Lumbrinerides shimodaensis Imajima, 1985

Miura, Tomoyuki, 2017, Classification and Morphological Variations of the Japanese Species of Lumbrinerides (Annelida: Lumbrineridae), Species Diversity (Auckland, N. Z.) 22 (1), pp. 7-27 : 16-21

Lumbrinerides shimodaensis Imajima, 1985 ( Figs 6–10)

Lumbrinerides shimodaensis Imajima, 1985: 174–176 , fig. 3a–i.

Lumbrinerides lineatus Imajima, 1985: 176–178 , fig. 4a–j. Syn. nov.

Lumbrinerides bidentatus Imajima, 1985: 178–180 , fig. 5a–l. Syn. nov.

Material examined. Holotype of Lumbrinerides shimodaensis , NSMT-Pol H-197, off Shimoda, 50–59 m, October 1981. Holotype and paratype of Lumbrinerides lineatus , NSMT-Pol H-198 and P-199, off Shimoda, 63–70 and 92– 102 m, respectively, October 1981. Holotype and paratype of Lumbrinerides bidentatus , NSMT-Pol H-200 and P-201, around Tsushima, 85 and 125 m, respectively, July to August 1968.

Comparative material. Four syntypes of Lumbriconereis acuta, USNM 12895, Rhode Island, off Block Island, 26 m, August 1874. Holotype and two paratypes of Lumbrinerides acutuss japonicus , NSMT-Pol H-202, off Shimoda, 63–70 m, October 1981 and NSMT-Pol P-203, off Shimoda, 50–60 m, October 1981, respectively.

Non-type material. ( EK B) Seisui-Maru Cruise 1985-R- 07, Stations 405 A: one female; 405B: one female, one immature; 406 A: one juvenile; 406 B: one female, one juvenile; 504 A: one female, four juveniles; 505 A: two females, two males, two immature, one juvenile; 505 B: one female, one immature, one juvenile; 506 A: two juvenile; 506 B: one immature. ( KII B) Tansei-Maru Cruise KT-84-12, Kii Channel, Station 12-1: five immature. ( SADO B) Cruise KT-85-14, Japan Sea, Stations D-2 SM-2: one immature; F2- SM 1: two juvenile; F2- SM 2: one immature; F2- SM 3: one immature; F2- SM 4: one immature, one juvenile; F3-BC1: one immature, one juvenile; F3-BC2: one immature, one juvenile; F3-BC3: one female, one immature; F3- SM 1: one female, one juvenile; F3- SM 2: two females, two immature, three juveniles; F3- SM 3: one female, six immature, five juvenile; F4- SM 1: one immature, one juvenile; F4- SM 2: two immature; F4- SM 3: one immature; F4- SM 4: two juveniles. ( MISA) two immature.

Description. Prostomium acorn-shaped with smooth surface without keel-like or other structure except wrinkles by shrinkage, 1.2–2.4 times longer than wide in larger specimens ( Fig. 6A). Peristomium with two apodous rings ( Fig. 6A). Three to five anterior parapodia reduced with low conical postchaetal lobe and inconspicuous prechaetal one ( Fig. 6B); fully developed parapodia with elongate subconical postchaetal lobe about twice as long as prechaetal one beginning from chaetigers 7–8 ( Fig. 6C, D); both lobes well- developed on far posterior parapodia. Four or more broadly limbate chaetae with tapering end occurring on less than ten anterior parapodia, three to one on posterior parapodia, disappearing on far posterior parapodia ( Figs 6 B–D, 9, 10). A single hooded hook occurring on parapodia 7–20 ( Fig. 6C), two or three on posterior parapodia ( Figs 6D, 9, 10), up to six on far posterior parapodia. Maxilla I normally with one accessory tooth ( Figs 6G, 7), occasionally without tooth ( Fig. 6E, right maxilla I). Maxilla II generally with three teeth ( Figs 6E, G, 7); each tooth always with a single inner cavity, even if with occasional bidentate outline or completely lacking third tooth in a single exceptional large specimen ( Fig. 8). Mandibles slender posteriorly, several concentric lines on anterior flared part ( Fig. 6F, H).

Variations. Accessory teeth on Maxilla I number zero or one in this species ( Fig. 2; EK B). The prostomium is 1.2 to 2.4 times longer than wide. The first simple hooks occur on chaetigers 4–6 in juveniles ( Fig. 4). The number of anterior reduced parapodia varies between three and five ( Table 3). In the Japan Sea population, individuals with three reduced parapodia were dominant ( Fig. 2; SADO B), whereas those with four reduced parapodia were dominant off the Pacific coast of Japan ( Fig. 2; EK B).

Remarks. In the shape of chaetae and parapodia, no significant difference was found in the type specimens of three species listed as synonymies. They were very short in- cluding 15–30 chaetigers and I could not find any difference in these characters as in the original description by Imajima (1985).

The basal tooth-like projection on the proximal parts of the inner edge of the maxilla I was not considered as an accessory tooth in this study. Although such projection was illustrated to imply a kind of functional teeth in the original descriptions of L. shimodaensis , L. lineatus and L. bidentatus ( Fig. 7 A-3, B-3, B-4, C-4, C-5), no second accessory tooth was found in the reexamined type specimens ( Fig. 7 A-1, B-1, B-2, C-1, C-2). Similarly, the left maxilla I of the paratype (NSMT-Pol P-199) of L. lineatus lacks accessory teeth, the dentition of maxillae I in those nominal species varying from zero to one. Maxillae II of the above three nominal species were also identical ( Fig. 7 A-2, C-3). The modified external dentation observed may have resulted from meshing between the maxillae II, and between the shafts of maxillae I and the plates of maxillae II. The true bidentate state of maxillae II, namely two external teeth and two pulp cavities was observed only on an exceptionally large specimen collected from the Bungo Channel ( Fig. 8 A-2).

The chaetal composition of all of the type specimens for the three nominal species erected by Imajima (1985) was also examined by counting both kinds of chaetae on each parapodium ( Fig. 9). In these specimens, a maximum of four limbate chaetae were found on each of the first five or six parapodia, becoming fewer thereafter. In compensation, simple bidentate hooded hooks appeared singly on each parapodium after chaetiger 7 or 8, increasing to two or three after chaetiger 20 ( Fig. 9). In other more intact specimens, chaetal composition was more clearly evaluated ( Fig. 10), specimen 505 A-01, for example, collected from Kumano Nada and measuring 0.51 mm wide, having four limbate chaetae each on the first seven parapodia, three on the following seven parapodia, and finally two on the remaining posterior parapodia. The same specimen had simple hooded hooks starting on parapodium 8, one on the next 12 parapodia, two on the next 11 parapodia and three on the subsequent parapodia ( Fig. 10). The change in chaetal compo- sition was almost stable in specimens with a body width of more than 0.4 mm ( Fig. 4). As a conclusion of revision, L. lineatus and L. bidentatus were regarded as synonyms of L. shimodaensis .

Lumbrinerides shimodaensis differs from all other Japanese species in having a single accessory tooth or none on the maxillae I, a small number of reduced anterior parapodia and simple bidentate hooded hooks starting on ca. chaetiger 7 in adult specimens. Lumbrinerides amoureuxi Miura, 1980 , L. crassicephala (Hartman, 1965) and L. platypygos (Fauchald, 1970) are also known to have simple hooks starting on ca. chaetigers 6–9. Lumbrinerides crassicephala has one accessory tooth on maxilla I and the remaining species differ from L. shimodaensis in having two teeth or none. Lumbrinerides crassicephala has a long prostomim (length to width ca. 3.0) compared with L. shimodaensis in which the proportion is 2.0.

The holotype and two paratypes of Lumbrinerides acutus japonicus are all immature and lack a considerable number of posterior chaetigers. In addition, most of the chaetae on the anterior parapodia and the initial position of simple hooks could not be determined. The occurrence of simple hooks mentioned by Imajima (1985) could not be confirmed, only a single hook on parapodium 4 in one paratype, and on parapodium 6 on the other paratypes and on the holotype ( Fig. 11) being found. The presence of three to five limbate chaetae on anterior parapodia in one of the paratypes suggests an absence of hooks on those parapodia as the maximal number of chaetae on a single anterior parapodium is thought to be four in most Japanese specimens, as mentioned above. This chaetal composition closely resembles that described for L. shimodaensis , in which the first several parapodia lack simple hooks and are provided with only four limbate chaetae, or possibly five ( Fig. 10). In these details, the specimens do not differ from L. shimodaensis . The presence of an accessory tooth on maxillae I is also consistent with the latter. Lumbrinerides acutus japonicu s is therefore thought to represent a juvenile phase of L. shimodaensis , which was recorded from the same locality. Imajima (1985) remarked that those specimens were similar to L. acuta , but differed in the number of anterior reduced parapodia, L. acuta having about ten reduced anterior parapodia, compared with four to six in L. acutus japonicus . The chaetal distribution of L. acuta is not comparable with other species because of damage to the anterior parts of the syntypes and consequent loss of most chaetae. The first occurrence of hooks in L. acuta has been termed ‘middle body region’ by many authors ( Pettibone 1963; Perkins 1979; Miura 1980; Uebelacker 1984). The types of L. acutus japonicus are also problematic for the taxonomic identification, because of the loss of many chaetae on the first several parapodia of the holotype. The exact taxonomic status of L. acutus japonicus thus remains unclear, despite the type series including damaged juvenile specimens of L. shimodaensis (based on their chaetal distribution).

Biological notes. Some ovigerous specimens were collected from the Irago Strait, off Ago Bay in September 1984 and south part of the Sado Strait in September 1985. The spawning season of this species is therefore thought to be in late summer.

Distribution. Off Shimoda (50–102 m), Irago Strait (120–150 m), off Ago Bay (102–158 m), off Misaki (110– 122 m), off Susami, Bungo Channel (72–101 m), South Sado Strait (75–143 m), North Sado Strait (148 m) and around Tsushima (75–125m), on sandy substrate, reported only in Japan.