Clear body with some red-orange patches. Both A1 bright red. Caudal rami are strongly pigmented.
Very similar to sympatric species N. flemingeri, but can be distinguished by the following features:
C5:
-Clear body with some red-orange patches. Both A1 bright red. Caudal rami are strongly pigmented.
-Body proportions: the ratio of cephalosome : cephalothorax is mostly >0.45
-Abdominal segments are narrower on average
-The 2nd bristle of caudal rami is more than 3 times longer than the abdomen length
-The setae on the 2 penultimate segments on A1 are long and densely plumose, brightly pigmented
-Mx2 longer than 0.42mm, with longer setae and setules more densely placed
Females:
-The line of fusion between the head and the 1st thoracic segments extends farther ventrally than in N. flemingeri
-Body proportions: the ratio of cephalosome : cephalothorax is mostly >0.45
-Genital segment: widest point at about half the length; the sides are strongly convex
-Spermatophore without coil and without amorphous patch of matter in the middle
-Mx2 larger relative to the cephalosome length
Males:
-Curvature of the head reaches farther antero-dorsally
-Body proportions: the ratio of cephalosome : cephalothorax is mostly =0.55-0.56
-Spermatophore forming organ extends only to the middle 3rd thoracic segment.
-The length of the 2nd abdominal segment is longer relative to width than in N. flemingeri.
-A1 reaches beyond the end of caudal rami by several segments
-Mx2 is larger relative to cephalosome length
-The 2nd exopodital segment of P5 is 1.3 times longer than the 3rd segment.
Endemic of the North Pacific: Sea of Japan, Sea of Okhotsk, and Bering Sea. Can be carried into the Chukchi Sea, some individual – into the Arctic Basin. Especially abundant in the Gulf of Alaska.
Oceanic, epi- to bathypelagic species
Annual cycle. Females do not feed, so all reproduction occurs based on lipids accumulated over the prior summer. Although they cannot exploit current production, it allows them to spawn much earlier than other co-occurring species. N. plumchrus diapause as C5, then need to molt and spawn, reaching the surface later. Nauplii feed at C3.
Female:
Body elongate-oval shaped in dorsal view. The head is smoothly rounded and does not extend in the anterior-dorsal quadrant. The cephalosome is fused to the 1st thoracic segment, but the line of fusion is visible dorsally and somewhat extends ventrally. On the posterior edge of the head a well-defined dorsal knob is present. The posterior corners of the last thoracic segment are smoothly rounded, without projections of points. The cephalosome is over 45% of the total cephalothorax length. The genital segment is about as long as wide; its ventral aspect has a rounded outline with the widest point at about half the length; it is strongly convex. The caudal rami are 1.75 times longer than wide. Caudal setae are placed at a narrow angle relative to each other.
The 2 penultimate segments on A1 carry 2 long and densely plumose chaetae.
Mouthparts reduced in many aspects. Reduction of Mx2 is especially extreme, its setae are tiny and flaccid.
Thoracic legs all have 3 segments in both branches. The second basipodite of P1 carries a round seta on its anterior distal corner, which extends along the medial side of the 1st endopodital segment, then bends to follow its distal edge. The anterior distal edge of the 1st segment of the endopodite of P1 carries a set of flexible, straight spines, the anterior surface carries patches of fine hairs. The 2nd segment of the endopodite of P3-P5 carries a thin, sharp projection on the lateral distal corner. P5 are similar to other legs, but are smaller and with a relatively longer projection on the lateral distal corner of the 2nd endopodital segment.
Male:
In profile the head extends far antero-dorsally, having roughly the brow profile of a sperm whale. The head and the 1st thoracic segment are practically fused except on the dorsal side, the knob on the posterior dorsal corner of the cephalosome is larger than in female. The posterior corners of the last thoracic segment are freely articulated with no hairs or spinules near the end. The second abdominal segment is the longest, more than twice longer than the 1st one, and about 1.17 times longer than wide. Caudal rami are 1.69 times longer than wide, slightly shorter than in the female.
A1 is more stout than in females, with 24 or 25 segments, when folded ventrally it extends past the caudal rami by several segments.
Thoracic legs are relatively longer than in females or C5’s. In particular, the 2nd and 3rd endopodital segments are longer, and the terminal spines are very long and stout.
The P5 have modifications comparable to those general in the family. The 2nd exopodital segment of P5 is about 1.3 times longer than the 3rd segment. The length of the left endopodite is less than the combined length of the first 2 exopodital segments of the corresponding leg.
Spermatophores have a simple spindle shape and extend from the genital opening back to the anal segment. The neck bends slightly, but never forms a loop. The duct extends into one of the receptacles and fills the left or the right side only.
Female: 4,00-6,32 mm
Male: 4,18-5,00 mm
Selective filter feeder. Females and males do not feed at adulthood.
Neocalanus plumchrus is a large species of copepod found in the Pacific and Arctic Oceans. It was described in 1921 by Marukawa. N. flemingeri was formerly considered as conspecific, likely as a form, until it was split in 1988 by Charles B. Miller.
Neocalanus plumchrus was originally described by Marukawa in 1921. It was eventually moved by Janet Bradford and John Jillett in 1974 from the genus Calanus to its current placement in Neocalanus. The species N. flemingeri was split out of this species in 1988, where it is considered by Charles B. Miller to have been placed as f. typica.[1]
Neocalanus plumchrus is considered to be a large copepod,[2] with females generally ranging from about 4 to 6.3 millimetres (0.16 to 0.25 in) in length. The males are usually between about 4.2 and 5 millimetres (0.17 and 0.20 in) in length.[3] Stage V copepodites usually are more than 4.3 millimetres (0.17 in) in length.[4] The females of N. plumchrus, contrasting to those of N. flemingeri, have convex first urosomal tagma. The cephalosome length to prosome length ratio is generally over 0.44. The spermatophore deposited in females lacks any coils. In males, the ratio of cephalosome length to prosome length is usually between 0.55 and 0.56. The first antenna extends beyond the caudal rami by multiple segments. In stage V copepodites, the colouration and the second from medial caudal seta (or II bristle) can be used to distinguish this species and N. flemingeri. In N. plumchrus, there is red-orange colouration along both of the first antennae, vertical stripes of colour along the sides of the thorax, and on the caudal rami. The II bristle is about 0.28 millimetres (0.011 in) in diameter 0.5 millimetres (0.020 in) from its base, and is over three times the length of the urosome when the former is in its entirety.[1]
In the Pacific, N. plumchrus is found in the Sea of Japan, the northern Pacific, and off California. It is also found in the Arctic Ocean.[3]
The timing of reproduction in N. plumchrus is variable; in the Strait of Georgia, it breeds between December and April,[5] whereas it breeds between July and February at Station P.[4] In both cases, it breeds at depth, usually below around 300 metres (980 ft) in the former, and below about 250 metres (820 ft) in the latter case.[5] It likely utilizes lipid stores to breed, instead of recently consumed food. After reproducing, the adults die; first the males, and then the females.[6] Copepodite stages I through V develop in the surface waters (stages II through IV are found in the top 250 metres (820 ft) throughout the year in waters off Japan, for example) late during the phytoplankton bloom.[7] Stage V copepodites enter diapause at depths of below 250 metres (820 ft)[4] during late summer.[2] At Station P, the number of copepodites in diapause remains about the same until September, when numbers decrease due to mortality and development into adults.[5] This contrasts to the Strait of Georgia, where diapause is from July to January, and maturation occurs during January and February.[4]
Neocalanus plumchrus is, as a whole, omnivorous, although there are regional variations. In the Strait of Georgia, for example, this copepod is mainly herbivorous, whereas in the ocean, omnivory is more prevalent; this affects the composition of lipids, with oceanic samples having (likely as an adaptation to lower concentrations of food) more monounsaturated fats with 20 or 22 carbon atoms.[8] It is able to uptake glucose directly from seawater from its dermal glands and midgut, which arthropods were thought to be incapable of due to their rigid exoskeleton.[9]
Neocalanus plumchrus is a large species of copepod found in the Pacific and Arctic Oceans. It was described in 1921 by Marukawa. N. flemingeri was formerly considered as conspecific, likely as a form, until it was split in 1988 by Charles B. Miller.
