Habrotrocha microcornis, Song & Lee, 2024

Song, Min Ok & Lee, Chang-Ho, 2024, Descriptions of three new species of Philodinida (Rotifera, Bdelloidea) from Korea, Zootaxa 5493 (1), pp. 36-54 : 41-43

Habrotrocha microcornis n. sp.

Figures 3 and 4

urn:lsid:zoobank.org:act:25ACBFBA-03EA-4206-BD2A-77F49449AA08

Holotype and paratypes. On permanent slides, deposited in the collection of the National Institute of Biological Resources, Incheon, Korea (holotype: NIBRIV0000879462; two paratypes: NIBRIV0000879463 and NIBRIV0000879464) .

Type locality. Galcheon-ri , Seo-myeon , Yangyang-gun, Gangwon-do, Korea. GPS coordinates based on WGS84 datum 37°54'3.0"N / 128°30'6.4"E .

Material. Four specimens sorted out from mosses and leaf litter, collected by Min Ok Song and Chang-Ho Lee on 20 June, 2020.

Differential diagnosis. This new species can be easily distinguished from its congeners by the tiny spurs with very wide interspace, which is about 4–5 times as wide as spur base width. In Habrotrocha , H. cuneata Murray, 1913 , H. flava Bryce, 1915 , H. soror Donner, 1950 and H. spicula Bryce, 1913 are the congeners with small spurs as well as very wide interspace between them. However, all of these congeners have upper lips with bell-shaped or round triangular median lobes, while this new species has a low and rimmed upper lip without a median lobe. These four species also have other unique characteristics that they do not share with the new species, as described below.

The cingulum pad of H. cuneata has a sharp projection on each lateral margin anteriorly, while that of the new species doesn’t have any projections on lateral margins. This new species has a small acute projection on sulcus base, which lacks in H. cuneata ( Murray 1913) .

This new species is distinguished from H. flava by the following characteristics: (1) the feeding head is very long in H. flava ( Donner, 1965, p. 82, fig. 61e; Bryce, 1915, pl. 38, fig. 3), while it is rather short in this new species, (2) the pharyngeal tube is longer than twice trophi length in H. flava , while it is shorter than trophi length in this new species, and (3) the dental formula is 5/4, 5/5, 6/6, and 7/ 7 in H. flava , while it is 5/ 5 in this new species ( Bryce 1915; Donner 1965).

This new species is distinguished from H. soror by the following characteristics: (1) the pharyngeal tube of H. soror is much longer than trophi length and has loops, while that of this new species much shorter than trophi length and straight, (2) the gastric gland of H. soror is big, long and with coarse granules, while it is otherwise in this new species, and (3) the interspace between spurs is about 3 times as wide as spur base width in H. soror , while it is about 4–5 times as wide as spur base width in this new species ( Donner 1950).

The preanal pseudosegment of H. spicula has a big conical process posterodorsally, which is absent in the new species. In addition, the first foot pseudosegment of H. spicula has a short conical process anterodorsally, which this new species doesn’t have ( Bryce 1913).

Description. Rostrum round, short and slightly longer than its width; the ratio of rostrum length to width about 1.16: 1–1.19: 1. Rostral lamella bilobed and without interspace; slightly wider than rostrum; each lobe round and short. Corona slightly wider than cingulum; the ratio of corona width to cingulum width about 1.07: 1–1.09: 1. Corona very slightly wider than cingulum pad; the ratio of corona width to cingulum pad width about 1.05: 1–1.06: 1. Pedicel short. Sulcus slightly narrower than a half of pedicel width; a small blunt projection on each side; a small acute projection on sulcus base medially. Upper lip arched, rimmed and narrow brim of hat-shaped; without median notch; slightly lower than sulcus base. Antenna short; antenna length about 1/3 of height of pseudosegment bearing antenna in creeping. Pharyngeal tube slightly shorter than trophi length in creeping. Teeth 5/5. Neck longer than head in creeping; the ratio of neck length to head length about 1.4: 1; posterior part bearing trophi plump; greatest neck width slightly wider than greatest trunk width in creeping; the ratio of greatest neck width to greatest trunk width about 1.09: 1–1.22: 1. Trunk with four pseudosegments and rump with two; two longitudinal center ridges on trunk and rump stretched X-shaped ( Figs. 3a , 4b ); the gap between two longitudinal center ridges gradually narrowing until about the end of the second trunk pseudosegment, disappearing from the third to the forth, and then gradually widening to the anterior part of anal pseudosegment of rump; preanal pseudosegment of rump constricted posteriorly and with a small hump posterolaterally; anal pseudosegment plump anteriorly and then tapering gradually to foot. Foot tapering gradually to pseudosegment bearing toes; with four pseudosegments; foot very short and about 1/10–1/13 of total body length in creeping; first foot pseudosegment with a small hump anterodorsally. Three toes short. Spurs small, conical and short; looking small and thin fingertip-shaped depending on the position as well as the degree of contraction and relaxation of foot; with wide interspace; interspace about 4–5 times as wide as spur base width.

Measurements. Total length in creeping 143–160 μm. Rostrum length 11–12 μm. Rostrum width 10 μm. Corona width 19–20 μm. Cingulum width 18 μm. Cingulum pad width 18–19 μm. Antenna length 6–7 μm. Trophi length 13–17 μm. Head length in feeding 28 μm. Greatest neck width in creeping 22–24 μm. Greatest trunk width in creeping 18–22 μm. Foot length in creeping 11–17 μm. Spur length 2 μm.

Distribution. This new species is known only from its type locality.

Etymology. The specific name microcornis is an adjective, referring to the small spurs of the new species.

Figures

FIGURE 3. Habrotrocha microcornis n. sp. (a) creeping, dorsal view; (b) feeding head and neck, dorsal view; (c) foot, spurs and toes, ventral view; (d) light microscopy photograph of feeding head, dorsolateral view (an arrow pointing at a projection on sulcus base); (e) light microscopy photograph of feeding head, dorsal view (an arrow pointing at upper lip) (scale bars: a = 25 μm; b, d, e = 20 μm; c = 10 μm).

FIGURE 4. Light microscopy photographs of Habrotrocha microcornis n. sp. (a–d) creeping, in different focal planes, dorsal view; (e) creeping, lateral view; (f) foot and spurs, dorsal view (scale bars: a–e = 25 μm; f = 10 μm).