Octomeris intermedia Nilsson-Cantell, 1921

Chan, Benny K. K., Tsao, Yao Feng & Ganmanee, Monthon, 2020, Morphological and molecular evidence support the intertidal barnacle Octomeris intermedia Nilsson-Cantell, 1921 (Thoracica, Chthamalidae) as a valid species in Indo-Pacific waters, ZooKeys 914, pp. 1-31 : 1

publication ID	https://dx.doi.org/10.3897/zookeys.914.49328
publication LSID	lsid:zoobank.org:pub:6EC16BE4-BC22-4559-9163-7F406EB24597
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scientific name	Octomeris intermedia Nilsson-Cantell, 1921
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Treatment

Octomeris intermedia Nilsson-Cantell, 1921 Figures 2A-F View Figure 2 , 10 View Figure 10 , 11 View Figure 11 , 12 View Figure 12 , 13 View Figure 13 , 14 View Figure 14 , 15A-C View Figure 15 , 16A-C View Figure 16

Octomeris brunnea Nilsson-Cantell, 1921: 303, figs 60, 61, pl 3, fig. 8.- 1925: 1 (erratum for type locality); 1932: 13; 1938: 33, fig. 5; Hiro 1939: 252; Pope 1965: 21; Jones 2012: tabs 1, 2.

Material examined.

ASIZCR-000431. Intertidal rocks at Ao Nang Beach, Krabi, Thailand (8°02.06'N, 98°48.58E, 3 July 2019, 1 specimen). CEL-Thai-359. Intertidal rocks at Ao Nang Beach, Krabi, Thailand (8°02.06'N, 98°48.58'E, 3 July 2019, 20 specimens). CEL-Thai-243 Intertidal rocks at Hey Island, Phuket, Thailand (7°44.73'N, 98°22.59E, 15 May 2019, 103 specimens).

Diagnosis.

Shell eight plated, very depressed, surface brown with longitudinal furrows on uneroded specimens, tergo-scutal junction sinuous, except for young specimens. Maxillule with very shallow notch at upper 1/3 of cutting edge, lower 1/3 slightly protruded.

Description.

Shell eight-plated, composed of single rostrum (R) and carina (C), and paired rostro-laterals (RL), carino-laterals (CL) and laterals (L) (Fig. 2D-F View Figure 2 ). Shell very depressed, brown surface with longitudinal furrows on uneroded specimens (Fig. 2D-F View Figure 2 ). Tergal-scutal junction sinuous, except for young specimen which has shell length <10 mm (Fig. 3 View Figure 3 ). Sutures of shell plates serrated (Fig. 4C, D View Figure 4 ). Scutum triangular, outer surface with horizontal growth lines. Inner surface of scutum brown, occluding margin straight, basal margin slightly convex, tergal margin sinuous with deep articular ridge. Adductor muscle scar shallow (Fig. 4C, D View Figure 4 ). Basal margin of tergum strongly bended in angle, scutal margin sinuous and with deep articular ridge, crests of depressor muscle crests distinct, muscle crests extended slightly out of the carinal margin of tergum (Fig. 4C, D View Figure 4 ).

Cirrus I, rami subequal (Fig. 10A-D View Figure 10 ). Posterior ramus shorter, eight-segmented. Anterior ramus seven-segmented. Segments in both rami with greater height than width. Both rami bear bidentate serrate setae and simple setae (Fig. 10C, D View Figure 10 ). Bidentate serrate setae present up to seven segments in anterior ramus and present up to first four distal segments in posterior ramus. Cirrus II, posterior ramus nine-segmented, anterior ramus ten-segmented (Fig. 10E, H View Figure 10 ). Bidentate serrate setae present up to six segments in anterior ramus and nine distal segments in posterior ramus (Fig. 10G, H View Figure 10 ). Cirri III-VI similar in morphology, being long and slender (Figs 11 View Figure 11 , 12 View Figure 12 ). Cirrus III, anterior and posterior rami 12-segmented (Fig. 11A-D View Figure 11 ). Cirrus IV, anterior and posterior rami 16-segmented (Fig. 11E-H View Figure 11 ). Cirrus V, anterior and posterior rami 17 segmented (Fig. 12A-C View Figure 12 ). Cirrus VI, anterior ramus 17 segmented and posterior ramus 16 segmented (Fig. 12D-F View Figure 12 ). Intermediate segments of cirri III-VI bear three pairs of long and one pair of short simple setae (Figs 11B, D, F View Figure 11 , 12B, E View Figure 12 ). Distal segments of cirrus III bear two pairs of long and one pair of short setae (Fig. 11C, H View Figure 11 ; 12C, F View Figure 12 ). Caudal appendages absent. Penis long, annulated, tip with simple setae (Fig. 12G, H View Figure 12 ).

Maxilla subtriangular, inner margin with an inconspicuous notch, inner and outer margins with serrulate setae (Fig. 13A-D View Figure 13 ). Maxillule with two very shallow notches on upper 1/3 and lower 1/3 of cutting edge. Cutting edge more or less straight but the region above notch with one large and a few setae; middle margin has nine setae; cutting edge below upper notch has> 20 short setae (Fig. 13E-H View Figure 13 ). Mandibles with three teeth, first tooth with smooth edge and second teeth with slightly serrated edge, third tooth with smooth edge but occasionally with some spine on edge region (Figs 14A-D View Figure 14 , 15A-C View Figure 15 ). Mandibular palp elongated, with serrulate setae on outer margin (Fig. 14E, F View Figure 14 ). Cutting margin of labrum concave, with small fine teeth (Fig. 14G-H View Figure 14 ).

Distribution.

Java in Indonesia, Mergui Archipelago in Myanmar, Phuket and Krabi in Thailand.

Remarks.

O. intermedia collected in the present study represents the specimens described by Nilsson-Cantell (1921, 1938) who collected O. intermedia from Java and the Mergui Archipelago; Phuket and Krabi are approximately 300 km south of the Mergui Archipelago. The morphology of our specimens fits the description in Nilsson-Cantell (1921, 1938): the shell is depressed and has a sinuous junction between the tergum and scutum. The external shell morphology of O. brunnea and O. intermedia is very similar. Old and eroded specimens of O. brunnea have a sinuous junction line between scutum and tergum, which is one of the characteristics of O. intermedia described by Nilsson-Cantell (1921). There are, however, several consistent diagnostic features between O. intermedia and O. brunnea . The shell of O. intermedia is much depressed in comparison to that of O. brunnea . The junction of the tergum and scutum in O. intermedia is sinuous, even at the young stage (except for very small individuals, RC-diameter <10 mm; Fig. 3 View Figure 3 ). In contrast, young individuals of O. brunnea have a straight junction between the scutum and tergum, and this junction line becomes sinuous when the barnacles get older (Fig. 3 View Figure 3 ). There are some variations in the number of spines (-2-4) on the region between the second and third teeth of mandibles in O. brunnea and O. intermedia (Fig. 15 View Figure 15 ). But both species have similar range of variations and there are no diagnostic differences between the two species (Fig. 15 View Figure 15 ). The maxillule of O. brunnea has very deep notches on the upper and lower 1/3 portions of the cutting edge dividing it into three distinct portions. While the maxillule of O. intermedia has shallow notches on the upper and lower 1/3 portions of the cutting margin looking more or less straight without being dividing into three distinct regions as in O. brunnea . Such differences are considered consistent based on observations of the additional three specimens from both species (Fig. 16 View Figure 16 ).

Nilsson-Cantell (1921) has not state any deposition nor specimen number of type or paratype specimens of O. intermedia . The foreword section of Nilsson-Cantell (1921) stated majority of specimens in Nilsson-Cantell (1921) were obtained from collections in Swedish Imperial Museum in Stockholm, Sweden and Zoological Museum in Uppsala, Sweden. The specimens of O. intermedia are possibly housed in either one of the two museums above. Before checking the presences or absences of O. intermedia in museum collections in Sweden, the present study did not attempt to establish any neotypes of O. intermedia to avoid taxonomic confusion. The information of the COI gene in GenBank for O. intermedia is currently adequate for future studies to confirm identification of specimens collected.