Morphometric and meristic data for 17 specimens of female Echinorhynchus salmonis Muller, 1784 (Acanthocephala: Echinorhynchidae) from the Bothnian Bay, Baltic Sea. The acanthocephalans were collected from the sea spawning form of the whitefish Coregonus lavaretus L. and the smelt Osmerus eperlanus (L.) from the Bothnian Bay, northern Baltic Sea. The specimens from which these data were collected are deposited in The Natural History Museum, London: Host Voucher Specimens Coregonus lavaretus L. BMNH 2002.2.4.132-226 Osmerus eperlanus (L.) BMNH 2002.2.4.227-263 Comma separated value file with the following columns: 1: specimen (unique identifier for specimen) 2: ML (metasoma (trunk) length) 3: RL (length of reproductive system) 4: MW (metasoma width) 5: PL (proboscis length) 6: PW (proboscis width) 7: NL (neck length) 8: NW (neck width) 9: PRL (proboscis receptacle length) 10: PRW (proboscis receptacle width) 11: LL (lemniscus length) 12: LW (lemniscus width) 13: TD (distance between testes) 14: TO (overlap of testes) 15: ATL (anterior testis length) 16: ATW (anterior testis width) 17: PTL (posterior testis length) 18: PTW (posterior testis width) 19: CGW (cement gland width) 20: SPL (Saefftigen's pouch length) 21: SPW (Saefftigen's pouch width) 22: PEN_W (penis width) 23: BSD (bursal sucker diameter) 24: ROWS_OF_HKS (number of longitudinal rows of hooks) 25: HKS_PER_ROW (number of hooks per longitudinal row) 26: ML_MW (trunk length to width ratio) 27: RL_ML (relative length of reproductive system expressed as a percentage of trunk length) 28: PL_PW (proboscis length to width ratio) All measurements are in micrometres. The unique identifier (column 1) is composed of two parts: 1 The number before the dash indicates the host of the acanthocephalan, either C. lavaretus (5) or O. eperlanus (17). 2 The number after the dash is the specimen number.