A 9-year-old neutered male cat was presented in November 2020 with a 1-month history of soft tissue swelling on the right side of the face. The lesion had an inflamed surface and produced a white discharge when incised with a needle. The cat was treated with an antibiotic (amoxicillin, 20 mg/kg, BID, for 8 d) and corticosteroids (oral, 0.3 mg/kg, BID, for 8 d). In January 2021, the cat was brought back to the hospital owing to increased swelling of the lesion. The lesion was surgically removed under general anesthesia. Complete excision of the mass was challenging because of limited skin availability, and a portion of the lesion remained in the surrounding area. White foreign structures were observed on the excised tissue surfaces. Histopathological examination revealed multiple worm sections, leading to the diagnosis of helminthic infection. The cat was administered with the Broadline® spot-on solution (Merial, Japan), a combination product comprising praziquantel, eprinomectin, fipronil, (S)-methoprene four times per month. However, the cat continued to scratch its face. An Elizabethan collar was fitted, and corticosteroids (1 mg /kg, SID, 4 d, followed by 0.6 mg/kg, SID, for 6 d) were administered. In April 2021, the skin lesions recurred and became pruritic. Corticosteroids (1 mg/kg, SID, PO) were administered for 1 year necessarily to relieve itching. In January 2022, the lesions had spread further. Biopsy tissues from the skin lesions were fixed in 10% neutral-buffered formalin and processed into paraffin blocks using routine procedures. Paraffin-embedded tissues were cut into 5 μm sections and stained with hematoxylin and eosin stain. Microscopic observation showed numerous worm sections of various sizes and shapes in the subcutaneous tissue, extending into the intracutaneous muscles and dermis just below the epidermis. The worms were surrounded by macrophages, neutrophils, lymphocytes, and plasma cells, resulting in granulomatous inflammation. These worms were characterized as acephalic without a rostellum and suckers, having tegument bearing microtriches, parenchyma with numerous calcareous bodies, enlarged excretory canals within a loose stroma, bilateral symmetry and irregularly developed musculature. Based on these, the worms were identified as proliferative spargana of S. proliferum. DNA was extracted from two 10 μm formalin-fixed paraffin-embedded sections using the GeneRead DNA FFPE kit (Qiagen) according to the manufacturer’s protocol. A total of 420 and 1,460 ng DNA was obtained from the two sections with A260/A280 (absorbance at 260 nm and 280 nm) ratios of 1.92 and 1.86, respectively. An Illumina sequencing library was prepared from each extracted DNA sample (100 ng) using an Illumina DNA Library Prep Kit (Illumina) following the manufacturer’s protocol. Those libraries were sequenced on MiSeq using the MiSeq reagent kit v3 producing 300-bp paired-end reads. The resulting 4.2 and 3.9 Gbp raw sequencing data was deposited under DDBJ BioProject no. PRJDB16823. Metagenomic species profiling of the total reads was performed using CCMetagen []. The results indicated that ~ 47% of the reads were from Cestoda, ~ 38% were from Mammalia (mainly Felis), and ~ 17% were from Drosophila. Approximately 20% of Cestoda reads were classified at the genus level (Spirometra). To identify the species, we extracted mitochondrial reads from the metagenome dataset and constructed mitochondrial genomes using the GetOrganelle pipeline []. Those libraries were sequenced on MiSeq using the MiSeq reagent kit v3 producing 300 bp paired-end reads. The circular mitochondrial genome assembly (accession no. ERZ21839573) was 13,643 bp long and showed high similarity (87–99%) to the mitochondrial sequences of Spirometra spp. A maximum likelihood tree was generated using the cytochrome c oxidase subunit I gene (1,566 bp) of mitochondria with 71 sequences deposited as cytochrome c oxidase subunit I gene of Spirometra spp. in the sequence repository. The tree showed six well-defined clusters corresponding to separate species with a clear geographical pattern as described in Kuchta et al. []. The mitochondrial sequence obtained in this study was placed in the middle of S. mansoni cluster with 100% identity with that from China (accession no. KY114886). The examination results were presented to the owner with the need for additional surgery; however, the owner declined. The cat was brought back to the hospital on April 16, 2022. The lesion on the right side extended from under the eye to the nose and cheek and spread further to the inner corner of the right eye. When the lesion was incised, numerous motile, white, glandular, and irregularly shaped spargana were observed in the subcutaneous tissue and on the skin surface. The lesion was thoroughly excised, and skin flap surgery was performed on the head. Intraoperatively, a five-fold dilution of praziquantel was administered into the normal subcutaneous tissue after removing the lesion for several minutes. On April 30, 2022, the sutures were removed. Praziquantel (0.5 ml/kg) was administered subcutaneously on the scapula, with two doses administered on April 30, 2022 and 2 months later. As of October 2023, there was no recurrence of the lesion at the surgical site.