﻿A new species of Ampithoe (Amphipoda, Ampithoidae) from Korea, with a redescription of A.tarasovi

﻿Abstract An ampithoid species, previously known as A.tarasovi in Korea, is assigned as a new species, A.changbaensissp. nov. based on the reexamination of the holotype of A.tarasovi. The new species shows different morphological characteristics compared to A.tarasovi, especially in male gnathopods 1 and 2. The type material of A.tarasovi is redescribed and illustrated here and a key to the Korean species of Ampithoe is provided.


Introduction
The genus Ampithoe Leach, 1814 is a herbivorous amphipod group associated with algae and seagrasses in coastal regions worldwide (Myers and Lowry 2003;Shin et al. 2015;Peart and Ahyong 2016). Ampithoe is the most speciose genus of the family Ampithoidae and includes more than 70 species worldwide (Horton et al. 2021).
To date, eight species of the genus Ampithoe have been reported from Korea: A. akuolaka J.L. Barnard, 1970;A. brevipalma Kim & Kim, 1988;A. lacertosa Bate, 1858;A. ramondi Audouin, 1826;A. shimizuensis Stephensen, 1944;A. tarasovi Bulycheva, 1952;A. valida Smith, 1873;and A. youngsanensis Kim & Kim, 1988 (Kim and Kim 1988;Shin et al. 2010;Kim 2011;Jung and Yoon 2014;Peart and Ahyong 2016). Among them, A. lacertosa, collected in Korea, was described by Kim andKim (1987, 1988). After the study, the material of the Korean specimens of A. lacertosa was stored in the collections of the Seoul National University. Later, the deposited Korean material identified as A. lacertosa was reexamined in a taxonomic study of Shin et al. in 2010, and in this material a second species identified as A. tarasovi was found. These two species, however, were identified based on the original descriptions and other published records only. However, the type specimens of these two species were not examined by Shin et al. (2010).
For a precise identification of species, type specimens and detailed original descriptions are essential for taxonomy and a flawless identification. If type material is lost and the original texts and illustrations are short and poor in quality, it may lead to misidentifications of species.
In this study, the holotype of A. tarasovi collected in Russia was reexamined. Through the examination, the Korean material of A. tarasovi was identified as a distinct species having morphological characteristics differing from the type material of A. tarasovi. The examined specimens (previously known as A. tarasovi in Korea) are assigned as a new species, A. changbaensis sp. nov., which is described based on the specimens previously misidentified as A. tarasovi by Shin et al. (2010). Moreover, the type material of A. tarasovi is redescribed and illustrated.

Materials and methods
To designate the type material of the new species, the specimens which have been deposited at the Laboratory of Systematics and Molecular Evolution in the Seoul National University were used. Other material was collected in Korea among algae in tide pools, in the intertidal zone, and in shallow water at low tide. The holotype of Ampithoe tarasovi was loaned from the Moscow Museum, Russia, and examined at the crustacean department of Museum für Naturkunde Berlin, Germany.
The specimens were analyzed and pencil drawn under a dissection microscope (Leica M250C), and appendages and mouthparts were drawn under a Leica DMLB; both microscopes were equipped with a camera lucida. The line drawings were made using the technique described by Coleman (2003Coleman ( , 2009. Body length was measured along the midbody line from the tip of the rostrum to the posterior end of urosomite 3. All examined material is currently being deposited at the Marine Arthropod Depository Bank of Korea (MADBK). The descriptions were produced from a DELTA (Dallwitz 2005) database to the ampithoid genera and species (initially compiled by our colleague Dr Jim Lowry).
Upper lip with midlateral notch on margins.
Uropod 1 reaching to end of uropod 2 rami; inner ramus longer than outer ramus; outer ramus slender, about 6 times as long as broad.
Uropod 2 inner ramus longer than outer ramus. Uropod 3 (Fig. 3E) peduncle much longer than broad (2.2 times as wide as long), 1.8 times as long as rami, 2 inner marginal robust setae, marginal slender setae present, with 7 distal peduncular robust setae; rami long, about twice as long as broad; outer ramus subequal in length to inner ramus, with 2 large recurved distal robust setae, and with 3 dorsomarginal robust setae, with lateral setal fringe; inner ramus with 4 distal robust setae, with 3 and 2 lateral robust setae on both inner and outer margins, respectively. Telson (Fig. 3F) subtriangular, apically rounded, with small apical cusps; with 3 groups of lateral plumose setae, and a pair row of setae on submedial margins.
Remarks. This species has been recognized as A. tarasovi in Korea since the species was described and illustrated by Shin et al. (2010). However, the type material of  A. tarasovi described from Russia was examined here, and as a result, important morphological differences were detected between Korean material and the Russian type specimen. The characteristics differing between the Korean specimens and the type material are as follows. In male gnathopod 1, the basis is expanded anterodistally in the Korean specimens, while it is narrow and straight in the type material. The length ratios of carpus and propodus of the Korean and Russian specimens are 1.3 and 1.8, respectively. The shape of gnathopod 1 carpus is more rectangular in the Russian material than in the Korean sample. The propodus of male gnathopod 2 is longer and more rectangular in the Russian material compared to the Korean sample. The apical margin of the telson is round in the Korean specimen, while it is subacute in the Russian type material. Based on the morphological differences mentioned above, the Korean material has been assigned to a new species, A. changbaensis sp. nov.
Uropod 3 (Fig. 7E) peduncle much longer than broad (2.3 times width), 2.2 times as long as rami, with 3 marginal robust setae, marginal slender setae present, with 8 distal peduncular robust setae; rami long, about twice as long as broad; outer ramus shorter than inner ramus, with 2 large recurved distal robust setae and 1 dorsal robust setae, with lateral setal fringe; inner ramus with 6 distal robust setae, with 2 lateral robust setae both inner and outer margins, respectively. Telson (Fig. 7F) subtriangular, apically subacute, with small apical cusps, with 4 or 5 of lateral setae on both margins, and 2 pairs of lateral plumose setae, with 2 or 3 submedial setae on both margins.
Remarks. This species has the following characteristics: the apical and medial lobes of the outer lobes are separated in the lower lip; the carpus of male gnathopod 1 is about 1.8 times as long as the propodus; the palm of the male gnathopod 2 has a sloped quadrate hump and posterodistal tooth. Bulycheva (1952) noted that A. tarasovi is very abundant in macroalgae and reefs in Petra Velikogo Bay and in the northern Sea of Japan.
Here we provide a key to the Korean species of Ampithoe and distributional information in four coastal regions of Korea in Table 1.