 6 View Fig , A 2 View Fig ): peduncle 2-segmented, scaphocerite 3–4-segmented, spine on scaphocerite long; endopod longer then scaphocerite.

Maxillule: coxal endite with 9–11 papposerrate setae, basial endite with 15 cuspidate setae, endopod unchanged.

Maxilla ( Fig. 6 View Fig , Mx2): coxal endite bilobed with 11+5 and 2+1 papposerrate setae; basial endite bilobed with 6+1 papposerrate setae in each lobe; endopod unchanged; scaphognathite with 18–24 marginal plumose setae.

First maxilliped ( Fig. 6 View Fig , Mp1): with large epipod, coxa and basis unchanged; exopod 2-segmented, with 1 or 2 setae subterminally on lateral margin and 3 long terminal plumose setae.

Second and third maxilliped ( Fig. 6 View Fig , Mp2–3) unchanged. At the base there are gills.

Pereopods ( Fig. 6 View Fig , P 1–3 View Fig View Fig View Fig ): exopod of the first pair with 12–14 long plumose setae; the second pair with 10–11 plumose setae available; third to fifth pair uniramous, distal segments long, pointed. At the base there are gills.

Pleon unchanged.

First pleopods ( Fig. 6 View Fig , pl1): long bilobed buds.

Second to fifth pleopods ( Fig. 6 View Fig , pl2–5): biramous, protopod naked, without spines; endopod with small appendix interna (a.i.).

Telson ( Fig. 6 View Fig , T): long margins expand slightly towards the end, with 2 pair of lateral spines and 6 pairs of terminal posterior processes and wide semicircular notch in terminal margin. Next stage of zoea is visible through cuticle.

ZOEA VI

Material examined: 3 larvae of this stage were caught in Olyutoro-Navarinsky region on September 10–13, 2010 over bottom depth of 51–52 m.

Dimensions: TL 9.47±0.42 (8.9–10.5) mm. CL 2.07±0.08 (1.9–2.2) mm. RL 1.1–1.15 mm.

Carapace ( Fig. 7 View Fig , GV): rostrum slightly longer than the front margin of eye; supraorbital spines large; pterygostomian spine present; anteroventral margin without spines.

Antennule ( Fig. 7 View Fig , A 1 View Fig ): peduncle unchanged; inner flagellum 5-segmented, with long distal segment; outer flagellum 6-segmented.

Antenna ( Fig. 7 View Fig , A 2 View Fig , Sc): peduncle unchanged; endopod 20–30-segmented, 1.5–2 time longer then scaphocerite; base with 2–3 short terminal setae. End of scaphocerite in left leg is not segmented, in the right one with separated 1–2 short segments; spine on scaphocerite reach anterior margin of scale. Scaphocerite bearing about 30 setae.

Maxillule: coxal endite with 11 papposerrate setae; basial endite with 16 cuspidate setae in one appendage and 17 in the other; endopod unchanged.

Maxilla ( Fig. 7 View Fig , Mx2): coxal endite unchanged; basial endite bilobed with 7+1 papposerrate setae in each lobe; endopod unchanged; scaphognathite with 25–28 marginal plumose setae.

Maxillipeds ( Fig. 7 View Fig , Mp1–3): Ìð1 with large bilobed epipod and 5 terminal plumose setae in exopod; Ìð2 with small epipod and 10–11 plumose setae in exopod; Ìð3 unchanged.

Pereopods ( Fig. 7 View Fig , P 1–P View Fig 3 View Fig ): exopod of the first pair with 3 distal separated segments and 10–11 long plumose setae, chela in the first pair is much larger than in the second one; the second pair with 9–10 plumose setae; third to fifth pair uniramous; distal segments thin and long, pointed. At the base of pereopods and maxillipeds there are gills.

Pleon unchanged.

Pleopods ( Fig. 7 View Fig , pl1–5): protopod naked; first pleopod small, biramous; second to fifth pleopods bearing endopods with a.i. and 5–6 small spines, and exopods also with 8–10 small spines terminally.

Telson ( Fig. 7 View Fig , T): margins laterally parallel, with 2 pair of lateral spines and 6 pairs of terminal posterior processes; terminal margin of telson with small wide notch. The next stage is visible through the cuticle — decapodite with prominent terminal margin, a pair of central setae, 3 pairs of angular setae, and 3 pairs of lateral spines.