Idiomysis bumbumiensis, Nurshazwan & Sawamoto & Rahim, 2021

Nurshazwan, Ja'afar, Sawamoto, Shozo & Rahim, Azman bin Abdul, 2021, Idiomysis bumbumiensis sp. nov., a new mysid species (Mysida, Mysidae, Anisomysini) from Southeast Asia, Zoosystematics and Evolution 97 (2), pp. 345-354 : 345

publication ID	https://dx.doi.org/10.3897/zse.97.68486
publication LSID	lsid:zoobank.org:pub:C21D141B-0CDF-427F-8EE3-1FCABAD668C6
persistent identifier	https://treatment.plazi.org/id/BA9ADF20-A7DB-4C50-B301-D3036F77925B
taxon LSID	lsid:zoobank.org:act:BA9ADF20-A7DB-4C50-B301-D3036F77925B
treatment provided by	Zoosystematics and Evolution by Pensoft
scientific name	Idiomysis bumbumiensis
status	sp. nov.

Treatment

Idiomysis bumbumiensis sp. nov.

Figs 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4 , 5 View Figure 5 , 6 View Figure 6

Type material.

Holotype, adult male (BL. 2.3 mm, UKMMZ-1611); Allotype, ovigerous female (BL. 3.2 mm, UKMMZ-1612); Paratypes, two males (BL. 2.0 and 2.2 mm), one female (BL. 2.2 mm) (UKMMZ-1613); two females (BL. 2.6 and 3.1 mm, UKMMZ-1614), ND Divers House reef, Pulau Bum Bum, Semporna, Sabah, Malaysia, 4°26'43.2"N, 118°39'08.1"E, SCUBA diving, 29 November 2018, 10.5 m depth, collectors: Abu-Bakar A.Z., Azman B.A.R. and Dendy A.O.

Diagnosis.

Antennal scale 2-segmented, with short apical segment, scale without any spine; rostrum subtriangular with broad rounded apex; thoracic exopod 1-8 with 7-9 segments; thoracic endopod 1-2 robust, thoracic endopod 3-8 elongate; all pleopods longer than wide; fourth male pleopod with distinct exopod and endopod not separated by sutures at the base, exopod terminally with 1 large barbed seta (armed with a few setules); endopod of uropod shorter than exopod; telson with a pair of minute spines on terminal margin; telson length ratio to sixth abdominal somite is 0.8.

Description for male. Head and cephalic appendage.

A pale-white and brownish body part (Fig. 2A, B View Figure 2 ). Orange to the yellowish-red cornea (Fig. 2A, B View Figure 2 ). Stout and bulky body (Figs 2A View Figure 2 , 3A View Figure 3 ) due to slightly double-flexed pleon antero-dorsally; short carapace, exposed last three thoracic somites, upwards-pointed trapezoid-shaped wing-like extension (Fig. 3A View Figure 3 ); subtriangular shaped rostrum (Fig. 3B View Figure 3 ) with broad rounded apex (subtriangular and bluntly pointed) extending between eyes reaching a middle basal segment of antennule peduncle; very large eyes (Fig. 3B View Figure 3 ), globular; the cornea is wider than eyestalk, covering almost all of the eye surface.

Antennule peduncle (Fig. 3D View Figure 3 ) with three segments; the basal segment is the longest with a ventral short lobe on subterminal position with three setae; the median segment is the shortest with a ventral short lobe on subterminal position with three setae; the terminal segment is almost 0.5 times as long as the first/basal segment, with eight setae and one plumose seta, hirsute appendix masculina present; inner flagellum with four segments; outer flagellum with 9-10 segments; aesthetascs present. Antennal peduncle (Fig. 3E View Figure 3 ) is very short and stout, with three segments; antennal scale is extending beyond antennule peduncle, long, robust and broad; suture present at 11-14% from apex; terminal segment with five plumose setae; proximal outer margin without plumose setae from the base of antennal scale is 64%, while proximal inner margin without plumose setae is 27%.

Mandible (Fig. 3F View Figure 3 ) with incisor and molar process; well-developed lacinia mobilis; the molar process is present; palp with three segments; small basal segment without setae; median segment with eight setae along the outer (lateral) margin and three setae along inner (mesial) margin; terminal segment with six normal setae and four plumose setae. Normal maxilla (Fig. 3G View Figure 3 ) for the genus; exopod bearing five apical setae; two-segmented endopod, the sub-ellipsoidal shaped terminal segment with seven setae including two normal setae. Normal maxillula (Fig. 3H View Figure 3 ); basal lobe with nine large spines; precoxal lobe with two long setae and two small setae.

Thoracopods.

A round basal plate of thoracic exopod at both distal corners with 7-9 segments with the last 3-4 segments bearing 1-2 plumose setae; robust thoracopods 1-2, slender and elongated thoracopods 3-8; carpopropodus of thoracic endopod 1-8 with 2, 2, 2, 1-2, 3, 1-2, 1, 1 segments, but some segmental borders are not well distinct in thoracopods 3-8; smaller dactylus of thoracopods 3-8 than thoracopods 1-2; nail of thoracopods 3-8 is more slender compared to thoracopods 1-2. The first thoracopod epipod (Fig. 4A View Figure 4 ) is linguiform-subtriangular without seta; seven-segmented exopod, first four segments without seta, the fifth segment with one plumose seta, the sixth and seventh segments with two plumose setae; normal and robust endopod, densely setose along both lateral margins of the ischium to dactylus, each segment bearing 1-2 plumose setae; nail with a swollen base. Second thoracic exopod (Fig. 4B View Figure 4 ) with eight segments, last three segments with 1-2 plumose setae; robust thoracic endopod similar to the first thoracopod, but armed with lesser setae, from basis to dactylus bearing 1, 0, 2, 2, 6, 7 setae, respectively.

Third thoracic exopod (Fig. 4C, D View Figure 4 ) with nine segments, the last four segments with 1-2 plumose setae; thoracic endopod is more slender and elongate instead of robust, two-segmented carpopropodus, all segments are armed with setae, dactylus is smaller than in thoracopods 1-2, the nail is more slender than first and second thoracopods. The fourth thoracic endopod (Fig. 4E View Figure 4 ) is similar to the third thoracopod, carpopropodus, with 1-2 segments. The fifth thoracic endopod (Fig. 4F View Figure 4 ) is slightly longer than in the fourth thoracopod, merus nearly equal in length to the preceding segment, three-segmented carpopropodus, elongated and slender nail. Eighth thoracic exopod (Fig. 4G View Figure 4 ) with seven segments; thoracic endopod is smaller and more slender than other thoracopods, merus is longer than the preceding segment, separate carpopropodus, short and small dactylus, the nail is shorter than other thoracopods.

Pleopods.

Pleopods 1, 2, 3 and 5 (Fig. 5A, C, E View Figure 5 ) reduce to simple separate plates, each with 4-6 setae of different lengths, longer than width; length of pleopod is more than twice its width. Male pleopod 4 (Fig. 5D View Figure 5 ) has distinct endopod and exopod, both undivided and basally not separated by sutures; endopod with three plumose setae; exopod has one small terminal seta and a large-barbed seta (armed with a few setules).

Uropod and telson.

Uropod (Figs 3C View Figure 3 , 5F View Figure 5 ) has a shorter endopod than exopod; both endopod and exopod have plumose setae all around, without setae on both margins of the proximal part of endopod and exopod; endopod with 14 plumose setae; exopod with 19 plumose setae; large statocyst (there are circular borders between ambitus versus tegmen and ambitus versus fundus). Telson (Figs 3C View Figure 3 , 5G View Figure 5 ) is approximately 1.12 times longer than the width and 0.8 times longer than the sixth abdominal somite; short, subtriangular with rounded tip; extending halfway across statocyst of endopod; smooth margin, except for apex with a pair of minute spines.

Female.

Similar to male, except for the following differences: stouter and bulkier body (Fig. 6A View Figure 6 ) than male due to marsupium; marsupium of female on the eighth thoracopod is larger than seventh thoracopod, large with short setae along the distal margin. Antennule (Fig. 6B View Figure 6 ); inner flagellum with seven segments; outer flagellum with 12 segments; aesthetascs is present. Antennal scale (Fig. 6C View Figure 6 ) with suture present at 10%-14% from apex; from the base of antennal scale, 70% of the proximal outer margin is without plumose setae while 45% of the proximal inner margin is without plumose setae. Pleopod 4 (Fig. 6D View Figure 6 ) is similar to male pleopods 1-3, 5; longer than its width with six setae. Telson (Fig. 6E View Figure 6 ) is approximately 1.03 wider than its length; apex with a pair of minute spines.

Etymology.

The specific epithet refers to the type locality; Pulau Bum Bum, Sabah, Borneo, Malaysia.

Colouration in freshly fixed specimens

(based on UKMMZ-1611, BL. 2.3 mm; UKMMZ-1612, BL. 3.2 mm; Fig. 2A, B View Figure 2 ). Zesty orange eyes. Antennal scale, carapace including thoracic and translucent abdominal somites with a combination of small orange, yellow and black patches.

Remarks.

The present species is the seventh member of the genus Idiomysis , but it is the first species of this genus to be described in Southeast Asia. It is also the third species of the tribe Anisomysini found in Malaysian waters besides Anisomysis (Anisomysis) aikawai Ii, 1964 and A. (Paranisomysis) ohtsukai Murano, 1994 ( Moriya 2016; Tan and Azman 2018). The genus Idiomysis can be easily classified into two groups, based on the antennal scale; (i) entire or (ii) 2 segments. Idiomysis inermis , I. mozambica , I. robusta and I. tsurnamali are in the group of an entire antennal scale, while I. diadema and I. japonica are in the group of two-segmented antennal scale. The presence of the spine, which is exclusively in I. robusta , distinguishes the group with the entire antennal scale. The present new species, Idiomysis bumbumiensis sp. nov., has two antennal scale segments, similar to I. diadema and I. japonica . However, they can be differentiated by observing the apex of the telson. Both I. diadema and I. bumbumiensis sp. nov have a pair of minute apical spines exclusive to these two species; on the other hand, I. japonica has a bluntly rounded telson apex. The endopodal uropod in I. diadema shows a clear extension beyond the exopod, but this structure is shorter than the exopod in I. bumbumiensis .